Definition
Major histocompatibility complex (MHC) proteins are a group of highly polymorphic genes whose products appear on the surface of cells imparting the property of self (belonging to that organism). A genetic region found in all mammals whose products are primarily responsible for the rapid rejection of tissue grafts between individuals, and function in signaling between lymphocytes and cells expressing antigen.
Discovery
Discovery of the mouse MHC (H-2) - In 1916, Little and Tyzzer analyzed the fate of tumours transplanted between mice and demonstrated that several dominant genes influenced the outcome of allogenic tumour grafts1. The MHC was further characterized by Snell in transplantation studies in congenic mouse lines and he called the genes as histocompatibility (H) genes 2.
Discovery of the human MHC (HLA)-The human MHC is called the human leukocyte antigen (HLA) system and it was discovered from multiparous women or from transfused persons contained Abs which agglutinated leukocytes3. Initially, the serological typing techniques identified only two polymorphic gene loci, the HLA-A and HLA-B allelic series, but soon HLA-C and other gene loci in the MHC were identified 4.
Molecules related to MHC antigens, have been discovered. MHC class lb molecules are nonpolymorphic MHC class I-like molecules which fulfill functions divergent from the classical, MHC class la molecules. The human intestine is a unique immunologic compartment, which expresses two of these molecules: the neonatal Fc receptor for IgG (FcRn) and CDl5.
Structural Characteristics
The MHC genes, coding for the HLAs are located on the short arm of chromosome 6. Class I MHC is a heterodimer of membrane-bound a chain and non-covalently associated b2-microglobulin. Both ? chain and b2-microglobulin are members of the Ig superfamily and share with antibody, a disulfide-bonded domain structure. Class I? chain is encoded by highly polymorphic genes in the MHC. It has three domains named ?1, ?2, and ?3 and a region adjoining ?3 that anchors it in the plasma membrane. b2-microglobulin is encoded by a gene on another chromosome. b2-microglobulin molecules are non-covalently associated with Class Ia chain.
Class II MHC is a non-covalently bonded heterodimer of a and ß chains, called HLA-DP, HLA-DQ, and HLA-DR in humans and IA and IE in mice. Peptide antigen (13-18 residues) binds Class II a1 and ß1 domains, which are variable from allele to allele. a1 and ß1 domains also bind to T-cell receptors(TCR). The membrane-bound a2 and ß2 domains are invariant and a2 binds CD4. Class II peptide-binding site is similar in structure to that of Class I, except that its ends are more open so that longer peptides can be bound 6.
Mode of Action
MHC proteins must bind peptide, and Class I must be complexed with b2-microglobulin in intracellular compartments before MHC can be expressed on the cell surface. Peptide binding to MHC is less specific than epitope binding to Ig or TCR; each MHC presents many different epitopes. Peptide must bind MHC with enough affinity to be retained on the plasma membrane and not exchange with soluble peptide. For example, a virus-infected cell synthesizes virus proteins on ribosomes in its cytoplasm. In order to be presented, these proteins must be broken down into short peptides and transported into endoplasmic reticulum to bind to newly synthesized Class I MHC proteins. In the cytosolic processing pathway, cytosolic proteins are degraded to peptides in proteasomes, cylindrical arrays of proteolytic enzymes with their active sites towards the center of the cylinder. Both pathogen proteins and self cell proteins can be complexed with ubiquitin to target them to the proteasome for processing. Two proteases encoded in the MHC II region (LMP2 and LMP7) and a third subunit not encoded in MHC are produced in response to interferon, which is synthesized in response to virus infection. These inducible proteases replace constitutive proteases in the proteasome and produce peptides with basic and hydrophobic carboxyl terminal residues preferred as anchor residues in Class I peptide binding sites and for transport from the cytosol into the ER 7.
Functions
MHC proteins allow T cells to distinguish self from non-self. In every cell in the body, antigens are constantly broken up and presented to passing T cells. Without this presentation, other aspects of the immune response cannot occur. Class I MHC proteins present antigens to cytotoxic T lymphocytes (CTLs). Most CTLs possess both T-cell receptors (TCR) and CD8 molecules on their surfaces. These TCRs are able to recognize peptides when they are expressed in complexes with MHC Class I molecules. The TCR have a structure which allows it to bind the peptide-MHC complex. The accessory molecule CD8, bind to the alpha-3 domain of the MHC Class I molecule.
The MHC Class II proteins (found only on B lymphocytes, macrophages, and other cells that present antigens to T cells), primarily present peptides which have been digested from external sources and are needed for T-cell communication with B-cells and macrophages. Class II MHC proteins presenting antigens are detected by a different group of T cells (called T-helper or TH cells) to Class I MHC proteins (which are detected by CTLs cells) 7.
References
1.Little CC, Tyzzer EE (1916). Further experimental studies on the inheritance of susceptibility to a transplantable tumor, carcinoma (JWA) of the Japanese waltzing mouse. J. Med. Res., 33:393-453.
2.Snell GD (1948). Methods for the study of histocompatibility genes. J. Genet., 49:87-108.
3.Payne R, Rolfs MR (1958). Fetomaternal leukocyte incompatibility. J. Clin. Invest., 37(12):1756-1763.
4.Bain B, Vaz MR, Lowenstein L (1964). The development of large immature mononuclear cells in mixed lymphocyte culture. Blood, 23:108-116.
5.Blumberg RS, Simister N, Christ AD, Israel EJ, Colgan SP, Balk SP (1996). MHC-like Molecules on Mucosal Epithelial Cells. Essentials of Mucosal Immunology, 8:85-99.
6.Stern LJ, Wiley DC (1994). Antigenic peptide binding by class I and class II histocompatibility proteins. Structure, 2(4):245-51. Hughes AL, (1997). Molecular evolution of the vertebrate immune system. Bioessays, 19(9), 777-786.
Friday, September 4, 2009
Melittins
Definition
Melittins is a toxic protein in bee venom that causes localized pain and inflammation but also has a moderate antibacterial and antifungal effect.
Discovery
It was first identified as a ‘direct lytic factor’ since it induced haemolysis in the absence of added lecithin1,2. The active peptide melittin is released from its precursor, promelittin, during its biosynthesis in honey bee and later gets formylated2.
Structural Characteristics
It is a small linear peptide composed of 26 amino acid residues (NH2- GIGAVLKVLTTGLPALISWIKRKRQQ-CONH2) in which the amino-terminal region (residues 1–20) is predominantly hydrophobic whereas the carboxy-terminal region (residues 21–26) is hydrophilic due to the presence of a stretch of positively charged amino acids. The amphiphilic property of this peptide makes it water-soluble and yet it spontaneously associates with natural and artificial membranes 3. There is an asymmetric distribution of polar and non-polar amino acids which makes melittin amphipathic when the peptide is aligned in a a-helical configurations a helical wheel diagram3.
Mode of Action
The characteristic action of melittin is its hemolytic activity, since the target for the action of melittin is the erythrocyte membrane. At sub-micromolar concentrations and higher, melittin binds rapidly to erythrocytes (within seconds) and induces the release of haemoglobin into the extracellular medium. Melittin-induced haemolysis follows reproducible, temperature-dependent biphasic kinetics with characteristic fast and slow phases which dominate lysis at 4 and 37 0C, respectively. The fast phase is interpreted as resulting from the perturbation of membrane structure and organization due to the rapid accumulation of melittin in the outer leaflet of the erythrocyte membrane and its decay into a slow phase is a result of the reorganization of peptide and membrane lipids to recover favourable packing geometry. It has been proposed that the internalization of the melittin dimer underlies the slow phase of haemoglobin release because of the second order dependence of the rate on peptide concentration 4,5.
Functions
Voltage-gated Channel Formation- Melittin disrupts the barrier function of cell membranes and has been shown to form channels in planar bilayers. In the presence of a trans-negative membrane potential, melittin has been reported to induce increased permeability of ions in planar lipid membranes. This observed change in conductance, under high ionic strength conditions, exhibits discrete multilevel conductances3.
Micellization and Fusion of Bilayers- Melittin-induced permeabilization of membranes is known to cause the breakdown of membranes into micelles at high peptide concentration. This is similar to the solubilisation of membranes by detergents3.
Melittin and Pore Formation- It is commonly believed that multimeric pore formation is the mode of action of many naturally produced peptides such as antimicrobial peptides and toxins. Under certain conditions, melittin molecules insert into the lipid bilayer and form multiple aggregated forms that are controlled by temperature, pH, ionic strength, lipid composition and lipid-to-peptide
Ratio3.
Cellular Activities of Melittin- Action of Melittin on Membrane Proteins Apart from its ability to disrupt lipid bilayers, melittin affects the dynamics of membrane proteins. For instance, it has been shown that lytic concentrations of melittin dramatically reduce the rotational mobility of band 3 proteins in human erythrocyte membranes and of bacteriorhodopsin in lipid vesicles3.
Melittin and Cell Transformation- Oncogenes play an important role in the initiation and progression of the neoplastic phenotype. The ras oncogene is especially important with respect to human cancer since at least one-third of all human colorectal tumours analyzed express an activated ras oncogene. Interestingly, it has been demonstrated that melittin specifically selects against cells in culture that express high levels of the ras oncogene. Melittin therefore exerts its anti-transformation effect(s) by specifically eliminating cells that express the oncoprotein3.
Melittin and Signal Transduction- It is known that cationic amphiphilic peptides such as mastoparan and melittin directly stimulate nucleotide exchange by heterotrimeric GTP-binding proteins (G-proteins) in a manner similar to that of G-protein coupled receptors3.
Leishmanicidal Activity of Melittin- Melittin induces membrane permeabilization and lyses prokaryotic as well as eukaryotic cells in a non-selective manner. This mode of action is responsible for its hemolytic, anti-microbial, anti-fungal, anti-tumour and leishmanicidal activities of melittin3.
Anti-viral Activity of Melittin- It has been shown that melittin reduces HIV-1 production in a dose-dependent manner. The reduction in viral infectivity is proposed to be due to the affinity of melittin for the gag/pol precursor, thereby preventing the processing of gag/ pol by the HIV protease3.
References
1.Neumann W, Habermann E, Hansen H (1953). Differentiation of two hemolytic factors in bee venom. Naunyn-Schmiedebergs Arch Exp Path Pharma., 217(2):130-143.
2.Habermann E (1972). Bee and wasp venoms. Science, 177(43): 314-322.
3.Raghuraman H, Chattopadhyay A (2007). Melittin: a Membrane-active Peptide with Diverse Functions. Biosci Rep., 27:189-223.
4.Dathe M, Wieprecht T (1999). Structural features of helical antimicrobial peptides: their potential to modulate activity on model membranes and biological cells. Biochim Biophys Acta., 1432:71-87.
5.Dempsey CE (1990). The actions of melittin on membranes. Biochim Biophys Acta., 1031(2):143-131.
Melittins is a toxic protein in bee venom that causes localized pain and inflammation but also has a moderate antibacterial and antifungal effect.
Discovery
It was first identified as a ‘direct lytic factor’ since it induced haemolysis in the absence of added lecithin1,2. The active peptide melittin is released from its precursor, promelittin, during its biosynthesis in honey bee and later gets formylated2.
Structural Characteristics
It is a small linear peptide composed of 26 amino acid residues (NH2- GIGAVLKVLTTGLPALISWIKRKRQQ-CONH2) in which the amino-terminal region (residues 1–20) is predominantly hydrophobic whereas the carboxy-terminal region (residues 21–26) is hydrophilic due to the presence of a stretch of positively charged amino acids. The amphiphilic property of this peptide makes it water-soluble and yet it spontaneously associates with natural and artificial membranes 3. There is an asymmetric distribution of polar and non-polar amino acids which makes melittin amphipathic when the peptide is aligned in a a-helical configurations a helical wheel diagram3.
Mode of Action
The characteristic action of melittin is its hemolytic activity, since the target for the action of melittin is the erythrocyte membrane. At sub-micromolar concentrations and higher, melittin binds rapidly to erythrocytes (within seconds) and induces the release of haemoglobin into the extracellular medium. Melittin-induced haemolysis follows reproducible, temperature-dependent biphasic kinetics with characteristic fast and slow phases which dominate lysis at 4 and 37 0C, respectively. The fast phase is interpreted as resulting from the perturbation of membrane structure and organization due to the rapid accumulation of melittin in the outer leaflet of the erythrocyte membrane and its decay into a slow phase is a result of the reorganization of peptide and membrane lipids to recover favourable packing geometry. It has been proposed that the internalization of the melittin dimer underlies the slow phase of haemoglobin release because of the second order dependence of the rate on peptide concentration 4,5.
Functions
Voltage-gated Channel Formation- Melittin disrupts the barrier function of cell membranes and has been shown to form channels in planar bilayers. In the presence of a trans-negative membrane potential, melittin has been reported to induce increased permeability of ions in planar lipid membranes. This observed change in conductance, under high ionic strength conditions, exhibits discrete multilevel conductances3.
Micellization and Fusion of Bilayers- Melittin-induced permeabilization of membranes is known to cause the breakdown of membranes into micelles at high peptide concentration. This is similar to the solubilisation of membranes by detergents3.
Melittin and Pore Formation- It is commonly believed that multimeric pore formation is the mode of action of many naturally produced peptides such as antimicrobial peptides and toxins. Under certain conditions, melittin molecules insert into the lipid bilayer and form multiple aggregated forms that are controlled by temperature, pH, ionic strength, lipid composition and lipid-to-peptide
Ratio3.
Cellular Activities of Melittin- Action of Melittin on Membrane Proteins Apart from its ability to disrupt lipid bilayers, melittin affects the dynamics of membrane proteins. For instance, it has been shown that lytic concentrations of melittin dramatically reduce the rotational mobility of band 3 proteins in human erythrocyte membranes and of bacteriorhodopsin in lipid vesicles3.
Melittin and Cell Transformation- Oncogenes play an important role in the initiation and progression of the neoplastic phenotype. The ras oncogene is especially important with respect to human cancer since at least one-third of all human colorectal tumours analyzed express an activated ras oncogene. Interestingly, it has been demonstrated that melittin specifically selects against cells in culture that express high levels of the ras oncogene. Melittin therefore exerts its anti-transformation effect(s) by specifically eliminating cells that express the oncoprotein3.
Melittin and Signal Transduction- It is known that cationic amphiphilic peptides such as mastoparan and melittin directly stimulate nucleotide exchange by heterotrimeric GTP-binding proteins (G-proteins) in a manner similar to that of G-protein coupled receptors3.
Leishmanicidal Activity of Melittin- Melittin induces membrane permeabilization and lyses prokaryotic as well as eukaryotic cells in a non-selective manner. This mode of action is responsible for its hemolytic, anti-microbial, anti-fungal, anti-tumour and leishmanicidal activities of melittin3.
Anti-viral Activity of Melittin- It has been shown that melittin reduces HIV-1 production in a dose-dependent manner. The reduction in viral infectivity is proposed to be due to the affinity of melittin for the gag/pol precursor, thereby preventing the processing of gag/ pol by the HIV protease3.
References
1.Neumann W, Habermann E, Hansen H (1953). Differentiation of two hemolytic factors in bee venom. Naunyn-Schmiedebergs Arch Exp Path Pharma., 217(2):130-143.
2.Habermann E (1972). Bee and wasp venoms. Science, 177(43): 314-322.
3.Raghuraman H, Chattopadhyay A (2007). Melittin: a Membrane-active Peptide with Diverse Functions. Biosci Rep., 27:189-223.
4.Dathe M, Wieprecht T (1999). Structural features of helical antimicrobial peptides: their potential to modulate activity on model membranes and biological cells. Biochim Biophys Acta., 1432:71-87.
5.Dempsey CE (1990). The actions of melittin on membranes. Biochim Biophys Acta., 1031(2):143-131.
Mating Factors
Definition
Mating factors are a family of pheromones that were initially discovered in Saccharomyces cerevisiae, necessary for fungal conjugation. The alpha-factor pheromone induces conjugation in yeast by binding to Ste2p protein.
Discovery
In Saccharomyces cerevisiae, the peptide mating pheromones a-factor and a-factor function to promote conjugation between cells of the opposite mating type, MATa and MATa. Manney et al described the mutants of Saccharomyces cerevisiae with an altered response to mating factor (either more resistant or more sensitive) that permitted a genetic dissection of the pathway of hormone action. One such class of mutants, the a factor resistant mutants, has been isolated and found to be sterile (nonmating), implying that the ability to respond to a factor is essential for mating1,2. The maturation of a-factor is well characterized and involves the "classical" secretory pathway. Subsequent to its translocation across the endoplasmic reticulum membrane, the a-factor precursor undergoes signal sequence cleavage, glycosylation, a series of proteolytic processing steps in the lumenal compartments of the secretory pathway, and then exits the cell via exocytosis. In contrast a-factor biogenesis is mediated by a "nonclassical" export mechanism3.
Structural Characteristics
Mature bioactive a-factor is a prenylated and methylated dodecapeptide, derived by the posttranslational maturation of a precursor encoded by the similar and functionally redundant genes MFA1 and MFA2. The a-factor precursor can be subdivided into three functional segments: (a) the mature portion, which is ultimately secreted; (b) the NH2-terminal extension; and (c) the COOH-terminal CAAX motif (C is cysteine, A is aliphatic, and X is one of many residues). Biogenesis of mating factor occurs by an ordered series of events involving first COOH-terminal CAAX modification, then NH2-terminal processing, and finally export from the cell4,5.
Mode of Action
Mating factor binds and activates specific cell surface receptors, thereby inducing behavioral or physiological responses in the responding organism or cell that leads to the transfer or union of genetic material between organisms or cells. MATa cells make a linear tridecapeptide, called a factor that arrests MATa cells in the G1 phase of the cell cycle; MATa cells make a decapeptide, called a factor, which has similar effects on MATa cells. The a and a factor pheromones apparently prepare cells for mating by inducing agglutination between the two cell types and by synchronizing their cell cycles 6.The mating pheromone can either be retained on the cell surface or secreted. A signal transduction process resulting in the relay, amplification or dampening of a signal generated in response to pheromone exposure in organisms that undergo conjugation with cellular fusion.
Response to pheromone elicits arrest in the G1 phase of the cell cycle, cell wall changes, morphological alterations, and induction of genes that encode products involved in aspects of mating or pheromone response. Mutants defective in pheromone production or response are sterile7. Addition of exogenous a-factor can partially alleviate these mating defects under certain conditions.
Functions
In Saccharomyces cerevisiae, mating type and the ability to sporulate are controlled by two alternative alleles of the mating-type locus MAT. Cells that express either the MATa or the MATa allele, regardless of ploidy or dosage, can mate with cells that express the alternative allele. Cells that are heterozygous at this locus can sporulate. Normally, mating and sporulation are mutually exclusive. Although mating and sporulation are determined by this single locus, these phenotypes involve the expression of many specific and nonspecific functions coded by genes that are not linked to the mating-type locus. Consequently, the MAT locus appears to regulate the expression of the structural genes that are necessary for mating and sporulation.
MATa is complex codes for a MATa1 and MATa2, MATa1 functions as a positive regulator of a-specific functions, such as secretion of the mating pheromone, a-factor, synthesis of the a-specific surface agglutinin, and the ability to respond to the a-specific pheromone, a-factor. MATa2 acts as a negative regulator of a- specific functions, such as secretion of a-factor, synthesis of the barrier activity (which inactivates a-factor), synthesis of the a-specific surface agglutinin, and as a positive regulator of sporulation 8.
References
1.Hartwell LH (1980). Mutants of Saccharomyces cerevisiae unresponsive to cell division control by polypeptide mating hormones. J. Cell Biol., 85(3):811-822.
2.Manney TR, Woods V (1976). Mutants of Saccharomyces cerevisiae resistant to the a- mating-type factor. Genetics., 82(4):639-644.
3.Kuchler K, Sterne RE, Thorner J (1989). Saccharomyces cerevisiae STE6 gene product: a novel pathway for protein export in eukaryotic cells. EMBO., 8(13):3973-3984.
4.Michaelis S, Herskowitz I (1988). The a-factor pheromone of Saccharomyces cerevisiae is essential for mating. Mol. Cell. Biol., 8:1309-1318.
5.Sapperstein S, Berkower C, Michaelis S (1994). Nucleotide sequence of the yeast STE14 gene, which encodes farnesylcysteine carboxyl methyltransferase, and demonstration of its essential role in a-factor export. Mol. Cell. Bio., 14:1438-1449.
6.Book : Sexual Interactions in Eukaryotic Microbes. Chapter: The Isolation, Characterization, and Physiological Effects of the Saccharomyces cerevisiae Sex Pheromones., 21-51. By Manney TR, Duntzer W, Betz R
7.Cross F, Hartwell LH, Jackson C, Konopka JB (1988). Corljugation in Saccharomyces cerevisiae. Annu. Rev. Cell Biol., 4:430-457.
8.Manney TR, Jackson P, Meade J (1983). Two Temperature-sensitive Mutants of Saccharomyces cerevisiae with Altered Expression of Mating-Type Functions. The journal of cell biology., 96:1592-1600.
Mating factors are a family of pheromones that were initially discovered in Saccharomyces cerevisiae, necessary for fungal conjugation. The alpha-factor pheromone induces conjugation in yeast by binding to Ste2p protein.
Discovery
In Saccharomyces cerevisiae, the peptide mating pheromones a-factor and a-factor function to promote conjugation between cells of the opposite mating type, MATa and MATa. Manney et al described the mutants of Saccharomyces cerevisiae with an altered response to mating factor (either more resistant or more sensitive) that permitted a genetic dissection of the pathway of hormone action. One such class of mutants, the a factor resistant mutants, has been isolated and found to be sterile (nonmating), implying that the ability to respond to a factor is essential for mating1,2. The maturation of a-factor is well characterized and involves the "classical" secretory pathway. Subsequent to its translocation across the endoplasmic reticulum membrane, the a-factor precursor undergoes signal sequence cleavage, glycosylation, a series of proteolytic processing steps in the lumenal compartments of the secretory pathway, and then exits the cell via exocytosis. In contrast a-factor biogenesis is mediated by a "nonclassical" export mechanism3.
Structural Characteristics
Mature bioactive a-factor is a prenylated and methylated dodecapeptide, derived by the posttranslational maturation of a precursor encoded by the similar and functionally redundant genes MFA1 and MFA2. The a-factor precursor can be subdivided into three functional segments: (a) the mature portion, which is ultimately secreted; (b) the NH2-terminal extension; and (c) the COOH-terminal CAAX motif (C is cysteine, A is aliphatic, and X is one of many residues). Biogenesis of mating factor occurs by an ordered series of events involving first COOH-terminal CAAX modification, then NH2-terminal processing, and finally export from the cell4,5.
Mode of Action
Mating factor binds and activates specific cell surface receptors, thereby inducing behavioral or physiological responses in the responding organism or cell that leads to the transfer or union of genetic material between organisms or cells. MATa cells make a linear tridecapeptide, called a factor that arrests MATa cells in the G1 phase of the cell cycle; MATa cells make a decapeptide, called a factor, which has similar effects on MATa cells. The a and a factor pheromones apparently prepare cells for mating by inducing agglutination between the two cell types and by synchronizing their cell cycles 6.The mating pheromone can either be retained on the cell surface or secreted. A signal transduction process resulting in the relay, amplification or dampening of a signal generated in response to pheromone exposure in organisms that undergo conjugation with cellular fusion.
Response to pheromone elicits arrest in the G1 phase of the cell cycle, cell wall changes, morphological alterations, and induction of genes that encode products involved in aspects of mating or pheromone response. Mutants defective in pheromone production or response are sterile7. Addition of exogenous a-factor can partially alleviate these mating defects under certain conditions.
Functions
In Saccharomyces cerevisiae, mating type and the ability to sporulate are controlled by two alternative alleles of the mating-type locus MAT. Cells that express either the MATa or the MATa allele, regardless of ploidy or dosage, can mate with cells that express the alternative allele. Cells that are heterozygous at this locus can sporulate. Normally, mating and sporulation are mutually exclusive. Although mating and sporulation are determined by this single locus, these phenotypes involve the expression of many specific and nonspecific functions coded by genes that are not linked to the mating-type locus. Consequently, the MAT locus appears to regulate the expression of the structural genes that are necessary for mating and sporulation.
MATa is complex codes for a MATa1 and MATa2, MATa1 functions as a positive regulator of a-specific functions, such as secretion of the mating pheromone, a-factor, synthesis of the a-specific surface agglutinin, and the ability to respond to the a-specific pheromone, a-factor. MATa2 acts as a negative regulator of a- specific functions, such as secretion of a-factor, synthesis of the barrier activity (which inactivates a-factor), synthesis of the a-specific surface agglutinin, and as a positive regulator of sporulation 8.
References
1.Hartwell LH (1980). Mutants of Saccharomyces cerevisiae unresponsive to cell division control by polypeptide mating hormones. J. Cell Biol., 85(3):811-822.
2.Manney TR, Woods V (1976). Mutants of Saccharomyces cerevisiae resistant to the a- mating-type factor. Genetics., 82(4):639-644.
3.Kuchler K, Sterne RE, Thorner J (1989). Saccharomyces cerevisiae STE6 gene product: a novel pathway for protein export in eukaryotic cells. EMBO., 8(13):3973-3984.
4.Michaelis S, Herskowitz I (1988). The a-factor pheromone of Saccharomyces cerevisiae is essential for mating. Mol. Cell. Biol., 8:1309-1318.
5.Sapperstein S, Berkower C, Michaelis S (1994). Nucleotide sequence of the yeast STE14 gene, which encodes farnesylcysteine carboxyl methyltransferase, and demonstration of its essential role in a-factor export. Mol. Cell. Bio., 14:1438-1449.
6.Book : Sexual Interactions in Eukaryotic Microbes. Chapter: The Isolation, Characterization, and Physiological Effects of the Saccharomyces cerevisiae Sex Pheromones., 21-51. By Manney TR, Duntzer W, Betz R
7.Cross F, Hartwell LH, Jackson C, Konopka JB (1988). Corljugation in Saccharomyces cerevisiae. Annu. Rev. Cell Biol., 4:430-457.
8.Manney TR, Jackson P, Meade J (1983). Two Temperature-sensitive Mutants of Saccharomyces cerevisiae with Altered Expression of Mating-Type Functions. The journal of cell biology., 96:1592-1600.
MAP kinases
Definition
Mitogen activated protein kinases (MAP kinases) is a large kinase network in which upstream kinases activate downstream kinases in response to phosphorylation, translocate to the nucleus and activate different transcription factors.
Discovery
Between 1989 and 1991 the sequences of the first MAP kinase, Kss1p and Fus3p in the pheromone response pathway of the budding yeast and the mammalian MAP kinases ERK1, ERK2 and ERK3, became available, revealing that these enzymes were members of a newly identified protein kinase family1,2. The concept that there were multiple MPKs with distinct regulation and functions arose from the description of additional pathways found initially in yeast, the high osmolarity glycerol (HOG) pathway containing the MAP kinase HOG1 and the cell wall pathway containing the kinase MPK1, and then in metazoans c-Jun N-terminal kinases/stress-activated protein kinases (JNK/SAPKs), p38 enzymes 3,4.
Structural Characteristics
Catalytic domain- All the MAP kinases share strong amino-acid sequence identity over their catalytic domains (37%-50%), with members of certain subgroups sharing up to 75% identity.
CH2 domains- The amino terminus is much less conserved in the MAP kinases than the catalytic domain. Nevertheless, all MAP kinases contain at their amino terminus two conserved regions that show similarity to the Ccd25 phosphatase, designated CH2 domains.
Docking sites- All MAP kinases have, near to their amino termini, a MAP kinase docking site, which consists of a cluster of positively charged amino acids. It has been proposed that the number of consecutive positively charged residues in this docking site of MAP kinases may play a role in determining binding specificity and therefore catalytic activity
PEST sequences-The subgroup MAP kinases, have an extended carboxyl terminus containing PEST sequences (abundant in proline, glutamate, serine and threonine residues) that are frequently found in rapidly degraded proteins 5.
Mode of Action
MAP kinases are regulated by phosphorylation cascades. Two upstream protein kinases activated in series lead to activation of a MAP kinase, and additional kinases may also be required upstream of this three-kinase module. In all currently known MAP kinase cascades, the kinase immediately upstream of the MAP kinase is a member of the MAP/ERK kinase (MEK or MKK) family. These are dual specificity enzymes that can phosphorylate hydroxyl side chains of serine/threonine and tyrosine residues in their MAP kinase substrates. In spite of their ability to phosphorylate proteins on both aliphatic and aromatic side chains in the appropriate context, the substrate specificity of the known MEKs is very narrow, each MEK phosphorylates only one or a few of the MAP kinase . There are several characteristics of MAP kinases that result from their activation by kinase cascades. Important among these is that the intermediates provide distinct mechanisms for detecting inputs from other signaling pathways to enhance or suppress the signal to the MAP kinase 6.
Functions
One of the best studied signaling routes is the MAP kinase signal transduction pathway and it plays a crucial role in many aspects of immune mediated inflammatory responses. There are several characteristics of MAP kinase that result from their activation by kinase cascades. Important among these is that the intermediates provide distinct mechanisms for detecting inputs from other signaling pathways to enhance or suppress the signal to the MAP kinase. Another is signal amplification, can occur if each successive protein in the cascade is more abundant than its regulator. This may be true at one or both steps within MAP kinase modules. Studies combining over expression and immunoblotting might be interpreted to indicate that each step in the MAP kinase module of the pheromone response pathway in yeast is represented by a successively more abundant protein, so that the signal may be amplified at both steps within the module. In the case of the ERK1/2 pathway, amplification occurs at the Raf-MEK step, because MEK1 is much more abundant (perhaps as high as 1 µM) than Raf, but is not the major function of the MEK-ERK step because the relevant MEKs (MEK1/2) and ERK1/2 are present at approximately the same concentrations. Several MEK family members contain sites that are phosphorylated by kinases in other pathways; these events may influence the ability of MEKs to interact in complexes. Integration may also occur early in the signaling pathway and at the top of the kinase module. Some MEKKs may regulate more than one MAP kinase cascade, and some cascades may be controlled by several, unrelated MEKKs 7.
References
1.Courchesne WE, Kunisawa R, Thorner J (1989). A putative protein kinase overcomes pheromone-induced arrest of cell cycling in S. cerevisiae. Cell., 58:1107–1119.
2.Boulton TG, Yancopoulos GD, Gregory JS, Slaughter C, Moomaw C, Hsu J, Cobb MH (1990). An insulin-stimulated protein kinase similar to yeast kinases involved in cell cycle control. Science., 249:64–67.
3.Brewster JL, de Valoir T, Dwyer ND, Winter E, Gustin MC (1993). An osmosensing signal transduction pathway in yeast. Science., 259:1760–1763.
4.Lee KS, Irie K, Gotoh Y, Watanabe Y, Araki H, Nishida E, Matsumoto K, Levin DE (1993). A yeast mitogen-activated protein kinase homolog (Mpk1p) mediates signalling by protein kinase C. Mol Cell Biol., 13:3067–3075.
5.Theodosiou A, Ashworth A (2002). MAP kinase phosphatises.Genome Biology., 3(7):1-10.
6.Frost JA, Steen H, Shapiro PS, Lewis R, Ahn J, Shaw PE, Cobb MH (1997). Cross-cascade activation of ERKs and ternary complex factors by Rho family proteins. EMBO J., 16:6426–6438.
7.Pearson G, Robinson F, Gibson TB, Bing-e Xu, Karandikar M, Berman K, Cobb MH (2001). Mitogen-Activated Protein (MAP) Kinase Pathways: Regulation and Physiological Functions. Endocrine Reviews., 22 (2):153-183.
Mitogen activated protein kinases (MAP kinases) is a large kinase network in which upstream kinases activate downstream kinases in response to phosphorylation, translocate to the nucleus and activate different transcription factors.
Discovery
Between 1989 and 1991 the sequences of the first MAP kinase, Kss1p and Fus3p in the pheromone response pathway of the budding yeast and the mammalian MAP kinases ERK1, ERK2 and ERK3, became available, revealing that these enzymes were members of a newly identified protein kinase family1,2. The concept that there were multiple MPKs with distinct regulation and functions arose from the description of additional pathways found initially in yeast, the high osmolarity glycerol (HOG) pathway containing the MAP kinase HOG1 and the cell wall pathway containing the kinase MPK1, and then in metazoans c-Jun N-terminal kinases/stress-activated protein kinases (JNK/SAPKs), p38 enzymes 3,4.
Structural Characteristics
Catalytic domain- All the MAP kinases share strong amino-acid sequence identity over their catalytic domains (37%-50%), with members of certain subgroups sharing up to 75% identity.
CH2 domains- The amino terminus is much less conserved in the MAP kinases than the catalytic domain. Nevertheless, all MAP kinases contain at their amino terminus two conserved regions that show similarity to the Ccd25 phosphatase, designated CH2 domains.
Docking sites- All MAP kinases have, near to their amino termini, a MAP kinase docking site, which consists of a cluster of positively charged amino acids. It has been proposed that the number of consecutive positively charged residues in this docking site of MAP kinases may play a role in determining binding specificity and therefore catalytic activity
PEST sequences-The subgroup MAP kinases, have an extended carboxyl terminus containing PEST sequences (abundant in proline, glutamate, serine and threonine residues) that are frequently found in rapidly degraded proteins 5.
Mode of Action
MAP kinases are regulated by phosphorylation cascades. Two upstream protein kinases activated in series lead to activation of a MAP kinase, and additional kinases may also be required upstream of this three-kinase module. In all currently known MAP kinase cascades, the kinase immediately upstream of the MAP kinase is a member of the MAP/ERK kinase (MEK or MKK) family. These are dual specificity enzymes that can phosphorylate hydroxyl side chains of serine/threonine and tyrosine residues in their MAP kinase substrates. In spite of their ability to phosphorylate proteins on both aliphatic and aromatic side chains in the appropriate context, the substrate specificity of the known MEKs is very narrow, each MEK phosphorylates only one or a few of the MAP kinase . There are several characteristics of MAP kinases that result from their activation by kinase cascades. Important among these is that the intermediates provide distinct mechanisms for detecting inputs from other signaling pathways to enhance or suppress the signal to the MAP kinase 6.
Functions
One of the best studied signaling routes is the MAP kinase signal transduction pathway and it plays a crucial role in many aspects of immune mediated inflammatory responses. There are several characteristics of MAP kinase that result from their activation by kinase cascades. Important among these is that the intermediates provide distinct mechanisms for detecting inputs from other signaling pathways to enhance or suppress the signal to the MAP kinase. Another is signal amplification, can occur if each successive protein in the cascade is more abundant than its regulator. This may be true at one or both steps within MAP kinase modules. Studies combining over expression and immunoblotting might be interpreted to indicate that each step in the MAP kinase module of the pheromone response pathway in yeast is represented by a successively more abundant protein, so that the signal may be amplified at both steps within the module. In the case of the ERK1/2 pathway, amplification occurs at the Raf-MEK step, because MEK1 is much more abundant (perhaps as high as 1 µM) than Raf, but is not the major function of the MEK-ERK step because the relevant MEKs (MEK1/2) and ERK1/2 are present at approximately the same concentrations. Several MEK family members contain sites that are phosphorylated by kinases in other pathways; these events may influence the ability of MEKs to interact in complexes. Integration may also occur early in the signaling pathway and at the top of the kinase module. Some MEKKs may regulate more than one MAP kinase cascade, and some cascades may be controlled by several, unrelated MEKKs 7.
References
1.Courchesne WE, Kunisawa R, Thorner J (1989). A putative protein kinase overcomes pheromone-induced arrest of cell cycling in S. cerevisiae. Cell., 58:1107–1119.
2.Boulton TG, Yancopoulos GD, Gregory JS, Slaughter C, Moomaw C, Hsu J, Cobb MH (1990). An insulin-stimulated protein kinase similar to yeast kinases involved in cell cycle control. Science., 249:64–67.
3.Brewster JL, de Valoir T, Dwyer ND, Winter E, Gustin MC (1993). An osmosensing signal transduction pathway in yeast. Science., 259:1760–1763.
4.Lee KS, Irie K, Gotoh Y, Watanabe Y, Araki H, Nishida E, Matsumoto K, Levin DE (1993). A yeast mitogen-activated protein kinase homolog (Mpk1p) mediates signalling by protein kinase C. Mol Cell Biol., 13:3067–3075.
5.Theodosiou A, Ashworth A (2002). MAP kinase phosphatises.Genome Biology., 3(7):1-10.
6.Frost JA, Steen H, Shapiro PS, Lewis R, Ahn J, Shaw PE, Cobb MH (1997). Cross-cascade activation of ERKs and ternary complex factors by Rho family proteins. EMBO J., 16:6426–6438.
7.Pearson G, Robinson F, Gibson TB, Bing-e Xu, Karandikar M, Berman K, Cobb MH (2001). Mitogen-Activated Protein (MAP) Kinase Pathways: Regulation and Physiological Functions. Endocrine Reviews., 22 (2):153-183.
Kyotorphins
Definition
Kyotorphins are endogenous peptides that take part in the regulation of various adaptive reactions of the organism. They play a role in pain modulation in the mammalian CNS (central nervous system).
Discovery
Kyotorphins (Tyr-Arg) is a dipeptide originally found in bovine and rat brain synaptosomes, is formed from tyrosine and arginine by a specific synthetase. Kyotorphins is a neuroactive peptide named after its place of discovery, Kyoto, Japan1. It has a specific receptor coupled to G i and phospholipase C and elicits enkephalin release.
Structural Characteristics
At biological pH kyotorphins have a neutral net charge. The phenolic rings interact with phospholipid molecules (partition coefficient varies from 6 × 102 to 2 × 104, depending on the lipid and pH used) despite being exposed to the aqueous bulk medium. The lowest energy transition dipole moment is displaced from the normal to the lipid bilayer by 20° on average. The observed extensive interaction, pKa, precise location, and well-defined orientation in membranes combined with the ability to discriminate rigid raft like membrane domains suggest that kyotorphin meets the structural constraints needed for receptor-ligand interaction. The acylated kyotorphin derivative mimics kyotorphin properties and represents a promising way for entrapment in a drug carrier and transport across the blood-brain barrier 2.
Mode of Action
Previous studies suggested that kyotorphin-induced opioid like analgesia may be mediated via a release of Met-enkephalin from the brain. Kyotorphin elicited a release of Met-enkephalin from brain slices but not of [3H]-noradrenaline, [3H]-GABA, [3H]-aspartate and endorphin. The neurochemical basis of mechanisms suggests that Kyotorphins stimulates its specific receptor, followed by G i and phospholipase C (PLC) activations. PLC mechanism leads to a Ca2+ influx in nerve ending particles or synaptosomes. Inositol 1, 4, 5-trisphosphate (InsP3) elicits Ca2+ transport through plasmalemmal InsP3 receptor but not through intra synaptosomal Ca2+ stores. Kyo-induced antinociceptive responses are mediated through its specific receptor. However, at extremely low doses (below femtomolar ranges) of nociceptin/orphanin the endogenous ligand of opioid receptor-like orphan receptor it is coupled to G i, elicits nociceptive responses through its receptor and G i. Potent peripheral nociceptive action of Kyo occur through an InsP3-receptor-gated Ca2+ influx 3,4.
Functions
Kyotorphin improve cardiovascular and cerebral resuscitation after heart arrest - The rate of post resuscitational restoration and survival after a 12-min heart arrest shows that kyotorphin accelerates restoration of vital functions, improve cardiovascular and neurological status within several days after resuscitation 5.
Kyotorphin synthetase activity in rat adrenal glands and spinal cord- Kyotorphin is formed by kyotorphin synthetase from its constituent amino acids, L-Tyr and L-Arg, in the brain in an ATP-Mg2+-dependent manner. To elucidate the physiological role of kyotorphin in organs other than the brain, Kawabata et al., have examined the activity of kyotorphin synthetase in the rat adrenal glands and spinal cord. The activity of adrenal kyotorphin synthetase was inhibited by some L-Arg analogues. Activity was inhibited by NG-nitro-L-arginine methyl ester, alpha-methyl-L-ornithine and D-Arg, but not by NG-nitro-L-arginine and N-iminoethyl-L-ornithine. In the crude soluble extracts from the adrenal glands and spinal cord, kyotorphin was formed by kyotorphin synthetase, and also by the enzymatic processing of the precursor proteins, in the presence of physiological concentrations of L-Tyr and L-Arg in addition to ATP and MgCl2. Kyotorphin synthetase resembling that in the brain is also found to present in the rat adrenal glands and spinal cord, helps in the formation of kyotorphin6.
Kyotorphin suppresses proliferation and Ca2+ signaling in brown preadipocytes-Kyotorphin abolished the stimulatory effect of norepinephrine on proliferation of cultured cells and cold-induced [3H]-thymidine incorporation into DNA of mouse brown adipose tissue in vivo. These changes correlated with peptide-induced suppression of slow calcium signalling in brown preadipocytes.
References
1.Takagi H, Shiomi H, Ueda H, Amano H (1979). A novel analgesic dipeptide from bovine brain is a possible Met-enkephalin release. Nature, 282(5737):410–412.
2.Lopes SC , Soares CM, Baptista AM, Goormaghtigh E, Cabral B , Castanho MA (2006). Conformational and Orientational Guidance of the Analgesic Dipeptide Kyotorphin Induced by Lipidic Membranes: Putative Correlation toward Receptor Docking. J Phys Chem., 110(7):3385–3394.
3.Cheng ZJ, Fan GH, Zhao J, Zhang Z, Wu YL, Jiang LZ, Zhu Y, Pei G, Ma L (1997). Endogenous opioid receptor-like receptor in human neuroblastoma SK-N-SH cells: Activation of inhibitory G protein and homologous desensitization. Neuroreport., 27:1913-1918.
4.Inoue M, Kobayashi M, Kozaki S, Zimmer A, Ueda H (1998). Nociceptin/orphanin FQ-induced nociceptive responses through substance P release from peripheral nerve endings in mice. PNAS, 95:10949-10953.
5.Kharchenko IB, Ziganshin RK, Volkov AV, Koshelev VB (1997). Neokyotorphin and kyotorphin improve cardiovascular and cerebral resuscitation after heart arrest. Bulletin of Experimental Biology and Medicine, 123:450-452.
6.Kawabata A, Muguruma H, Tanaka M, Takagi H (1996). Kyotorphin synthetase activity in rat adrenal glands and spinal cord. Peptide, 17:407-411.
Kyotorphins are endogenous peptides that take part in the regulation of various adaptive reactions of the organism. They play a role in pain modulation in the mammalian CNS (central nervous system).
Discovery
Kyotorphins (Tyr-Arg) is a dipeptide originally found in bovine and rat brain synaptosomes, is formed from tyrosine and arginine by a specific synthetase. Kyotorphins is a neuroactive peptide named after its place of discovery, Kyoto, Japan1. It has a specific receptor coupled to G i and phospholipase C and elicits enkephalin release.
Structural Characteristics
At biological pH kyotorphins have a neutral net charge. The phenolic rings interact with phospholipid molecules (partition coefficient varies from 6 × 102 to 2 × 104, depending on the lipid and pH used) despite being exposed to the aqueous bulk medium. The lowest energy transition dipole moment is displaced from the normal to the lipid bilayer by 20° on average. The observed extensive interaction, pKa, precise location, and well-defined orientation in membranes combined with the ability to discriminate rigid raft like membrane domains suggest that kyotorphin meets the structural constraints needed for receptor-ligand interaction. The acylated kyotorphin derivative mimics kyotorphin properties and represents a promising way for entrapment in a drug carrier and transport across the blood-brain barrier 2.
Mode of Action
Previous studies suggested that kyotorphin-induced opioid like analgesia may be mediated via a release of Met-enkephalin from the brain. Kyotorphin elicited a release of Met-enkephalin from brain slices but not of [3H]-noradrenaline, [3H]-GABA, [3H]-aspartate and endorphin. The neurochemical basis of mechanisms suggests that Kyotorphins stimulates its specific receptor, followed by G i and phospholipase C (PLC) activations. PLC mechanism leads to a Ca2+ influx in nerve ending particles or synaptosomes. Inositol 1, 4, 5-trisphosphate (InsP3) elicits Ca2+ transport through plasmalemmal InsP3 receptor but not through intra synaptosomal Ca2+ stores. Kyo-induced antinociceptive responses are mediated through its specific receptor. However, at extremely low doses (below femtomolar ranges) of nociceptin/orphanin the endogenous ligand of opioid receptor-like orphan receptor it is coupled to G i, elicits nociceptive responses through its receptor and G i. Potent peripheral nociceptive action of Kyo occur through an InsP3-receptor-gated Ca2+ influx 3,4.
Functions
Kyotorphin improve cardiovascular and cerebral resuscitation after heart arrest - The rate of post resuscitational restoration and survival after a 12-min heart arrest shows that kyotorphin accelerates restoration of vital functions, improve cardiovascular and neurological status within several days after resuscitation 5.
Kyotorphin synthetase activity in rat adrenal glands and spinal cord- Kyotorphin is formed by kyotorphin synthetase from its constituent amino acids, L-Tyr and L-Arg, in the brain in an ATP-Mg2+-dependent manner. To elucidate the physiological role of kyotorphin in organs other than the brain, Kawabata et al., have examined the activity of kyotorphin synthetase in the rat adrenal glands and spinal cord. The activity of adrenal kyotorphin synthetase was inhibited by some L-Arg analogues. Activity was inhibited by NG-nitro-L-arginine methyl ester, alpha-methyl-L-ornithine and D-Arg, but not by NG-nitro-L-arginine and N-iminoethyl-L-ornithine. In the crude soluble extracts from the adrenal glands and spinal cord, kyotorphin was formed by kyotorphin synthetase, and also by the enzymatic processing of the precursor proteins, in the presence of physiological concentrations of L-Tyr and L-Arg in addition to ATP and MgCl2. Kyotorphin synthetase resembling that in the brain is also found to present in the rat adrenal glands and spinal cord, helps in the formation of kyotorphin6.
Kyotorphin suppresses proliferation and Ca2+ signaling in brown preadipocytes-Kyotorphin abolished the stimulatory effect of norepinephrine on proliferation of cultured cells and cold-induced [3H]-thymidine incorporation into DNA of mouse brown adipose tissue in vivo. These changes correlated with peptide-induced suppression of slow calcium signalling in brown preadipocytes.
References
1.Takagi H, Shiomi H, Ueda H, Amano H (1979). A novel analgesic dipeptide from bovine brain is a possible Met-enkephalin release. Nature, 282(5737):410–412.
2.Lopes SC , Soares CM, Baptista AM, Goormaghtigh E, Cabral B , Castanho MA (2006). Conformational and Orientational Guidance of the Analgesic Dipeptide Kyotorphin Induced by Lipidic Membranes: Putative Correlation toward Receptor Docking. J Phys Chem., 110(7):3385–3394.
3.Cheng ZJ, Fan GH, Zhao J, Zhang Z, Wu YL, Jiang LZ, Zhu Y, Pei G, Ma L (1997). Endogenous opioid receptor-like receptor in human neuroblastoma SK-N-SH cells: Activation of inhibitory G protein and homologous desensitization. Neuroreport., 27:1913-1918.
4.Inoue M, Kobayashi M, Kozaki S, Zimmer A, Ueda H (1998). Nociceptin/orphanin FQ-induced nociceptive responses through substance P release from peripheral nerve endings in mice. PNAS, 95:10949-10953.
5.Kharchenko IB, Ziganshin RK, Volkov AV, Koshelev VB (1997). Neokyotorphin and kyotorphin improve cardiovascular and cerebral resuscitation after heart arrest. Bulletin of Experimental Biology and Medicine, 123:450-452.
6.Kawabata A, Muguruma H, Tanaka M, Takagi H (1996). Kyotorphin synthetase activity in rat adrenal glands and spinal cord. Peptide, 17:407-411.
Neurotensins and Related Peptides
Definition
Neurotensin (NT) is a biologically active tridecapeptide isolated from the hypothalamus. It has been shown to induce hypotension in the rat, to stimulate contraction of guinea pig ileum and rat uterus, and to cause relaxation of rat duodenum. There is also evidence that it acts as both a peripheral and a central nervous system neurotransmitter1.
Related peptides
NT gene was isolated and sequenced and found to consist of a 10.2-kilobase segment containing 4 exons and 3 introns. The gene encodes a 170-amino acid precursor protein containing both the tridecapeptide NT and a closely related hexapeptide, neuromedin N (NN). The four amino acids at the carboxy terminal of NT and NN are identical, and amino acids 8-13 of NT are essential for biologic activity. The NT/neuromedin N (NT/NN) gene is highly conserved between species2.
Discovery
NT2 was first isolated in 1973 from bovine hypothalamus by Carraway and Leeman. In 1988, the rat NT gene was isolated and sequenced by Kislauskis et al. in 19882.
Structural Characteristics
NT is a 13-amino acid peptide (pGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu) and its analogue neuromedin-N (Lys-Ile-Pro-Tyr-Ile-Leu) (Minamino et al., 1984) is synthesized by a common precursor in mammalian brain (Kislauskis et al., 1988) and intestine (Dobner et al., 1987) 3,4. NT shares significant similarity in its 6 C-terminal amino acids with several other neuropeptides, including neuromedin N. This region is responsible for the biological activity, the N-terminal portion having a modulatory role5.
Mode of Action
NT is a brain and gastrointestinal peptide that fulfils many central and peripheral functions through its interaction with specific receptors. Three subtypes of neurotensin receptors have been cloned. Two of them belong to the family of G protein-coupled receptors, whereas the third one is an entirely new type of neuropeptide receptor and is identical to gp95/sortilin, a 100 kDa-protein with a single transmembrane domain4. Both central and peripheral modes of action of neurotensin imply as a first step the recognition of the peptide by a specific receptor located on the plasma membrane of the target cell. Formation of the neurotensin-receptor complex is then translated inside the cell by a change in the activity of an intracellular enzyme1.
Functions
Like many other neuropeptides, NT is a messenger of intracellular communication working as a neurotransmitter or neuromodulator in the brain and as a local hormone in the periphery. Thus, several pharmacological, morphological, and neurochemical data suggest that one of the functions of NT in the brain is to regulate dopamine neurotransmission along the nigrostriatal and mesolimbic pathways. NT is distributed throughout the central nervous system, with highest levels in the hypothalamus, amygdala and nucleus accumbens. It induces a variety of effects, including: analgesia, hypothermia and increased locomotor activity. It is also involved in regulation of dopamine pathways. On the other hand, the likely role of NT as a parahormone in the gastrointestinal tract has been well documented. In the periphery, NT is found in endocrine cells of the small intestine, where it leads to secretion and smooth muscle contraction1,6.
References
1.Vincent JP (1995). Neurotensin receptors: binding properties, transduction pathways, and structure. Cell Mol Neurobiol., 15(5):501-512.
2.Kislauskis E, Bullock B, McNeil S, Dobner PR.(1988). The rat gene encoding neurotensin and neuromedin N. Structure, tissue-specific expression, and evolution of exon sequences. J Biol Chem., 263(10):4963-4968.
3.Minamino N, Kangawa K, Matsuo H.(1984). Neuromedin N: a novel neurotensin-like peptide identified in porcine spinal cord. Biochem Biophys Res Commun., 122(2):542-549.
4.Dobner PR, Barber DL, Villa-Komaroff L, McKiernan C.( 1987). Cloning and sequence analysis of cDNA for the canine neurotensin/neuromedin N precursor. PNAS., 84(10):3516-20.
5.Binder EB, Kinkead B, Owens MJ and Nemeroff CB. (2001). Neurotensin and Dopamine Interactions. Pharmacol Rev., 53(4):453-486.
6.Vincent JP, Mazella J, Kitabgi P. (1999). Neurotensin and neurotensin receptors. Trends Pharmacol Sci., 20(7):302-309.
Neurotensin (NT) is a biologically active tridecapeptide isolated from the hypothalamus. It has been shown to induce hypotension in the rat, to stimulate contraction of guinea pig ileum and rat uterus, and to cause relaxation of rat duodenum. There is also evidence that it acts as both a peripheral and a central nervous system neurotransmitter1.
Related peptides
NT gene was isolated and sequenced and found to consist of a 10.2-kilobase segment containing 4 exons and 3 introns. The gene encodes a 170-amino acid precursor protein containing both the tridecapeptide NT and a closely related hexapeptide, neuromedin N (NN). The four amino acids at the carboxy terminal of NT and NN are identical, and amino acids 8-13 of NT are essential for biologic activity. The NT/neuromedin N (NT/NN) gene is highly conserved between species2.
Discovery
NT2 was first isolated in 1973 from bovine hypothalamus by Carraway and Leeman. In 1988, the rat NT gene was isolated and sequenced by Kislauskis et al. in 19882.
Structural Characteristics
NT is a 13-amino acid peptide (pGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu) and its analogue neuromedin-N (Lys-Ile-Pro-Tyr-Ile-Leu) (Minamino et al., 1984) is synthesized by a common precursor in mammalian brain (Kislauskis et al., 1988) and intestine (Dobner et al., 1987) 3,4. NT shares significant similarity in its 6 C-terminal amino acids with several other neuropeptides, including neuromedin N. This region is responsible for the biological activity, the N-terminal portion having a modulatory role5.
Mode of Action
NT is a brain and gastrointestinal peptide that fulfils many central and peripheral functions through its interaction with specific receptors. Three subtypes of neurotensin receptors have been cloned. Two of them belong to the family of G protein-coupled receptors, whereas the third one is an entirely new type of neuropeptide receptor and is identical to gp95/sortilin, a 100 kDa-protein with a single transmembrane domain4. Both central and peripheral modes of action of neurotensin imply as a first step the recognition of the peptide by a specific receptor located on the plasma membrane of the target cell. Formation of the neurotensin-receptor complex is then translated inside the cell by a change in the activity of an intracellular enzyme1.
Functions
Like many other neuropeptides, NT is a messenger of intracellular communication working as a neurotransmitter or neuromodulator in the brain and as a local hormone in the periphery. Thus, several pharmacological, morphological, and neurochemical data suggest that one of the functions of NT in the brain is to regulate dopamine neurotransmission along the nigrostriatal and mesolimbic pathways. NT is distributed throughout the central nervous system, with highest levels in the hypothalamus, amygdala and nucleus accumbens. It induces a variety of effects, including: analgesia, hypothermia and increased locomotor activity. It is also involved in regulation of dopamine pathways. On the other hand, the likely role of NT as a parahormone in the gastrointestinal tract has been well documented. In the periphery, NT is found in endocrine cells of the small intestine, where it leads to secretion and smooth muscle contraction1,6.
References
1.Vincent JP (1995). Neurotensin receptors: binding properties, transduction pathways, and structure. Cell Mol Neurobiol., 15(5):501-512.
2.Kislauskis E, Bullock B, McNeil S, Dobner PR.(1988). The rat gene encoding neurotensin and neuromedin N. Structure, tissue-specific expression, and evolution of exon sequences. J Biol Chem., 263(10):4963-4968.
3.Minamino N, Kangawa K, Matsuo H.(1984). Neuromedin N: a novel neurotensin-like peptide identified in porcine spinal cord. Biochem Biophys Res Commun., 122(2):542-549.
4.Dobner PR, Barber DL, Villa-Komaroff L, McKiernan C.( 1987). Cloning and sequence analysis of cDNA for the canine neurotensin/neuromedin N precursor. PNAS., 84(10):3516-20.
5.Binder EB, Kinkead B, Owens MJ and Nemeroff CB. (2001). Neurotensin and Dopamine Interactions. Pharmacol Rev., 53(4):453-486.
6.Vincent JP, Mazella J, Kitabgi P. (1999). Neurotensin and neurotensin receptors. Trends Pharmacol Sci., 20(7):302-309.
Neurokinins
Definition
The neurokinins are a family of neuropeptides which includes substance P (SP) and the two structurally related peptides, neurokinin A (NKA) and neurokinin B (NKB). These neurotransmitters appear to play a key role in the regulation of emotions, and antagonists of their receptors may be novel psychotropic drugs of the future1.
Related peptides
These carboxyl terminal-amidated peptides are derived from two preprotachykinin genes - the PPT-A gene encodes the sequences of Substance P, Neurokinin A, and neuropeptide K and the PPT-B gene encodes the sequence of Neurokinin B1.
Discovery
In 1931 von Euler and Gaddum suggested the existence of SP in the extract of mammalian guts. The structure was finally confirmed and sequenced by Chang et al. in 1971. Subsequently NKA and NKB were both isolated from porcine spinal cord in 1983. The structures were elucidated by the independent contributions of Kimura et al. and Kangawa et al1.
Structural Characteristics
Substance P: Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2.
NKA:His-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met-NH2,
NKB:Asp-Met-His-Asp-Phe-Phe-Val-Gly-Leu-Met-NH2.
The neurokinins are characterized by a common C-terminal sequence, Phe-X-Gly-Leu-Met-NH2, where X is a phenylalanine or a valine1.
Mode of Action
Glutamate, through activation of post-synaptic N-methyl-D-aspartate (NMDA) and a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors, contributes to neurokinin signaling in the nucleus of the solitary tract (NST) 2. .Once released, SP and NKA exert their biological effects on target cells by interacting with specific receptors, which have been cloned, characterized, and found to have seven transmembrane spanning sequences and to be coupled to G-proteins and the phosphoinositide-signaling pathway. To date, three distinct receptors have been identified, termed neurokinin-1 receptor (NK-1R), neurokinin-2 receptor (NK-2R), and neurokinin-3 receptor (NK-3R). SP preferentially activates the NK-1R, NKA the NK-2R, and neurokinin B the NK-3R; however, at high ligand concentrations each tachykinin can activate each of the tachykinin receptors3.
Functions
Neurokinins exert quite diverse functions in the whole body. For instance, SP acts in the CNS as a pain transmitter and also as a regulator of dopaminergic and adrenergic neurons. In the peripheral system, SP and/or NKA are involved in activation of the immune system, vasodilation, smooth muscle contraction, bronchoconstriction, stimulation of salivary secretion, neurogenic inflammation, and so on1. Neurokinin B may play an important role in the olfactory, gustatory, visceral, and neuroendocrine processing information. Neurokinin B is potent bronchioconstrictor and has neuromodulatory roles in various brain functions. Neurokinin B stimulate the production of immunoglobulins in peripheral B lymphocytes, This conditional response to Neurokinin B is likely due NK-3 receptors present only following co-culture and activation3.
References
1.Takaya. T (1996). Discovery of neurokinin antagonists. Pure & Appl. Chem., 68(4):875-880.
2.Colin I, Blondeau C, Baude A.(2002). Neurokinin release in the rat nucleus of the solitary tract via NMDA and AMPA receptors. Neuroscience., 115(4)1023-1033
3.Renzi D, Pellegrini B, Tonelli F, Surrenti C, Calabrò A (2000). Substance P (Neurokinin-1) and Neurokinin A (Neurokinin-2) Receptor Gene and Protein Expression in the Healthy and Inflamed Human Intestine. Am J Pathol., 157(5):1511-1522
The neurokinins are a family of neuropeptides which includes substance P (SP) and the two structurally related peptides, neurokinin A (NKA) and neurokinin B (NKB). These neurotransmitters appear to play a key role in the regulation of emotions, and antagonists of their receptors may be novel psychotropic drugs of the future1.
Related peptides
These carboxyl terminal-amidated peptides are derived from two preprotachykinin genes - the PPT-A gene encodes the sequences of Substance P, Neurokinin A, and neuropeptide K and the PPT-B gene encodes the sequence of Neurokinin B1.
Discovery
In 1931 von Euler and Gaddum suggested the existence of SP in the extract of mammalian guts. The structure was finally confirmed and sequenced by Chang et al. in 1971. Subsequently NKA and NKB were both isolated from porcine spinal cord in 1983. The structures were elucidated by the independent contributions of Kimura et al. and Kangawa et al1.
Structural Characteristics
Substance P: Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2.
NKA:His-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met-NH2,
NKB:Asp-Met-His-Asp-Phe-Phe-Val-Gly-Leu-Met-NH2.
The neurokinins are characterized by a common C-terminal sequence, Phe-X-Gly-Leu-Met-NH2, where X is a phenylalanine or a valine1.
Mode of Action
Glutamate, through activation of post-synaptic N-methyl-D-aspartate (NMDA) and a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors, contributes to neurokinin signaling in the nucleus of the solitary tract (NST) 2. .Once released, SP and NKA exert their biological effects on target cells by interacting with specific receptors, which have been cloned, characterized, and found to have seven transmembrane spanning sequences and to be coupled to G-proteins and the phosphoinositide-signaling pathway. To date, three distinct receptors have been identified, termed neurokinin-1 receptor (NK-1R), neurokinin-2 receptor (NK-2R), and neurokinin-3 receptor (NK-3R). SP preferentially activates the NK-1R, NKA the NK-2R, and neurokinin B the NK-3R; however, at high ligand concentrations each tachykinin can activate each of the tachykinin receptors3.
Functions
Neurokinins exert quite diverse functions in the whole body. For instance, SP acts in the CNS as a pain transmitter and also as a regulator of dopaminergic and adrenergic neurons. In the peripheral system, SP and/or NKA are involved in activation of the immune system, vasodilation, smooth muscle contraction, bronchoconstriction, stimulation of salivary secretion, neurogenic inflammation, and so on1. Neurokinin B may play an important role in the olfactory, gustatory, visceral, and neuroendocrine processing information. Neurokinin B is potent bronchioconstrictor and has neuromodulatory roles in various brain functions. Neurokinin B stimulate the production of immunoglobulins in peripheral B lymphocytes, This conditional response to Neurokinin B is likely due NK-3 receptors present only following co-culture and activation3.
References
1.Takaya. T (1996). Discovery of neurokinin antagonists. Pure & Appl. Chem., 68(4):875-880.
2.Colin I, Blondeau C, Baude A.(2002). Neurokinin release in the rat nucleus of the solitary tract via NMDA and AMPA receptors. Neuroscience., 115(4)1023-1033
3.Renzi D, Pellegrini B, Tonelli F, Surrenti C, Calabrò A (2000). Substance P (Neurokinin-1) and Neurokinin A (Neurokinin-2) Receptor Gene and Protein Expression in the Healthy and Inflamed Human Intestine. Am J Pathol., 157(5):1511-1522
Neuroendocrine Regulatory Peptide
Definition
are derived from distinct regions of VGF, a neurosecretory protein that was originally identified as a product of a nerve growth factor-responsive gene in rat PC12 cells. NERPs are novel hypothalamic peptides involved in the control of body fluid homeostasis by regulating vasopressin release1.
Related peptides
The two amidated peptides NERP 1 and 2, with monoisotopic masses of 2677.4 and 4062.2, were derived from distinct regions of the neurosecretory protein VGF; one is from human VGF-(281–306), and the other is from VGF-(310 –347) 2.
Discovery
Yamaguchi et al, analyzed peptides secreted from human medullary thyroid carcinoma TT cells that produce amidated peptides. They identified two novel amidated peptides and designated them as neuroendocrine regulatory peptide (NERP)-1 and NERP-22.
Structural Characteristics
Molecular masses of human NERP-1 and 2 were found to be 2677 Da and 4062 Da, respectively2. The amino acid length of human NERP-1 is 26, and that of rat NERP-1 is 25. Human and rat NERP-2 are both 38 amino acid peptides1. The processing and amidation of NERPs occur intracellularly before secretion, as is known with amidated bioactive peptides secreted by endocrine cells. Bioactivity of NERPs requires C-terminal amidation which is a post translational modification1.
Mode of Action
Vasopressin release is regulated by the electrical activity of vasopressin neurons, which are modulated by various neurotransmitters and neuromodulators. The major neural signals to vasopressin neurons are excitatory and inhibitory postsynaptic currents generated by presynaptic release of glutamate and ?-aminobutyric acid, respectively. Angiotensin-II (AII) and NaCl potentiate excitatory postsynaptic currents in vasopressin neurons, thereby stimulating vasopressin secretion. Although cell-surface receptors or target proteins of NERPs have not been identified yet, the actions of NERP to suppress AII- and NaCl-induced vasopressin release from the hypothalamus may suggest that they presynaptically inhibit the glutamatergic inputs or enhance GABAergic inputs to vasopressin neurons2.
Functions
NERPs are novel bioactive peptides involved in body fluid homeostasis; they appear to modulate the actions and secretions of other neuropeptides. NERPs participate in the hypothalamic control of plasma osmolarity balance. Both NERP-1 and NERP-2 are potent endogenous suppressors of vasopressin release. All these actions were observed with C-terminally amidated forms only2.
References
1.Toshinai K and Nakazato M (2009). Neuroendocrine regulatory peptide-1 and -2: Novel bioactive peptides processed from VGF. Cell. Mol. Life Sci., 66(11-12):1939-1945.
2.Yamaguchi H, Sasaki K, Satomi Y, Shimbara T, Kageyama H, Mondal MS, Toshinai K, Date Y, González LJ, Shioda S, Takao T, Nakazato M, Minamino N (2007). Peptidomic Identification and Biological Validation of Neuroendocrine Regulatory Peptide-1 and -2. J Biol Chem., 282(36):26354-26360.
are derived from distinct regions of VGF, a neurosecretory protein that was originally identified as a product of a nerve growth factor-responsive gene in rat PC12 cells. NERPs are novel hypothalamic peptides involved in the control of body fluid homeostasis by regulating vasopressin release1.
Related peptides
The two amidated peptides NERP 1 and 2, with monoisotopic masses of 2677.4 and 4062.2, were derived from distinct regions of the neurosecretory protein VGF; one is from human VGF-(281–306), and the other is from VGF-(310 –347) 2.
Discovery
Yamaguchi et al, analyzed peptides secreted from human medullary thyroid carcinoma TT cells that produce amidated peptides. They identified two novel amidated peptides and designated them as neuroendocrine regulatory peptide (NERP)-1 and NERP-22.
Structural Characteristics
Molecular masses of human NERP-1 and 2 were found to be 2677 Da and 4062 Da, respectively2. The amino acid length of human NERP-1 is 26, and that of rat NERP-1 is 25. Human and rat NERP-2 are both 38 amino acid peptides1. The processing and amidation of NERPs occur intracellularly before secretion, as is known with amidated bioactive peptides secreted by endocrine cells. Bioactivity of NERPs requires C-terminal amidation which is a post translational modification1.
Mode of Action
Vasopressin release is regulated by the electrical activity of vasopressin neurons, which are modulated by various neurotransmitters and neuromodulators. The major neural signals to vasopressin neurons are excitatory and inhibitory postsynaptic currents generated by presynaptic release of glutamate and ?-aminobutyric acid, respectively. Angiotensin-II (AII) and NaCl potentiate excitatory postsynaptic currents in vasopressin neurons, thereby stimulating vasopressin secretion. Although cell-surface receptors or target proteins of NERPs have not been identified yet, the actions of NERP to suppress AII- and NaCl-induced vasopressin release from the hypothalamus may suggest that they presynaptically inhibit the glutamatergic inputs or enhance GABAergic inputs to vasopressin neurons2.
Functions
NERPs are novel bioactive peptides involved in body fluid homeostasis; they appear to modulate the actions and secretions of other neuropeptides. NERPs participate in the hypothalamic control of plasma osmolarity balance. Both NERP-1 and NERP-2 are potent endogenous suppressors of vasopressin release. All these actions were observed with C-terminally amidated forms only2.
References
1.Toshinai K and Nakazato M (2009). Neuroendocrine regulatory peptide-1 and -2: Novel bioactive peptides processed from VGF. Cell. Mol. Life Sci., 66(11-12):1939-1945.
2.Yamaguchi H, Sasaki K, Satomi Y, Shimbara T, Kageyama H, Mondal MS, Toshinai K, Date Y, González LJ, Shioda S, Takao T, Nakazato M, Minamino N (2007). Peptidomic Identification and Biological Validation of Neuroendocrine Regulatory Peptide-1 and -2. J Biol Chem., 282(36):26354-26360.
Nesfatins
Definition
Nesfatin-1, corresponding to nucleobindin2 (NUCB2) is a novel satiety molecule that is associated with melanocortin signaling in the hypothalamus. It is a feeding inhibitory peptide encoded in the precursor protein, nucleobindin 2 (pronesfatin) 1.
Related peptides
NUCB2, a 396 aa peptide, is highly conserved between humans and rodents, and mRNA and immunoreactive cell bodies can be found in several hypothalamic nuclei; however, only the paraventricular nucleus expression was decreased by fasting. NUCB2 has several sites for posttranslational cleavage by prohormone convertases, and intracerebroventricular (i.c.v.) injection of NUCB2 or its first 82 amino acids (termed nesfatin-1 for NEFA/nucleobindin2-encoded satiety factor) acutely, transiently, and dose dependently inhibited dark phase food intake in rats. Other posttranslational products of NUCB2, or a NUCB2 mutant that cannot be cleaved at aa 82–83, did not inhibit food intake. These NUCB2 fragments (termed nesfatin-2 and -3) have structures similar to that of DNA or calcium binding proteins2.
Discovery
Oh-I et al in 2006 reported the discovery of a novel satiety molecule called Nesfatin, corresponding to NEFA/NUCB2, a secreted protein of unknown function, expressed in the appetite-control hypothalamic nuclei in rats3.
Structural Characteristics
NUCB2 (also called NEFA for DNA binding /EF-hand /acidic protein) is a hypothalamus-secreted protein that is highly conserved in human, mice and rat. NUCB2/Nesfatin is composed of a signal peptide of 24 amino acids and a protein structure containing 396 amino acids4. NUCB2 is cleaved post translationally by prohormone convertases into an N-terminus-fragment Nesfatin-1 and two C-terminal peptides, Nesfatin-2 and Nesfatin-32.
Mode of Action
Nesfatin-1 is found in discrete nuclei of the hypothalamus where it probably activates a leptin-independent melanocortin pathway. Nesfatin-1 crosses the Blood Brain Barrier (BBB) in both the blood-to-brain and brain-to-blood directions by a nonsaturable system4.. Calcium binding nesfatins mediate their action through G-protein coupled receptors5.
Functions
Nesfatin is a satiety molecule with anorexigenic properties4. Nesfatin-1 in rat stimulates calcium influx and interacts with a G protein-coupled receptor still to be characterized5. Nesfatin has potential clinical applications. It could be used as a diagnostic index in various diseases Nesfatin-1-related drugs may improve metabolic disorders by reducing body weight of patients with obesity and metabolic syndrome4.
References
1.Gonzalez R, Tiwari A, Unniappan S. (2009). Pancreatic beta cells colocalize insulin and pronesfatin immunoreactivity in rodents. Biochem Biophys Res Commun., 381(4):643-648.
2.Cowley MA and Grove KL (2006). To be or NUCB2, is nesfatin the answer? Cell Metab., 4(6):421-422.
3.Oh-I S, Shimizu H, Satoh T, Okada S, Adachi S, Inoue K, Eguchi H, Yamamoto M, Imaki T, Hashimoto K, Tsuchiya T, Monden T, Horiguchi K, Yamada M, Mori M. (2006). Identification of nesfatin-1 as a satiety molecule in the hypothalamus. Nature, 443(7112):709-712.
4.Shimizu H, Oh-I S, Okada S, Mori M (2009). Nesfatin-1: An Overview and Future Clinical Application. Endoc J., 56(4):537-543.
5.Brailoiu GC, Dun SL, Brailoiu E, Inan S, Yang J, Chang JK, Dun NJ. (2009). Nesfatin-1: Distribution and Interaction with a G Protein-Coupled Receptor in the Rat Brain. Endocrinology,148(10):5088–5094.
Nesfatin-1, corresponding to nucleobindin2 (NUCB2) is a novel satiety molecule that is associated with melanocortin signaling in the hypothalamus. It is a feeding inhibitory peptide encoded in the precursor protein, nucleobindin 2 (pronesfatin) 1.
Related peptides
NUCB2, a 396 aa peptide, is highly conserved between humans and rodents, and mRNA and immunoreactive cell bodies can be found in several hypothalamic nuclei; however, only the paraventricular nucleus expression was decreased by fasting. NUCB2 has several sites for posttranslational cleavage by prohormone convertases, and intracerebroventricular (i.c.v.) injection of NUCB2 or its first 82 amino acids (termed nesfatin-1 for NEFA/nucleobindin2-encoded satiety factor) acutely, transiently, and dose dependently inhibited dark phase food intake in rats. Other posttranslational products of NUCB2, or a NUCB2 mutant that cannot be cleaved at aa 82–83, did not inhibit food intake. These NUCB2 fragments (termed nesfatin-2 and -3) have structures similar to that of DNA or calcium binding proteins2.
Discovery
Oh-I et al in 2006 reported the discovery of a novel satiety molecule called Nesfatin, corresponding to NEFA/NUCB2, a secreted protein of unknown function, expressed in the appetite-control hypothalamic nuclei in rats3.
Structural Characteristics
NUCB2 (also called NEFA for DNA binding /EF-hand /acidic protein) is a hypothalamus-secreted protein that is highly conserved in human, mice and rat. NUCB2/Nesfatin is composed of a signal peptide of 24 amino acids and a protein structure containing 396 amino acids4. NUCB2 is cleaved post translationally by prohormone convertases into an N-terminus-fragment Nesfatin-1 and two C-terminal peptides, Nesfatin-2 and Nesfatin-32.
Mode of Action
Nesfatin-1 is found in discrete nuclei of the hypothalamus where it probably activates a leptin-independent melanocortin pathway. Nesfatin-1 crosses the Blood Brain Barrier (BBB) in both the blood-to-brain and brain-to-blood directions by a nonsaturable system4.. Calcium binding nesfatins mediate their action through G-protein coupled receptors5.
Functions
Nesfatin is a satiety molecule with anorexigenic properties4. Nesfatin-1 in rat stimulates calcium influx and interacts with a G protein-coupled receptor still to be characterized5. Nesfatin has potential clinical applications. It could be used as a diagnostic index in various diseases Nesfatin-1-related drugs may improve metabolic disorders by reducing body weight of patients with obesity and metabolic syndrome4.
References
1.Gonzalez R, Tiwari A, Unniappan S. (2009). Pancreatic beta cells colocalize insulin and pronesfatin immunoreactivity in rodents. Biochem Biophys Res Commun., 381(4):643-648.
2.Cowley MA and Grove KL (2006). To be or NUCB2, is nesfatin the answer? Cell Metab., 4(6):421-422.
3.Oh-I S, Shimizu H, Satoh T, Okada S, Adachi S, Inoue K, Eguchi H, Yamamoto M, Imaki T, Hashimoto K, Tsuchiya T, Monden T, Horiguchi K, Yamada M, Mori M. (2006). Identification of nesfatin-1 as a satiety molecule in the hypothalamus. Nature, 443(7112):709-712.
4.Shimizu H, Oh-I S, Okada S, Mori M (2009). Nesfatin-1: An Overview and Future Clinical Application. Endoc J., 56(4):537-543.
5.Brailoiu GC, Dun SL, Brailoiu E, Inan S, Yang J, Chang JK, Dun NJ. (2009). Nesfatin-1: Distribution and Interaction with a G Protein-Coupled Receptor in the Rat Brain. Endocrinology,148(10):5088–5094.
Nephilatoxins
Definition
Nephilatoxins are Joro spider toxins (JSTX) originally derived from Nephila clavata. These toxins have been found to block excitatory postsynaptic potentials and glutamate-evoked responses in the neuromuscular synapse of crustacea, the squid giant synapse and the mammalian brain synapse1.
Related peptides
JSTX from Nephila clavata, NSTX from Nephila maculata, and argiopine (argiotoxin) from Argiope lobata, act postsynaptically on glutamate receptors. These toxins share a common structure of a phenolic moiety connected to a polyamine. Chemical synthesis of these low molecular weight toxins has enabled morphological and biochemical studies of the glutamate receptors2.
Discovery
The acylpolyaminetoxins constitute a common class of neuroblockers, occurring as complex mixtures of similar compounds containing an aromatic group at the end of a polyamine chain in the venoms of spiders. They were first described by Kawai et al in 1982 and the first structures were characterized from the venom of Nephila masculata by Aramaki et al in 1986 3.
Structural Characteristics
Structures of the toxins (JSTXs, NSTXs) of spiders belonging to the genus Nephila were determined and it was found that a unique 2,4-dihydroxyphenylacetyl asparaginyl cadaverine part was conserved between all toxins, indicating that this part is intimately involved in the blocking activity1.These are polyamine peptides comprising an aryl L-asparaginyl residue and a polyamine chain attached to a number of cationic L-amino acids. The presence of an indole-3-acetyl or 6-hydroxy-indole-3-acetyl residue is a common feature of this family of neurotoxins4.
Mode of Action
The blocking action of Nephila clavata spider neurotoxin, or JSTX, on ionic currents activated by L-glutamate and its agonists when applied to the membrane of neurons isolated from the rat hippocampus was investigated using a concentration clamp technique. Crude JSTX venom was found to block L-glutamate-, quisqualate, and kainate-activated ionic currents induced by activating non-N-methyl-D-aspartate (non-NMDA) membrane receptors. Following the effects of JSTX, ionic currents activated by L-glutamate and its agonists declined to 34–36% of their initial value with no recovery during JSTX washout. It is postulated that JSTX interacts with chemically-operated non-NMDA ionic channels, blocking their transition into a number of their possible open states5.The 2,4 dihydroxyphenylacetyl asparagine in the toxin structure was responsible for suppressive action, while the remaining part containing a polyamine was related to the agonist binding site with the polycationic part enhancing the toxic activity6.
Functions
JSTX derived from Nephila clavata has been found to block excitatory postsynaptic potentials and glutamate-evoked responses in the neuromuscular synapse of crustacea, the squid giant synapse and the mammalian brain synapse1. Many kinds of venomous principles modulate physiological responses of mammalian signal transduction systems, on which they act selectively as enhancers, inhibitors or some other kind of effectors. These toxins become useful tools for physiological research7.
References
1.Kawai N and Nakajima T (1990). Characterization of Glutamate Receptor by Spider Toxin. Toxin Reviews, 9(2):203-223.
2.Kawai N (1991). Neuroactive Toxins of Spider Venoms. Toxin Reviews., 10(2):131-167
3.Palma MS, Itagaki Y, Fujita T, Naoki H, Nakajima T(1998). Structural characterization of a new acylpolyaminetoxin from the venom of Brazilian Garden Spider Nephilengys cruentata. Toxicon., 36(3):485-493.
4.Bycroft BW, Chan WC, Hone ND, Millington S, I. A. Nash IA. (1994). Synthesis of the Spider Toxins Nephilatoxin-9 and -11 by a Novel Solid-Phase Strategy. J. Am. Chem. Soc., 116(16)7415–7416.
5.Kiskin NI, Kliuchko EM, Kryshtal' OA, Tsyndrenko AIa, Akaike N. (1989). Blocking action of Nephila clavata spider toxin on ionic currents activated by glutamate and its agonists in isolated hippocampal neurons. Neirofiziologiia, 21(2):152-160.
6.Kawai N, Miwa A, Shimazaki K, Sahara Y, Robinson HP, Nakajima T(1991). Spider toxin and the glutamate receptors. Comp Biochem Physiol C., 98:87-95.
7.Terumi Nakajima. 2006. Nanoanalysis of the arthropod neuro-toxins. Proceedings of the Japan Academy, 82(8):297-310.
Nephilatoxins are Joro spider toxins (JSTX) originally derived from Nephila clavata. These toxins have been found to block excitatory postsynaptic potentials and glutamate-evoked responses in the neuromuscular synapse of crustacea, the squid giant synapse and the mammalian brain synapse1.
Related peptides
JSTX from Nephila clavata, NSTX from Nephila maculata, and argiopine (argiotoxin) from Argiope lobata, act postsynaptically on glutamate receptors. These toxins share a common structure of a phenolic moiety connected to a polyamine. Chemical synthesis of these low molecular weight toxins has enabled morphological and biochemical studies of the glutamate receptors2.
Discovery
The acylpolyaminetoxins constitute a common class of neuroblockers, occurring as complex mixtures of similar compounds containing an aromatic group at the end of a polyamine chain in the venoms of spiders. They were first described by Kawai et al in 1982 and the first structures were characterized from the venom of Nephila masculata by Aramaki et al in 1986 3.
Structural Characteristics
Structures of the toxins (JSTXs, NSTXs) of spiders belonging to the genus Nephila were determined and it was found that a unique 2,4-dihydroxyphenylacetyl asparaginyl cadaverine part was conserved between all toxins, indicating that this part is intimately involved in the blocking activity1.These are polyamine peptides comprising an aryl L-asparaginyl residue and a polyamine chain attached to a number of cationic L-amino acids. The presence of an indole-3-acetyl or 6-hydroxy-indole-3-acetyl residue is a common feature of this family of neurotoxins4.
Mode of Action
The blocking action of Nephila clavata spider neurotoxin, or JSTX, on ionic currents activated by L-glutamate and its agonists when applied to the membrane of neurons isolated from the rat hippocampus was investigated using a concentration clamp technique. Crude JSTX venom was found to block L-glutamate-, quisqualate, and kainate-activated ionic currents induced by activating non-N-methyl-D-aspartate (non-NMDA) membrane receptors. Following the effects of JSTX, ionic currents activated by L-glutamate and its agonists declined to 34–36% of their initial value with no recovery during JSTX washout. It is postulated that JSTX interacts with chemically-operated non-NMDA ionic channels, blocking their transition into a number of their possible open states5.The 2,4 dihydroxyphenylacetyl asparagine in the toxin structure was responsible for suppressive action, while the remaining part containing a polyamine was related to the agonist binding site with the polycationic part enhancing the toxic activity6.
Functions
JSTX derived from Nephila clavata has been found to block excitatory postsynaptic potentials and glutamate-evoked responses in the neuromuscular synapse of crustacea, the squid giant synapse and the mammalian brain synapse1. Many kinds of venomous principles modulate physiological responses of mammalian signal transduction systems, on which they act selectively as enhancers, inhibitors or some other kind of effectors. These toxins become useful tools for physiological research7.
References
1.Kawai N and Nakajima T (1990). Characterization of Glutamate Receptor by Spider Toxin. Toxin Reviews, 9(2):203-223.
2.Kawai N (1991). Neuroactive Toxins of Spider Venoms. Toxin Reviews., 10(2):131-167
3.Palma MS, Itagaki Y, Fujita T, Naoki H, Nakajima T(1998). Structural characterization of a new acylpolyaminetoxin from the venom of Brazilian Garden Spider Nephilengys cruentata. Toxicon., 36(3):485-493.
4.Bycroft BW, Chan WC, Hone ND, Millington S, I. A. Nash IA. (1994). Synthesis of the Spider Toxins Nephilatoxin-9 and -11 by a Novel Solid-Phase Strategy. J. Am. Chem. Soc., 116(16)7415–7416.
5.Kiskin NI, Kliuchko EM, Kryshtal' OA, Tsyndrenko AIa, Akaike N. (1989). Blocking action of Nephila clavata spider toxin on ionic currents activated by glutamate and its agonists in isolated hippocampal neurons. Neirofiziologiia, 21(2):152-160.
6.Kawai N, Miwa A, Shimazaki K, Sahara Y, Robinson HP, Nakajima T(1991). Spider toxin and the glutamate receptors. Comp Biochem Physiol C., 98:87-95.
7.Terumi Nakajima. 2006. Nanoanalysis of the arthropod neuro-toxins. Proceedings of the Japan Academy, 82(8):297-310.
Neoendorphins
Definition
Neoendorphins are opioid peptides cleaved from prodynorphin. Alpha and beta-neoendorphins (a- and ß-NEO) are [Leu5] enkephalin segment - derived opioid peptides and ? and ?-type opioid receptor agonists1.
Related peptides
Post-translational processing of a precursor protein, prodynorphin yields 5 different opioid peptide products, a-NEO, ß-NEO, within the first COOH terminally extended [Leu5] enkephalin segment, Dynorphin (Dyn) A (1-17), its fragment, Dyn A (1-8) are present within the second segment. The third opioid segment in prodynorphin corresponds to the 13-amino acid peptide sequence, Dyn B. This prodynorphin-derived peptide family together with the proenkephalin products and pro-opiomelanocortin opioid products compose the three distinct groups of endogenous opioids1.
Discovery
a- Neoendorphin (aNEO) and ß-neoendorphin (ßNEO), originally described by Matsuo and co-workers in the 1980’s 2,3.
Structural Characteristics
a-NEO is an opiate decapeptide derived from the prodynorphin protein. The full sequence of a-NEO-endorphin has been determined to be:
Tyr-Gly-Gly-Phe-Leu-Arg-Lys-Tyr-Pro-Lys2.
ß-NEO is a nonapeptide whose complete amino acid sequence has been elucidated to be: Tyr-Gly-Gly-Phe-Leu-Arg-Lys-Tyr-Pro3.
Mode of Action
Dynorphins A and B and a-NEO appear to be the endogenous ligands for opioid ? receptors. The ? receptors are located predominantly in the cerebral cortex, nucleus accumbens, claustrum and hypothalamus of rat and mouse, and have been implicated in the regulation of nociception, diuresis, feeding, neuroendocrine and immune system functions. ß-NEO is an agonist of ?-receptors4.
Functions
Dynorphin and a -NEO bind to the K subtype of opioid receptors and have been shown to inhibit the release of noradrenaline from cardiac sympathetic axons. They play a important role in a number of physiological functions, including pain perception and responses to stress5.
References
1.Chavkin C, Bakhit C, Weber E, Bloom FE (1983). Relative contents and concomitant release of prodynorphin/neoendorphin-derived peptides in rat hippocampus. PNAS, 80(24):7669-7673.
2.Kangawa K, Minamino N, Chino N, Sakakibara S, Matsuo H (1981). The complete amino acid sequence of alpha-neo-endorphin. Biochem Biophys Res Comm.,. 99(3):871-878.
3.Minamino N, Kangawa K, Chino N, Sakakibara S, Matsuo H (1981). Beta-neo-endorphin, a new hypothalamic "big" Leu-enkephalin of porcine origin: its purification and the complete amino acid sequence. Biochem Biophys Res Commun., 99 (3):864-870.
4.Wegener K, Kummer W (1994). Sympathetic IMoradrenergic Fibers as the Source of Immunoreactive Alpha-Neoendorphin and Dynorphin in the Guinea Pig Heart. Acta Anat 151(2):112-119.
5.Book: Dentate Gyrus: a comprehensive guide to structure function and clinical implications By Helen. E. Scharfman.
Neoendorphins are opioid peptides cleaved from prodynorphin. Alpha and beta-neoendorphins (a- and ß-NEO) are [Leu5] enkephalin segment - derived opioid peptides and ? and ?-type opioid receptor agonists1.
Related peptides
Post-translational processing of a precursor protein, prodynorphin yields 5 different opioid peptide products, a-NEO, ß-NEO, within the first COOH terminally extended [Leu5] enkephalin segment, Dynorphin (Dyn) A (1-17), its fragment, Dyn A (1-8) are present within the second segment. The third opioid segment in prodynorphin corresponds to the 13-amino acid peptide sequence, Dyn B. This prodynorphin-derived peptide family together with the proenkephalin products and pro-opiomelanocortin opioid products compose the three distinct groups of endogenous opioids1.
Discovery
a- Neoendorphin (aNEO) and ß-neoendorphin (ßNEO), originally described by Matsuo and co-workers in the 1980’s 2,3.
Structural Characteristics
a-NEO is an opiate decapeptide derived from the prodynorphin protein. The full sequence of a-NEO-endorphin has been determined to be:
Tyr-Gly-Gly-Phe-Leu-Arg-Lys-Tyr-Pro-Lys2.
ß-NEO is a nonapeptide whose complete amino acid sequence has been elucidated to be: Tyr-Gly-Gly-Phe-Leu-Arg-Lys-Tyr-Pro3.
Mode of Action
Dynorphins A and B and a-NEO appear to be the endogenous ligands for opioid ? receptors. The ? receptors are located predominantly in the cerebral cortex, nucleus accumbens, claustrum and hypothalamus of rat and mouse, and have been implicated in the regulation of nociception, diuresis, feeding, neuroendocrine and immune system functions. ß-NEO is an agonist of ?-receptors4.
Functions
Dynorphin and a -NEO bind to the K subtype of opioid receptors and have been shown to inhibit the release of noradrenaline from cardiac sympathetic axons. They play a important role in a number of physiological functions, including pain perception and responses to stress5.
References
1.Chavkin C, Bakhit C, Weber E, Bloom FE (1983). Relative contents and concomitant release of prodynorphin/neoendorphin-derived peptides in rat hippocampus. PNAS, 80(24):7669-7673.
2.Kangawa K, Minamino N, Chino N, Sakakibara S, Matsuo H (1981). The complete amino acid sequence of alpha-neo-endorphin. Biochem Biophys Res Comm.,. 99(3):871-878.
3.Minamino N, Kangawa K, Chino N, Sakakibara S, Matsuo H (1981). Beta-neo-endorphin, a new hypothalamic "big" Leu-enkephalin of porcine origin: its purification and the complete amino acid sequence. Biochem Biophys Res Commun., 99 (3):864-870.
4.Wegener K, Kummer W (1994). Sympathetic IMoradrenergic Fibers as the Source of Immunoreactive Alpha-Neoendorphin and Dynorphin in the Guinea Pig Heart. Acta Anat 151(2):112-119.
5.Book: Dentate Gyrus: a comprehensive guide to structure function and clinical implications By Helen. E. Scharfman.
Natriuretic Peptides
Definition
Natriuretic peptides are a family of structurally related but genetically distinct hormones/paracrine factors that regulate blood volume, blood pressure, ventricular hypertrophy, pulmonary hypertension, fat metabolism, and long bone growth. The mammalian members are atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), C-type natriuretic peptide (CNP) 1.
Discovery
De Bold et al reported the first direct evidence of natriuretic substance in 19812. They found that the IV injection of atrial, but not ventricular, homogenates into rats elicited a rapid decrease in blood pressure that was accompanied by increased renal sodium and water excretion. After this seminal observation, several groups purified peptides of varying sizes from atrial tissue that possess both natriuretic and smooth muscle-relaxing activity. These peptides were given a number of different names such as ANP, cardionatrin, cardiodilatin, atriopeptin, and the first description is most often used today. BNP, which was originally called brain natriuretic peptide and CNP were subsequently purified from porcine brain extracts based on their ability to relax smooth muscle.
Structural Characteristics
The natriuretic peptides are a family of ring shaped vasoactive hormones showing considerable sequence homology. All three members contain the conserved sequence CFGXXXDRIXXXXGLGC where X is any amino acid. The flanking cysteines form a 17-amino-acid disulfide-linked ring that is required for biological activity. All natriuretic peptides are synthesized as preprohormones. Human preproANP is 151 amino acids in length. Cleavage of the amino terminal signal sequence results in the 126-amino-acid proANP, which is the predominant form stored in atrial granules. ProANP is rapidly cleaved upon secretion by the transmembrane cardiac serine protease called corin to form the biologically active carboxyl-terminal 28-amino-acid peptide. Human BNP is synthesized as a preprohormone of 134 residues containing a signal sequence that is cleaved to yield a 108-amino-acid prohormone. Additional cleavage by an unknown protease results in an inactive 76-residue amino-terminal fragment and a 32-residue carboxyl-terminal biologically active peptide. CNP is the most conserved natriuretic peptide. Human proCNP contains 103 residues, and the intracellular endoprotease furin has been shown to process proCNP to the mature 53-amino-acid peptide in vitro. In some tissues, CNP-53 is cleaved to CNP-22 by an unknown extracellular enzyme. CNP-53 is the major form in the brain, endothelial cells, and heart, whereas CNP-22 predominates in human plasma and cerebral spinal fluid1.
Mode of Action
Natriuretic peptides elicit their physiological responses through the synthesis of cGMP, a classic intracellular second messenger. There are three known natriuretic peptide binding proteins in mammals: NPR-A, NPR-B, and NPR-C. They are also known as GC-A, GC-B, and the clearance receptor, or as NPR1, NPR2, and NPR3, respectively. NPR-A and NPR-B represent two of the five transmembrane guanylyl cyclases found in humans. The third natriuretic peptide receptor, NPR-C, does not possess any known intrinsic enzymatic activity.
Hypothetical model for NPR-A and NPR-B activation and desensitization:
Three states of receptor activation are labeled "basal," "active," and "desensitized." In the basal state, NPR-A and NPR-B are higher ordered oligomers. In the basal state, they are phosphorylated on five (NPR-B) or six (NPR-A) known sites within the kinase homology domain. It is hypothesized that phosphorylation "licenses" the receptor for hormonal activation. Natriuretic peptide (NP) binding to the highly phosphorylated, inactive basal receptor induces a conformational change that brings eventually brings about the dimerization of guanylyl cyclase domains. Prolonged ligand exposure stimulates receptor dephosphorylation, which results in reduced activity via a process called desensitization. The dephosphorylation primarily results from inhibition of the phosphorylation process. Release of ligand and rephosphorylation returns the enzyme to its basal state1.
Functions
Natriuretic peptides are often described simply as peptides involved in the regulation of blood pressure and volume. However, the effects of these peptides are widespread, and their levels change in response to a variety of pathological conditions.
Effects of the ANP/NPR-A system on blood pressure:
Although ANP was initially suggested to regulate blood pressure in a salt-sensitive manner, more recent data suggest that this is not the case. Its combined effects on intravascular volume, vasorelaxation, natriuresis, and diuresis mediate the hypotensive nature of ANP.
Effects of ANP and BNP on cardiac hypertrophy and fibrosis:
ANP and BNP have direct effects on the heart. Recent evidence suggests that the cardiac fibrosis involves matrix metalloproteinases (MMPs) which are in turn regulated by both ANP and BNP. Several reports indicate that the ANP/BNP/NPR-A system inhibits pressure-induced cardiac remodeling as well.
Effects of ANP on natriuresis and diuresis:
In the kidney, ANP increases glomerular filtration rate, inhibits sodium and water reabsorption, and reduces renin secretion.
Effects of CNP on vascular relaxation and remodeling:
The ability of the cardiac natriuretic peptides to relax precontracted aortic rings requires NPR-A. CNP relaxes aortic rings by a process that does not require NPR-A, presumably by activating NPR-B.
Effects of natriuretic peptides in the lung:
All three natriuretic peptide receptors are highly expressed in the lung. ANP stimulates the dilation of pulmonary airways and blood vessels. Infusion or inhalation of ANP stimulates bronchodilation in normal and asthmatic patients. CNP also reduces pulmonary hypertension and fibrosis.
ANP-dependent antagonism of the renin-aldosterone system:
ANP regulates blood pressure, in part, through the inhibition of the renin-angiotensin II-aldosterone system.
Effects of ANP on fat metabolism:
ANP-stimulated lipolysis is specific to primates presumably because primates contain a higher NPR-A to NPR-C ratio.
Neurological effects of natriuretic peptides:
All natriuretic peptides and natriuretic peptide receptors have been found in the brain, although CNP and NPR-B appear to be particularly abundant. Consistent with the systemic volume-depleting effects, injection of ANP into the third ventricle of the hypothalamus inhibits water intake induced by overnight dehydration or angiotensin II exposure.
Immunological effects of natriuretic peptides:
Natriuretic peptides and their receptors are found in many immune cells. Current evidence suggests a role for ANP in the allergen response of asthma and in immune-related post ischemic damage.
The CNP/NPR-B/cGMP/PKGII system and long bone growth:
The most obvious physiological effect of CNP is to stimulate long bone growth. It regulates many types of bone cells, but its major target appears to be the chondrocyte1.
Therapeutic applications of natriuretic peptides:
BNP and N-terminal-proBNP have become important diagnostic tools for assessing patients who present acutely with dyspnea. Natriuretic peptide levels have important prognostic value in multiple clinical settings, including in patients with stable coronary artery disease and with acute coronary syndromes. In patients with decompensated heart failure due to volume overload, a treatment-induced drop in wedge pressure is often accompanied by a rapid drop in NP levels3.
References
1.Lincoln R. Potter, Sarah Abbey-Hosch and Deborah M. Dickey(2006). Natriuretic Peptides, Their Receptors, and Cyclic Guanosine Monophosphate-Dependent Signaling Functions. Endocrine Reviews, 27(1):47-72.
2.de Bold AJ, Borenstein HB, Veress AT, Sonnenberg H (1981). A rapid and potent natriuretic response to intravenous injection of atrial myocardial extract in rats. Life Sci., 28(1):89-94.
3.Daniels LB, Maisel AS (2007). Natriuretic Peptides. J Am Coll Cardiol., 50(25):2357-2368.
Natriuretic peptides are a family of structurally related but genetically distinct hormones/paracrine factors that regulate blood volume, blood pressure, ventricular hypertrophy, pulmonary hypertension, fat metabolism, and long bone growth. The mammalian members are atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), C-type natriuretic peptide (CNP) 1.
Discovery
De Bold et al reported the first direct evidence of natriuretic substance in 19812. They found that the IV injection of atrial, but not ventricular, homogenates into rats elicited a rapid decrease in blood pressure that was accompanied by increased renal sodium and water excretion. After this seminal observation, several groups purified peptides of varying sizes from atrial tissue that possess both natriuretic and smooth muscle-relaxing activity. These peptides were given a number of different names such as ANP, cardionatrin, cardiodilatin, atriopeptin, and the first description is most often used today. BNP, which was originally called brain natriuretic peptide and CNP were subsequently purified from porcine brain extracts based on their ability to relax smooth muscle.
Structural Characteristics
The natriuretic peptides are a family of ring shaped vasoactive hormones showing considerable sequence homology. All three members contain the conserved sequence CFGXXXDRIXXXXGLGC where X is any amino acid. The flanking cysteines form a 17-amino-acid disulfide-linked ring that is required for biological activity. All natriuretic peptides are synthesized as preprohormones. Human preproANP is 151 amino acids in length. Cleavage of the amino terminal signal sequence results in the 126-amino-acid proANP, which is the predominant form stored in atrial granules. ProANP is rapidly cleaved upon secretion by the transmembrane cardiac serine protease called corin to form the biologically active carboxyl-terminal 28-amino-acid peptide. Human BNP is synthesized as a preprohormone of 134 residues containing a signal sequence that is cleaved to yield a 108-amino-acid prohormone. Additional cleavage by an unknown protease results in an inactive 76-residue amino-terminal fragment and a 32-residue carboxyl-terminal biologically active peptide. CNP is the most conserved natriuretic peptide. Human proCNP contains 103 residues, and the intracellular endoprotease furin has been shown to process proCNP to the mature 53-amino-acid peptide in vitro. In some tissues, CNP-53 is cleaved to CNP-22 by an unknown extracellular enzyme. CNP-53 is the major form in the brain, endothelial cells, and heart, whereas CNP-22 predominates in human plasma and cerebral spinal fluid1.
Mode of Action
Natriuretic peptides elicit their physiological responses through the synthesis of cGMP, a classic intracellular second messenger. There are three known natriuretic peptide binding proteins in mammals: NPR-A, NPR-B, and NPR-C. They are also known as GC-A, GC-B, and the clearance receptor, or as NPR1, NPR2, and NPR3, respectively. NPR-A and NPR-B represent two of the five transmembrane guanylyl cyclases found in humans. The third natriuretic peptide receptor, NPR-C, does not possess any known intrinsic enzymatic activity.
Hypothetical model for NPR-A and NPR-B activation and desensitization:
Three states of receptor activation are labeled "basal," "active," and "desensitized." In the basal state, NPR-A and NPR-B are higher ordered oligomers. In the basal state, they are phosphorylated on five (NPR-B) or six (NPR-A) known sites within the kinase homology domain. It is hypothesized that phosphorylation "licenses" the receptor for hormonal activation. Natriuretic peptide (NP) binding to the highly phosphorylated, inactive basal receptor induces a conformational change that brings eventually brings about the dimerization of guanylyl cyclase domains. Prolonged ligand exposure stimulates receptor dephosphorylation, which results in reduced activity via a process called desensitization. The dephosphorylation primarily results from inhibition of the phosphorylation process. Release of ligand and rephosphorylation returns the enzyme to its basal state1.
Functions
Natriuretic peptides are often described simply as peptides involved in the regulation of blood pressure and volume. However, the effects of these peptides are widespread, and their levels change in response to a variety of pathological conditions.
Effects of the ANP/NPR-A system on blood pressure:
Although ANP was initially suggested to regulate blood pressure in a salt-sensitive manner, more recent data suggest that this is not the case. Its combined effects on intravascular volume, vasorelaxation, natriuresis, and diuresis mediate the hypotensive nature of ANP.
Effects of ANP and BNP on cardiac hypertrophy and fibrosis:
ANP and BNP have direct effects on the heart. Recent evidence suggests that the cardiac fibrosis involves matrix metalloproteinases (MMPs) which are in turn regulated by both ANP and BNP. Several reports indicate that the ANP/BNP/NPR-A system inhibits pressure-induced cardiac remodeling as well.
Effects of ANP on natriuresis and diuresis:
In the kidney, ANP increases glomerular filtration rate, inhibits sodium and water reabsorption, and reduces renin secretion.
Effects of CNP on vascular relaxation and remodeling:
The ability of the cardiac natriuretic peptides to relax precontracted aortic rings requires NPR-A. CNP relaxes aortic rings by a process that does not require NPR-A, presumably by activating NPR-B.
Effects of natriuretic peptides in the lung:
All three natriuretic peptide receptors are highly expressed in the lung. ANP stimulates the dilation of pulmonary airways and blood vessels. Infusion or inhalation of ANP stimulates bronchodilation in normal and asthmatic patients. CNP also reduces pulmonary hypertension and fibrosis.
ANP-dependent antagonism of the renin-aldosterone system:
ANP regulates blood pressure, in part, through the inhibition of the renin-angiotensin II-aldosterone system.
Effects of ANP on fat metabolism:
ANP-stimulated lipolysis is specific to primates presumably because primates contain a higher NPR-A to NPR-C ratio.
Neurological effects of natriuretic peptides:
All natriuretic peptides and natriuretic peptide receptors have been found in the brain, although CNP and NPR-B appear to be particularly abundant. Consistent with the systemic volume-depleting effects, injection of ANP into the third ventricle of the hypothalamus inhibits water intake induced by overnight dehydration or angiotensin II exposure.
Immunological effects of natriuretic peptides:
Natriuretic peptides and their receptors are found in many immune cells. Current evidence suggests a role for ANP in the allergen response of asthma and in immune-related post ischemic damage.
The CNP/NPR-B/cGMP/PKGII system and long bone growth:
The most obvious physiological effect of CNP is to stimulate long bone growth. It regulates many types of bone cells, but its major target appears to be the chondrocyte1.
Therapeutic applications of natriuretic peptides:
BNP and N-terminal-proBNP have become important diagnostic tools for assessing patients who present acutely with dyspnea. Natriuretic peptide levels have important prognostic value in multiple clinical settings, including in patients with stable coronary artery disease and with acute coronary syndromes. In patients with decompensated heart failure due to volume overload, a treatment-induced drop in wedge pressure is often accompanied by a rapid drop in NP levels3.
References
1.Lincoln R. Potter, Sarah Abbey-Hosch and Deborah M. Dickey(2006). Natriuretic Peptides, Their Receptors, and Cyclic Guanosine Monophosphate-Dependent Signaling Functions. Endocrine Reviews, 27(1):47-72.
2.de Bold AJ, Borenstein HB, Veress AT, Sonnenberg H (1981). A rapid and potent natriuretic response to intravenous injection of atrial myocardial extract in rats. Life Sci., 28(1):89-94.
3.Daniels LB, Maisel AS (2007). Natriuretic Peptides. J Am Coll Cardiol., 50(25):2357-2368.
Myosin
Definition
Myosin is the most abundant protein in muscle fibrils, responsible for the elastic and contractile properties of muscle. It combines with actin to form actomyosin.
Discovery
A viscous protein was extracted from muscle with concentrated salt solution by Kühne (1864), who called it “myosin” and considered it responsible for the rigor state of muscle1. Muralt and Edsall (1930) showed that the “myosin” in solution had a strong flow birefringence with indications that the particles were uniform in size and shape2. In 1935, Weber (1935) developed a new technique for the in vitro study of contraction. He squirted “myosin” dissolved in high salt into water where it formed threads that became strongly birefringent upon drying 3.
Structural Characteristics
Myosin is a large asymmetric molecule; it has a long tail and two globular heads. The tail is about 1,600 Å long and 20 Å wide. Each head is about 165 Å long, 65 Å wide and 40 Å deep at its thickest part. The molecular weight of myosin is about 500kDa. In strong denaturing solutions, such as 5M guanidine-HCl or 8M urea, myosin dissociates into six polypeptide chains: two heavy chains (molecular weight of each heavy chain about 200 kDa) and four light chains (two with a molecular weight of 20 kDa, one with 15 kDa and another with 25 kDa). The two heavy chains are wound around each other to form a double helical structure. At one end both chains are folded into separate globular structures to form the two heads. In the muscle, the long tail portion forms the backbone of the thick filament and the heads protrude as cross bridges toward the thin filament. Each head contains two light chains. At low ionic strength, e.g. 0.03M KCl, myosin precipitates and forms myosin filaments. Electron micrographs reveal the specific structure of the filaments that is their central shaft and side projections. Myofibrils are tiny muscle fibers, prepared by homogenization of freshly dissected muscle in physiological salt solution. Myofibrils contain the contractile (myosin and actin) and the regulatory proteins (tropomyosin and troponin) of muscle.
Mode of Action
Muscles generate force and shortening in a cyclical interaction between the myosin head domains projecting from the myosin filaments and the adjacent actin filaments. Although many features of the dynamic performance of muscle are determined by the rates of attachment and detachment of myosin and actin, the primary event in force generation is thought to be a conformational change or 'working stroke' in the actin-bound myosin head 4. In the absence of calcium ions, tropomyosin blocks access to the myosin binding site of actin. When calcium binds to troponin, the positions of troponin and tropomyosin are altered on the thin filament and myosin then has access to its binding site on actin. Myosin hydrolyzes ATP and undergoes a conformational change into a high-energy state. The head group of myosin binds to actin forming a cross-bridge between the thick and thin filaments. The energy stored by myosin is released, and ADP and inorganic phosphate dissociate from myosin. The resulting relaxation of the myosin molecule entails rotation of the globular head, which induces longitudinal sliding of the filaments. When the calcium level decreases, troponin locks tropomyosin in the blocking position and the thin filament slides back to the resting state 5.
Functions
Myosin has multiple functions - Filament formation, ATPase activity, and reversible combination with actin. The use of proteolytic enzymes revealed different regions of the myosin molecule were responsible for each of these different functions.
Myosin-actin binding - One of the biologically important properties of myosin is its ability to combine with actin. The complex formed is called actomyosin. The actin binding by myosin is highly specific; no other protein can substitute actin. Physiologically, when actin and myosin combine the muscle produces force. There are several methods to measure the stoichiometry of actin to myosin combination.
ATPase activity of myosin - A Russian husband wife team, Engelhardt and Lyubimova, made the important discovery in 1939 that myosin is an enzyme that hydrolyzes ATP6. It was already known that ATP is the universal energy donor in living cells, thus Engelhardt and Lyubimova created the term mechanochemistry i.e. the contractile protein myosin that carries out the work also liberates the energy necessary for the work.
Myosin filament - At low ionic strength, e.g. 0.03M KCl, myosin precipitates and forms filaments. Since individual myosin molecules have a globular region at one end only, the filaments are formed by anti parallel association of myosin molecules. All the molecules in one half filaments are oriented in one direction and all those in the other half of the filaments are oriented in the opposite direction. Thus, in the middle of the filament the tails of antiparallel molecules overlap yielding a bare central shaft, and globular regions are projected at both ends of the filament7.
ATPase activity of myosin and speed of muscle shortening - The ATPase activity of myosin was determined in 25 different muscles with a 250-fold variation in the speed of shortening. A correlation was found between the ATPase activity of myosin and the speed of shortening. This suggests that the myosin ATPase determines the speed of muscle shortening 8.
References
1.Kühne, W. (1864). Untersuchungen über das Protoplasma und die Contractilitat. W. Engelmann, Leipzig.
2.Von Muralt, A. L., and Edsall, J. T. (1930). Studies in the physical chemistry of muscle globulin. J. Biol. Chem., 89:315 -350.
3.Weber, H.H. 1935. Der feinbau und die mechanischen eigenschaften des myosin-fadens. Arch. Physiol. 235:205–233.
4.Szent-Györgyi AG (2004). Early History of the Biochemistry of Muscle Contraction. J. Gen. Physiol., 123(6): 631–641.
5.Book : Neurobiology, molecules, cells and system By Gary G .Matthews.
6.Engelhardt, V.A., and M.N. Lyubimova (1939). Myosin and adenosinetriphosphatase. Nature., 144:668-669.
7.Hidalgo C, Padron R, Horowitz R, Zhao FG, Craig R (2001). Purification of native myosin filaments from muscle. Biophys. J., 81(5):2817-2826.
8.Bárány, M. (1967). ATPase activity of myosin correlated with speed of muscle shortening. J. Gen. Physiol., 50(6):197-218.
Myosin is the most abundant protein in muscle fibrils, responsible for the elastic and contractile properties of muscle. It combines with actin to form actomyosin.
Discovery
A viscous protein was extracted from muscle with concentrated salt solution by Kühne (1864), who called it “myosin” and considered it responsible for the rigor state of muscle1. Muralt and Edsall (1930) showed that the “myosin” in solution had a strong flow birefringence with indications that the particles were uniform in size and shape2. In 1935, Weber (1935) developed a new technique for the in vitro study of contraction. He squirted “myosin” dissolved in high salt into water where it formed threads that became strongly birefringent upon drying 3.
Structural Characteristics
Myosin is a large asymmetric molecule; it has a long tail and two globular heads. The tail is about 1,600 Å long and 20 Å wide. Each head is about 165 Å long, 65 Å wide and 40 Å deep at its thickest part. The molecular weight of myosin is about 500kDa. In strong denaturing solutions, such as 5M guanidine-HCl or 8M urea, myosin dissociates into six polypeptide chains: two heavy chains (molecular weight of each heavy chain about 200 kDa) and four light chains (two with a molecular weight of 20 kDa, one with 15 kDa and another with 25 kDa). The two heavy chains are wound around each other to form a double helical structure. At one end both chains are folded into separate globular structures to form the two heads. In the muscle, the long tail portion forms the backbone of the thick filament and the heads protrude as cross bridges toward the thin filament. Each head contains two light chains. At low ionic strength, e.g. 0.03M KCl, myosin precipitates and forms myosin filaments. Electron micrographs reveal the specific structure of the filaments that is their central shaft and side projections. Myofibrils are tiny muscle fibers, prepared by homogenization of freshly dissected muscle in physiological salt solution. Myofibrils contain the contractile (myosin and actin) and the regulatory proteins (tropomyosin and troponin) of muscle.
Mode of Action
Muscles generate force and shortening in a cyclical interaction between the myosin head domains projecting from the myosin filaments and the adjacent actin filaments. Although many features of the dynamic performance of muscle are determined by the rates of attachment and detachment of myosin and actin, the primary event in force generation is thought to be a conformational change or 'working stroke' in the actin-bound myosin head 4. In the absence of calcium ions, tropomyosin blocks access to the myosin binding site of actin. When calcium binds to troponin, the positions of troponin and tropomyosin are altered on the thin filament and myosin then has access to its binding site on actin. Myosin hydrolyzes ATP and undergoes a conformational change into a high-energy state. The head group of myosin binds to actin forming a cross-bridge between the thick and thin filaments. The energy stored by myosin is released, and ADP and inorganic phosphate dissociate from myosin. The resulting relaxation of the myosin molecule entails rotation of the globular head, which induces longitudinal sliding of the filaments. When the calcium level decreases, troponin locks tropomyosin in the blocking position and the thin filament slides back to the resting state 5.
Functions
Myosin has multiple functions - Filament formation, ATPase activity, and reversible combination with actin. The use of proteolytic enzymes revealed different regions of the myosin molecule were responsible for each of these different functions.
Myosin-actin binding - One of the biologically important properties of myosin is its ability to combine with actin. The complex formed is called actomyosin. The actin binding by myosin is highly specific; no other protein can substitute actin. Physiologically, when actin and myosin combine the muscle produces force. There are several methods to measure the stoichiometry of actin to myosin combination.
ATPase activity of myosin - A Russian husband wife team, Engelhardt and Lyubimova, made the important discovery in 1939 that myosin is an enzyme that hydrolyzes ATP6. It was already known that ATP is the universal energy donor in living cells, thus Engelhardt and Lyubimova created the term mechanochemistry i.e. the contractile protein myosin that carries out the work also liberates the energy necessary for the work.
Myosin filament - At low ionic strength, e.g. 0.03M KCl, myosin precipitates and forms filaments. Since individual myosin molecules have a globular region at one end only, the filaments are formed by anti parallel association of myosin molecules. All the molecules in one half filaments are oriented in one direction and all those in the other half of the filaments are oriented in the opposite direction. Thus, in the middle of the filament the tails of antiparallel molecules overlap yielding a bare central shaft, and globular regions are projected at both ends of the filament7.
ATPase activity of myosin and speed of muscle shortening - The ATPase activity of myosin was determined in 25 different muscles with a 250-fold variation in the speed of shortening. A correlation was found between the ATPase activity of myosin and the speed of shortening. This suggests that the myosin ATPase determines the speed of muscle shortening 8.
References
1.Kühne, W. (1864). Untersuchungen über das Protoplasma und die Contractilitat. W. Engelmann, Leipzig.
2.Von Muralt, A. L., and Edsall, J. T. (1930). Studies in the physical chemistry of muscle globulin. J. Biol. Chem., 89:315 -350.
3.Weber, H.H. 1935. Der feinbau und die mechanischen eigenschaften des myosin-fadens. Arch. Physiol. 235:205–233.
4.Szent-Györgyi AG (2004). Early History of the Biochemistry of Muscle Contraction. J. Gen. Physiol., 123(6): 631–641.
5.Book : Neurobiology, molecules, cells and system By Gary G .Matthews.
6.Engelhardt, V.A., and M.N. Lyubimova (1939). Myosin and adenosinetriphosphatase. Nature., 144:668-669.
7.Hidalgo C, Padron R, Horowitz R, Zhao FG, Craig R (2001). Purification of native myosin filaments from muscle. Biophys. J., 81(5):2817-2826.
8.Bárány, M. (1967). ATPase activity of myosin correlated with speed of muscle shortening. J. Gen. Physiol., 50(6):197-218.
Thursday, September 3, 2009
Myelin Basic Protein Fragments (MBPs)
Definition
One of the two major classes of myelin proteins is the myelin basic proteins (MBPs), a family of proteins derived by alternative splicing of the MBP gene.
Discovery
Campagnoni et al identified a novel transcription unit of 105 kbp (called the Golli-mbp gene) that encompasses the mouse myelin basic protein (MBP) gene. Three unique exons within this gene are alternatively spliced into MBP exons and introns to produce a family of MBP gene- related mRNAs that are under individual developmental regulation. These mRNAs are temporally expressed within cells of the oligodendrocyte lineage at progressive stages of differentiation. Thus, the MBP gene is a part of a more complex gene structure, the products of which play a role in oligodendrocyte differentiation prior to myelination1.
Structural Characteristics
There are multiple isoforms of MBP that are produced through the translation of separate mRNAs, resulting in a heterogeneous population of MBP structures. MBP is an ‘intrinsically unstructured’ protein with a high proportion ( 75%) of random coil, but postulated to have core elements of ß-sheet and a-helix. In solution, MBP is “intrinsically unstructured” (or “natively unfolded”). Upon binding to detergents or lipids, the levels of beta-sheet and especially alpha-helical structure increase dramatically. MBP was an amphipathic alpha-helix located at the interface between the oligodendrocyte cytoplasm and the membrane. In a solution circular dichroism (CD) and Fourier transform infrared spectroscopic study, MBP peptides were found to have both helix and sheet structures in methanol, with the latter increasing in amount in progressively shorter peptides 2, 3.
Mode of Action
In order to clarify insulinotropic effects of the myelin basic protein (MBP) Kolehmainen et al studied mode of association and distribution of MBP in the pancreatic islets and tested the insulin-releasing activity of various MBP peptides. Rat pancreatic islets were first stimulated in a static incubation with 10 µM bovine MBP (bMBP) at a substimulatory (3.5 mM) glucose concentration. The islets exposed to MBP released significantly more insulin and glucagon in a second incubation in the absence of added stimulant and in the presence of 11.5 mM arginine than the incubated, non-stimulated islets and islets initially stimulated with 15 mM glucose. Response to stimulation with 15 mM glucose in the second incubation by islets exposed first to MBP was impaired compared to incubated, non-stimulated islets. Immunoelectron microscopy showed that MBP had entered into the islet cells and associated with membranes of intracellular vacuoles, most of which represented enlarged, often fused insulin granules. MBP was also present at the islet edge and in the intercellular spaces. Of the purified MBP peptides of sizes of 4.8–13.6 kDa, produced from the digestion with brain acid proteinase and with pepsin and covering the entire bMBP sequence, only the large peptides (1–88, 9.8 kDa and 43–169, 13.6 kDa) stimulated insulin secretion significantly. Heterogeneous peptide mixtures, obtained from a time-course digestion of bMBP by myelin calcium-activated neutral protease, consisting of peptides of approximate molecular weights of 8–11 kDa and larger, also stimulated insulin release. The glucagon-releasing activity of MBP peptides was low and followed the same pattern as the insulin-releasing activity. These results suggest that MBP-induced fusion of the membranes of hormone granules is involved in MBP-induced insulin release. The hormone-releasing activity of the large peptides in addition to that of the intact molecule is explained as being due to the ability of these peptides to associate with membranes. MBP-induced hormone release and related effects could be associated with neuropathological conditions such as stroke and multiple sclerosis 4.
Functions
MBP plays a key role in the pathology of MS, although its mechanism of action has remained unclear. Antigenically related MBP was isolated from the cerebrospinal fluid of patients with multiple sclerosis (MS) 5. Induction of experimental allergic encephalomyelitis (EAE) with MBP produced a monophasic inflammatory disease process in guinea pigs with minimal demyelination, whereas the addition of galactocerebrosides or the use of whole myelin produced EAE with demyelination, suggesting that MBP plays a role in demyelination when in synergy with myelin lipids 6. It was demonstrated that a single transfer of MBP-sensitized T cells from animals with EAE produced a relapsing disease process in mice with both inflammation and demyelination, similar to what is found in MS. This discovery suggests MBP isoforms as candidate autoantigens7.
References
1.Campagnoni AT, Pribyl TM, Campagnoni CW, Kampf K, Amur- Umarjee S, Landry CF, Handley VW, Newman SL, Garbay B, Kitamura K (1993). Structure and developmental regulation of golli-mbp, a 105 kb gene that encompasses the myelin basic protein gene and is expressed in cells in the oligodendrocyte lineage in the brain. J Biol Chem., 268: 4930-4938.
2.Hill CM, Bates IR, White GF, Hallett, FR, Harauz G (2002). Effects of the osmolyte trimethylamine-N-oxide on conformation, self-association, and two-dimensional crystallization of myelin basic protein. J Struct Biol., 139: 13-26.
3.Whitaker JN, Moscarello MA, Herman PK, Epand RM, Surewicz, WK (1990) Conformational correlates of the epitopes of human myelin basic protein peptide 80-89. J. Neurochem., 55:568-576.
4.Kolehmainen E. (1995). Evidence supporting membrane fusion as the mechanism of myelin basic protein-induced insulin release from rat pancreatic islets. Neurochem Intl., 26 (5):503-518.
5.Carson JH, Barbarese E, Braun PE, McPherson TA (1978). Components in multiple sclerosis cerebrospinal fluid that are detected by radioimmunoassay for myelin basic protein. PNAS, 75(4):1976–1978.
6.Raine CS, Traugott U, Farooq M, Bornstein MB, Norton WT (1981). Augmentation of immune-mediated demyelination by lipid haptens. Lab. Invest., 45:174–182.
7.Mokhtarian F, McFarlin DE, Raine CS (1984). Adoptive transfer of myelin basic protein-sensitized T cells produces chronic relapsing demyelinating disease in mice. Nature, 309:356–358.
One of the two major classes of myelin proteins is the myelin basic proteins (MBPs), a family of proteins derived by alternative splicing of the MBP gene.
Discovery
Campagnoni et al identified a novel transcription unit of 105 kbp (called the Golli-mbp gene) that encompasses the mouse myelin basic protein (MBP) gene. Three unique exons within this gene are alternatively spliced into MBP exons and introns to produce a family of MBP gene- related mRNAs that are under individual developmental regulation. These mRNAs are temporally expressed within cells of the oligodendrocyte lineage at progressive stages of differentiation. Thus, the MBP gene is a part of a more complex gene structure, the products of which play a role in oligodendrocyte differentiation prior to myelination1.
Structural Characteristics
There are multiple isoforms of MBP that are produced through the translation of separate mRNAs, resulting in a heterogeneous population of MBP structures. MBP is an ‘intrinsically unstructured’ protein with a high proportion ( 75%) of random coil, but postulated to have core elements of ß-sheet and a-helix. In solution, MBP is “intrinsically unstructured” (or “natively unfolded”). Upon binding to detergents or lipids, the levels of beta-sheet and especially alpha-helical structure increase dramatically. MBP was an amphipathic alpha-helix located at the interface between the oligodendrocyte cytoplasm and the membrane. In a solution circular dichroism (CD) and Fourier transform infrared spectroscopic study, MBP peptides were found to have both helix and sheet structures in methanol, with the latter increasing in amount in progressively shorter peptides 2, 3.
Mode of Action
In order to clarify insulinotropic effects of the myelin basic protein (MBP) Kolehmainen et al studied mode of association and distribution of MBP in the pancreatic islets and tested the insulin-releasing activity of various MBP peptides. Rat pancreatic islets were first stimulated in a static incubation with 10 µM bovine MBP (bMBP) at a substimulatory (3.5 mM) glucose concentration. The islets exposed to MBP released significantly more insulin and glucagon in a second incubation in the absence of added stimulant and in the presence of 11.5 mM arginine than the incubated, non-stimulated islets and islets initially stimulated with 15 mM glucose. Response to stimulation with 15 mM glucose in the second incubation by islets exposed first to MBP was impaired compared to incubated, non-stimulated islets. Immunoelectron microscopy showed that MBP had entered into the islet cells and associated with membranes of intracellular vacuoles, most of which represented enlarged, often fused insulin granules. MBP was also present at the islet edge and in the intercellular spaces. Of the purified MBP peptides of sizes of 4.8–13.6 kDa, produced from the digestion with brain acid proteinase and with pepsin and covering the entire bMBP sequence, only the large peptides (1–88, 9.8 kDa and 43–169, 13.6 kDa) stimulated insulin secretion significantly. Heterogeneous peptide mixtures, obtained from a time-course digestion of bMBP by myelin calcium-activated neutral protease, consisting of peptides of approximate molecular weights of 8–11 kDa and larger, also stimulated insulin release. The glucagon-releasing activity of MBP peptides was low and followed the same pattern as the insulin-releasing activity. These results suggest that MBP-induced fusion of the membranes of hormone granules is involved in MBP-induced insulin release. The hormone-releasing activity of the large peptides in addition to that of the intact molecule is explained as being due to the ability of these peptides to associate with membranes. MBP-induced hormone release and related effects could be associated with neuropathological conditions such as stroke and multiple sclerosis 4.
Functions
MBP plays a key role in the pathology of MS, although its mechanism of action has remained unclear. Antigenically related MBP was isolated from the cerebrospinal fluid of patients with multiple sclerosis (MS) 5. Induction of experimental allergic encephalomyelitis (EAE) with MBP produced a monophasic inflammatory disease process in guinea pigs with minimal demyelination, whereas the addition of galactocerebrosides or the use of whole myelin produced EAE with demyelination, suggesting that MBP plays a role in demyelination when in synergy with myelin lipids 6. It was demonstrated that a single transfer of MBP-sensitized T cells from animals with EAE produced a relapsing disease process in mice with both inflammation and demyelination, similar to what is found in MS. This discovery suggests MBP isoforms as candidate autoantigens7.
References
1.Campagnoni AT, Pribyl TM, Campagnoni CW, Kampf K, Amur- Umarjee S, Landry CF, Handley VW, Newman SL, Garbay B, Kitamura K (1993). Structure and developmental regulation of golli-mbp, a 105 kb gene that encompasses the myelin basic protein gene and is expressed in cells in the oligodendrocyte lineage in the brain. J Biol Chem., 268: 4930-4938.
2.Hill CM, Bates IR, White GF, Hallett, FR, Harauz G (2002). Effects of the osmolyte trimethylamine-N-oxide on conformation, self-association, and two-dimensional crystallization of myelin basic protein. J Struct Biol., 139: 13-26.
3.Whitaker JN, Moscarello MA, Herman PK, Epand RM, Surewicz, WK (1990) Conformational correlates of the epitopes of human myelin basic protein peptide 80-89. J. Neurochem., 55:568-576.
4.Kolehmainen E. (1995). Evidence supporting membrane fusion as the mechanism of myelin basic protein-induced insulin release from rat pancreatic islets. Neurochem Intl., 26 (5):503-518.
5.Carson JH, Barbarese E, Braun PE, McPherson TA (1978). Components in multiple sclerosis cerebrospinal fluid that are detected by radioimmunoassay for myelin basic protein. PNAS, 75(4):1976–1978.
6.Raine CS, Traugott U, Farooq M, Bornstein MB, Norton WT (1981). Augmentation of immune-mediated demyelination by lipid haptens. Lab. Invest., 45:174–182.
7.Mokhtarian F, McFarlin DE, Raine CS (1984). Adoptive transfer of myelin basic protein-sensitized T cells produces chronic relapsing demyelinating disease in mice. Nature, 309:356–358.
Subscribe to:
Posts (Atom)