Saturday, October 31, 2009

Anti-Drug Antibodies

Pharmaceutical industries are increasingly using biological or biotechnological products for drug development. The biologics or biopharmaceuticals, as they are commonly called, are generally composed of large, complex proteins which may or may not be glycosylated and are of human, plant or animal origin. These products have the potential to induce anti-drug-antibody (ADA) or cell-mediated immune response in patients. The immune response can range from a transient appearance of antibodies without any clinical significance to severe life threatening conditions such as severe hypersensitivity-type reactions, decrease in efficacy and induction of autoimmunity, including antibodies to the endogenous form of the protein. Anti-Drug Antibody (ADA) responses can lead to allergic reactions, reduction or neutralization of drug activity and potential cross reactivity. Moreover, in preclinical studies, ADA can affect drug exposure, affecting the interpretation of the toxicity, pharmacokinetic and pharmaco-dynamic data.

Factors causing immunogenicity
The factors that cause immunogenicity of these products could be patient-related, disease-related and product-related. The patient-related factors could be: genetic factors, age of the patient, disease related factors including other treatments and exposure to similar immunogens owing to concomitant treatment, duration, route of administration and treatment modalities, and previous exposure to similar products. The patient’s underlying disease can also be responsible for inducing immunogenicity. Some patients with chronic infections may be more prone to an immune response against a therapeutic protein. Patients with autoimmune disease, with an altered immunological tolerance to self-proteins, may react differently. In some conditions such as malnutrition, advanced metastatic disease, organ failure, an immune response against a therapeutic protein might be less likely to occur due to an impaired immune system. For some products, it has been reported that the susceptibility to an antibody response can be different for different indications. Product-related factors that might influence an immune response are: the origin and nature of the active substance (structural homology, post translational modifications), modification of the native protein (e.g. pegylation), product and process related impurities such as break down products, aggregates and host cell proteins, source of the protein, manufacturing process (impurity profile, contaminants), formulation and stability characteristics (degradation products, aggregates) of the protein, its dose, dosing interval and duration of treatment.

Thus to ensure clinical safety and efficacy of the numerous biologics used in drug development, immunogenicity testing has become very vital. Food and Drug Administration (FDA) in the USA has a policy to include immunogenicity as part of the review of clinical safety assessments for biologic license applications. Similar requirements exist for other regulatory agencies such as European Medicines Agency (EMEA) in Europe. However as of now, no comprehensive guidelines exist on the approaches that are required for immunogenicity testing during product development. Similarly, there is no single source of the requirements for non-clinical or clinical studies and no specific guidance for performing or interpreting assays.

The various analytical approaches that have been used to monitor or detect the presence of antidrug antibodies in the last couple of decades are:

1) Immunological based technologies (e. g. Western blots, immunoassay)
2) Chromatographic formats (e.g. size exclusion, capillary electrophoresis)
3) Surface plasma resonance biosensors and
4) Bioassays (e. g. immortalized cell lines).

Antibodies are needed for western blot, immune precipitation, and protein purification among other methods. Manufacturing a protein made recombinant involves cumbersome steps - cloning the cDNA, expressing the protein and purifying the protein. These processes can be bypassed by outsourcing the whole process of manufacturing the peptides or the antibodies to a vendor who can synthesize the specific peptides of choice as well as manufactures antibodies.

Synthetic peptides could be used for the following purposes:

• To verify the structure of naturally occurring peptides
• To study the relationship between structure and activity of biologically active proteins and peptides and establish their molecular mechanisms and
• To develop new peptide-based immunogens, antibodies, hormones, vaccines, etc.

Synthetic peptides may range from 2 to 120 amino acids. Small synthetic peptides (in general less than 10 amino acids in length) have the advantage of rarely inducing antibody formation and can be tailored to move across blood brain barrier. Peptides for antibody production are generally of 15 to 25 amino acids. Such peptides can be conjugated to a protein carrier such as KLH, BSA etc. which can induce antibody production and used for both in vitro and in vivo assays.

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Syndyphalins

Definition
Syndyphalins are enkephalin-like synthetic tripeptides with analgesic action 1,2.

Discovery
Kiso, et al., in 1981, synthesized tripeptide hydroxyalkylamide derivatives in order to obtain more stable and potent ENK analogues and reported that a simple peptide, Tyr-D-Met(O)-Gly-MePheol, named 'syndyphalin(SD)-25' was 23300 times and 9 times as active as morphine in the in vitro assay using guinea pig ileum and in the tail flick analgesic test after administration, respectively 3.

Structural Characteristics
Syndyphalin-33: Tyr-D-Met(O)-Gly-MPA; (Tyr-D-Met(O)-Gly-N-methylphenethylamide;Syndyphalin-25: Tyr-D-Met (O)-Gly-MePheol.

Mode of Action
The ability of naloxone to block SD33-stimulated growth hormone (GH) secretion suggests that this peptide acts via µ­opiate receptors 1.

Functions
A simple tripeptide alkylamine, syndyphalin 33 (SD33, Tyr-DMet (O)-Gly-methylphenethylamide) was shown to stimulate GH secretion in sheep, hogs and rats following peripheral administration 1.SD-25 possesses potent central nervous system actions closely similar to those of morphine, but its effect on blood pressure and respiration is weaker than that of morphine 2.

References
1. Nakamura H, Kiso Y, Motoyoshi S, Yoshida N, Ishii K, Yokoyama Y, Kadokawa T, Shimizu M (1982). Analgesic and other pharmacological activities of an enkephalin analogue, syndyphalin (SD)-25. Eur J Pharmacol., 85(2):133-142.
2. Buonomo FC, Tou JS, Kaempfe LA (1991). Stimulation of somatotropin secretion following peripheral administration of the tripeptide, syndyphalin 33 in sheep, pigs and rats. Life Sci., 48(20):1953-1961.
3. Kiso Y, Yamaguchi M, Akita T, Moritoki H, Takei M, Nakamura H (1981). Super-active Enkephalin Analogues.Simple Tripeptide Hydroxyalkylamides http://www.biosyn.com/Catelog.aspx?Id=PE&CatId=319&CatN=SyndyphalinsExhibit Surprisingly High and Long-lasting Opioid Activities. Naturwissenschaften, 68(4):210-212.

For more detail regarding Peptide please visit here : Custom Peptide Synthesis

Syndyphalins

Definition
Syndyphalins are enkephalin-like synthetic tripeptides with analgesic action 1,2.

Discovery
Kiso, et al., in 1981, synthesized tripeptide hydroxyalkylamide derivatives in order to obtain more stable and potent ENK analogues and reported that a simple peptide, Tyr-D-Met(O)-Gly-MePheol, named 'syndyphalin(SD)-25' was 23300 times and 9 times as active as morphine in the in vitro assay using guinea pig ileum and in the tail flick analgesic test after administration, respectively 3.

Structural Characteristics
Syndyphalin-33: Tyr-D-Met(O)-Gly-MPA; (Tyr-D-Met(O)-Gly-N-methylphenethylamide;Syndyphalin-25: Tyr-D-Met (O)-Gly-MePheol.

Mode of Action
The ability of naloxone to block SD33-stimulated growth hormone (GH) secretion suggests that this peptide acts via µ­opiate receptors 1.

Functions
A simple tripeptide alkylamine, syndyphalin 33 (SD33, Tyr-DMet (O)-Gly-methylphenethylamide) was shown to stimulate GH secretion in sheep, hogs and rats following peripheral administration 1.SD-25 possesses potent central nervous system actions closely similar to those of morphine, but its effect on blood pressure and respiration is weaker than that of morphine 2.

References
1. Nakamura H, Kiso Y, Motoyoshi S, Yoshida N, Ishii K, Yokoyama Y, Kadokawa T, Shimizu M (1982). Analgesic and other pharmacological activities of an enkephalin analogue, syndyphalin (SD)-25. Eur J Pharmacol., 85(2):133-142.
2. Buonomo FC, Tou JS, Kaempfe LA (1991). Stimulation of somatotropin secretion following peripheral administration of the tripeptide, syndyphalin 33 in sheep, pigs and rats. Life Sci., 48(20):1953-1961.
3. Kiso Y, Yamaguchi M, Akita T, Moritoki H, Takei M, Nakamura H (1981). Super-active Enkephalin Analogues.Simple Tripeptide Hydroxyalkylamides http://www.biosyn.com/Catelog.aspx?Id=PE&CatId=319&CatN=SyndyphalinsExhibit Surprisingly High and Long-lasting Opioid Activities. Naturwissenschaften, 68(4):210-212.

For more detail regarding Peptide please visit here : Custom Peptide Synthesis

Thymopoietin (TP) Fragments

Definition
Thymopoietin (TP) was originally isolated as a 5-kDa, 49-amino acid protein from bovine thymus in studies of the effects of thymic extracts on neuromuscular transmission and was subsequently observed to affect T-cell differentiation and function 1.

Related Peptides
The pentapeptide thymopentin (TP5), which represents the active sequence of the originally described TP. TP was identified as a fragment of the thymopoietins (TMPOs), a family of nuclear proteins 2. Three alternatively spliced mRNAs encode three distinct human T-cell TPs. Proteins encoded by these mRNAs have been named TPa (75 kDa), TPß (51 kDa), and TP? (39 kDa), which contain identical N-terminal regions, including sequences nearly identical to that of the originally isolated 49-amino acid protein, but divergent C-terminal regions 1.

Discovery
Three alternatively spliced mRNAs that encode three distinct human T-cell TPs were identified by Harris et al., in 1994 and named the proteins encoded by these mRNAs, TPa, TPß, and TP? 1.

Structural Characteristics
Distinct structural domains and functional motifs in TPs a, ß and ? suggest that the proteins have unique functions and may be directed to distinct subcellular compartments. The first 49 amino acid predicted by the human TP a, ß and ? cDNAs are closely similar to the sequence determined for the originally purified bovine 5-kDa TP, differing at only 5 amino acids. The sequences predicted from the human TP a, ß and ? cDNAs are similar to the sequence predicted from the bovine cDNA reported by Zevin-Sonkin et al., from amino acid 1 through amino acid 81, differing only at positions 13 (Asp in human, Glu in bovine) and 53-56 (Pro-Ala-Gly-Thr in human, Ala-Thr-Ser-Ala in bovine); but beyond amino acid 81 there is no further homology, either in nucleotide or in amino acid sequence 1.

Mode of Action
In vitro assays show that TP5 affects the function of T cells and monocytes measured by enhanced cGMP level and the triggering of cellular signalling, respectively 2.

Functions
Thymopentin, an active fragment of TP, reduces endocrine and behavioral responses to experimental stress, possibly by lowering plasma TP (pTP) levels. (The significant association of elevated pTP with nonresponsiveness to antidepressant drugs may signify a distinct pathogenesis for the depression of patients with elevated pT 3. The maturation and activity of T lymphocytes can be augmented by the TP fragments TP-3, TP-4 and TP-5. T cell differentiation is enhanced with these TP fragments at a rather early phase in bone marrow and at a later phase in the circulation. The ability of the TP fragments TP-3, TP-4 and TP-5 to restore antibody production and phagocytosis was analysed in a study. The phagocytic capacity of peritoneal macrophages was reduced by vincristine, methotrexate and cyclophosphamide treatment. In this respect, TP-3 protected the function of macrophages against vincristine and cyclophosphamide treatment. TP-4 was active in the case of damage caused by vincristine and methotrexate, and TP-5 interfered with the phagocytosis-inhibiting effect of methotrexate. Each TP fragment seems to have a specific target orientation within the immune system. This also means that the proper TP fragment should always be chosen for combination therapy with various types of cytotoxic drugs 4.

References
1. Crafford A. Harris, Paula J. Andryuk, Scott Cline, H. Karen Chan, Anan Natarajan, John J. Siekierka and Gideon Goldstein (1994). Three distinct human thymopoietins are derived from alternatively spliced mRNAs. PNAS.,91:6283-6287..
2. Gonser S, Weber E, Folkers G (1999). Peptides and polypeptides as modulators of the immune response: thymopentin — an example with unknown mode of action. Pharmaceutica Acta Helvetiae, 73(6):265-273.
3. Goldstein G, Fava M, Culler M, Fisher A, Rickels K, Lydiard RB, Rosenbaum J (2000). Elevated plasma thymopoietin associated with therapeutic nonresponsiveness in major depression. Biological Psychiatry, 48(1):65-69.
4. Dénes L, Szende B, Hajós G, Szporny L, Lapis K (1990). Selective restoration of immunosuppressive effect of cytotoxic agents by thymopoietin fragments. Cancer Immunol Immunother., 32:51-54.

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Substance P, Analogs and Fragments

Definition
Substance P (SP) an undecapeptide, is abundant both in the periphery and in the CNS, where it is usually co-localised with one of the classical neurotransmitters, most commonly serotonin (5- HT) 1.

Related Peptides
SP belongs to a family of neuropeptides known as tachykinins that share the common C-terminal sequence: Phe-X-Gly-Leu-Met-NH2. The three most common tachykinins are SP, neurokinin A (NKA), and neurokinin B (NKB); their biologic actions are mediated through specific cell-surface receptors designated NK1, NK2, and NK3, with SP the preferred agonist for NK1 receptors, NKA for NK2 receptors, and NKB for NK3 receptors 2.

Discovery
SP was originally discovered in 1931 by von Euler and Gaddum as a tissue extract that caused intestinal contraction in vitro; its biologic actions and tissue distribution were further investigated over subsequent decades 3.

Structural Characteristics
SP is an 11-residue neuropeptide with the sequence Arg-Pro-Lys-Pro-Gln-Glin-Phe-Gly-Leu-Met-NH2) 4. In a study, the C- and N-terminal fragments of SP were compared to the parent molecule with respect to their ability to: (a) contract the isolated guinea pig ileum, (b) induce salivation in the rat, (c) excite single cat dorsal horn neurones, and (d) induce scratching by intracranial injections in mice. C-terminal fragments as small as the heptapeptide were potent SP agonists on all assay systems. C-terminal fragments containing five amino acids or less were, at most, only weakly active. N-terminal fragments were totally inactive on the isolated guinea pig ileum. On the rat salivation and central nervous system assays, however, N-terminal fragments were capable of weak SP-like activity 5. The results obtained, indicated that while the carboxy terminal of SP is essential for peptide bronchoactivity, loss of amino terminal peptides (up to four residues) actually enhances bronchoconstrictor responses to the peptide. Part of this enhancement appears to result from differences in the enzymatic degradation of SP and SP5-11. The data suggest that cleavage of SP by dipeptidyl aminopeptidases could enhance its bioactivity 6. SP analogs: Senktide (succinyl-[Asp6,Me-Phe8]SP-(6-11)), a selective analog for the NK-3 (SP-N) receptor, is 20-100 times more potent than SP and about 1000-fold more potent than the selective analogs for the NK-1 (SP-P) receptor, which resides on muscle cells 7. Effects of five SP analogs on the licking, biting and scratching response induced by neurokinin (NK) 1 receptor agonists such as SP, physalaemin and (p-Glu6,Pro9)-SP (6-11) (septide) were studied after intrathecal injections in mice. Peptide brought about a SP-like behavioral response, and was approximately 25 times more potent than the D-Pro9 analog, D-septide. Septide-induced response was significantly reduced by lower doses of (D-Arg1, D-Pro2,4, D-Phe7, D-His9, Leu11)-SP than (D- Phe7, D-His9, Leu11)-SP (6-11). In contrast, (D-Arg1, D-Pro2,4, D-Phe7, D-His9)-SP (0.5-1.0 nmol) and (D-Phe7, D-His9)-SP (6-11) (0.5-2.0 nmol) inhibited only SP-induced behavioral response, but not physalaemin- or septide-induced response. The results of this study indicate that NK-1 receptor agonists are not necessarily affected to a same degree by SP analogs containing D-His 8. Analogues of substance P, [D-Arg1,D-Phe5,D-Trp7,9,Leu11] SP (SpD) and [Arg6,D-Trp7,9,NmePhe8]substance P can inhibit neuropeptide-stimulated Ca2+ mobilization, tyrosine phosphorylation, and ERK activation . Crucially, SpD and [Arg6,D-Trp7,9,NmePhe8] SP inhibit SCLC cell growth in vivo and in vitro and stimulate SCLC cell apoptosis. SP analogues were characterized originally as "broad spectrum neuropeptide antagonists" 9.

Mode of Action
The SP receptor is a G protein-coupled receptor, in many respects similar to other well-studied receptors in psychiatry, particularly monoamine receptors 2. The interaction of SP with its receptor activates Gq, which in turn activates phospholipase C to break down phosphatidyl inositol bisphosphate into inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 acts on specific receptors in the sarcoplasmic reticulum to release intracellular stores of Ca2+, while DAG acts via protein kinase C to open L-type calcium channels in the plasma membrane. The rise in intracellular [Ca2+] induces the tissue response. With an array of actions as diverse as that seen with SP, there is scope for numerous therapeutic possibilities 10.

Functions
In the central nervous system, SP is associated with the regulation of mood disorders, anxiety, stress, reinforcement, neurogenesis, neurotoxicity and pain. In the digestive tract, SP, along with some other tachykinins, are neurotransmitters that regulate motor activity, secretion of ions and fluid, as well as vascular functions 11, 12.

References
1. Argyropoulos SV, Nutt DJ (2000). Substance P antagonists: novel agents in the treatment of depression. Expert Opin Investig Drugs, 9(8):1871-1875.
2. Book: Substance P and Related Tachykinins. Chapter 13: Neuropsychopharmacology: By Nadia MJ, Kramer MS.
3. Senba E, Tohyama M (1985). Origin and fine structure of substance P-containing nerve terminals in the facial nucleus of the rat:an immunohistochemical study. Exp Brain Res., 57(3):537-546.
4. Seidel MF, Tsalik J, Vetter H, Müller W (2007). Substance P in Rheumatic Diseases. Current Rheumatology Reviews, 3:17-30.
5. Piercey MF, Dobry PJ, Einspahr FJ, Schroeder LA, Masiques N (1982) Use of substance P fragments to differentiate substance P receptors of different tissues. Regulatory Peptides, 3(5-6):337-349.
6. Shore SA, Drazen JM (1988). Airway responses to substance P and substance P fragments in the guinea pig. Pulm Pharmacol., 1(3):113-118.
7. Hanani M, Chorev M, Gilon C, Selinger Z (1988). The actions of receptor-selective substance P analogs on myenteric neurons: an electrophysiological investigation. European journal of pharmacology, 153(2-3):247-253.
8. Sakurada T, Yamada T, Tan-no K, Manome Y, Sakurada S, Kisara K, Ohba M (1991). Differential effects of substance P analogs on neurokinin 1 receptor agonists in the mouse spinal cord. J Pharmacol Exp Ther., 259:205-210
9. MacKinnon AC, Waters C, Jodrell D, Haslett C, Sethi T (2001). Bombesin and Substance P Analogues Differentially Regulate G-protein Coupling to the Bombesin Receptor. J. Biol. Chem., 276(30):28083-28091..
10. Khawaja AM, Rogers DF (1996). Tachykinins: receptor to effector. Int J Biochem Cell Biol., 28(7):721-738.
11. Leeman SE, Mroz EA (1974). Substance P. Life Sci., 15(12):2033–2044.
12. Wiesenfeld-Hallin Z, Xu XJ (1993). The differential roles of substance P and neurokinin A in spinal cord hyperexcitability and neurogenic inflammation. Regul Pept., 46(1-2):165-173

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Stichodactyla helianthus Neurotoxins

Definition
The Caribbean sea anemone Stichodactyla helianthus produces a 48-amino acid residue neurotoxin (ShI) that is employed for defence and the capture of prey. This small protein, which is much more active against crustacea than mammals, binds to the neuronal voltage-gated sodium channel, thereby slowing down channel inactivation and delaying the repolarization phase of the action potential 1.

Related Peptides
ShI resembles a group of proteins from sea anemones of the genera Anthopleura and Anemonia which act on nerve and striated muscle sodium channels from mammals as well as crustacea. However, it appears that ShI, together with a series of four homologous proteins from the anemones Heteractis macrodactylus and H. paumotensis, form a separate group distinguishable from the actiniid (i.e. Anthopleura and Anemonia) proteins on the basis of their different amino acid sequences, lack of immunological cross-reactivity, and their inability to prevent binding of the actiniid proteins to the sodium channel 1.

Sticholysins I and II are two highly hemolytic polypeptides purified from the Caribbean Sea anemone Stichodactyla helianthus. Their high sequence homology (93%) indicates that they correspond to isoforms of the same hemolysin. The spectroscopic measurements show a close similarity in the secondary structure content, conformation and stability of both toxins 2.

Discovery
The polypeptide ShI is selectively toxic to crustaceans was isolated from the aqueous exudate collected from frozen and thawed bodies of a Caribbean sea anemone, Stichodactyla (formerly Stoichactis) helianthus, by Kem et al., in 1989 3.

Structural Characteristics
The three-dimensional structure of the sea anemone polypeptide Stichodactyla helianthus neurotoxin I in aqueous solution has been determined using distance geometry and restrained molecular dynamics simulations based on NMR data acquired at 500 MHz. The structure consists of a core of twisted, four-stranded, antiparallel beta- sheet encompassing residues 1-3, 19-24, 29-34, and 40-47, joined by three loops, two of which are well defined by the NMR data. The third loop, encompassing residues 7-16, is poorly defined by the data and is assumed to undergo conformational averaging in solution 1.

Mode of Action
Expression of the two lymphocyte potassium channels, the voltage-gated channel Kv1.3 and the calcium activated channel IKCa1, changes during differentiation of human T cells. ShK, the 35-residue polypeptide toxin from Stichodactyla helianthus, blocks Kv1.3 implicated in the pathogenesis of experimental autoimmune encephalomyelitis, at low pM concentrations. ShK adopts a central helix-kink-helix fold, and alanine-scanning and other mutagenesis studies have defined its channel-binding surface. Models have been developed of how this toxin effects K+channel blockade and how its docking configuration might differ in ShK-Dap22, which contains a single side chain substitution that confers specificity for Kv1.3 blockade 4.

Functions
This ShK analog containing a fluorescein-6-carboxyl group attached through an {2-[2-amino-ethoxy]-ethoxy}-acetic acid (AEEAc) linker to the a-amino group of Arg1, selectively blocked the voltage gated T-lymphocyte K+ Kv1.3 channels implicated in the pathogenesis of experimental autoimmune encephalomyelitis. It potently blocked Kv1.3 channels at pM concentrations and exhibited >80 fold specificity for Kv1.3 over Kv1.1 and other Kv channels. In flow cytometry experiments, chronically activated rat and human T-lympocytes with >600 Kv1.3 channels/cell were readily distinguished from resting and acutely activated T-lymphocytes with lower Kv1.3 channel numbers. 6-FAM-AEEAc-Stichodactyla helianthus neurotoxin (ShK) may therefore be a useful tool to detect the presence of T-lymphocytes with high expression of Kv1.3 channels in normal and diseased tissues 5.

References
1. Fogh RH, Kem WR, Norton RS (1990). Solution structure of neurotoxin I from the sea anemone Stichodactyla helianthus. A nuclear magnetic resonance, distance geometry, and restrained molecular dynamics study. J. Biol. Chem., 265(22):13016-13028..
2. Martinez D, Campos AM, Pazos F, Alvarez C, Lanio ME, Casallanovo F, Schreier S, Salinas RK, Vergara C, Lissi E (2001). Properties of St I and St II, two isotoxins isolated from Stichodactyla helianthus: a comparison. Toxicon., 39(10):1547-1560.
3. Kem WR, Parten B, Pennington MW, Price DA, Dunn BM (1989). Isolation, characterization, and amino acid sequence of a polypeptide neurotoxin occurring in the sea anemone Stichodactyla helianthus. Biochemistry, 28(8): 3483-3489.
4. Norton RS, Pennington MW, Wulff H (2004). Potassium channel blockade by the sea anemone toxin ShK for the treatment of multiple sclerosis and other autoimmune diseases. Curr Med Che., 11(23):3041-3052.
5. Beeton C, Wulff H, Singh S, Botsko S, Crossley G, Gutman GA, Cahalan MD, Pennington M, Chandy KG (2003). A Novel Fluorescent Toxin to Detect and Investigate Kv1.3 Channel Up-regulation in Chronically Activated T Lymphocytes.. J. Biol. Chem., 278(11):928-9937.

Selectin Related Peptides

Definition
The selectins are three related receptors that initiate rolling of leukocytes on activated platelets or endothelium through Ca2+-dependent recognition of cell surface carbohydrates 1.

Related Peptides
The selectin family consists of three closely related cell-surface molecules with differential expression by leukocytes, [L-selectin (MEL-14, LAM-i, CD62L)], platelets, [P-selectin (PADGEM, GMP-140, CD62P)], and vascular endothelium [E-(ELAM-i, CD62E) and P-selectin] 2.

Discovery
Before 1989, L-, P-, and E-selectin were on different experimental pathways, although certain similarities can be seen in retrospect. All three selectins were identified using antibodies. L-selectin, the first of the selectins to be studied and was recognized as an adhesion molecule by using a monoclonal antibody (MEL-14) raised against a murine lymphoma. P-selectin (CD62) was discovered by investigators interested in the biochemical events associated with platelet activation. The discovery of E-selectin involved a monoclonal antibody-based strategy that combined identification of a cellular activation antigen and adhesion blocking 3.

Structural Characteristics
All of the selectins have a unique and characteristic extracellular region composed of an amino terminal calcium-dependent lectin domain, an epidermal growth factor (EGF)2 -like domain, and two to nine short consensus repeat (SCR) units homologous to domains found in complement binding proteins 2.

Mode of Action
Leukocyte rolling and adhesion to endothelium are dynamic processes that involve multiple adhesion receptors and the active participation of the cells involved. It is unlikely that the selectins merely mediate the passive “adsorption” of leukocytes to the endothehial surface, but rather the selectins are likely to direct these processes. Regulatory mechanisms that control these events include the rapid mobilization of presynthesized P-selectin to the cell surface, increased rates of selectin protein synthesis, induced transcription of the E-selectin gene, changes in cycling of E- and P-selectins from the cell surface to intracellular compartments, rapid shedding of L-selectin from the cell surface, activation-induced changes in L-selectin avidity for ligands, and alterations in cytoskeletal associations. Control of selectin ligand function through induction of their synthesis, differential glycosylation, and release from the cell surface are also important regulatory events. Further, coordinated selectin and integrin function is essential for leukocyte entry into tissues. Also important are a host of locally active inflammatory mediators and chemokines responsible for initiating and perpetuating the inflammatory process. The tetrasaccharide sialyl Lewisx (sLex, CD158) has been identified as a prototype ligand for both P- and E-selectin, although all three selectins can bind sLex and sialyl Lewisx under the appropriate conditions. L-selectin (CD62L) binds to a ligand tentatively designated as GIyCAM while E-selectin (CD62E) and P-selectin (CD62P) bind to ligands bearing sLex (CD158) -related determinants on the surface of the neutrophil. Rolling is hypothesized to allow the leukocytes to interact with locally released inflammatory mediators and chemokines such as IL-8. This initiates firm adhesion mediated through the integrins (CD11a and CD11b) binding to ICAM-1 (CD54) and other ligands followed by leukocyte diapedesis between endothelial cells, which is mediated in part by CD31 2.

Functions
The selectin family of adhesion molecules mediates the initial attachment of leukocytes to venular endothelial cells before their firm adhesion and diapedesis at sites of tissue injury and inflammation. In contrast to most other adhesion molecules, selectin function is restricted to leukocyte interactions with vascular endothelium. Multiple studies indicate that the selectins mediate neutrophil, monocyte, and lymphocyte rolling along the venular wall. The generation of selectin-deficient mice has confirmed these findings and provided further insight into how the overlapping functions of these receptors regulate inflammatory processes. Selectin-directed therapeutic agents are now proven to be effective in blocking many of the pathological effects resulting from leukocyte entry into sites of inflammation. Future studies are focused on how the selectins interact with the increasing array of other adhesion molecules and inflammatory mediators 2.

References
1. McEver RP (1994). Selectins. Curr Opin Immunol., 6(1):75-84.
2. Tedder TF, Steeber DA, Chen A, Engel P (1995). The selectins: vascular adhesion molecules. Faseb J, 9(10):866-873.
3. Bevilacqua MP, Nelson RM (1993). Selectins. J. Clin. Invest., 91(2)379-387.

Saposin Related Peptides

Definition
Saposins A, B, C, and D are a group of structurally similar glycoproteins derived by proteolytic processing from a single precursor protein, prosaposin. All saposins contain about 80 amino acids and have 6 identically placed cysteine residues 1.

Related peptides
Processing of prosaposin (70 kDa) generates saposin proteins, A, B, C, and D, from its first, second, third, and fourth domains 2. It has been noted that other proteins have the same polypeptide motif characterized by the similar location of six cysteines. These saposin-like (SAPLIP) proteins are surfactant protein B (SP-B), Entamoeba histolytica pore forming peptide, NK-lysin, acid sphingomyelinase and acyloxyacyl hydrolase. The structural homology and the conserved disulfide bridges suggest for all SAPLIPs a common fold, called saposin fold 3.

Discovery
The first saposin (now called saposin B) was described by Jatzkewitz and his colleagues in 1964 as a required heat-stable factor for hydrolysis of sulfatides by arylsulfatase A. The second saposin (saposin C) was discovered in 1971 by Ho and OBrien and was found to stimulate the hydrolysis of glucosylceramidase and to accumulate in tissues of Gaucher disease patients. The discovery of the two remaining saposins, A and D, resulted from cloning and sequencing of the prosaposin cDNA. The discovery that all four saposins are part of a single precursor protein, prosaposin, began with the cloning of a cDNA encoding saposin B and the discovery that the human cDNA sequence was homologous with a protein in rat testis, SGP-1 4.

Structural Characteristics
All four saposins are structurally similar to one another, including placement of six cysteines, a glycosylation site, and conserved proline residues in identical positions 1. A three-dimensional model comparing saposins A and C reveals significant sequence homology between them, especially preservation of conserved acidic and basic residues in their middle regions. Each appears to possess a conformationally rigid hydrophobic pocket stabilized by three internal disulfide bridges, with amphipathic helical regions interrupted by helix breakers 2. The different activities of the saposins must reside within the module of the a-helices and/or in additional specific regions of the molecule 3. The trophic activity of prosaposin on human neuroblastoma cells resides in the aminoterminal hydrophilic sequence (LIDNNRTEEILY) of human saposin C. Nanomolar concentrations of a 22-mer peptide encompassing this region stimulate neurite outgrowth and choline acetyltransferase activity, and prevents cell death in neuroblastoma cells. In primary cerebellar granule cells, the 22-mer also stimulates neurite outgrowth. Peptides encompassing the neurotrophic sequence in prosaposin have been termed prosaptides 5.

Mode of Action
Saposins, through their interaction with glycosphingolipid hydrolases and their substrates, increase lysosomal hydrolytic activities. Saposins and prosaposin are expressed by various cell types and as a secretory protein in body fluids including blood, seminal plasma, seminiferous tubular fluid, and prostatic secretions. Prosaposin and its active domain, saposin C, are known for their potent neurotrophic activities and are involved in neuro-embryological development. The neurotrophic activity of prosaposin has been attributed to the NH2-terminal portion of the saposin C domain of the molecule which is the source for a number of biologically active synthetic peptides such as prosaptides TX14A. Prosaptides (i.e., TX14A), saposin C, and prosaposin exert their biological effects by binding to a partially characterized single high-affinity G-protein coupled receptor (GPCR) 6.

Functions
The apparent function of the saposins is that of promoting the enzymatic degradation of sphingolipids in lysosomes. It has been reported that saposin A (Sap A) and saposin C (Sap C) stimulate the hydrolysis of glucosylceramide and galactosylceramide, saposin B (Sap B) that of several sphingolipids including sulfatide and G-ganglioside, and saposin D (Sap D) that of sphingomyelin. The physiological significance of Sap B and C has been unequivocally assessed by the discovery that a defect of Sap B results in a variant form of metachromatic leukodistrophy, and a defect of Sap C causes a variant form of Gaucher disease. The tissue accumulation of sulfatides in the first case and of glucosylceramides in the second indicates that in vivo Sap B has a fundamental role in the regulation of arylsulfatase A activity and Sap C in that of glucosylceramidase. The functional properties of Sap B and C have been extensively investigated in vitro. The mechanism by which Sap B promotes sphingolipid degradation has been well characterized by showing that it forms water-soluble complexes with several sphingolipids (sulfatide, globotriaosylceramide, ganglioside G, etc.) thus making them accessible to the respective sphingolipid hydrolases 1.

References
1. Vaccaro AM, Salvioli R, Barca A, Tatti M, Ciaffoni F, Maras B, Siciliano R, Zappacosta F, Amoresano A, Pucci P (1995). Structural Analysis of Saposin C and B. Complete Localization Of Disulfide Bridges. J. Biol. Chem., 270(17):9953-9960.
2. Morimoto S, Martin BM, Yamamoto Y, Kretz KA, O'Brien JS, Kishimoto Y (1989). Saposin A: second cerebrosidase activator protein. PNAS., 86(9):3389-3393
3. Vaccaro AM, Salvioli R, Tatti M, Ciaffoni F (1999). Saposins and Their Interaction with Lipids. Neurochemical Research, 24(2):307-314.
4. Kishimoto Y, Hiraiwa M, O'Brien' JS. 1992. Saposins: structure, function, distribution, and molecular genetics. Journal of Lipid Research, 33:1255-1267
5. O'Brien JS, Carson GS, Seo HC, Hiraiwa M, Weiler S, Tomich JM, Barranger JA, Kahn M, Azuma N, Kishimoto Y (1995). Identification of the neurotrophic factor sequence of prosaposin. Faseb., 9(8):681-685.
6. Lee TJ, Sartor O, Luftig RB, Koochekpour S (2004). Saposin C promotes survival and prevents apoptosis via PI3K/Akt-dependent pathway in prostate cancer cells. Molecular Cancer, 3:31

RESA Peptides

Definition
RESA peptides are identical to the immunodominant T cell epitopes of the merozoite antigen, Pf155/RESA (ring-infected erythrocyte surface antigen). In cell culture experiments significant IgG secretion could be achieved with these peptides 1.

Related Peptides
RESA is deposited on the erythrocyte membrane has been considered an important vaccine candidate. Synthetic vaccines based on repeat sequences of malarial antigens have shown poor protection or inconsistent results during clinical trials. This has been attributed to lack of efficient T cell help or genetic restriction of the immune response at the host level. To overcome these limitations and to increase the immune response to peptide antigens, chimeric immunogens containing well defined Th determinant (CS.T3) with B cell antigenic sequences (RESA peptides) made by covalent linkage were synthesized 2.

Discovery
Chougnet et al., showed that two synthetic peptides representing major T cell epitopes from RESA protein, namely (EENVEHDA)4 and LGRSGGDIIKMQTL, induced the secretion of antibodies, reacting with the corresponding B cell epitope, as well as with RESA protein and the parasite, in cell culture supernatants 3.

Structural Characteristics
The P. falciparum antigen Pf155/RESA, which is deposited in the erythrocyte membrane during merozoite invasion, is considered to be a candidate for a blood-stage vaccine. The C-terminal part of Pf155/RESA comprises a region of repeated subunits of eight, four, or three amino acids. The octapeptide subunit EENVEHDA is immunogenic in rabbits, and a large fraction of human antibodies to Pf155/RESA also react with this linear sequence, suggesting that the octapeptide is part of a major antigenic region of Pf155/RESA4. RESA protein contains three tandemly repeated immunodominant B cell epitopes viz EENV, EENVEHDA and DDEHVEEPTVA. These peptides are found to be antigenically dominant and antibodies raised against them have been shown to inhibit merozoite invasion of RBCs 2.

Mode of Action
RESA peptide mediated protection is correlated with the presence of serum reactivity with the Pf155/RESA peptides leading to the production of antibodies 3.

Functions
RESA peptides are found to be antigenically dominant and antibodies raised against them have been shown to inhibit merozoite invasion of RBCs 2.

References
1. Fievet N, Chougnet C, Dubois B, Deloron P (1993). Quantification of antibody-secreting lymphocytes that react with Pf155/RESA from Plasmodium falciparum: an ELISPOT assay for field studies. Clin Exp Immunol., 91(1):63-67.
2. Rao DN, Chaba B, Kumar P, Haq W, Sabhnani L (1997). Developing peptide based immunogen against human malaria delivered in liposomes containing non-toxic adjuvants. Indian Journal of Clinical Biochemistry, 12:52-54.
3. Chougnet C, Troye-Blomberg M, Deloron P (1991). Human immune response in Plasmodium falciparum malaria: synthetic peptides corresponding to known epitopes of the Pfl 55/RESA antigen induce production of parasite specific antibody in vitro. J Immunol., 147:2295-2301.
4. Sjölander A, Ståhl S, Nygren PA, Aslund L, Ahlborg N, Wåhlin B, Scherf A, Berzins K, Uhlén M, Perlmann P (1990). Anders Sjolander et al., 1990. Immunogenicity and Antigenicity in Rabbits of a Repeated Sequence of Plasmodium falciparum Antigen Pf155/RESA Fused to Two Immunoglobulin G-Binding Domains of Staphylococcal Protein. Infect Immun., 58(4):854-859.

Renin Inhibitors

Definition
Renin inhibitors represent an alternative to angiotensin-converting enzyme inhibitors (ACEI) for the treatment of hypertension. They inhibit the renin-angiotensin system at its first and rate limiting step, the renin-angiotensinogen reaction 1.

Related Peptides
Renin can be inhibited by peptides derived from its prosegment. The design of compounds based on pepstatin and on angiotensinogen sequence has led to very potent and specific human renin inhibitors. Such inhibitors are active by the intravenous route in primates but still lack of good oral activity 1.

Discovery
To investigate whether peptides related to the renin prosegment were able to inhibit renin activity, Evin et al., synthesized four peptides having the following structures: Arg-Ile-Pro-OMe, butyloxycarbonyl(Boc)-Leu-Lys-Lys-Met-Pro-OMe, Boc-Arg-Ile-Pro-Leu-Lys-Lys-Met-Pro-OMe, and Boc-Glu-Arg-Ile-Pro-Leu-Lys-Lys-Met-Pro-OMe (corresponding to amino acids 12-14, 15-19, 12-19, and 11-19, respectively, of the renin prosegment). All four peptides were found to inhibit the activity of pure mouse submaxillary renin on a porcine synthetic tetra-decapeptide in vitro 2.
However, peptidic renin inhibitors have been found to be poorly absorbed across the intestine or rapidly eliminated by the liver and have been reported to have oral bioavailabilities of less than 2%. A peptide-based renin inhibitor, A-72517 (molecular mass of 7 kDa) with considerable oral bioavailability, was devised and reported by HD Kleinert et al., in 1992. This inhibitor had oral bioavailabilities of 8, 24, 32, and 53% in the monkey, rat, ferret, and dog, respectively 3.

Structural Characteristics
On the basis of the minimal octapeptide sequence of the renin substrate, a series of peptides was synthesized containing (3S, 4S)-4-amino-3-hydroxy-6-methylheptanoic acid (statine) or (3S, 4S)-4-amino-3-hydroxy-5-phenylpentanoic acid (AHPPA) at the P1P1' position. Some of these peptides also contained Nin-formyltryptophan at the P5, P3, or P3' position. Renin-inhibitory potency varied over a wide range (from inactive to IC50 = 3 nM). Potency was reduced by at least 10-fold when the peptide was shortened by two residues at either the amino or carboxy terminus. The AHPPA-containing inhibitors were several-fold less potent than the statine-containing inhibitors. Analysis of models for the three-dimensional structure of inhibitors at the active site of human renin suggests that the diminished potency of the AHPPA peptides in comparison with the statine-containing peptides was caused by a shift in the peptide backbone due to a steric conflict between the phenyl ring of the AHPPA residue and the S1 subsite. The importance of the side chain and the 3(S)-hydroxyl group of the statine residue was demonstrated by substituting 5-aminovaleric acid for a dipeptide unit at the P1P1' position, which resulted in a peptide devoid of renin-inhibitory activity. Substitutions of other basic amino acids for histidine at the P2 position caused a great loss in potency, possibly due to disruption of a hydrogen bond as suggested by molecular modeling. Studies on the plasma renins of four nonhuman species suggest that the isoleucine-histidine segment at the P2'P3' position is important to defining the human specificity of the substrate4.

Mode of Action
Renin inhibitors interfere with the first, rate-limiting step in the synthesis of angiotensin II by binding directly to the highly specific enzyme, renin. This approach may represent a more focused alternative to angiotensin-converting enzyme inhibitor therapy with an improved side-effect profile 5.

Functions
Renin inhibitors may offer an exciting new therapeutic means of blocking the actions of the renin-angiotensin-aldosterone system. Renin inhibitors given parenterally safely lower blood pressure in patients with essential hypertension and improve the hemodynamic profile of patients with congestive heart failure. Under conditions of salt limitation, normal subjects show increases in renal plasma flow during infusion of renin inhibitors. The systemic and renal hemodynamic responses to renin inhibition are accompanied by suppression of plasma renin activity, plasma angiotensin II and plasma aldosterone levels 5

References
1. Corvol P, Menard J (1989). Renin inhibition: immunological procedures and renin inhibitor peptides. Fundam Clin Pharmacol., 3(4):347-362.
2. Evin G, Devin J, Castro B, Menard J, Corvol P (1984). Synthesis of peptides related to the prosegment of mouse submaxillary gland renin precursor: an approach to renin inhibitors. PNAS., 81(1): 48–52.
3. Kleinert HD, Rosenberg SH, Baker WR, Stein HH, Klinghofer V, Barlow J, Spina K, Polakowski J, Kovar P, Cohen J (1992). Discovery of a peptide-based renin inhibitor with oral bioavailability and efficacy. Science, 257(5078):1940-1943.
4. Hui KY, Carlson WD, Bernatowicz MS, Haber E (1987). Analysis of structure-activity relationships in renin substrate analogue inhibitory peptides. J Med-Chem., 30(8): 1287-1295.
5. Kleinert HD (1996). Hemodynamic Effects of Renin Inhibitors. Am J Nephrol., 16:252-260.

pTH-Related Protein Sequences

Definition
Parathyroid hormone–related peptide (PTHrP), a peptide hormone derived from normal and tumor cells that regulates bone metabolism and vascular tone, is a naturally occurring angiogenesis inhibitor.

Discovery
PTHrP was discovered in association with certain types of cancer that caused elevated blood Ca2+ levels (a syndrome called humoral hypercalcemia of malignancy, or HHM) in affected patients 1.

Structural Characteristics
The mature PTHrP of teleost fish is 161 amino acids long 2. There are regions of high conservation across all the vertebrates, including 22 of the first 34 amino acids, which suggest they interact with the common PTH/PTHrP receptors. Other regions of high conservation are 11 of the 18 amino acids of the Arg-rich RNA binding region 3 and 7 of the 15 amino acids of the nuclear localization sequence 4. Comparison of the COOH-terminal region of PTHrPs reveals it is much shorter in fish than in tetrapods 2.

Mode of Action
In a study, mice with a targeted deletion of parathyroid hormone (PTH)-related peptide (PTHrP) develop a form of dyschondroplasia resulting from diminished proliferation and premature maturation of chondrocytes. Therefore, PTHrP appears to modulate cell proliferation and differentiation in both the pre and post natal period. PTH/PTHrP receptor expression in the mouse is controlled by two promoters. Furthermore, it is found that, while the downstream promoter controls PTH/PTHrP receptor gene expression in bone and cartilage, it is differentially regulated in the two tissues. 1-alpha, 25-dihydroxyvitamin D3 downregulated the activity of the downstream promoter in osteoblasts, but not in chondrocytes, both in vivo and in vitro. Most of the biological activity of PTHrP is thought to be mediated by binding of its amino terminus to the PTH/PTHrP receptor. However, recent evidence suggests that amino acids 87-107, outside of the amino terminal binding domain, act as a nucleolar targeting signal. Chondrocytic cell line, CFK2, transfected with wild-type PTHrP cDNA showed PTHrP in the nucleoli as well as in the secretory pathway. Therefore, PTHrP appears to act as a bifunctional modulator of both chondrocyte proliferation and differentiation, through signal transduction linked to the PTH/PTHrP receptor and by its direct action in the nucleolus 5.

Functions
Effect of PTHrP on human platelet activation: A study conducted was to determine whether PTHrP might be involved in human platelet activation, by using a turbidimetric method to determine platelet aggregation. The expression of PTH1R (PTH type 1 receptor) in human platelets was analysed by western blot and flow cytometry analyses. PTHrP-(1–36) by itself failed to modify the activation of platelets. However, it significantly enhanced ADP-induced platelet activation, and also increased the ability of other agonists (thrombin, collagen and arachidonic acid) to induce platelet aggregation 6. H89 and Rp-cAMPS two protein kinase A inhibitors, and bisindolylmaleimide I, a protein kinase C inhibitor, partially decreased the enhancing effect of PTHrP-(1–36) on ADP-induced platelet activation. Meanwhile, PTHrP-(7–34), a PTH1R antagonist, as well as PD098059, a MAPK (mitogen-activated protein kinase) inhibitor, or a farnesyltransferase inhibitor abolished this effect of PTHrP-(1–36). Moreover, PTHrP-(1–36) increased (2-fold over control) MAPK activation in human platelets. PTH1R was detected in platelets, and the number of platelets expressing it on their surface in patients during AMI (acute myocardial infarction) was not different from that in a group of patients with similar cardiovascular risk factors without AMI 6. Western blot analysis showed that total PTH1R protein levels were markedly higher in platelets from control than those from AMI patients. These results indicate that human platelets express the PTH1R. PTHrP can interact with this receptor to enhance human platelet activation induced by several agonists through a MAPK-dependent mechanism 6.

Localization of PTHrP in breast cancer metastases: PTHrP has recently been identified in 60% of a series of primary breast cancers. The detection of a bone-resorbing factor in tumors with a propensity to metastasize to bone prompted study of PTHrP in breast cancer metastasis. PTHrP was localized by immunohistology in 12 of 13 (92%) breast cancer metastases in bone and in 3 of 18 (17%) metastases in non-bone sites. The statistical difference was highly significant (P < 0.0001). Production of PTHrP as a bone-resorbing agent may contribute to the ability of breast cancers to grow as bone metastases.

References
1. Moseley JM, Kubota M, Diefenbach-Jagger H, Wettenhall RE, Kemp BE, Suva LJ, Rodda CP, Ebeling PR, Hudson PJ, Zajac JD (1987). Parathyroid hormone-related protein purified from a human lung cancer cell line. PNAS., 84:5048–5052.
2. Canario AVM, Rotllant J, Fuentes J, Guerreiro PM, Rita Teodosio H, Power DM, Clark MS (2006). Novel bioactive parathyroid hormone and related peptides in teleost fish. FEBS Lett., 580:291-299.
3. Aarts MM, Levy D, He B, Stregger S, Chen T, Richard S, Henderson JE (1999). Parathyroid hormone-related protein interacts with RNA. J. Biol. Chem., 274:4832–4838.
4. Henderson JE, Amizuka N, Warshawsky H, Biasotto D, Lanske BM, Goltzman D, Karaplis AC (1995). Nucleolar localization of parathyroid hormone- related peptide enhances survival of chondrocytes under conditions that promote apoptotic cell death. Mol. Cell. Biol., 15:4064–4075.
5. Amizuka N, Henderson JE, White JH, Karaplis AC, Goltzman D, Sasaki T, Ozawa H (2000). Recent studies on the biological action of parathyroid hormone (PTH)-related peptide (PTHrP) and PTH/PTHrP receptor in cartilage and bone. Histol Histopathol., 15(3):957-970.
6. Ortega A, Pérez de Prada MT, Mateos-Cáceres PJ, Ramos Mozo P, González-Armengol JJ, González Del Castillo JM, Martín Sánchez J, Villarroel P, Santiago JL, Bosch RJ, Macaya C, Esbrit P, López-Farré AJ (2007). Effect of parathyroid-hormone-related protein on human platelet activation. Clinical Science, 113(7):319–327.
7. Powell GJ, Southby J, Danks JA, Stillwell RG, Hayman JA, Henderson MA, Bennett RC, Martin TJ (1991). Localization of Parathyroid Hormone-related Protein in Breast Cancer Metastases: Increased Incidence in Bone Compared with Other Sites. Cancer Research, 51:3059-3061.

pTH, Sequences and Analogs

Definition
Parathyroid hormone (PTH) is secreted by the parathyroid glands as a polypeptide containing 84 amino acids.

Discovery
In 1925, Collip prepared hot hydrochloric acid extracts of the parathyroid glands, an approach which he correctly deduced was needed to free the active substance from other gland stromal components and render it soluble. The author showed that these acid extracts of the parathyroid gland would completely relieve the tetany that followed parathyroidectomy, and established the parathyroids as an endocrine gland which secreted hormone (PTH) 1.

Structural Characteristics
Amino acid composition: Bovine parathyroid hormone has been isolated in homogeneous form from a trichloroacetic acid precipitate of defatted parathyroid glands. Disc gel electrophoresis of the purified hormone revealed a single electrophoretic band, and Edman amino terminal analysis showed a single amino acid, PTH-alanine. The purified hormone consisted of 84 amino acids.The amino acid composition of the isolated hormone, determined by a combination of timed acid hydrolysis and total enzymatic digestion, is as follows: Lys9, His4, Arg5, Trpl, Tyr1, Phe2, Leu8, ILe3, Met2, Val8, Ala7, Pro2, Gly4, Glu6, Gln5, Ser8, Asp6, Asn3. Cystine and threonine are absent 2.

Mode of Action
PTH acts on the PTH/PTHrP receptor (P1R), a class II G protein-coupled receptor which stimulates the adenylyl cyclase/cAMP and phospholipase C/inositol phosphate (IP) signaling pathways. Peptide deletion studies have shown that the N-terminal residues of PTH play a crucial role in P1R activation 3 and cross-linking and receptor mutagenesis studies have revealed that the N-terminal residues of PTH interact with the portion of the P1R that contains the extracellular loops and extracellular ends of the transmembrane helices (the juxtamembrane or J domain) 4.

Peptide Analogs
Parathyroid Hormone (PTH)-(1-14) and -(1-11) Analogs Conformationally Constrained by a -Aminoisobutyric Acid Mediate Full Agonist Responses via the Juxtamembrane Region of the PTH-1 Receptor: The N-terminal portion of parathyroid hormone is critical for PTH-1 receptor (P1R) activation and has been postulated to be a-helical when bound to the receptor. In a study it was investigated whether substitution of the sterically hindered and helix-promoting amino acid a -aminoisobutyric acid (Aib) in N-terminal PTH oligopeptides would improve the capacity of the peptide to activate the P1R. Analysis of the effects of individual Aib substitutions at each position in [Ala3,12,Gln10,Har11,Trp14]PTH(1-14)NH2 ([M]PTH(1-14)) on cAMP-stimulating potency in HKRK-B28 cells revealed that Aib at most positions diminished potency; however, Aib at positions 1 and 3 enhanced potency. Thus [Aib1,3,M]PTH(1-14) was ~100-fold more potent than [M]PTH(1-14), ~100,000-fold more potent than native PTH(1-14), and 2-fold more potent than PTH(1-34). The shorter peptide, [Aib1,3,M]PTH(1-11), was also fully efficacious and 1,000-fold more potent than [M]PTH(1-11). In cAMP stimulation assays performed in COS-7 cells expressing P1R-delNt, a receptor that lacks most of the N-terminal extracellular domain, [Aib1,3,M]PTH(1-14) was 50-fold more potent than [M]PTH(1-14) and 1,000-fold more potent than PTH(1-34). [Aib1,3,M]PTH(1-14), but not PTH(1-34), inhibited the binding of 125I-[Aib1,3 ,Nle8 ,Gln10 ,Har11 ,Ala12 ,Trp14 ,Arg19 ,Tyr21]PTH(1-21)NH2 to hP1R-delNt. The Aib1,3 substitutions in otherwise unmodified PTH(1-34) enhanced potency and binding affinity on hP1R-delNt, but they had no effect for this peptide on hP1R-WT. Circular dichroism spectroscopy demonstrated that the Aib-1,3 substitutions increased helicity in all peptides tested, including PTH(1-34). Thus it has been suggested that the N-terminal residues of PTH are intrinsically disordered but become conformationally constrained, possibly as an a -helix, upon interaction with the activation domain of the PTH-1 receptor 5.

Functions
PTH, its fragments and their analogs for the treatment of osteoporosis: The susceptibility to traumatic fracturing of osteopenic bones, and the spontaneous fracturing of osteoporotic bones by normal body movements caused by the microstructural deterioration and loss of bone, are currently treated with antiresorptive drugs, such as the bisphosphonates, calcitonin, estrogens, and selective estrogen receptor modulators. These antiresorptive agents target osteoclasts and, as their name indicates, reduce or stop bone resorption. They cannot directly stimulate bone formation, increase bone mass above normal values in ovariectomized rat models, or improve microstructure. However, there is a family of agents - the PTH and some of its fragments and their analogs - which directly stimulate bone growth and improve microstructure independently from impairing osteoclasts. These drugs are about to make their clinical debut in treating patients with osteoporosis and, probably not too far in the future, for accelerating fracture healing. They stimulate osteoblast accumulation and bone formation in three ways via signals from the type 1 PTH/PTH-related protein (PTHR1) receptors on proliferatively inactive preosteoblasts, osteoblasts, osteocytes and bone-lining cells. The receptor signals shut down the proliferative machinery in preosteoblasts and push their maturation to osteoblasts, cause the osteoblastic cells to make and secrete several factors that stimulate the extensive proliferation of osteoprogenitors without PTHRI receptors, stimulate the reversion of bone-lining cells to osteoblasts, and extend osteoblast lifespan and productivity by preventing them from suicidally initiating apoptosis 6.

References
1. Collip JB (1925). The extraction of a parathyroid hormone which will prevent or control parathyroid tetany and which regulates the level of blood calcium. Journal of Biological Chemistry, 63:395-438.
2. Brewer HB Jr, Ronan R (1970). Bovine Parathyroid Hormone: Amino Acid Sequence. Proceedings of the National Academy of Sciences, 67(4):1862-1869.
3. Takasu H, Gardella TJ, Luck MD, Potts JT, Jr and Bringhurst FR (1999). Amino-Terminal Modifications of Human Parathyroid Hormone (PTH) Selectively Alter Phospholipase C Signaling via the Type 1 PTH Receptor: Implications for Design of Signal-Specific PTH Ligands. Biochemistry, 38:13453-13460.
4. Hoare SRJ, Gardella TJ, and Usdin TB (2001). Evaluating the Signal Transduction Mechanism of the Parathyroid Hormone 1 Receptor. J. Biol. Chem., 276:7741-7753.
5. Shimizu N, Guo J, Gardella TJ (2001). Parathyroid Hormone (PTH)-(1-14) and -(1-11) Analogs Conformationally Constrained by a -Aminoisobutyric Acid Mediate Full Agonist Responses via the Juxtamembrane Region of the PTH-1 Receptor. J. Biol. Chem., 276 (52):49003-49012.
6. Whitfield JF, Morley P, Willick GE (2002). Parathyroid hormone, its fragments and their analogs for the treatment of osteoporosis. Treat Endocrinol., 1(3):175-190.

Protein tyrosine kinases

Definition
A prion is a proteinaceous infectious particle that lacks nucleic acid.

Discovery
Creutzfeldt-Jakob disease (CJD) remained a curious, rare neurodegenerative disease of unknown etiology for more than three score years. Only the transmission of CJD to apes by inoculation of brain extracts from patients who had died of CJD initiated a path of scientific investigation that was to demystify that fascinating area of biomedicine 1. In 1982 Prusiner had purified the hypothetical infectious prion, and that the infectious agent consisted mainly of a specific protein. Prusiner coined the word "prion" as a name for the infectious agent 2. While the infectious agent was named a prion, the specific protein that the prion was composed of is also known as the Prion Protein (PrP), though this protein may occur both in infectious and non-infectious forms.

Structural Characteristics
Prions are devoid of nucleic acid. The cellular prion protein (PrPC) is a sialoglycoprotein of Mr 33–35 kDa that is expressed predominantly in neurons. The normal cellular form of prion protein (PrPC) is a precursor to the pathogenic protease-resistant forms (PrPSc) believed to cause scrapie, bovine spongiform encephalopathy (BSE) and Creutzfeldt-Jakob disease 3. Its amino terminus contains the octapeptide PHGGGWGQ, which is repeated four times and is among the best-preserved regions of mammalian PrPC. PrPC is converted into PrPSc through a process whereby a portion of its a-helical and coil structure is refolded into ß-sheet. This structural transition is accompanied by profound changes in the physicochemical properties of the PrP. When the secondary structures of the PrP isoforms were compared by optical spectroscopy, they were found to be markedly different. Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy studies showed that PrPC contains about 40% a helix and little ß sheet while PrPSc is composed of about 30% a helix and 45% ß sheet 4.

Mode of Action
Prions, the causative agents of prion diseases, consist of the abnormal isoform of prion protein, PrPSc. PrPSc is generated by conformational conversion of the normal isoform of prion protein, PrPC, a glycosyl-phosphatidyl-inositol-anchored glycoprotein abundantly expressed on the surface of neurons. Prions or PrPSc having invaded the body interact with PrPC and induce changes in structure of the interacting PrPC into that of PrPSc, leading to prion replication. At the same time, this constitutive conversion causes the detrimental accumulation of PrPSc in the brain tissue 5.

Functions
Neurotoxicity of a prion protein fragment: In transmissible and genetic neurodegenerative disorders such as scrapie of sheep, spongiform encephalopathy of cattle and Creutzfeldt–Jakob or Gerstmann–Sträussler–Scheinker diseases of humans, PrPSc accumulates in the central nervous system of affected individuals, and its protease-resistant core aggregates extracellularly into amyloid fibrils. The process is accompanied by nerve cell loss. Also there is a report that neuronal death results from chronic exposure of primary rat hippocampal cultures to micromolar concentrations of a peptide corresponding to residues 106–126 of the amino-acid sequence deduced from human PrP complementary DNA. DNA fragmentation of degenerating neurons indicates that cell death occurred by apoptosis. The PrP peptide 106–126 has a high intrinsic ability to polymerize into amyloid-like fibrils in vitro. These suggest that cerebral accumulation of PrPSc and its degradation products may play a role in the nerve cell degeneration that occurs in prion-related encephalopathies 6.

References
1. Gibbs CJ, Gajdusek DC, Asher DM, Alpers MP, Beck E, Daniel PM, Matthews WB. (1968). Creutzfeldt-Jakob disease (spongiform encephalopathy): transmission to the chimpanzee. Science, 161: 388–389.
2. Prusiner SB (1982). Novel proteinaceous infectious particles cause scrapie. Science, 216:136–144.
3. Brown DR, Qin K, Herms JW, Madlung A, Manson J, Strome R, Fraser PE, Kruck T, von Bohlen A, Schulz-Schaeffer W, Giese A, Westaway D, Kretzschmar H (1997). The cellular prion protein binds copper in vivo. Nature, 390(6661):684-687.
4. Pan KM, Baldwin M, Nguyen J, Gasset M, Serban A, Groth D, Mehlhorn I, Huang Z, Fletterick RJ, Cohen FE, Prusiner SB (1993). Conversion of alpha-helices into beta-sheets features in the formation of the scrapie prion proteins. PNAS., 90:10962–10966.
5. Sakaguchi S (2007). Mechanisms of prion transmission. Nippon. Rinsho., 65(8):1391-1395.
6. Forloni G, Angerett N, Chiesa R, Monzani E, Salmona M, Bugiani O, Tagliavini F (1993). Neurotoxicity of a prion protein fragment. Nature, 362:543-546.

Prion Protein (Prp) Fragments and Prion Disease Related Products

Definition
A prion is a proteinaceous infectious particle that lacks nucleic acid.

Discovery
Creutzfeldt-Jakob disease (CJD) remained a curious, rare neurodegenerative disease of unknown etiology for more than three score years. Only the transmission of CJD to apes by inoculation of brain extracts from patients who had died of CJD initiated a path of scientific investigation that was to demystify that fascinating area of biomedicine 1. In 1982 Prusiner had purified the hypothetical infectious prion, and that the infectious agent consisted mainly of a specific protein. Prusiner coined the word "prion" as a name for the infectious agent 2. While the infectious agent was named a prion, the specific protein that the prion was composed of is also known as the Prion Protein (PrP), though this protein may occur both in infectious and non-infectious forms.

Structural Characteristics
Prions are devoid of nucleic acid. The cellular prion protein (PrPC) is a sialoglycoprotein of Mr 33–35 kDa that is expressed predominantly in neurons. The normal cellular form of prion protein (PrPC) is a precursor to the pathogenic protease-resistant forms (PrPSc) believed to cause scrapie, bovine spongiform encephalopathy (BSE) and Creutzfeldt-Jakob disease 3. Its amino terminus contains the octapeptide PHGGGWGQ, which is repeated four times and is among the best-preserved regions of mammalian PrPC. PrPC is converted into PrPSc through a process whereby a portion of its a-helical and coil structure is refolded into ß-sheet. This structural transition is accompanied by profound changes in the physicochemical properties of the PrP. When the secondary structures of the PrP isoforms were compared by optical spectroscopy, they were found to be markedly different. Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy studies showed that PrPC contains about 40% a helix and little ß sheet while PrPSc is composed of about 30% a helix and 45% ß sheet 4.

Mode of Action
Prions, the causative agents of prion diseases, consist of the abnormal isoform of prion protein, PrPSc. PrPSc is generated by conformational conversion of the normal isoform of prion protein, PrPC, a glycosyl-phosphatidyl-inositol-anchored glycoprotein abundantly expressed on the surface of neurons. Prions or PrPSc having invaded the body interact with PrPC and induce changes in structure of the interacting PrPC into that of PrPSc, leading to prion replication. At the same time, this constitutive conversion causes the detrimental accumulation of PrPSc in the brain tissue 5.

Functions
Neurotoxicity of a prion protein fragment: In transmissible and genetic neurodegenerative disorders such as scrapie of sheep, spongiform encephalopathy of cattle and Creutzfeldt–Jakob or Gerstmann–Sträussler–Scheinker diseases of humans, PrPSc accumulates in the central nervous system of affected individuals, and its protease-resistant core aggregates extracellularly into amyloid fibrils. The process is accompanied by nerve cell loss. Also there is a report that neuronal death results from chronic exposure of primary rat hippocampal cultures to micromolar concentrations of a peptide corresponding to residues 106–126 of the amino-acid sequence deduced from human PrP complementary DNA. DNA fragmentation of degenerating neurons indicates that cell death occurred by apoptosis. The PrP peptide 106–126 has a high intrinsic ability to polymerize into amyloid-like fibrils in vitro. These suggest that cerebral accumulation of PrPSc and its degradation products may play a role in the nerve cell degeneration that occurs in prion-related encephalopathies 6.

References
1. Gibbs CJ, Gajdusek DC, Asher DM, Alpers MP, Beck E, Daniel PM, Matthews WB. (1968). Creutzfeldt-Jakob disease (spongiform encephalopathy): transmission to the chimpanzee. Science, 161: 388–389.
2. Prusiner SB (1982). Novel proteinaceous infectious particles cause scrapie. Science, 216:136–144.
3. Brown DR, Qin K, Herms JW, Madlung A, Manson J, Strome R, Fraser PE, Kruck T, von Bohlen A, Schulz-Schaeffer W, Giese A, Westaway D, Kretzschmar H (1997). The cellular prion protein binds copper in vivo. Nature, 390(6661):684-687.
4. Pan KM, Baldwin M, Nguyen J, Gasset M, Serban A, Groth D, Mehlhorn I, Huang Z, Fletterick RJ, Cohen FE, Prusiner SB (1993). Conversion of alpha-helices into beta-sheets features in the formation of the scrapie prion proteins. PNAS., 90:10962–10966.
5. Sakaguchi S (2007). Mechanisms of prion transmission. Nippon. Rinsho., 65(8):1391-1395.
6. Forloni G, Angerett N, Chiesa R, Monzani E, Salmona M, Bugiani O, Tagliavini F (1993). Neurotoxicity of a prion protein fragment. Nature, 362:543-546.

Pancreatic, Pancreastatin and Chromogranin A Polypeptides

Definition
Pancreatic polypeptide (PP) is a hormone produced by endocrine cells of the duodenal pancreas.
Pancreastatin (PST) is a regulatory peptide with a general inhibitory effect on secretion, is derived from chromogranin A, a glycoprotein present throughout the neuroendocrine system. Chromogranin A (CgA) is also referred to as secretory protein I, is an acidic protein expressed by many neuroendocrine cells and neurons.

Structural Characteristics
PP contains 36 amino acids, has a molecular weight of 4.2 kDa and the isoelectric point is pH 6 to 7. The amino acid sequence of the peptide 1 is Gly-Pro-Ser-Gln-Pro-Thr-Tyr-Pro-Gly-Asp-Asp-Ala-Pro-Val-Glu-Asp-Leu-Ile-Arg-Phe-Tyr-Asp-Asn-Leu-Gln-Gln-Tyr-Leu-Asn-Val-Val-Thr-Arg-His-Arg-Tyr-NH2. The human CgA is a 439-residue protein preceded by an 18-residue signal peptide. Comparison of the protein sequence of human CgA with that of bovine CgA shows high conservation of the NH2-terminal and COOH terminal domains as well as the potential dibasic cleavage sites, whereas the middle portion shows remarkable sequence variation (36%). The PST sequence contained in human CgA is flanked by sites for proteolytic processing. This suggests that human CgA may be the precursor for a human Pancreastatin molecule and possibly for other, as yet unidentified, biologically active peptides 2.

Mode of Action
PP is secreted from and controls differentiation through its specific receptors: In a study, the regulatory roles of PP and its Y receptors were studied using MC3T3-E1 cells, a murine transformed osteoblastic cell line. It was found that PP mRNA was detected and increased during cell-contact-induced differentiation in MC3T3-E1 cells. Furthermore, all the types of NPY family receptor mRNAs (Y1, Y2, Y4, Y5, and y6) were found to increase during differentiation. Also it was found that PP stimulated differentiation in MC3T3-E1 cells in terms of alkaline phosphatase (ALP) mRNA and bone morphogenetic protein-2 (BMP-2) mRNA. These findings suggested that MC3T3-E1 cells produce and secrete PP, which may in turn stimulate the differentiation of MC3T3-E1 through its specific receptors in an autocrine manner 3. PST, a CgA-derived peptide, has been found to modulate glucose, lipid, and protein metabolism in rat adipocytes. PST has an overall counter regulatory effect on insulin action by activating a specific receptor–effector system (Gaq/11protein-PLC-ß-PKC classical). However, PST stimulates both basal and insulin-mediated protein synthesis in rat adipocytes. PST dose-dependently stimulates Thr421/Ser424 phosphorylation of S6 kinase. Moreover, PST promotes phosphorylation of regulatory sites in 4E-BP1 (PHAS-I) (Thr37, Thr46). The initiation factor eIF4E itself, whose activity is also increased upon phosphorylation, is phosphorylated in Ser209 by PST stimulation. Also, it has been shown that that these effects of PST on S6 kinase and the translation machinery can be blocked by preventing the activation of PKC. These results indicate that PST stimulates protein synthesis machinery by activating PKC and provides some evidence of the molecular mechanisms involved, i.e., the activation of S6K and the phosphorylation of 4E-BP1 (PHAS-I) and the initiation factor eIF4E 4.

Functions
Mouse pancreatic polypeptide modulates food intake: A study was conducted to investigate the effects of synthetic mouse pancreatic polypeptide (mPP) on feeding and anxiety in mice. It was found that the intracerebroventricular (i.c.v.) injection of mPP (0.003-3 nmol) dose-dependently increased food intake. A significant increase was observed 20 min after i.c.v. injection and continued for 4 h. Further the intraperitoneal (i.p.) injection of mPP (0.03-30 nmol) dose-dependently decreased food intake. A significant decrease was observed 20 min after i.p. injection and continued for 4 h. In the elevated plus maze test, the i.c.v. injection of mPP (0.003-3 nmol) did not affect anxiety behavior. These results suggest that mPP modulates food intake and the Y4 receptor in the brain may contribute to the regulation of feeding, whereas appearing not to influence anxiety in mice 5.

Effects of PST and CgA on insulin release stimulated by various insulinotropic agents: The effects of porcine PST on insulin release stimulated by insulinotropic agents, glucagon, cholecystokinin-octapeptide (CCK-8), gastric inhibitory polypeptide (GIP) and L-arginine, were compared to those of bovine chromogranin A (CGA) using the isolated perfused rat pancreas. PST significantly potentiated glucagon-stimulated insulin release (first phase: 12.5 ± 0.9 ng/8 min; second phase: 34.5 ± 1.6 ng/25 min in controls; 16.5 ± 1.1 ng/8 min and 44.0 ± 2.2 ng/25 min in pancreastatin group), whereas CgA was ineffective. Similarly, CGA did not affect insulin release stimulated by CCK-8 or GIP. These findings suggest that PST stimulates insulin release in the presence of glucagon. Because PST can have multiple effects on insulin release, which are dependent upon the local concentration of insulin effectors, PST may participate in the fine tuning of insulin release from B cells 6.

References
1. Kimmel JR, Hayden LJ, Pollock HG (1975). Isolation and characterization of a new pancreatic polypeptide hormone. J. Biol. Chem., 250(24):9369-9376.
2. Konecki DS, Benedum UM, Gerdes HH, Huttner WB (1987). The Primary Structure of Human Chromogranin A and Pancreastatin. J. Biol. Chem., 262(35):17026-17030.
3. Hosaka H, Nagata A, Yoshida T, Shibata T, Nagao T, Tanaka T, Saito Y, Tatsuno I (2008). Pancreatic polypeptide is secreted from and controls differentiation through its specific receptors in osteoblastic MC3T3-E1 cells. Peptides, 29(8):1390-1395.
4. González-Yanes C, Sánchez-Margalet V (2002). Pancreastatin, a chromogranin A-derived peptide, activates protein synthesis signaling cascade in rat adipocytes. Biochemical and Biophysical Research Communications, 299(4):525-531.
5. Asakawa A (1999). Mouse pancreatic polypeptide modulates food intake, while not influencing anxiety in mice. Peptides, 20(12):1445-1448.
6. Ishizuka J, Tatemoto K, Cohn DV, Thompson JC, Greeley GH Jr (1991). Effects of pancreastatin and chromogranin A on insulin release stimulated by various insulinotropic agents. Regulatory Peptides, 34(1):25-32.

MART-1 Peptides

Definition
MART-1 (melanoma antigen recognized by T-cells) is an antigen expressed by melanoma cells. Antibodies against the antigen are used in the medical specialty of anatomic pathology in order to recognize cells of melanocytic differentiation, useful for the diagnosis of a melanoma.

Discovery
MART-1 was discovered by two groups of researchers who independently sequenced the gene for this antigen in 1994. Both names are currently in common use. Kawakami et al., at the National Cancer Institute coined the term MART-1, which stands for "Melanoma Antigen Recognized by T-cells." Coulie et al., of Belgium called the gene Melan-A, an abbreviation for "melanocyte antigen." MART-1 is a widely shared melanoma antigen recognized by the T lymphocytes of patients with established malignancy 1, 2. In the case of melanoma, MART-1 has lineage-specific protein expressed in ~75–100% of primary and metastatic melanomas depending on their clinical stage 3.

Structural Characteristics
MART-1 gene is 18 kb long and comprises five exons. MART-1 is a transmembrane protein consisting of 118 amino acids. It has a single transmembrane domain 2. Two overlapping epitopes spanning amino acid residues 26 through 35 are of particular interest: numerous clinical studies have been performed using variants of the MART-1 26–35 decamer, although only the 27–35 nonamer has been found on the surface of targeted melanoma cells 4. The crystallographic structures of the various MART-126/27–35 nonamers and decamers indicate that there are two general conformational classes available to these peptides: an extended conformation adopted by the nonamers, and a bulged conformation adopted by the decamers and nonamers.

Mode of Action
In cancer immunotherapy, epitopes and variants derived from the MART-1/Melan-A protein are widely used as clinical vaccines. Numerous clinical studies have been performed using variants of the MART-1 26–35 decamer. 26–35 and 27–35 peptides of MART-1 strikingly adopt different conformations when bound to HLA-A2. Clonally distinct MART-126/27–35-reactive T cells show broad cross-reactivity towards these ligands. Many of the cross-reactive T cells remain unable to recognize anchor-modified variants with very subtle structural differences. Findings also indicate that for design of immunotherapeutics based on the MART-1 26/27–35 epitopes, as neither cross-reactivity nor selectivity is predictable based on the analysis of the structures alone5.

Functions
The MART-1 / Melan-A antigen is specific for the melanocyte lineage, found in normal skin, the retina, and melanocytes, but not in other normal tissues. It is a useful as a marker for melanocytic tumors (melanomas). MART-1 / Melan-A represents an attractive candidate for generic immunotherapy of HLA-A*0201 melanoma patients. A superagonist variant of the nonameric Melan-A27–35 peptide has been shown to elicit an enhanced anti-melanoma CD8+CTL response. Clinical trials have been undertaken for peptide vaccination using the decameric analog Melan-A26–35A27L (ELAGIGILTV). In addition to exhibiting improved HLA-A*0201 binding properties (higher affinity and more stable HLA-A*0201/ peptide complexes), Melan-A26–35A27L displays more potent antigenicity and immunogenicity than the natural Melan-A peptides. A large majority of CTL raised either in vitro or in vivo against Melan-A26–35A27L are fully cross-reactive with the Melan-A parental peptide sequences and able to specifically lyse Melan-A-expressing tumor cells 6, 7. Protease-resistant, nonnatural tumor antigem derivatives are highly immunogenic and potent activators of melanoma-specific CTL. They represent promising new tools for molecular anti-melanoma immunotherapy.

References
1. Kawakami Y, Eliyahu S, Delgado CH, Robbins PF, Rivoltini L, Topalian SL, Miki T, Rosenberg SA (1994). Cloning of the gene coding for a shared human melanoma antigen recognized by autologous T cells infiltrating into tumor. PNAS., 91(9) 3515-3519.
2. Coulie PG, Brichard V, Van Pel A, Wolfel T, Schneider J, Traversari C, Mattei S, De Plaen E, Lurquin C, Szikora JP, Renauld JC, Boon T (1994). A new gene coding for a differentiation antigen recognized by autologous cytolytic T lymphocytes on HLA-A2 melanomas. J Exp Med.,180(1):35-42.
3. Hofbauer GF, Kamarashev J, Geertsen R, Boni R, Dummer R (1998). Melan A/MART-1 immunoreactivity in formalin-fixed paraffin-embedded primary and metastatic melanoma: frequency and distribution. Melanoma Res., 8(4): 337-343.
4. Kawakami Y, Eliyahu S, Sakaguchi K, Robbins PF, Rivoltini L, Yannelli JR Appella E, Rosenberg SA (1994). Identification of the immunodominant peptides of the MART-1 human melanoma antigen recognized by the majority of HLA-A2-restricted tumor infiltrating lymphocytes. J. Expt. Med., 180: 347–352.
5. Borbulevych OY, Insaidoo FK, Baxter TK, Powell DJ Jr, Johnson LA, Restifo NP, Baker BM (2007). Structures of MART-126/27–35 Peptide/HLA-A2 Complexes Reveal a Remarkable Disconnect between Antigen Structural Homology and T Cell Recognition Mol. Biol. 372(5):1123–1136.
6. Valmori D, Fonteneau JF, Lizana CM, Gervois N, Lienard D, Rimoldi D, Jongeneel V, Jotereau F, Cerottini JC, Romero P(1998). Enhanced generation of specific tumor-reactive CTL in vitro by selected Melan-A/MART-1 immunodominant peptide analogues. J. Immunol., 160: 1750-1758.
7. Men Y, Miconnet I, Valmori D, Rimoldi D, Cerottini JC, Romero P (1999). Assessment of immunogenicity of human Melan-A peptide analogues in HLA-A*0201/Kb transgenic mice. J. Immunol., 162:3566-3573.

Leucopyrokinin (LPK) and Fragments

Definition
Leucopyrokinin (LPK) is a myotropic substance originally isolated from head extracts of the Madeira cockroach, Leucophaea maderae.

Discovery
The first investigations into the role of neuropeptide hormones in insect physiology was by Kopec in 1917 and the first report of the isolation and sequence analysis of an insect neuropeptide was in 1975. Since then a large number of insect neuropeptides that have been identified . Evaluation of analogs of the blocked insect myotropic neuropeptide leucopyrokinin (LPK) has demonstrated its relative insensitivity to amino acid substitution in the N-terminal in contrast to the C-terminal region. Truncated analogs of LPK without the first, second, and third N-terminal amino acids retain a significant 144%, 59% and 30% of the activity of the parent octapeptide, respectively. The [2-8] LPK analog is the first fragment of an insect neuropeptide to exhibit greater activity than the parent hormone. In contrast, truncated analogs of the insect myotropic, proctolin, exhibit little or no activity. The pentapeptide fragment Phe-Thr-Pro-Arg-Leu-NH2 has been identified as the active core of LPK 1.

Structural Characteristics
The active conformation of a cyclic pyrokinin analog was determined by both experimental and computational techniques. The tight constraints on the active core structure of this cyclized peptide, which maintains biological activity despite its relative rigidity, suggest that this is the conformation recognized by the myotropic receptor. Members of this insect neuropeptide family share the common C-terminal pentapeptide sequence Phe-Xaa-Pro-Arg- Leu-NH2 (Xaa = Ser, Thr, or Val). Circular dichroic, nuclear magnetic resonance, and molecular dynamics analyses of the conformationally restricted cyclic pyrokinin analog cydo(-Asn- Thr-Ser-Phe-Thr-Pro-Arg-Leu-) indicated the presence of a ß-turn in the active core region encompassing residues Thr- Pro-Arg-Leu. The rigid cyclic analog retains biological activity, suggesting that its C-terminal ß-turn is the active pyrokinin conformation recognized by the myotropic receptor. As individual pyrokinins and pyrokinin-like neuropeptides demonstrate both oviduct-contractile and pheromone-biosynthesis
activities in various insects, the biologically active ß-turn structure holds broad significance for many biological processes 2.

Mode of Action
The pyrokinin insect neuropeptides stimulate contractions of cockroach proctodeum (hindgut) and oviduct, and their myotropic activity can be readily tested with the isolated hindgut bioassay, which is both rapid and reproducible. Intact central innervation is essential for the action of LPK on puparial contraction, whereas central neurones take no part in mediation of LPK action on tanning of the cuticle. An analysis of tensiometric recordings of muscular activity revealed that the actual time of LPK accelerated puparial contraction coincides with the beginning of the immobilisation/retraction phase. LPK accelerates the switch from wandering behaviour to immobilisation/retraction behaviour but has no effect on the onset and duration of motor patterns that normally underlie puparial contraction in controls. The morphology of an accelerated puparium is normal but its formation is temporally dissociated from normal ‘contraction patterns’ that are performed a long time after the puparium has contracted. It means that neuromuscular activity of larvae accelerated by LPK does not cease upon formation of the white puparium, but continues until the whole motor programme of pupariation behaviour is completed. Apparently the peptide acts on the integument by stimulating it to contract and shrink, and no specific patterns of muscular contractions are needed to properly shape the puparium.

Functions
LPK found in the corpora cardiaca, a neurosecretory organ analogous to the pituitary and hypothalamus glands of the vertebrate endocrine system. Three related neuropeptides from the locust are more potent stimulators of oviduct than hindgut contraction 3, 4. Insect neuropeptide leucopyrokinin and [2-8]-leucopyrokinin, a truncated analog without the first aminoacid of leucopyrokinin peptide chain exert an antinociceptive effect in rats.

An insect neuropeptide LPK (pQTSFTPRLamide) accelerates pupariation in wandering larvae of the fleshfly Sarcophaga bullata. The period of sensitivity to the action of LPK begins approximately 4 h before pupariation. Within this period the degree of acceleration of contraction into the shape of a puparium is practically independent of the age at which the larvae are injected, while acceleration of tanning is distinctly more age dependent.

LPK elicited consistent proctolin-like responses on the hindgut, foregut, oviduct and heart of the Madeira cockroach, Leucophaea maderae, with increases in both amplitude and frequency of contraction. The brain and internal organs distribution of 125I-labeled [2-8]-leucopyrokinin ([2-8]-LPK), a truncated analog of LPK, an insect myotropic peptide injected into the lateral brain ventricle was determined in rats. A high accumulation of this analog in adrenals and in the hypothalamus and hippocampus of the brain was found. A lesser but significant [2-8]-LPK accumulation in other internal organs and parts of the brain was also observed 5.


References
1. Nachman RJ, Holman GM, Cook BJ (1986). Active fragments and analogs of the insect neuropeptide leucopyrokinin: structure-function studies. Biochem Biophys Res Commun., 137:936-942.
2. Nachman RJ, Victoria A. Robertso VA, Dyson HJ, Holman GM, Tainer JA (1991). Active conformation of an insect neuropeptide family (pyrokInin/P-turn/molecular dynamlcs/NMR/pheromone). PNAS., 88:4518-4522.
3. Schoofs L, Holman GM, Hayes TK, Tips A, Nachman RJ, Vandesaande F, DeLoof A (1990). Isolation, identification and synthesis of locustamyotropin (Lom-MT), a novel biologically active insect peptide. Peptide., 11(3):427-433.
4. Schoofs L, Holman GM, Hayes TK, Nachman RJ, DeLoof A (1990). Locustatachykinin I and II, two novel insect neuropeptides with homology to peptides of the vertebrate tachykinin family. FEBS Lett., 261(2):397-401.
5. Plech A, Rykaczewska-Czerwinska M, Ryszka F, Suszka-Switek A, Dolinska B, Konopinska D (2005). Distribution of 125I-labeled [2-8]-leucopyrokinin, active analog of leucopyrokinin in rats. Acta poloniae pharmaceutica 62(5):393-397.