Ceratotoxin Peptides

Definition
Ceratotoxins are antibacterial peptides produced in the female reproductive accessory glands of the medfly Ceratitis capitata1. Their expression is not affected by bacterial infection, but is enhanced after mating and is modulated by juvenile hormone1.

Discovery
Ceratotoxin peptides were first purified from the secretion of the female reproductive accessory glands of the dipteran insect Ceratitis capitata in 19932.

Classification
Ceratotoxins are antibacterial peptides. Three different ceratotoxins have been purified: Ceratotoxins A, B and C1.

Structural Characteristics
All three ceratotoxins are 29 amino acids in length with a difference in two amino acids at positions 6 and 19. They are heat stable and strongly basic3. They are all amphiphilic in nature with their polar amino acids lying parallel to their alpha-helices3. Their antibacterial nature is attributed to this amphiphilic property3.

Mode of action
Ceratotoxins are effective against both gram negative and gram positive bacteria4. They bind to the cell membrane and form voltage dependent ion channels which are responsible for destroying the bacteria4.

Functions
Ceratotoxins are mainly expressed in an adult female insect5. Their main function is to protect the genital tract from bacterial infections during fertilization5.

References
1.Rosetto M, De Filippis T, Manetti AG, Marchini D, Baldari CT, Dallai R (1997). The genes encoding the antibacterial sex-specific peptides ceratotoxins are clustered in the genome of the medfly Ceratitis capitata, Insect Biochem Mol Biol, 27(12), 1039-46.
2.Marchini D, Giordano PC, Amons R, Bernini LF, Dallai R (1993). Purification and primary structure of ceratotoxin A and B, two antibacterial peptides from the female reproductive accessory glands of the medfly Ceratitis capitata (Insecta:Diptera), Insect Biochem Mol Biol, 23(5), 591-8.
3.Book: Molecular mechanisms of immune responses in insects: Paul T. Brey, Dan Hultmark, 74-80.
4.Marri L, Dallai R, Marchini D (1996). The novel antibacterial peptide ceratotoxin A alters permeability of the inner and outer membrane of Escherichia coli K-12, Curr Microbiol, 33(1):40-3.
5.Rosetto M, Manetti AG, Giordano PC, Marri L, Amons R, Baldari CT, Marchini D, Dallai R (1996). Molecular characterization of ceratotoxin C, a novel antibacterial female-specific peptide of the ceratotoxin family from the medfly Ceratitis capitata, Eur J Biochem, 241(2), 330-7.