Cloning, characterization and expression study of an antimicrobial peptide, piscidin, from Atlantic cod (Gadus morhua)

Antimicrobial peptides (AMPs) are low molecular weight, cationic peptides that play an important role as the first line of host defence against invading microorganisms. The piscidin family comprises potent AMPs of 22-44 amino acid residues that have broad-spectrum activity against bacteria, virus, fungi and parasites. They were first isolated from the mast cells of hybrid striped bass but recent reports have shown that piscidins are found in various species of Acanthopterygii. We have identified a gene encoding for piscidin in Atlantic cod (Gadus morhua). The predicted mature cod piscidin contains 22 residues, including the four conserved histidines and its sequence shows very high similarity with other reported piscidins and piscidin-like peptides from fish. Expression studies showed that expression of cod piscidin was up-regulated after immune challenge, indicating that it may play an important role in the innate immune response. Importantly, our results demonstrate for the first time that piscidins are ancient defence factors that are more widespread amongst teleosts than hitherto thought.