GALLINACINS - CYSTEINE-RICH ANTIMICROBIAL PEPTIDES OF CHICKEN LEUKOCYTES

We purified three homologous antimicrobial peptides ('gallinacins') fr om chicken leukocytes, examined their antimicrobial activity in vitro, and established their primary sequences by a combination of gas phase microsequencing and on-line LC-ESI-MS analysis of endo- and exoprotea se peptide digests. The peptides contained 36-39 amino acid residues, were relatively cationic due to their numerous lysine and arginine res idues, and each contained 3 intramolecular cystine disulfide bonds. Ga llinacins showed primary sequence homology to the recently delineated beta-defensin family, heretofore found only in the respiratory epithel ial cells and neutrophils of cattle, suggesting that beta-defensins or iginated at least 250 million years ago, before avian and mammalian li neages diverged. The 9 invariant residues (6 cysteines, 2 glycines and 1 proline) common to avian gallinacins and bovine beta-defensins are likely to constitute the essential primary structural motif of this an cient family of host-defense peptides.