Porcine leukocytes contained three homologous peptides, PG‐1, 2 and 3, that manifested potent microbicidal activity against Escherichia coli, Listeria monocytogenes and Candida albicans in vitro. The peptides (‘protegrins’) were composed of 16 (PG‐2) or 18 amino acid residues, and, like tachyplesins (broad‐spectrum antibiotic peptides of horseshoe crab hemocytes), they contained two intramolecular cystine disulfide bonds. Considerably smaller than defensins, protegrins nevertheless showed substantial homology to them, especially to the ‘corticostatic’ rabbit defensin, NP‐3a. The relatively simple structure of protegrins should provide useful prototypes for constructing congeners with selectively enhanced host defense activities.
We purified three homologous antimicrobial peptides ('gallinacins') from chicken leukocytes, examined their antimicrobial activity in vitro, and established their primary sequences by a combination of gas phase microsequencing and on-line IX-ESI-MS analysis of endo-and exoprotease peptide digests. The peptides contained 3&39 amino acid residues, were relatively cationic due to their numerous lysine and arginine residues, and each contained 3 intramolecular cystine disulfide bonds. Gallinacins showed primary sequence homology to the recently delineated p-defensin family, heretofore found only in the respiratory epithelial cells and neutrophils of cattle, suggesting that /3-defensins originated at least 250 million years ago, before avian and mammalian lineages diverged. The 9 invariant residues (6 cysteines, 2 glycines and 1 proline) common to avian gallinacins and bovine p-defensins are likely to constitute the essential primary structural motif of this ancient family of host-defense peptides.
This novel model assay system makes new studies on the role of KSHV and KSHV-induced cellular products on the pathogenesis of KS possible. It also provides a high volume screening method to detect agents that inhibit KSHV infection of primary endothelial cells.
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