Molecular cloning and characterization of novel cathelicidin-derived myeloid antimicrobial peptide from Phasianus colchicus.

Cathelicidins were initially characterized as a family of antimicrobial peptides. Now it is clear that they fulfill several immune functions in addition to their antimicrobial activity. In the current work, three cDNA sequences encoding pheasant cathelicidins were cloned from a constructed bone marrow cDNA library of Phasianus colchicus, using a nested-PCR-based cloning strategy. The three deduced mature antimicrobial peptides, Pc-CATH1, 2 and 3 are composed of 26, 32, and 29 amino acid residues, respectively. Unlike the mammalian cathelicidins that are highly divergent even within the same genus, Pc-CATHs are remarkably conserved with chicken fowlicidins with only a few of residues mutated according to the phylogenetic analysis result. Synthetic Pc-CATH1 exerted strong antimicrobial activity against most of bacteria and fungi tested, including the clinically isolated (IS) drug-resistant strains. Most MIC values against Gram-positive bacteria were in the range of 0.09-2.95 μM in the presence of 100mM NaCl. Pc-CATH1 displayed a negligible hemolytic activity against human erythrocytes, lysing 3.6% of erythrocytes at 3.15 μM (10 μg/ml), significantly higher than the corresponding MIC. Pc-CATH1 was stable in the human serum for up to 72 h, revealing its extraordinary serum stability. These specific features of Pc-CATH1 may make its applications much wider given the potency and breadth of the peptide's bacteriocidal capacity and its resistance towards serum and high-salt environments.