Chicken NK-lysin is an alpha-helical cationic peptide that exerts its antibacterial activity through damage of bacterial cell membranes.

The antimicrobial peptides (AMP) are important elements of the first line of defense against pathogens in animals, and an important constituent of innate immunity. Antimicrobial peptides act on a broad spectrum of microbial organisms. NK-Lysin is a cationic antibacterial peptide that was originally isolated from porcine intestinal tissue based on its antibacterial activity. We synthesized peptides corresponding to each helical region of chicken NK-lysin and analyzed their secondary structures in addition to their antimicrobial activity. Circular dichroism spectroscopy of the synthetic chicken NK-lysin (cNK-78) and 4 small peptides in negatively charged liposomes demonstrated transition in the conformation of α-helical peptides relative to the charged environment. Chicken NK-lysin inhibits the growth of a representative gram-negative bacterium, Escherichia coli. The antimicrobial activity of 2 peptides designated H23 and H34 was similar to that of mature NK-lysin, cNK-78. Microscopic analyses revealed the death of bacterium with disrupted membranes after peptide treatment, suggesting that chicken NK-lysin, an alpha-helical cationic peptide, exerts its antimicrobial activity by damaging the bacterial cell membrane.