Mapping and Functional Analysis of NK-Lysin in Chicken

The antimicrobial peptides (AMPs) are important elements of the first line of defense against pathogens in animals, and an important constituent of innate immunity. NK-lysin is a cationic AMP that plays a critical role in innate immunity against infectious pathogens. We synthesized peptides corresponding to each helical region of chicken NK-lysin and analyzed their antimicrobial activity. Chicken NK-lysin inhibits the growth of a representative Gram-negative bacterium, Escherichia coli. The antimicrobial activity of two peptides designated H23 and H34 were 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 bacterial cell membrane. The chicken NK-lysin gene has been cloned but its location in the chicken genome is still unknown. A 6000 rad radiation hybrid panel (ChickRH6) was used to map the NK-lysin gene to the distal end of chromosome 22. Two additional genes, the adipocyte enhancer-binding protein 1-like gene and the DNA polymerase delta subunit 2-like gene, located in same NW_003779909 contig, were also mapped to chromosome 22. We previously described a functionally significant single nucleotide polymorphism (SNP) at the position 271 nucleotide of the NK-lysin coding sequence in two different chicken breeds. Here, we examined this SNP among a large number different inbred lines and heritage breeds. The A allele is more predominant than the G allele in these heritage breeds and inbred lines.