Anti-infection peptidomics of amphibian skin.

Peptidomics and genomics analyses were used to study an anti-infection array of peptides of amphibian skin. 372 cDNA sequences of antimicrobial peptides were characterized from a single individual skin of the frog Odorrana grahami that encode 107 novel antimicrobial peptides. This contribution almost triples the number of currently reported amphibian antimicrobial peptides. The peptides could be organized into 30 divergent groups, including 24 novel groups. The diversity in peptide coding cDNA sequences is, to our knowledge, the most extreme yet described for any animal. The patterns of diversification suggest that point mutations as well as insertion, deletion, and "shuffling" of oligonucleotide sequences were responsible for the diversity. The diversity of antimicrobial peptides may have resulted from the diversity of microorganisms. These diverse peptides exhibited both diverse secondary structure and "host defense" properties. Such extreme antimicrobial peptide diversity in a single amphibian species is amazing. This has led us to reconsider the strong capability of innate immunity and molecular genetics of amphibian ecological diversification and doubt the general opinion that 20-30 different antimicrobial peptides can protect an animal because of the relatively wide specificity of the peptide antibiotics. The antimicrobial mechanisms of O. grahami peptides were investigated. They exerted their antimicrobial functions by various means, including forming lamellar mesosome-like structures, peeling off the cell walls, forming pores, and inducing DNA condensation. With respect to the development of antibiotics, these peptides provide potential new templates to explore further.