The Significance of Hypervariability and Conserved Motifs in Antimicrobial Peptides from Tree Frogs

Amphibians' skin is a rich source of natural antimicrobial peptides (AMPs). These AMPs exhibit marked inter- and intraspecific sequence divergence linked to the arms race between host and pathogens. Here, we combine peptidomics, molecular modeling, and phylogenetic analyses to understand the evolution of AMPs in Cophomantini, a diverse clade of neotropical tree frogs, and to investigate their interaction with bacterial membranes. Consistent with results in other amphibians, all species of Cophomantini secrete a mixture of peptides. We selected the hylin peptide family to survey sequence variability and the presence of common amino acid motifs. We found that most species secrete a unique set of hylins that, though variable, share the conserved motif Gly-X-X-X-Pro-Ala-X-X-Gly, with Gly and Pro colocalizing with charged or polar residues. Our modeling revealed that Pro curves the peptide through a hinge, facilitating its insertion into the bacterial membrane and, once inserted, contributes to stabilizing the pore structure. The phylogenetic inference using hylid prepro-peptides showed the need to classify new AMPs using the full-length sequence of the prepro-peptide region and highlighted the complex relationships between peptide families. Our findings revealed that conserved motifs occurred independently in distinct AMP families, suggesting a convergent evolution and a significant role in peptide-membrane interactions.