Host-defense peptides in skin secretions of African clawed frogs (Xenopodinae, Pipidae)

Abstract

African clawed frogs of the Xenopodinae (Xenopus+Silurana) constitute a well-defined system in which to study the evolutionary trajectory of duplicated genes and are a source of antimicrobial peptides with therapeutic potential. Allopolyploidization events within the Xenopodinae have given rise to tetraploid, octoploid, and dodecaploid species. The primary structures and distributions of host-defense peptides from the tetraploid frogs Xenopus borealis, Xenopus clivii, Xenopus laevis, Xenopus muelleri, "X. muelleri West", and Xenopus petersii may be compared with those from the octoploid frogs Xenopus amieti and X. andrei. Similarly, components in skin secretions from the diploid frog Silurana tropicalis may be compared with those from the tetraploid frog Silurana paratropicalis. All Xenopus antimicrobial peptides may be classified in the magainin, peptide glycine-leucine-amide (PGLa), caerulein-precursor fragment (CPF), and xenopsin-precursor fragment (XPF) families. However, the numbers of paralogs from the octoploid frogs were not significantly greater than the corresponding numbers from the tetraploid frogs. Magainins were not identified in skin secretions of Silurana frogs and the multiplicity of the PGLa, CPF, and XPF peptides from S. paratropicalis was not greater than that of S. tropicalis. The data indicate, therefore, that nonfunctionalization (gene silencing) has been the most common fate of antimicrobial peptide genes following polyploidization. While some duplicated gene products retain high antimicrobial potency (subfunctionalization), the very low activity of others suggests that they may be evolving towards a new biological role (neofunctionalization). CPF-AM1 and PGLa-AM1 from X. amieti show potential for development into anti-infective agents for use against antibiotic-resistant gram-negative bacteria.