Genome duplications within the Xenopodinae do not increase the multiplicity of antimicrobial peptides in Silurana paratropicalis and Xenopus andrei skin secretions

A putative genome duplication event within the Silurana lineage has given rise to the tetraploid frog S. paratropicalis and a second polyploidization within the Xenopus lineage has produced the octoploid frog X. andrei. Peptidomic analysis of norepinephrine-stimulated skin secretions of S. paratropicalis and X. andrei led to identification of multiple peptides with growth-inhibitory activity against Escherichia coli and Staphylococcus aureus. Structural characterization demonstrated that the S. paratropicalis components comprised three peptides belonging to the caerulein-precursor fragment family (CPF-SP1, -SP2 and -SP3), two peptides from the xenopsin-precursor fragment family (XPF-SP1 and -SP2), and one peptide orthologous to peptide glycine-leucine-amide (PGLa-SP1). The CPF peptides showed potent, broad-spectrum antimicrobial activity. The X. andrei components comprised two peptides from the magainin family, (magainin-AN1 and -AN2), two from the XPF family (XPF-AN1 and -AN2), two from the PGLa family(PGLa-AN1 and -AN2), and one caerulein-precursor fragment (CPF-AN1).The primary structures of these peptides indicate a close phylogenetic relationship between X. andrei and the octoploid frog X. amieti. Under the same experimental conditions, seven orthologous antimicrobial peptides were previously isolated from the diploid frog S. tropicalis, nine from the tetraploid frog X. borealis, and five from the tetraploid frog X. clivii. The data indicate, therefore, that nonfunctionalization (gene deletion) has been the most common fate of duplicated antimicrobial peptide genes following polyploidization events in the Silurana and Xenopus lineages.