Host-defense peptides from skin secretions of Fraser's clawed frog Xenopus fraseri (Pipidae): Further insight into the evolutionary history of the Xenopodinae

Peptidomic analysis of norepinephrine-stimulated skin secretions of the tetraploid frog Xenopus fraseri Boulenger, 1905 (Pipidae) led to identification of 13 host-defense peptides. The primary structures of the peptides demonstrate that they belong to the magainin (3 peptides), peptide glycine-leucine-amide, PGLa (4 peptides), and xenopsin-precursor fragment, XPF (2 peptides) families, first identified in Xenopus laevis, together with caerulein precursor fragment-related peptides, CPF-RP (4 peptides), first identified in Silurana tropicalis. In addition, the secretions contain a molecular variant of xenopsin displaying the substitution Arg⁴ → Lys compared with X. laevis xenopsin and peptide glycine-tyrosine-amide (PGYa) (GRIIPIYPEFERVFA KKVYPLY.NH₂) whose function is unknown. The most potent antimicrobial peptide identified is CPF-RP-F1 (GFGSVLGKALKFGANLL.NH₂) with MIC = 12.5 μM against Staphylococcus aureus and 50 μM against Escherichia coli. On the basis of similarities in morphology and advertisement calls, X. fraseri has been placed in a species group that includes the octoploids Xenopus amieti and Xenopus andrei, and the tetraploid Xenopus pygmaeus. Cladistic analyses based upon the primary structures of magainin, PGLa, and CPF-RP peptides support a close evolutionary relationship between X. fraseri, X. amieti and X. andrei but suggest a more distant relationship with X. pygmaeus.