The hymenochirins: a family of host-defense peptides from the Congo dwarf clawed frog Hymenochirus boettgeri (Pipidae).

Skin secretions of frogs from the subfamily Xenopodinae (Xenopus+Silurana) within the family Pipidae are a rich source of antimicrobial peptides with therapeutic potential but species from the sister taxon Hymenochirus in the subfamily Pipinae (Hymenochirus+Pseudhymenochirus+Pipa) have not been investigated. Peptidomic analysis of norepinephrine-stimulated skin secretions from two distinct populations of the Congo dwarf clawed frog Hymenochirus boettgeri (Tornier, 1896) has led to identification of five structurally related peptides with broad-spectrum antimicrobial activity. Hymenochirin-1B (IKLSPETKDNLKKVLKGAIKGAIAVAKMV.NH(2)) is C-terminally α-amidated whereas hymenochirins-2B-5B have the general structure XKIPX(2)VKDTLKKVAKGX(2)SX(2)AGAX(3).COOH. Hymenochirin-3B (IKIPAVVKDTLKKVAKGVLSAVAGALTQ) was the most abundant peptide in the secretions. The hymenochirins show very low structural similarity with the antimicrobial peptides isolated from skin secretions of Silurana tropicalis and Xenopus laevis consistent with the proposed ancient divergence of the Pipinae and Xenopodinae. Synthetic replicates of hymenochirin-1B-4B inhibit the growth of Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Staphylococcus aureus (MIC in the range 10-40 μM) and Candida albicans (MIC=80 μM). The peptides display relatively weak hemolytic activity against human erythrocytes (LC(50) in the range 160 to >300 μM).