Senegalin: a novel antimicrobial/myotropic hexadecapeptide from the skin secretion of the African running frog, Kassina senegalensis

Amphibian skin is a rich and unique source of novel bioactive peptides most of which are endowed with either antimicrobial or pharmacological properties. Here, we report the identification and structural characterization of a novel peptide, named senegalin, which possesses both activities. Senegalin is a hexadecapeptide amide (FLPFLIPALTSLISSL-NH2) of unique primary structure found in the skin secretion of the African running frog, Kassina senegalensis. The structure of the biosynthetic precursor of senegalin, deduced from cloned skin cDNA, consists of 76 amino acid residues and displays the typical domain organization of an amphibian skin peptide precursor. Both natural senegalin and its synthetic replicate displayed antimicrobial and myotropic activities. Senegalin was active against Staphylococcus aureus (MIC 50 μM) and Candida albicans (MIC 150 μM) but was non-haemolytic at concentrations up to and including 150 μM. In contrast, senegalin induced a dose-dependent contraction of rat urinary bladder smooth muscle (EC50 2.9 nM) and a dose-dependent relaxation of rat tail artery smooth muscle (EC50 37.7 nM). Senegalin thus represents a prototype biologically active amphibian skin peptide and illustrates the fact that amphibian skin secretion peptidomes continue to be unique sources of such molecules.