GK-22 amide: a novel myotropic peptide from the skin secretion of the bamboo leaf odorous frog, Odorrana versabilis

The skin secretions produced by many amphibians are formidable chemical/biological weapons deployed as a defence against predators. Bioactive peptides are often the predominant class of biochemical within these secretions and the inventory of such remains incomplete with each individual taxon producing unique cocktails contained within which are some signature peptides, such as bradykinins and tachykinins. These secretions have been the source of many peptides subsequently found to have structural homologues in vertebrate neuroendocrine systems (bombesin/GRP; sauvagine/CRF; caerulein/CCK) and vice versa (bradykinin, CGRP, NMU). They are thus unequivocally intriguing resources for novel bioactive peptide discovery. Here we describe a novel 22-mer amidated peptide, named GK-22 amide (N-terminal Gly (G) and C-terminal Lys (K) amide) with an internal disulphide bridge between Cys (C) 11 and 20 from the skin secretion of Odorrana versabilis. Molecular cloning indicated that it is encoded as a single copy on a biosynthetic precursor of 59 amino acid residues consisting of a signal peptide, an acidic amino acid residue-rich spacer domain and a mature peptide encoding domain flanked N-terminally by a classical -Lys-Arg- (KR) propeptide convertase processing site and C-terminally by a Gly (G) residue amide donor. A synthetic replicate of this peptide produced potent and dose-dependent contraction of the smooth muscle of rat urinary bladder. GK-22 amide thus represents the prototype of a novel class of myotropic peptide from amphibian skin and its discovery illustrates the continuing potential of this resource to this end.