Ranachensinin: A Novel Aliphatic Tachykinin from the Skin Secretion of the Chinese Brown Frog, Rana chensinensis

Yuxin      Wu; Renjie      Li; Jie      Ma; Mei      Zhou; Lei      Wang; Timothy   I.   McClure; Jiqun      Cai; Tianbao      Chen; Chris      Shaw

Abstract

Amphibian skin secretions contain a plethora of pharmacologically-active substances and represent established sources of bioactive peptides, including tachykinins. Tachykinins are one of the most widely-studied peptide families in animals and are found in neuroendocrine tissues from the lowest vertebrates to mammals. They are characterized by the presence of a highly-conserved C-terminal pentapeptide amide sequence motif (-FXGLM-amide) that also constitutes the bioactive core of the peptide. Amidation of the C-terminal methioninyl residue appears to be mandatory in the expression of biological activity. Here, we describe the isolation, characterization and molecular cloning of a novel tachykinin named ranachensinin, from the skin secretion of the Chinese brown frog, Rana chensinensis. This peptide, DDTSDRSN QFIGLM-amide, contains the classical C-terminal pentapeptide amide motif in its primary structure and an Ile (I) residue in the variable X position. A synthetic replicate of ranachensinin, synthesized by solid-phase Fmoc chemistry, was found to contract the smooth muscle of rat urinary bladder with an EC₅₀ of 20.46 nM. However, in contrast, it was found to be of low potency in contraction of rat ileum smooth muscle with an EC₅₀ of 2.98 µM. These data illustrate that amphibian skin secretions continue to provide novel bioactive peptides with selective effects on functional targets in mammalian tissues.

Keywords: Amphibian, peptide, skin, smooth muscle, tachykinin.

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