Antimicrobial peptides derived from pepsinogens in the stomach of the bullfrog, Rana catesbeiana

Abstract

Three antimicrobial peptides, which had strong antimicrobial activity against a broad spectrum of microorganisms, were isolated from the stomach of the bullfrog, Rana catesbeiana. Two of the antimicrobial peptides were found to be derived from the N-terminal sequences of pepsinogen A and C prosequences. The amino acid sequences of the new antimicrobial peptides, named bullfrog pepsinogen A-derived antimicrobial peptide (bPaAP) and bullfrog pepsinogen C-derived antimicrobial peptide (bPcAP), were Gly-Val-Val-Lys-Val-Ser-Arg-Leu-Lys-Gly-Glu-Ser-Leu-Arg-Ala-Arg-Leu (MW 1865.5) and Ile-Ile-Lys-Val-Pro-Leu-Lys-Lys-Phe-Lys-Ser-Met-Arg-Glu-Val-Met-Arg-Asp-His-Gly-Ile-Lys-Ala-Pro-Val-Val-Asp-Pro-Ala-Thr-Lys-Tyr (MW 3691.6), respectively. The bPaAP and bPcAP adopted 35% and 42% amphipathic α-helical structure in 50% trifluoroethanol, respectively, and were non-hemolytic up to a concentration of 200 μg/ml. Synthesized pepsinogen C prosequences of monkey and human, which had similar structural characteristics as bPaAP and bPcAP, also showed antimicrobial activity at concentrations of 10–200 μg/ml. The third peptide was buforin I, previously found in the stomach of the Asian toad, Bufo bufo gargarizans. These findings strongly suggest that peptides derived from the prosequences of pepsinogens, along with buforin I, may contribute to the antimicrobial function of the gastrointestinal mucosa of vertebrates, including human.