Identification and cloning of a trypsin inhibitor from skin secretions of chinese red-belly toad bombina maxima

摘要

A novel trypsin inhibitor was identified and purified from skin secretions of Chinese red-belly toad Bombina maxima. The partial N-terminal 29 amino acid residues of the peptide, named BMTI, were determined by automated Edman degradation. This allowed the cloning of a full-length cDNA encoding BMTI from a cDNA library prepared from the toad skin. The deduced complete amino acid sequence of BMTI indicates that mature BMTI is composed of 60 amino acids. A FASTA search in the databanks revealed that BMTI exhibits 81.7% sequence identity with BSTI, a trypsin/thrombin inhibitor from European toad Bombina bombina skin secretions. Sequence differences between BMTI and BSTI were due to 11 substitutions at positions 2,9,25,36-37,39,41-42,50 and 56. BMTI potently inhibited trypsin with a K_i value of 0.06 #mu#M, similar to that of BSTI. However, unlike BSTI, which also inhibited thrombin with a K_i value of 1 #mu#M, no inhibitory effect of BMTI on thrombin was observed under the assay conditions.