Isolation, expression and characterization of a novel dual serine protease inhibitor, OH-TCI, from king cobra venom

Abstract

Snake venom Kunitz/BPTI members are good tools for understanding of structure–functional relationship between serine proteases and their inhibitors. A novel dual Kunitz/BPTI serine proteinase inhibitor named OH-TCI ( trypsin- and chymotrypsin-dual inhibitor from Ophiophagus hannah) was isolated from king cobra venom by three chromatographic steps of gel filtration, trypsin affinity and reverse phase HPLC. OH-TCI is composed of 58 amino acid residues with a molecular mass of 6339 Da. Successful expression of OH-TCI was performed as the maltose-binding fusion protein in E. coli DH5α. Much different from Oh11-1, the purified native and recombinant OH-TCI both had strong inhibitory activities against trypsin and chymotrypsin although the sequence identity (74.1%) between them is very high. The inhibitor constants ( K i) of recombinant OH-TCI were 3.91 × 10 −7 and 8.46 × 10 −8 M for trypsin and chymotrypsin, respectively. To our knowledge, it was the first report of Kunitz/BPTI serine proteinase inhibitor from snake venom that had equivalent trypsin and chymotrypsin inhibitory activities.