Chemical synthesis, molecular cloning and expression of gene coding for a Bowman-Birk-type proteinase inhibitor

A gene coding for a Bowman-Birk-type proteinase inhibitor was synthesized chemically, cloned and expressed in Escherichia coli as a fusion protein with a beta-galactosidase fragment. The corresponding mutant inhibitor, carrying a P1 = Arg16 instead of Lys and an Ile27 instead of Met was obtained after cyanogen bromide cleavage, refolding and affinity chromatography on trypsin-Sepharose. Dissociation constants of complexes with trypsin of this mutant and wild-type Bowman-Birk inhibitor are identical within experimental error. This is explained by differential patterns of hydrogen bonds between side-chains of Arg or Lys in proteinase inhibitors and the primary specificity pocket of trypsin.