Construction of novel subtilisin E with high specificity, activity and productivity through multiple amino acid substitutions

Through three cumulative amino acid substitutions, we constructed novel mutant subtilisins E of Bacillus subtilis, all with high specificity, activity and productivity, The substitution of conserved Gly127, constituting P1 substrate-binding pocket, with Ala and Val showed a marked preference for the small P1 substrate, Leu was then substituted for Ile31 next to the cataltyic Asp32 to enhance the catalytic activity. Both double mutants (I31L/G127A and I31L/G127V) showed a 3-5-fold increase in catalytic efficiency due to a large k(cat), without any change in the specificity of the mutants at position 127, Molecular modeling suggests that large P1 residues were unable to access the pocket because of steric hindrance, A third mutation was introduced by replacing Tyr(-1) with Ala in the propeptide essential for autoprocessing to active mature subtilisin in vivo, A prominent 7-20-fold increase in active enzyme production occurred in the triple mutants (Y-1A/I31L/G127A and Y-1A/I31L/G127V).