A Single Ser85Ala Mutation Enhances the Catalytic Efficiency of Subtilisin E from Bacillus subtilis 168

A single mutation of Ser for Ala was introduced into the highly conserved 83-Gly-Val-Ala-85 region of AprE (subtilisin E) which resulted in the generation of a subtilisin mutant with an enhanced catalytic efficiency. The position of the mutation was placed in the conserved N-terminal end of the loop that connects a β-sheet with the α-helix containing the catalytic residue His64. The mutant Ser85Ala aprE gene was over expressed in a protease deficient B. subtilis genetic background and its product purified to homogeneity. The Ser85Ala AprE protein exhibited a catalytic efficiency two fold higher than that of its wild type parent AprE due to a larger kcat. Other biochemical properties such as thermal stability, optimum pH and temperature remained unchanged with respect to those exhibited by the pure wild type subtilisin. These results support the idea that mutations on the conserved stretch bend 83-Gly-Val-Ser-85 which connects two elements of secondary structure in AprE cause alterations on the catalytic properties of AprE and other subtilisins.