Significantly enhanced specific activity of Bacillus subtilis (2,3)-butanediol dehydrogenase through computer-aided refinement of its substrate-binding pocket

Abstract

(2,3)-Butanediol dehydrogenases (BDHs) are widely utilized for the stereoselective interconversion between α-hydroxy ketones and vicinal diols to produce various functional building blocks. In this study, to enhance the specific activity towards (R)-phenyl-1,2-ethanediol (1a) for 2-hydroxyacetophenone (1b), the substrate-binding pocket of a Bacillus subtilis BDH (BsBDHA) was refined through site-directed mutagenesis. Based on molecular docking simulations, 14 residues were identified and subjected to alanine scanning mutagenesis. After screening, two residues, His42 and Gly292, were singled out for partial site-saturation mutagenesis. The results revealed that BsBDHAH42A and BsBDHAG292A displayed high activities of 3.21 and 1.97 U/mg, respectively. Employing combinatorial mutagenesis, a superior mutant, BsBDHAI49L/V266L/G292A, was developed, exhibiting significantly enhanced specific activity and catalytic efficiency towards (R)-1a, achieving 14.81 U/mg and 4.47 mM−1 s−1, respectively, which were 27.4- and 55.9-fold higher than those of BsBDHA. Further substrate spectrum analysis revealed that the superior mutant displayed increased specific activities for (R)-2a–6a by 1.4- to 10.3-fold. The integration of BsBDHAI49L/V266L/G292A into a three-enzymatic cascade for the synthesis of 1b effectively elevated the yield from 58.1 to 82.4%. Molecular mechanism analysis indicated that the mutation-induced changes in intermolecular forces resulted in a higher frequency of reactive conformations for (R)-1a in BsBDHAI49L/V266L/G292A compared to BsBDHA.