Epoxide hydrolase-catalyzed enantioselective conversion of trans -stilbene oxide: Insights into the reaction mechanism from steady-state and pre-steady-state enzyme kinetics

Computer-aided understanding and engineering of enzymatic selectivity

Enzymes offering chemo-, regio-, and stereoselectivity enable the asymmetric synthesis of high-value chiral molecules. Unfortunately, the drawback that naturally occurring enzymes are often inefficient or have undesired selectivity toward non-native substrates hinders the broadening of biocatalytic applications. To match the demands of specific selectivity in asymmetric synthesis, biochemists have implemented various computer-aided strategies in understanding and engineering enzymatic selectivity, diversifying the available repository of artificial enzymes. Here, given that the entire asymmetric catalytic cycle, involving precise interactions within the active pocket and substrate transport in the enzyme channel, could affect the enzymatic efficiency and selectivity, we presented a comprehensive overview of the computer-aided workflow for enzymatic selectivity. This review includes a mechanistic understanding of enzymatic selectivity based on quantum mechanical calculations, rational design of enzymatic selectivity guided by enzyme-substrate interactions, and enzymatic selectivity regulation via enzyme channel engineering. Finally, we discussed the computational paradigm for designing enzyme selectivity in silico to facilitate the advancement of asymmetric biosynthesis.

Enhancement of Soluble Expression and Biochemical Characterization of Two Epoxide Hydrolases from Bacillus

Background

Enantiopure epoxides are important intermediates in the synthesis of high-value chiral chemicals. Epoxide hydrolases have been exploited in biocatalysis for kinetic resolution of racemic epoxides to produce enantiopure epoxides and vicinal diols. It is necessary to obtain sufficient stable epoxide hydrolases with high enantioselectivity to meet the requirements of industry.

Objectives

Enhancement of soluble expression and biochemical characterization of epoxide hydrolases from Bacillus pumilus and B. subtilis.

Material and Methods

Homologous genes encoding epoxide hydrolases from B. pumilus and B. subtilis were cloned and expressed in Escherichia coli. The recombinant epoxide hydrolases were characterized biochemically.

Results

Low temperature induction of expression and a C-terminal-fused His-tag enhanced soluble expression of the epoxide hydrolases from the two Bacillus species in E. coli. These epoxide hydrolases could hydrolyze various epoxide substrates, with stereoselectivity toward some epoxides such as styrene oxide and glycidyl tosylate.

Conclusions

The position of the His-tag and the induction temperature were found to play a vital role in soluble expression of these two epoxide hydrolases in E. coli. In view of their catalytic properties, the epoxide hydrolases from Bacillus have potential for application in kinetic resolution of some epoxides to prepare enantiopure epoxides and vicinal diols.