Epoxide hydrolysis as a model system for understanding flux through a branched reaction scheme

Summary, in English

The epoxide hydrolase StEH1 catalyzes the hydrolysis of trans-methylstyrene oxide to 1-phenyl-propane-1,2-diol. The (S,S)-epoxide is exclusively transformed into the (1R,2S)-diol, while hydrolysis of the (R,R)-epoxide results in a mixture of product enantiomers. In order to understand the differences in the stereoconfigurations of the products, the reactions were studied kinetically during both the pre-steady-state and steady-state phases. A number of closely related StEH1 variants were analyzed in parallel, and the results were rationalized by structure-activity analysis using the available crystal structures of all tested enzyme variants. Finally, empirical valence-bond simulations were performed in order to provide additional insight into the observed kinetic behaviour and ratios of the diol product enantiomers. These combined data allow us to present a model for the flux through the catalyzed reactions. With the (R,R)-epoxide, ring opening may occur at either C atom and with similar energy barriers for hydrolysis, resulting in a mixture of diol enantiomer products. However, with the (S,S)-epoxide, although either epoxide C atom may react to form the covalent enzyme intermediate, only the pro-(R,S) alkylenzyme is amenable to subsequent hydrolysis. Previously contradictory observations from kinetics experiments as well as product ratios can therefore now be explained for this biocatalytically relevant enzyme.

• Author: Åsa Janfalk Carlsson; Paul Bauer; Doreen Dobritzsch; Shina C L Kamerlin; Mikael Widersten
• Publishing year: 2018-05-01
• Language: English
• Pages: 269-282
• Publication/Series: IUCrJ
• Volume: 5
• Issue: Pt 3
• Links: http://dx.doi.org/10.1107/S2052252518003573
• Document type: Journal article review
• Publisher: International Union of Crystallography
• Status: Published
• ISBN/ISSN/Other: ISSN: 2052-2525