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

IUCrJ. 2018 Mar 22;5(Pt 3):269-282. doi: 10.1107/S2052252518003573. eCollection 2018 May 1.


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.

Keywords: biocatalysis; empirical valence-bond simulations; epoxide hydrolase; reaction flux; stereoselectivity; trans-methylstyrene oxide.

Publication types

  • Review

Grants and funding

This work was funded by Vetenskapsrådet grant 621-2011-6055 to Mikael Widersten. FP7 Ideas: European Research Council grant FP7/2007-2013 to S. C. Lynn Kamerlin. Sven and Lily Lawski Foundation grant to Paul Bauer.