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

Janfalk Carlsson, Åsa ; Bauer, Paul ; Dobritzsch, Doreen ; Kamerlin, Shina C L LU orcid and Widersten, Mikael (2018) In IUCrJ 5(Pt 3). p.269-282
Abstract

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... (More)

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.

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author
; ; ; and
publishing date
type
Contribution to journal
publication status
published
in
IUCrJ
volume
5
issue
Pt 3
pages
14 pages
publisher
International Union of Crystallography
external identifiers
  • pmid:29755743
  • scopus:85046534973
ISSN
2052-2525
DOI
10.1107/S2052252518003573
language
English
LU publication?
no
id
2d2179e5-885a-4b89-a459-c702e48c1a6f
date added to LUP
2025-01-11 21:12:17
date last changed
2025-01-18 03:18:29
@article{2d2179e5-885a-4b89-a459-c702e48c1a6f,
  abstract     = {{<p>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.</p>}},
  author       = {{Janfalk Carlsson, Åsa and Bauer, Paul and Dobritzsch, Doreen and Kamerlin, Shina C L and Widersten, Mikael}},
  issn         = {{2052-2525}},
  language     = {{eng}},
  month        = {{05}},
  number       = {{Pt 3}},
  pages        = {{269--282}},
  publisher    = {{International Union of Crystallography}},
  series       = {{IUCrJ}},
  title        = {{Epoxide hydrolysis as a model system for understanding flux through a branched reaction scheme}},
  url          = {{http://dx.doi.org/10.1107/S2052252518003573}},
  doi          = {{10.1107/S2052252518003573}},
  volume       = {{5}},
  year         = {{2018}},
}