Determinants of Reactivity and Selectivity in Soluble Epoxide Hydrolase from Quantum Mechanics/Molecular Mechanics Modeling

Richard Lonsdale, Simon Hoyle, Daniel T. Grey, Lars Ridder, Adrian J. Mulholland*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

56 Citations (Scopus)

Abstract

Soluble epoxide hydrolase (sEH) is an enzyme involved in drug metabolism that catalyzes the hydrolysis of epoxides to form their corresponding diols. sEH has a broad substrate range and shows high regio- and enantioselectivity for nucleophilic ring opening by Asp333. Epoxide hydrolases therefore have potential synthetic applications. We have used combined quantum mechanics/molecular mechanics (QM/MM) umbrella sampling molecular dynamics (MD) simulations (at the AM1/CHARMM22 level) and high-level ab initio (SCS-MP2) QM/MM calculations to analyze the reactions, and determinants of selectivity, for two substrates: trans-stilbene oxide (t-SO) and trans-diphenylpropene oxide (t-DPPO). The calculated free energy barriers from the QM/MM (AM1/CHARMM22) umbrella sampling MD simulations show a lower barrier for phenyl attack in t-DPPO, compared with that for benzylic attack, in agreement with experiment. Activation barriers in agreement with experimental rate constants are obtained only with the highest level of QM theory (SCS-MP2) used. Our results show that the selectivity of the ring-opening reaction is influenced by several factors, including proximity to the nucleophile, electronic stabilization of the transition state, and hydrogen bonding to two active site tyrosine residues. The protonation state of His523 during nucleophilic attack has also been investigated, and our results show that the protonated form is most consistent with experimental findings. The work presented here illustrates how determinants of selectivity can be identified from QM/MM simulations. These insights may also provide useful information for the design of novel catalysts for use in the synthesis of enantiopure compounds.

Original languageEnglish
Pages (from-to)1774-1786
Number of pages13
JournalBiochemistry
Volume51
Issue number8
DOIs
Publication statusPublished - 28 Feb 2012

Keywords

  • ALKYL-ENZYME INTERMEDIATE
  • CORRELATED MOLECULAR CALCULATIONS
  • CITRATE SYNTHASE
  • GAUSSIAN-BASIS SETS
  • PLESSET PERTURBATION-THEORY
  • CATALYTIC MECHANISM
  • PHOSPHATASE-ACTIVITY
  • AGROBACTERIUM-RADIOBACTER AD1
  • CHORISMATE MUTASE
  • GLUTATHIONE-S-TRANSFERASE

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