title: Structure-Based Insight into the Asymmetric Bioreduction of the C=C Double Bond of alpha,beta-Unsaturated Nitroalkenes by Pentaerythritol Tetranitrate Reductase.
abstract: Biocatalytic reduction of alpha- or beta-alkyl-beta-arylnitroalkenes provides a convenient and efficient method to prepare chiral substituted nitroalkanes. Pentaerythritol tetranitrate reductase (PETN reductase) from Enterobacter cloacae st. PB2 catalyses the reduction of nitroolefins such as 1-nitrocyclohexene (1) with steady state and rapid reaction kinetics comparable to other old yellow enzyme homologues. Furthermore, it reduces 2-aryl-1-nitropropenes (4a-d) to their equivalent (S)-nitropropanes 9a-d. The enzyme shows a preference for the (Z)-isomer of substrates 4a-d, providing almost pure enantiomeric products 9a-d (ees up to > 99%) in quantitative yield, whereas the respective (E)-isomers are reduced with lower enantioselectivity (63-89% ee) and lower product yields. 1-Aryl-2-nitropropenes (5a, b) are also reduced efficiently, but the products (R)-10 have lower optical purities. The structure of the enzyme complex with 1-nitrocyclohexene (1) was determined by X-ray crystallography, revealing two substrate-binding modes, with only one compatible with hydride transfer. Models of nitropropenes 4 and 5 in the active site of PETN reductase predicted that the enantioselectivity of the reaction was dependent on the orientation of binding of the (E)- and (Z)-substrates. This work provides a structural basis for understanding the mechanism of asymmetric bioreduction of nitroalkenes by PETN reductase.
authors.affiliation: Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K.
authors.forename: Helen S
authors.initials: HS
authors.lastname: Toogood
authors.forename: Anna
authors.initials: A
authors.lastname: Fryszkowska
authors.forename: Victoria
authors.initials: V
authors.lastname: Hare
authors.forename: Karl
authors.initials: K
authors.lastname: Fisher
authors.forename: Anna
authors.initials: A
authors.lastname: Roujeinikova
authors.forename: David
authors.initials: D
authors.lastname: Leys
authors.forename: John M
authors.initials: JM
authors.lastname: Gardiner
authors.forename: Gill M
authors.initials: GM
authors.lastname: Stephens
authors.forename: Nigel S
authors.initials: NS
authors.lastname: Scrutton
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