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X-ray Crystal Structure of a Double Bond Reductase from Nicotiana tabacum
Structural highlights
FunctionDBR_TOBAC Reduces the C=C double bonds of alpha, beta unsaturated enones, but has no activity on enones with an endocyclic C=C double-bond. Shows a high specificity for NADPH as the hybrid donor. Substrates are 1-nitrocyclohexene, 2-methylpentenal, trans-cinnamaldehyde, methyl-trans-2-methylcinnamaldehyde, trans-2-nonenal and 1-octen-3-one. Reduced activity with aplha-methyl transcinnamaldehyde, 1-cyclohexene-1-carboxaldehyde, methyl crotonate, (R)-pulegone, and dimethyl itaconate and no activity with maleimides, citral, (5R)- or (5S)-carvone, (S)-perillyl alcohol, and substituted cyclohexenones and cyclopentenones (PubMed:17945329, Ref.3). May also act as a allyl-alcohol dehydrogenase by catalyzing the dehydrogenation of secondary allylic alcohols rather than saturated secondary alcohols. Allyl-alcohol dehydrogenase is specific for the S-stereoisomer of the alcohols (PubMed:11117876).[1] [2] [REFERENCE:3] Publication Abstract from PubMedThe application of biocatalysis for the asymmetric reduction of activated C=C is a powerful tool for the manufacture of high-value chemical commodities. The biocatalytic potential of "-ene" reductases from the Old Yellow Enzyme (OYE) family of oxidoreductases is well-known; however, the specificity of these enzymes toward mainly small molecule substrates has highlighted the need to discover "-ene" reductases from different enzymatic classes to broaden industrial applicability. Here, we describe the characterization of a flavin-free double bond reductase from Nicotiana tabacum (NtDBR), which belongs to the leukotriene B4 dehydrogenase (LTD) subfamily of the zinc-independent, medium chain dehydrogenase/reductase superfamily of enzymes. Using steady-state kinetics and biotransformation reactions, we have demonstrated the regio- and stereospecificity of NtDBR against a variety of alpha,beta-unsaturated activated alkenes. In addition to catalyzing the reduction of typical LTD substrates and several classical OYE-like substrates, NtDBR also exhibited complementary activity by reducing non-OYE substrates (i.e., reducing the exocyclic C=C double bond of (R)-pulegone) and in some cases showing an opposite stereopreference in comparison with the OYE family member pentaerythritol tetranitrate (PETN) reductase. This serves to augment classical OYE "-ene" reductase activity and, coupled with its aerobic stability, emphasizes the potential industrial value of NtDBR. Furthermore, we also report the X-ray crystal structures of the holo-, binary NADP(H)-bound, and ternary [NADP(+) and 4-hydroxy-3-methoxycinnamaldehyde (9a)-bound] NtDBR complexes. These will underpin structure-driven site-saturated mutagenesis studies aimed at enhancing the reactivity, stereochemistry, and specificity of this enzyme. Biocatalytic Asymmetric Alkene Reduction: Crystal Structure and Characterization of a Double Bond Reductase from Nicotiana tabacum.,Mansell DJ, Toogood HS, Waller J, Hughes JM, Levy CW, Gardiner JM, Scrutton NS ACS Catal. 2013 Mar 1;3(3):370-379. doi: 10.1021/cs300709m. Epub 2013 Jan 21. PMID:27547488[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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