Journal article
Determination of the Structure and Catalytic Mechanism of Sorghum bicolor Caffeic Acid O-Methyltransferase and the Structural Impact of Three brown midrib12 Mutations
Plant physiology (Bethesda), Vol.165(4), pp.1440-1456
08/2014
Handle:
https://hdl.handle.net/2376/114324
PMID: 24948836
Abstract
Using S-adenosyl-methionine as the methyl donor, caffeic acid O-methyltransferase from sorghum (Sorghum bicolor; SbCOMT) methylates the 5-hydroxyl group of its preferred substrate, 5-hydroxyconiferaldehyde. In order to determine the mechanism of SbCOMT and understand the observed reduction in the lignin syringyl-to-guaiacyl ratio of three brown midrib12 mutants that carry COMT gene missense mutations, we determined the apo-form and S-adenosyl-methionine binary complex SbCOMT crystal structures and established the ternary complex structure with 5-hydroxyconiferaldehyde by molecular modeling. These structures revealed many features shared with monocot ryegrass (Lolium perenne) and dicot alfalfa (Medicago sativa) COMTs. SbCOMT steady-state kinetic and calorimetric data suggest a random bi-bi mechanism. Based on our structural, kinetic, and thermodynamic results, we propose that the observed reactivity hierarchy among 4,5-dihydroxy-3-methoxycinnamyl (and 3,4-dihydroxycinnamyl) aldehyde, alcohol, and acid substrates arises from the ability of the aldehyde to stabilize the anionic intermediate that results from deprotonation of the 5-hydroxyl group by histidine-267. Additionally, despite the presence of other phenylpropanoid substrates in vivo, sinapaldehyde is the preferential product, as demonstrated by its low K
for 5-hydroxyconiferaldehyde. Unlike its acid and alcohol substrates, the aldehydes exhibit product inhibition, and we propose that this is due to nonproductive binding of the S-cis-form of the aldehydes inhibiting productive binding of the S-trans-form. The S-cis-aldehydes most likely act only as inhibitors, because the high rotational energy barrier around the 2-propenyl bond prevents S-trans-conversion, unlike alcohol substrates, whose low 2-propenyl bond rotational energy barrier enables rapid S-cis/S-trans-interconversion.
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- Title
- Determination of the Structure and Catalytic Mechanism of Sorghum bicolor Caffeic Acid O-Methyltransferase and the Structural Impact of Three brown midrib12 Mutations
- Creators
- Abigail R Green - School of Molecular Biosciences (A.R.G., C.K.) and Department of Chemistry (K.M.L., J.T.B., J.P.J., C.K.), Washington State University, Pullman, Washington 99164;Department of Biochemistry and Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53726 (F.L., J.R.);Department of Microbiology and Cell Science and Genetics Institute, University of Florida, Gainesville, Florida 32610 (W.V.); andUnited States Department of Agriculture-Agricultural Research Service, Grain Forage and Bioenergy Research Unit, Lincoln, Nebraska 68583 (S.E.S.)Kevin M Lewis - School of Molecular Biosciences (A.R.G., C.K.) and Department of Chemistry (K.M.L., J.T.B., J.P.J., C.K.), Washington State University, Pullman, Washington 99164;Department of Biochemistry and Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53726 (F.L., J.R.);Department of Microbiology and Cell Science and Genetics Institute, University of Florida, Gainesville, Florida 32610 (W.V.); andUnited States Department of Agriculture-Agricultural Research Service, Grain Forage and Bioenergy Research Unit, Lincoln, Nebraska 68583 (S.E.S.)John T Barr - School of Molecular Biosciences (A.R.G., C.K.) and Department of Chemistry (K.M.L., J.T.B., J.P.J., C.K.), Washington State University, Pullman, Washington 99164;Department of Biochemistry and Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53726 (F.L., J.R.);Department of Microbiology and Cell Science and Genetics Institute, University of Florida, Gainesville, Florida 32610 (W.V.); andUnited States Department of Agriculture-Agricultural Research Service, Grain Forage and Bioenergy Research Unit, Lincoln, Nebraska 68583 (S.E.S.)Jeffrey P Jones - School of Molecular Biosciences (A.R.G., C.K.) and Department of Chemistry (K.M.L., J.T.B., J.P.J., C.K.), Washington State University, Pullman, Washington 99164;Department of Biochemistry and Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53726 (F.L., J.R.);Department of Microbiology and Cell Science and Genetics Institute, University of Florida, Gainesville, Florida 32610 (W.V.); andUnited States Department of Agriculture-Agricultural Research Service, Grain Forage and Bioenergy Research Unit, Lincoln, Nebraska 68583 (S.E.S.)Fachuang Lu - School of Molecular Biosciences (A.R.G., C.K.) and Department of Chemistry (K.M.L., J.T.B., J.P.J., C.K.), Washington State University, Pullman, Washington 99164;Department of Biochemistry and Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53726 (F.L., J.R.);Department of Microbiology and Cell Science and Genetics Institute, University of Florida, Gainesville, Florida 32610 (W.V.); andUnited States Department of Agriculture-Agricultural Research Service, Grain Forage and Bioenergy Research Unit, Lincoln, Nebraska 68583 (S.E.S.)John Ralph - School of Molecular Biosciences (A.R.G., C.K.) and Department of Chemistry (K.M.L., J.T.B., J.P.J., C.K.), Washington State University, Pullman, Washington 99164;Department of Biochemistry and Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53726 (F.L., J.R.);Department of Microbiology and Cell Science and Genetics Institute, University of Florida, Gainesville, Florida 32610 (W.V.); andUnited States Department of Agriculture-Agricultural Research Service, Grain Forage and Bioenergy Research Unit, Lincoln, Nebraska 68583 (S.E.S.)Wilfred Vermerris - School of Molecular Biosciences (A.R.G., C.K.) and Department of Chemistry (K.M.L., J.T.B., J.P.J., C.K.), Washington State University, Pullman, Washington 99164;Department of Biochemistry and Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53726 (F.L., J.R.);Department of Microbiology and Cell Science and Genetics Institute, University of Florida, Gainesville, Florida 32610 (W.V.); andUnited States Department of Agriculture-Agricultural Research Service, Grain Forage and Bioenergy Research Unit, Lincoln, Nebraska 68583 (S.E.S.)Scott E Sattler - School of Molecular Biosciences (A.R.G., C.K.) and Department of Chemistry (K.M.L., J.T.B., J.P.J., C.K.), Washington State University, Pullman, Washington 99164;Department of Biochemistry and Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53726 (F.L., J.R.);Department of Microbiology and Cell Science and Genetics Institute, University of Florida, Gainesville, Florida 32610 (W.V.); andUnited States Department of Agriculture-Agricultural Research Service, Grain Forage and Bioenergy Research Unit, Lincoln, Nebraska 68583 (S.E.S.)ChulHee Kang - School of Molecular Biosciences (A.R.G., C.K.) and Department of Chemistry (K.M.L., J.T.B., J.P.J., C.K.), Washington State University, Pullman, Washington 99164;Department of Biochemistry and Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53726 (F.L., J.R.);Department of Microbiology and Cell Science and Genetics Institute, University of Florida, Gainesville, Florida 32610 (W.V.); andUnited States Department of Agriculture-Agricultural Research Service, Grain Forage and Bioenergy Research Unit, Lincoln, Nebraska 68583 (S.E.S.) chkang@wsu.edu
- Publication Details
- Plant physiology (Bethesda), Vol.165(4), pp.1440-1456
- Academic Unit
- Chemistry, Department of
- Publisher
- United States
- Grant note
- T32 GM008336 / NIGMS NIH HHS
- Identifiers
- 99900547527201842
- Language
- English
- Resource Type
- Journal article