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https://hdl.handle.net/2440/149
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Type: | Journal article |
Title: | Three-dimensional structure of the barley beta-D-glucan glucohydrolase in complex with a transition state mimic |
Author: | Hrmova, M. De Gori, R. Smith, B. Vasella, A. Varghese, J. Fincher, G. |
Citation: | Journal of Biological Chemistry, 2004; 279(6):4970-4980 |
Publisher: | Amer Soc Biochemistry Molecular Biology Inc |
Issue Date: | 2004 |
ISSN: | 0021-9258 1083-351X |
Statement of Responsibility: | Maria Hrmova, Ross De Gori, Brian J. Smith, Andrea Vasella, Joseph N. Varghese, and Geoffrey B. Fincher |
Abstract: | Glucophenylimidazole (PheGlcIm), a tetrahydroimidazopyridine-type inhibitor and ⁴H₃ conformer mimic of a glucoside, binds very tightly to a barley β-D-glucan glucohydrolase, with a Ki constant of 2 x 10⁻⁹ M and a ΔG of 51 kJ mol⁻¹. PheGlcIm binds to the barley β-D-glucan glucohydrolase ~2 x 10⁵ times tighter than laminarin, which is the best non-synthetic ground-state substrate found so far for this enzyme, 10⁶ times tighter than 4-nitrophenyl β-D-glucopyranoside, and 2 x 10⁷ tighter than glucose. The three-dimensional structure of the β-D-glucan glucohydrolase with bound PheGlcIm indicates that the complex resembles a hypothetical transition state during the hydrolytic cycle, that the enzyme derives substrate binding energy from the "aglycone" portion of the ligand, and that it also reveals an anti-protonation trajectory for hydrolysis. Continuous electron densities at the 1.6 σlevel form between the three active site residues Asp⁹⁵, His²⁰⁷, and Asp²⁸⁵, and the C6OH, C7OH, C8OH, and C9OH groups of PheGlcIm. These electron densities correspond to the most favorable interactions in the three-dimensional structure of the β-D-glucan glucohydrolase-PheGlcIm complex and indicate atomic distances equal to or less than 2.55 Å. The crystallographic data were corroborated with ab initio molecular orbital calculations. The data indicate that the ⁴E conformation of the glucose part of PheGlcIm is critical for tight binding and provide the first evidence for probable substrate distortion during catalysis by this enzyme. |
Keywords: | Hordeum Macromolecular Substances Glucosidases Enzyme Inhibitors Crystallography, X-Ray Molecular Mimicry Catalytic Domain Kinetics Hydrogen-Ion Concentration Models, Molecular Static Electricity |
DOI: | 10.1074/jbc.M307188200 |
Published version: | http://dx.doi.org/10.1074/jbc.m307188200 |
Appears in Collections: | Agriculture, Food and Wine publications Aurora harvest 2 |
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