1lq2
From Proteopedia
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Crystal structure of barley beta-D-glucan glucohydrolase isoenzyme Exo1 in complex with gluco-phenylimidazole
Overview
Glucophenylimidazole (PheGlcIm), a tetrahydroimidazopyridine-type, inhibitor and 4H3 conformer mimic of a glucoside, binds very tightly to a, barley beta-d-glucan glucohydrolase, with a Ki constant of 2 x 10(-9) m, and a DeltaG of 51 kJ mol(-1). PheGlcIm binds to the barley beta-d-glucan, glucohydrolase approximately 2 x 10(5) times tighter than laminarin, which, is the best non-synthetic ground-state substrate found so far for this, enzyme, 10(6) times tighter than 4-nitrophenyl beta-d-glucopyranoside, and, 2 x 10(7) tighter than glucose. The three-dimensional structure of the, beta-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 sigma level 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 beta-d-glucan, glucohydrolase-PheGlcIm complex and indicate atomic distances equal to or, less than 2.55 A. 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.
About this Structure
1LQ2 is a Single protein structure of sequence from Hordeum vulgare with NAG, IDD and GOL as ligands. Active as Glucan 1,3-beta-glucosidase, with EC number 3.2.1.58 Full crystallographic information is available from OCA.
Reference
Three-dimensional structure of the barley beta-D-glucan glucohydrolase in complex with a transition state mimic., Hrmova M, De Gori R, Smith BJ, Vasella A, Varghese JN, Fincher GB, J Biol Chem. 2004 Feb 6;279(6):4970-80. Epub 2003 Nov 3. PMID:14597633
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