1LQ2

Crystal structure of barley beta-D-glucan glucohydrolase isoenzyme Exo1 in complex with gluco-phenylimidazole

Summary for 1LQ2

• Entry DOI: 10.2210/pdb1lq2/pdb
• Related: 1IEQ
• Descriptor: Beta-D-glucan glucohydrolase isoenzyme Exo1, 2-acetamido-2-deoxy-beta-D-glucopyranose-(1-2)-alpha-D-mannopyranose-(1-6)-alpha-D-mannopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose-(1-4)-[alpha-L-fucopyranose-(1-3)]2-acetamido-2-deoxy-beta-D-glucopyranose, beta-D-mannopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose-(1-4)-[alpha-L-fucopyranose-(1-3)]2-acetamido-2-deoxy-beta-D-glucopyranose, ... (7 entities in total)
• Functional Keywords: 2-domain fold, ligand-protein complex, hydrolase
• Biological source: Hordeum vulgare
• Total number of polymer chains: 1
• Total formula weight: 67474.37

Authors

Hrmova, M.,De Gori, R.,Smith, B.J.,Vasella, A.,Varghese, J.N.,Fincher, G.B. (deposition date: 2002-05-09, release date: 2003-11-18, Last modification date: 2023-08-16)

Primary citation

Hrmova, M.,De Gori, R.,Smith, B.J.,Vasella, A.,Varghese, J.N.,Fincher, G.B.
Three-dimensional Structure of the Barley {beta}-D-Glucan Glucohydrolase in Complex with a Transition State Mimic.
J.Biol.Chem., 279:4970-4980, 2004

PubMed Abstract: 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.

PubMed: 14597633
DOI: 10.1074/jbc.M307188200

Experimental method

X-RAY DIFFRACTION (2.7 Å)