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| - | '''Crystal structure of barley beta-D-glucan glucohydrolase isoenzyme Exo1 in complex with 2-deoxy-2-fluoro-alpha-D-glucoside'''
| + | ===Crystal structure of barley beta-D-glucan glucohydrolase isoenzyme Exo1 in complex with 2-deoxy-2-fluoro-alpha-D-glucoside=== |
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| - | ==Overview==
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| - | BACKGROUND: Barley beta-D-glucan glucohydrolases represent family 3 glycoside hydrolases that catalyze the hydrolytic removal of nonreducing glucosyl residues from beta-D-glucans and beta-D-glucooligosaccharides. After hydrolysis is completed, glucose remains bound in the active site. RESULTS: When conduritol B epoxide and 2', 4'-dinitrophenyl 2-deoxy-2-fluoro-beta-D-glucopyranoside are diffused into enzyme crystals, they displace the bound glucose and form covalent glycosyl-enzyme complexes through the Odelta1 of D285, which is thereby identified as the catalytic nucleophile. A nonhydrolyzable S-glycosyl analog, 4(I), 4(III), 4(V)-S-trithiocellohexaose, also diffuses into the active site, and a S-cellobioside moiety positions itself at the -1 and +1 subsites. The glycosidic S atom of the S-cellobioside moiety forms a short contact (2.75 A) with the Oepsilon2 of E491, which is likely to be the catalytic acid/base. The glucopyranosyl residues of the S-cellobioside moiety are not distorted from the low-energy 4C(1) conformation, but the glucopyranosyl ring at the +1 subsite is rotated and translated about the linkage. CONCLUSIONS: X-ray crystallography is used to define the three key intermediates during catalysis by beta-D-glucan glucohydrolase. Before a new hydrolytic event begins, the bound product (glucose) from the previous catalytic reaction is displaced by the incoming substrate, and a new enzyme-substrate complex is formed. The second stage of the hydrolytic pathway involves glycosidic bond cleavage, which proceeds through a double-displacement reaction mechanism. The crystallographic analysis of the S-cellobioside-enzyme complex with quantum mechanical modeling suggests that the complex might mimic the oxonium intermediate rather than the enzyme-substrate complex.
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| | ==About this Structure== | | ==About this Structure== |
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| | [[Category: Varghese, J N.]] | | [[Category: Varghese, J N.]] |
| | [[Category: 2-domain fold]] | | [[Category: 2-domain fold]] |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 19:55:42 2008'' | + | |
| | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 1 10:51:58 2008'' |
Revision as of 07:51, 1 July 2008
Template:STRUCTURE 1iew
Crystal structure of barley beta-D-glucan glucohydrolase isoenzyme Exo1 in complex with 2-deoxy-2-fluoro-alpha-D-glucoside
Template:ABSTRACT PUBMED 11709165
About this Structure
1IEW is a Single protein structure of sequence from Hordeum vulgare. Full crystallographic information is available from OCA.
Reference
Catalytic mechanisms and reaction intermediates along the hydrolytic pathway of a plant beta-D-glucan glucohydrolase., Hrmova M, Varghese JN, De Gori R, Smith BJ, Driguez H, Fincher GB, Structure. 2001 Nov;9(11):1005-16. PMID:11709165
Page seeded by OCA on Tue Jul 1 10:51:58 2008
