1qh6
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(New page: 200px<br /><applet load="1qh6" size="450" color="white" frame="true" align="right" spinBox="true" caption="1qh6, resolution 2.00Å" /> '''CATALYSIS AND SPECIF...)
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Revision as of 01:58, 25 November 2007
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CATALYSIS AND SPECIFICITY IN ENZYMATIC GLYCOSIDE HYDROLASES: A 2,5B CONFORMATION FOR THE GLYCOSYL-ENZYME INTERMIDIATE REVEALED BY THE STRUCTURE OF THE BACILLUS AGARADHAERENS FAMILY 11 XYLANASE
Overview
BACKGROUND: The enzymatic hydrolysis of glycosides involves the formation, and subsequent breakdown of a covalent glycosyl-enzyme intermediate via, oxocarbenium-ion-like transition states. The covalent intermediate may be, trapped on-enzyme using 2-fluoro-substituted glycosides, which provide, details of the intermediate conformation and noncovalent interactions, between enzyme and oligosaccharide. Xylanases are important in industrial, applications - in the pulp and paper industry, pretreating wood with, xylanases decreases the amount of chlorine-containing chemicals used., Xylanases are structurally similar to cellulases but differ in their, specificity for xylose-based, versus glucose-based, substrates. RESULTS:, The structure of the family 11 xylanase, Xyl11, from Bacillus, agaradhaerens has been solved using X-ray crystallography in both native, and xylobiosyl-enzyme intermediate forms at 1.78 A and 2.0 A resolution, respectively. The covalent glycosyl-enzyme intermediate has been trapped, using a 2-fluoro-2-deoxy substrate with a good leaving group. Unlike, covalent intermediate structures for glycoside hydrolases from other, families, the covalent glycosyl-enzyme intermediate in family 11 adopts an, unusual 2,5B conformation. CONCLUSIONS: The 2,5B conformation found for, the alpha-linked xylobiosyl-enzyme intermediate of Xyl11, unlike the 4C1, chair conformation observed for other systems, is consistent with the, stereochemical constraints required of the oxocarbenium-ion-like, transition state. Comparison of the Xyl11 covalent glycosyl-enzyme, intermediate with the equivalent structure for the related family 12, endoglucanase, CelB, from Streptomyces lividans reveals the likely, determinants for substrate specificity in this clan of glycoside, hydrolases.
About this Structure
1QH6 is a Single protein structure of sequence from Bacillus agaradhaerens with FXP as ligand. Active as Endo-1,4-beta-xylanase, with EC number 3.2.1.8 Full crystallographic information is available from OCA.
Reference
Catalysis and specificity in enzymatic glycoside hydrolysis: a 2,5B conformation for the glycosyl-enzyme intermediate revealed by the structure of the Bacillus agaradhaerens family 11 xylanase., Sabini E, Sulzenbacher G, Dauter M, Dauter Z, Jorgensen PL, Schulein M, Dupont C, Davies GJ, Wilson KS, Chem Biol. 1999 Jul;6(7):483-92. PMID:10381409
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