1l2a
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(New page: 200px<br /><applet load="1l2a" size="450" color="white" frame="true" align="right" spinBox="true" caption="1l2a, resolution 2.50Å" /> '''The Crystal Structur...)
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Revision as of 18:04, 20 November 2007
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The Crystal Structure and Catalytic Mechanism of Cellobiohydrolase CelS, the Major Enzymatic Component of the Clostridium thermocellum cellulosome
Overview
Cellobiohydrolase CelS plays an important role in the cellulosome, an, active cellulase system produced by the thermophilic anaerobe Clostridium, thermocellum. The structures of the catalytic domain of CelS in complex, with substrate (cellohexaose) and product (cellobiose) were determined at, 2.5 and 2.4 A resolution, respectively. The protein folds into an, (alpha/alpha)(6) barrel with a tunnel-shaped substrate-binding region. The, conformation of the loops defining the tunnel is intrinsically stable in, the absence of substrate, suggesting a model to account for the processive, mode of action of family 48 cellobiohydrolases. Structural comparisons, with other (alpha/alpha)(6) barrel glycosidases indicate that CelS and, endoglucanase CelA, a sequence-unrelated family 8 glycosidase with a, groove-shaped substrate-binding region, use the same catalytic machinery, to hydrolyze the glycosidic linkage, despite a low sequence similarity and, a different endo/exo mode of action. A remarkable feature of the mechanism, is the absence, from CelS, of a carboxylic group acting as the base, catalyst. The nearly identical arrangement of substrate and functionally, important residues in the two active sites strongly suggests an, evolutionary relationship between the cellobiohydrolase and endoglucanase, families, which can therefore be classified into a new clan of glycoside, hydrolases.
About this Structure
1L2A is a Single protein structure of sequence from Clostridium thermocellum. Active as Cellulase, with EC number 3.2.1.4 Full crystallographic information is available from OCA.
Reference
The crystal structure and catalytic mechanism of cellobiohydrolase CelS, the major enzymatic component of the Clostridium thermocellum Cellulosome., Guimaraes BG, Souchon H, Lytle BL, David Wu JH, Alzari PM, J Mol Biol. 2002 Jul 12;320(3):587-96. PMID:12096911
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