1ut9
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(New page: 200px<br /><applet load="1ut9" size="450" color="white" frame="true" align="right" spinBox="true" caption="1ut9, resolution 2.10Å" /> '''STRUCTURAL BASIS FOR...)
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Revision as of 02:15, 25 November 2007
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STRUCTURAL BASIS FOR THE EXOCELLULASE ACTIVITY OF THE CELLOBIOHYDROLASE CBHA FROM C. THERMOCELLUM
Overview
Numerous bacterial and fungal organisms have evolved elaborate sets of, modular glycoside hydrolases and similar enzymes aimed at the degradation, of polymeric carbohydrates. Presently, on the basis of sequence similarity, catalytic modules of these enzymes have been classified into 90 families., Representatives of a particular family display similar fold and catalytic, mechanisms. However, within families distinctions occur with regard to, enzymatic properties and type of activity against carbohydrate chains., Cellobiohydrolase CbhA from Clostridium thermocellum is a large, seven-modular enzyme with a catalytic module belonging to family 9. In, contrast to other representatives of that family possessing only endo-, and, in few cases, endo/exo-cellulase activities, CbhA is exclusively an, exocellulase. The crystal structures of the combination of the, immunoglobulin-like module and the catalytic module of CbhA (Ig-GH9_CbhA), and that of an inactive mutant Ig-GH9_CbhA(E795Q) in complex with, cellotetraose (CTT) are reported here. The detailed analysis of these, structures reveals that, while key catalytic residues and overall fold are, conserved in this enzyme and those of other family 9 glycoside hydrolases, the active site of GH9_CbhA is blocked off after the -2 subsite. This, feature which is created by an extension and altered conformation of a, single loop region explains the inability of the active site of CbhA to, accommodate a long cellulose chain and to cut it internally. This altered, loop region is responsible for the exocellulolytic activity of the enzyme.
About this Structure
1UT9 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
Structural basis for the exocellulase activity of the cellobiohydrolase CbhA from Clostridium thermocellum., Schubot FD, Kataeva IA, Chang J, Shah AK, Ljungdahl LG, Rose JP, Wang BC, Biochemistry. 2004 Feb 10;43(5):1163-70. PMID:14756552
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