1UT9

Structural Basis for the Exocellulase Activity of the Cellobiohydrolase CbhA from C. thermocellum

1UT9 の概要

• エントリーDOI: 10.2210/pdb1ut9/pdb
• 分子名称: CELLULOSE 1,4-BETA-CELLOBIOSIDASE (2 entities in total)
• 機能のキーワード: hydrolase, glycoside hydrolase, family 9, cellobiohydrolase
• 由来する生物種: CLOSTRIDIUM THERMOCELLUM
• タンパク質・核酸の鎖数: 1
• 化学式量合計: 68608.02

構造登録者

Schubot, F.D.,Kataeva, I.A.,Chang, J.,Shah, A.K.,Ljungdahl, L.G.,Rose, J.P.,Wang, B.C. (登録日: 2003-12-04, 公開日: 2004-02-12, 最終更新日: 2024-05-08)

主引用文献

Schubot, F.D.,Kataeva, I.A.,Chang, J.,Shah, A.K.,Ljungdahl, L.G.,Rose, J.P.,Wang, B.C.
Structural basis for the exocellulase activity of the cellobiohydrolase CbhA from Clostridium thermocellum.
Biochemistry, 43:1163-1170, 2004

PubMed Abstract: 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.

PubMed: 14756552
DOI: 10.1021/bi030202i

実験手法

X-RAY DIFFRACTION (2.1 Å)