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

Experimental Data Snapshot

  • Resolution: 2.10 Å
  • R-Value Free: 0.186 
  • R-Value Work: 0.147 
  • R-Value Observed: 0.149 

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Structural basis for the exocellulase activity of the cellobiohydrolase CbhA from Clostridium thermocellum.

Schubot, F.D.Kataeva, I.A.Chang, J.Shah, A.K.Ljungdahl, L.G.Rose, J.P.Wang, B.C.

(2004) Biochemistry 43: 1163-1170

  • DOI: https://doi.org/10.1021/bi030202i
  • Primary Citation of Related Structures:  
    1RQ5, 1UT9

  • 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.

  • Organizational Affiliation

    Department of Biochemistry & Molecular Biology, The University of Georgia, Athens, Georgia 30602, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
CELLULOSE 1,4-BETA-CELLOBIOSIDASE609Acetivibrio thermocellusMutation(s): 0 
Find proteins for Q6RSN8 (Acetivibrio thermocellus)
Explore Q6RSN8 
Go to UniProtKB:  Q6RSN8
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ6RSN8
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.10 Å
  • R-Value Free: 0.186 
  • R-Value Work: 0.147 
  • R-Value Observed: 0.149 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 74.546α = 90
b = 75.76β = 90
c = 137.498γ = 90
Software Package:
Software NamePurpose
PROTEUMdata reduction
PROTEUMdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2004-02-12
    Type: Initial release
  • Version 1.1: 2011-05-08
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance
  • Version 1.3: 2018-06-13
    Changes: Advisory, Data collection, Database references, Experimental preparation, Source and taxonomy
  • Version 1.4: 2024-05-08
    Changes: Advisory, Data collection, Database references, Other