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

Experimental Data Snapshot

  • Resolution: 2.40 Å
  • R-Value Free: 0.270 
  • R-Value Work: 0.210 
  • R-Value Observed: 0.210 

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This is version 2.3 of the entry. See complete history


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
Cellobiohydrolase610Acetivibrio thermocellusMutation(s): 1 
Find proteins for Q59325 (Acetivibrio thermocellus)
Explore Q59325 
Go to UniProtKB:  Q59325
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ59325
Sequence Annotations
  • Reference Sequence


Entity ID: 2
MoleculeChains Length2D Diagram Glycosylation3D Interactions
Glycosylation Resources
GlyTouCan:  G00025MO
GlyCosmos:  G00025MO
GlyGen:  G00025MO
Biologically Interesting Molecules (External Reference) 1 Unique
Experimental Data & Validation

Experimental Data

  • Resolution: 2.40 Å
  • R-Value Free: 0.270 
  • R-Value Work: 0.210 
  • R-Value Observed: 0.210 
  • Space Group: P 61
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 108.6α = 90
b = 108.6β = 90
c = 119.18γ = 120
Software Package:
Software NamePurpose
PROTEUM PLUSdata collection
PROTEUM PLUSdata reduction
PROTEUM PLUSdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2004-03-30
    Type: Initial release
  • Version 1.1: 2008-04-29
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance
  • Version 2.0: 2020-07-29
    Type: Remediation
    Reason: Carbohydrate remediation
    Changes: Advisory, Atomic model, Data collection, Derived calculations, Non-polymer description, Structure summary
  • Version 2.1: 2021-10-27
    Changes: Database references, Structure summary
  • Version 2.2: 2024-02-14
    Changes: Data collection
  • Version 2.3: 2024-04-03
    Changes: Refinement description