PDBsum entry: 1rq5

Hydrolase

PDB id: 1rq5

Contents

Protein chain

602 a.a. *

Ligands

CTT

Metals

_CA ×2

Waters ×387

* Residue conservation analysis

PDB id:

1rq5

Name:

Hydrolase

Title:

Structural basis for the exocellulase activity of the cellobiohydrolase cbha from c. Thermocellum

Structure:

Cellobiohydrolase. Chain: a. Engineered: yes. Mutation: yes

Source:

Clostridium thermocellum. Organism_taxid: 1515. Expressed in: escherichia coli bl21. Expression_system_taxid: 511693.

Resolution:

2.40Å R-factor: 0.210 R-free: 0.270

Authors:

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

Key ref:

F.D.Schubot et al. (2004). Structural basis for the exocellulase activity of the cellobiohydrolase CbhA from Clostridium thermocellum. Biochemistry, 43, 1163-1170. PubMed id: 14756552 DOI: 10.1021/bi030202i

Date:

04-Dec-03 Release date: 30-Mar-04

Protein chain

Q59325  (Q59325_CLOTM) -  Cellulose 1,4-beta-cellobiosidase

Seq: 1230 a.a.

Struc: 602 a.a.*

* PDB and UniProt seqs differ at 20 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.3.2.1.91 - Cellulose 1,4-beta-cellobiosidase (non-reducing end).
• Reaction: Hydrolysis of 1,4-beta-D-glucosidic linkages in cellulose and cellotetraose, releasing cellobiose from the non-reducing ends of the chains.

 Gene Ontology (GO) functional annotation 

• Biological process: carbohydrate metabolic process (1 term)
• Biochemical function: catalytic activity (2 terms)

DOI no: 10.1021/bi030202i

Biochemistry 43:1163-1170 (2004)

PubMed id: 14756552

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

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

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.