PDBsum entry 4b4h

Hydrolase

PDB id: 4b4h

Contents

Protein chains

413 a.a.

Waters ×821

PDB id:

4b4h

Name:

Hydrolase

Title:

Thermobifida fusca cellobiohydrolase cel6b(e3) catalytic domain

Structure:

Beta-1,4-exocellulase. Chain: a, b. Fragment: residues 177-596. Synonym: cel6b. Engineered: yes

Source:

Thermobifida fusca. Organism_taxid: 2021. Expressed in: streptomyces lividans. Expression_system_taxid: 1916.

Resolution:

1.50Å R-factor: 0.198 R-free: 0.232

Authors:

M.Sandgren,M.Wu,J.Stahlberg,S.Karkehabadi,C.Mitchinson,B.R.Kelemen, E.A.Larenas,H.Hansson

Key ref:

M.Sandgren et al. (2013). The structure of a bacterial cellobiohydrolase: the catalytic core of the Thermobifida fusca family GH6 cellobiohydrolase Cel6B. J Mol Biol, 425, 622-635. PubMed id: 23220193

Date:

30-Jul-12 Release date: 19-Dec-12

Protein chains

Q60029  (Q60029_THEFU) -  Glucanase from Thermobifida fusca

Seq: 596 a.a.

Struc: 413 a.a.

Enzyme reactions

• Enzyme class: E.C.3.2.1.- - ?????

J Mol Biol 425:622-635 (2013)

PubMed id: 23220193

The structure of a bacterial cellobiohydrolase: the catalytic core of the Thermobifida fusca family GH6 cellobiohydrolase Cel6B.

M.Sandgren, M.Wu, S.Karkehabadi, C.Mitchinson, B.R.Kelemen, E.A.Larenas, J.Ståhlberg, H.Hansson.

ABSTRACT

Cellulases, glycoside hydrolases that catalyze the degradation of cellulose, are classified as either endoglucanases or cellobiohydrolases (CBHs) based on their architecture and mode of action on the cellulose. CBHs bind the cellulose chain in a more or less closed tunnel and cleave off cellobiose units processively from one end of the cellulosic polymer, while endoglucanases have their active sites in a more or less open cleft and show a higher tendency to cut bonds internally in the polymer. The CBH Cel6A (also called CBH2) from the ascomycete Hypocrea jecorina has a much shorter substrate-binding tunnel and seems less processive than the CBH Cel7A (CBH1), from the same fungus. Here, we present the X-ray crystal structure of the catalytic domain of the CBH Cel6B, also called E3, from the soil bacterium Thermobifida fusca, both in its apo form and co-crystallized with cellobiose. The enzyme structure reveals that the Cel6B enzyme has a much longer substrate-binding site than its fungal GH6 counterparts. The tunnel is comparable in length to that of GH7 CBHs. In the ligand structure with cellobiose, the tunnel exit is completely closed by a 13-residue loop not present in fungal GH6 enzymes. The loop needs to be displaced to allow cellobiose product release for a processive action by the enzyme. When ligand is absent, seven of these residues are not visible in the electron density and the tunnel exit is open.