Cellulase (GH45)

 

Endoglucanase V (EGV) from Humicola insolens is a cellulase, catalysing the hydrolysis of the beta-(1,4) glycosidic bond of cellulose. Although the active site resembles lysozyme, with six hexose binding sites and similarly placed acidic residues, the enzymes are structurally different and produce products with different stereochemistries. It is a member of the glycoside hydrolase family 45.

 

Reference Protein and Structure

Sequence
P43316 UniProt (3.2.1.4) IPR000334 (Sequence Homologues) (PDB Homologues)
Biological species
Humicola insolens (Fungus) Uniprot
PDB
2eng - ENDOGLUCANASE V (1.5 Å) PDBe PDBsum 2eng
Catalytic CATH Domains
2.40.40.10 CATHdb (see all for 2eng)
Click To Show Structure

Enzyme Reaction (EC:3.2.1.4)

water
CHEBI:15377ChEBI
+
cellotetraose
CHEBI:62974ChEBI
→
cellobiose
CHEBI:17057ChEBI
Alternative enzyme names: 9.5 cellulase, Beta-1,4-endoglucan hydrolase, Beta-1,4-glucanase, Alkali cellulase, Avicelase, Celluase A, Celludextrinase, Cellulase A 3, Cellulosin AP, Endo-1,4-beta-D-glucanase, Endoglucanase D, Pancellase SS, Endo-1,4-beta-glucanase, Carboxymethyl cellulase, Endoglucanase, Endo-1,4-beta-D-glucanohydrolase, 1,4-(1,3;1,4)-beta-D-glucan 4-glucanohydrolase,

Enzyme Mechanism

Introduction

Asp 10 activates a water molecule via general base catalysis. The activated water can attack the electrophilic acetal carbon as hydroxide. SN2-type displacement of the linking oxygen occurs, with a protonated Asp 121 acting as a general acid donor to the oxygen. The products are a hemiacetal and secondary alcohol.

Catalytic Residues Roles

UniProt PDB* (2eng)
Asp10 Asp10A Asp 10 acts as a general base, deprotonating water to activate it as a nucleophile. activator, increase nucleophilicity, proton acceptor, proton donor
Asp121 Asp121A Asp 121 acts as a general acid to the linking oxygen of the breaking glycosidic bond. promote heterolysis, proton acceptor, proton donor
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

overall product formed, overall reactant used, proton transfer, bimolecular nucleophilic substitution, hydrolysis, inferred reaction step, native state of enzyme regenerated

References

  1. Davies GJ et al. (1993), Nature, 365, 362-364. Structure and function of endoglucanase V. DOI:10.1038/365362a0. PMID:8377830.
  2. Hirvonen M et al. (2003), J Mol Biol, 329, 403-410. Crystal Structure of a Family 45 Endoglucanase from Melanocarpus albomyces: Mechanistic Implications Based on the Free and Cellobiose-bound Forms. DOI:10.1016/S0022-2836(03)00467-4.
  3. Davies GJ et al. (1996), Acta Crystallogr D Biol Crystallogr, 52, 7-17. Structure determination and refinement of the Humicola insolens endoglucanase V at 1.5 Å Resolution. DOI:10.1107/s0907444995009280. PMID:15299721.

Step 1. Asp10 activates a water molecule which attacks the anomeric carbon causing the cleavage of the glycosidic bond upon protonation by Asp121.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Asp10A activator, increase nucleophilicity
Asp121A promote heterolysis
Asp10A proton acceptor
Asp121A proton donor

Chemical Components

overall product formed, overall reactant used, proton transfer, ingold: bimolecular nucleophilic substitution, hydrolysis

Step 2. Inferred step- active site regenerated.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Asp10A proton donor
Asp121A proton acceptor

Chemical Components

inferred reaction step, proton transfer, native state of enzyme regenerated
Download: Image, Marvin File

Step 1. Asp10 activates a water molecule which attacks the anomeric carbon causing the cleavage of the glycosidic bond upon protonation by Asp121.

Step 2. Inferred step- active site regenerated.

Products.

Contributors

Jonathan T. W. Ng, Gemma L. Holliday, James Willey