Glucan 1,3-beta-glucosidase

 

Fungal exo-beta-(1,3)-glucanases, such as that from the human pathogen Candida albicans, belong to the glycosyl hydrolase family 5 that also includes many bacterial cellulases. The Candida albicans enzyme is involved in the metabolism of cell wall glucan. It catalyses the hydrolytic removal of glucose residues from the non-reducing end of beta-1,3-glucan and (to a lesser extent) beta-1,6-glucan, the two main structural components of the Candida albicans cell wall. The enzyme also has glucosyl transferase activity in which a molecule other than water can accept the removed glucose residue. This may be important in shaping the cell wall during morphogenesis.

 

Reference Protein and Structure

Sequence
P29717 UniProt (2.4.1.-, 3.2.1.58) IPR001547 (Sequence Homologues) (PDB Homologues)
Biological species
Candida albicans SC5314 (Yeast) Uniprot
PDB
1cz1 - EXO-B-(1,3)-GLUCANASE FROM CANDIDA ALBICANS AT 1.85 A RESOLUTION (1.85 Å) PDBe PDBsum 1cz1
Catalytic CATH Domains
3.20.20.80 CATHdb (see all for 1cz1)
Click To Show Structure

Enzyme Reaction (EC:3.2.1.58)

D-glucopyranosyl-(1->3)-D-mannopyranose
CHEBI:52997ChEBI
+
water
CHEBI:15377ChEBI
→
D-mannopyranose
CHEBI:4208ChEBI
+
D-glucopyranose
CHEBI:4167ChEBI
Alternative enzyme names: Beta-1,3-glucan exo-hydrolase, Exo (1->3)-beta-glucanase, Exo-1,3-beta-D-glucanase, Exo-1,3-beta-glucanase, Exo-1,3-beta-glucosidase, Exo-beta-(1->3)-D-glucanase, Exo-beta-(1->3)-glucanohydrolase, Exo-beta-1,3-D-glucanase, Exo-beta-1,3-glucanase, 1,3-beta-glucan glucohydrolase,

Enzyme Mechanism

Introduction

The reaction proceeds by a double displacement mechanism with net retention of configuration at the anomeric C1 position. Nucleophilic attack by Glu 292 leads to displacement of the leaving group and formation of a covalent glucosyl-enzyme intermediate via a presumed oxo-carbenium ion-like transition state. Glu 192 acts as a general acid to protonate the departing leaving group.

Catalytic Residues Roles

UniProt PDB* (1cz1)
Glu230 Glu192(186)A Acts as a general acid to protonate the leaving group in formation of the glycosyl-enzyme intermediate. Later acts as a general base to abstract a proton from water so that it can carry out a nucleophilic attack on the the intermediate. proton acceptor, proton donor, activator, increase nucleophilicity, promote heterolysis
Glu330 Glu292(286)A Attacks the glycosidic bond to form a glycosyl-enzyme intermediate via a presumed oxo-carbenium ion-like transition state. covalently attached, nucleofuge, nucleophile
*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, intermediate formation, bimolecular nucleophilic substitution, proton transfer, hydrolysis, intermediate terminated

References

  1. Cutfield SM et al. (1999), J Mol Biol, 294, 771-783. The structure of the exo-β-(1,3)-glucanase from Candida albicans in native and bound forms: relationship between a pocket and groove in family 5 glycosyl hydrolases. DOI:10.1006/jmbi.1999.3287. PMID:10610795.
  2. Mackenzie LF et al. (1997), J Biol Chem, 272, 3161-3167. Identification of Glu-330 as the Catalytic Nucleophile of Candida albicans Exo- -(1,3)-glucanase. DOI:10.1074/jbc.272.6.3161. PMID:9013549.
  3. Chambers RS et al. (1993), FEBS Lett, 327, 366-369. Identification of a putative active site residue in the exo-β-(1,3)-glucanase ofCandida albicans. DOI:10.1016/0014-5793(93)81022-r. PMID:8348966.

Step 1. Glu292 performs a nucleophilic attack on C1, this leads to the displacement of the leaving group which is protonated by Glu192.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Glu292(286)A covalently attached
Glu192(186)A promote heterolysis
Glu292(286)A nucleophile
Glu192(186)A proton donor

Chemical Components

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

Step 2. Glu192 activates a water molecule which hydrolyses the intermediate.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Glu192(186)A activator, increase nucleophilicity, proton acceptor
Glu292(286)A nucleofuge

Chemical Components

overall product formed, hydrolysis, proton transfer, ingold: bimolecular nucleophilic substitution, intermediate terminated
Download: Image, Marvin File

Step 1. Glu292 performs a nucleophilic attack on C1, this leads to the displacement of the leaving group which is protonated by Glu192.

Step 2. Glu192 activates a water molecule which hydrolyses the intermediate.

Products.

Contributors

James Torrance, Gemma L. Holliday, James Willey