The structure of the exo-beta-(1,3)-glucanase from Candida albicans in native and bound forms: relationship between a pocket and groove in family 5 glycosyl hydrolases

J Mol Biol. 1999 Dec 3;294(3):771-83. doi: 10.1006/jmbi.1999.3287.


A group of fungal exo-beta-(1,3)-glucanases, including that from the human pathogen Candida albicans (Exg), belong to glycosyl hydrolase family 5 that also includes many bacterial cellulases (endo-beta-1, 4-glucanases). Family members, despite wide sequence variations, share a common mechanism and are characterised by possessing eight invariant residues making up the active site. These include two glutamate residues acting as nucleophile and acid/base, respectively. Exg is an abundant secreted enzyme possessing both hydrolase and transferase activity consistent with a role in cell wall glucan metabolism and possibly morphogenesis. The structures of Exg in both free and inhibited forms have been determined to 1.9 A resolution. A distorted (beta/alpha)8 barrel structure accommodates an active site which is located within a deep pocket, formed when extended loop regions close off a cellulase-like groove. Structural analysis of a covalently bound mechanism-based inhibitor (2-fluoroglucosylpyranoside) and of a transition-state analogue (castanospermine) has identified the binding interactions at the -1 glucose binding site. In particular the carboxylate of Glu27 serves a dominant hydrogen-bonding role. Access by a 1,3-glucan chain to the pocket in Exg can be understood in terms of a change in conformation of the terminal glucose residue from chair to twisted boat. The geometry of the pocket is not, however, well suited for cleavage of 1,4-glycosidic linkages. A second glucose site was identified at the entrance to the pocket, sandwiched between two antiparallel phenylalanine side-chains. This aromatic entrance-way must not only direct substrate into the pocket but also may act as a clamp for an acceptor molecule participating in the transfer reaction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Candida albicans / enzymology*
  • Crystallography, X-Ray
  • Glucan 1,3-beta-Glucosidase
  • Glycosylation
  • Humans
  • Indolizines / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Conformation
  • Protein Structure, Tertiary
  • Static Electricity
  • Structure-Activity Relationship
  • beta-Glucosidase / chemistry*
  • beta-Glucosidase / metabolism


  • Indolizines
  • beta-Glucosidase
  • Glucan 1,3-beta-Glucosidase
  • castanospermine

Associated data

  • PDB/1CZ1