2pc8

[[Image:2pc8.jpg|left|200px]]

'''E292Q mutant of EXO-B-(1,3)-Glucanase from Candida Albicans in complex with two separately bound glucopyranoside units at 1.8 A'''

==Overview==

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.

2PC8 is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Candida_albicans Candida albicans]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2PC8 OCA].

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., Cutfield SM, Davies GJ, Murshudov G, Anderson BF, Moody PC, Sullivan PA, Cutfield JF, J Mol Biol. 1999 Dec 3;294(3):771-83. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/10610795 10610795]

[[Category: Single protein]]

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