1eqc: Difference between revisions

[[Image:1eqc.gif|left|200px]]<br /><applet load="1eqc" size="350" color="white" frame="true" align="right" spinBox="true"  

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.

1EQC is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Candida_albicans Candida albicans] with <scene name='pdbligand=CTS:'>CTS</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Glucan_1,3-beta-glucosidase Glucan 1,3-beta-glucosidase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.2.1.58 3.2.1.58] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1EQC OCA].  

[[Category: Anderson, B F.]]

[[Category: Cutfield, J F.]]

[[Category: Cutfield, S M.]]

[[Category: Davies, G J.]]

[[Category: Moody, P C.]]

[[Category: Sullivan, P A.]]

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