1w9w
From Proteopedia
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STRUCTURE OF A BETA-1,3-GLUCAN BINDING CBM6 FROM BACILLUS HALODURANS IN COMPLEX WITH LAMINARIHEXAOSE
Overview
Enzymes that hydrolyze insoluble complex polysaccharide structures contain, non-catalytic carbohydrate binding modules (CBMS) that play a pivotal role, in the action of these enzymes against recalcitrant substrates. Family 6, CBMs (CBM6s) are distinct from other CBM families in that these protein, modules contain multiple distinct ligand binding sites, a feature that, makes CBM6s particularly appropriate receptors for the beta-1,3-glucan, laminarin, which displays an extended U-shaped conformation. To, investigate the mechanism by which family 6 CBMs recognize laminarin, we, report the biochemical and structural properties of a CBM6 (designated, BhCBM6) that is located in an enzyme, which is shown, in this work, to, display beta-1,3-glucanase activity. BhCBM6 binds, beta-1,3-glucooligosaccharides with affinities of approximately 1 x 10(5), m(-1). The x-ray crystal structure of this CBM in complex with, laminarihexaose reveals similarity with the structures of other CBM6s but, a unique binding mode. The binding cleft in this protein is sealed at one, end, which prevents binding of linear polysaccharides such as cellulose, and the orientation of the sugar at this site prevents glycone extension, of the ligand and thus conferring specificity for the non-reducing ends of, glycans. The high affinity for extended beta-1,3-glucooligosaccharides is, conferred by interactions with the surface of the protein located between, the two binding sites common to CBM6s and thus reveals a third ligand, binding site in family 6 CBMs. This study therefore demonstrates how the, multiple binding clefts and highly unusual protein surface of family 6, CBMs confers the extensive range of specificities displayed by this, protein family. This is in sharp contrast to other families of CBMs where, variation in specificity between different members reflects differences in, the topology of a single binding site.
About this Structure
1W9W is a Single protein structure of sequence from Bacillus halodurans with as ligand. Known structural/functional Site: . Full crystallographic information is available from OCA.
Reference
Family 6 carbohydrate binding modules recognize the non-reducing end of beta-1,3-linked glucans by presenting a unique ligand binding surface., van Bueren AL, Morland C, Gilbert HJ, Boraston AB, J Biol Chem. 2005 Jan 7;280(1):530-7. Epub 2004 Oct 22. PMID:15501830
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