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Lookup NU author(s): Dr Imma Venditto,
Ana De Jesus Vaz Luís,
Emeritus Professor Harry Gilbert
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Structural carbohydrates comprise an extraordinary source of energy that remains poorly utilized by the biofuel sector as enzymes have restricted access to their substrates within the intricacy of plant cell walls. Carbohydrate active enzymes (CAZYmes) that target recalcitrant polysaccharides are modular enzymes containing noncatalytic carbohydrate-binding modules (CBMs) that direct enzymes to their cognate substrate, thus potentiating catalysis. In general, CBMs are functionally and structurally autonomous from their associated catalytic domains from which they are separated through flexible linker sequences. Here, we show that a C-terminal CBM46 derived from BhCel5B, a Bacillus halodurans endoglucanase, does not interact with beta-glucans independently but, uniquely, acts cooperatively with the catalytic domain of the enzyme in substrate recognition. The structure of BhCBM46 revealed a beta-sandwich fold that abuts onto the region of the substrate binding cleft upstream of the active site. BhCBM46 as a discrete entity is unable to bind to beta-glucans. Removal of BhCBM46 from BhCel5B, however, abrogates binding to beta-1,3-1,4-glucans while substantially decreasing the affinity for decorated beta-1,4-glucan homopolymers such as xyloglucan. The CBM46 was shown to contribute to xyloglucan hydrolysis only in the context of intact plant cell walls, but it potentiates enzymatic activity against purified beta-1,3-1,4-glucans in solution or within the cell wall. This report reveals the mechanism by which a CBM can promote enzyme activity through direct interaction with the substrate or by targeting regions of the plant cell wall where the target glucan is abundant.
Author(s): Venditto I, Najnnudin S, Luis AS, Ferreira LMA, Sakka K, Knox JP, Gilbert HJ, Fontes CMGA
Publication type: Article
Publication status: Published
Journal: Journal of Biological Chemistry
Print publication date: 24/04/2015
Online publication date: 23/02/2015
Acceptance date: 01/01/1900
ISSN (print): 0021-9258
ISSN (electronic): 1083-351X
Publisher: American Society for Biochemistry and Molecular Biology, Inc.
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