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Crystal structure of a cellulosomal family 3 carbohydrate esterase from Clostridium thermocellum provides insights into the mechanism of substrate recognition

Lookup NU author(s): Dr Joseph Newman, Professor Rick Lewis, Emeritus Professor Harry Gilbert, Dr James Flint

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Abstract

The microbial degradation of the plant cell wall is of increasing industrial significance, exemplified by the interest in generating biofuels from plant cell walls. The majority of plant cell-wall polysaccharides are acetylated, and removal of the acetyl groups through the action of carbohydrate esterases greatly increases the efficiency of polysaccharide saccharification. Enzymes in carbohydrate esterase family 3 (CE3) are common in plant cell wall-degrading microorganisms but there is a paucity of structural and biochemical information on these biocatalysts. Clostridium thermocellum contains a single CE3 enzyme, CtCes3, which comprises two highly homologous (97% sequence identity) catalytic modules appended to a C-terminal type I dockerin that targets the esterase into the cellulosome, a large protein complex that catalyses plant cell wall degradation. Here, we report the crystal structure and biochemical properties of the N-terminal catalytic module (CtCes3-1) of CtCes3. The enzyme is a thermostable acetyl-specific esterase that exhibits a strong preference for acetylated xylan. CtCes3-1 displays an α/β hydrolase fold that contains a central five-stranded parallel twisted β-sheet flanked by six α-helices. In addition, the enzyme contains a canonical catalytic triad in which Ser44 is the nucleophile, His208 is the acid-base and Asp205 modulates the basic nature of the histidine. The acetate moiety is accommodated in a hydrophobic pocket and the negative charge of the tetrahedral transition state is stabilized through hydrogen bonds with the backbone N of Ser44 and Gly95 and the side-chain amide of Asn124. © 2008 Elsevier Ltd.

Publication metadata

Author(s): Correia M, Prates J, Brás J, Fontes C, Newman J, Lewis RJ, Gilbert HJ, Flint JE

Publication type: Article

Publication status: Published

Journal: Journal of Molecular Biology

Year: 2008

Volume: 379

Issue: 1

Pages: 64-72

ISSN (print): 0022-2836

ISSN (electronic): 1089-8638

Publisher: Academic Press

URL: http://dx.doi.org/10.1016/j.jmb.2008.03.037

DOI: 10.1016/j.jmb.2008.03.037

PubMed id: 18436237

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