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

Correia, Marcia A. S., Prates, Jose A. M., Bras, Joana , Fontes, Carlos M. G. A., Newman, Joseph A., Lewis, Richard J., Gilbert, Harry J. and Flint, James E. (2008) Crystal structure of a cellulosomal family 3 carbohydrate esterase from Clostridium thermocellum provides Insights into the mechanism of substrate recognition. Journal of Molecular Biology, 379 (1). pp. 64-72. ISSN 0022-2836

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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.

Keywords:acetic acid, acetic acid derivative, asparagine, aspartame, carbohydrate, carbohydrate esterase 3, cellulosome, esterase, glycine, histidine, hydrolase, polysaccharide, serine, xylan, alpha helix, amino terminal sequence, article, beta sheet, biocatalyst, carbohydrate metabolism, carboxy terminal sequence, catalysis, cell wall, Clostridium thermocellum, controlled study, crystal structure, enzyme substrate, hydrogen bond, nonhuman, nucleotide sequence, priority journal, protein degradation, protein folding, protein function, thermostability, Bacterial Proteins, Binding Sites, Carboxylesterase, Crystallography, X-Ray, Protein Conformation, Substrate Specificity, Clostridium thermocellum
Subjects:B Subjects allied to Medicine > B100 Anatomy, Physiology and Pathology
Divisions:College of Science > School of Life Sciences
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ID Code:12466
Deposited On:29 Oct 2013 09:03

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