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J. Biol. Chem., Vol. 282, Issue 26, 19177-19189, June 29, 2007

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Characterization and Three-dimensional Structures of Two Distinct Bacterial Xyloglucanases from Families GH5 and GH12^*

Tracey M. Gloster¹, Farid M. Ibatullin¹, Katherine Macauley¹, Jens M. Eklöf, Shirley Roberts, Johan P. Turkenburg, Mads E. Bjørnvad^¶, Per Linå Jørgensen^¶, Steffen Danielsen^¶, Katja S. Johansen^¶, Torben V. Borchert^¶, Keith S. Wilson, Harry Brumer², and Gideon J. Davies³

From the York Structural Biology Laboratory, Department of Chemistry, University of York, York YO10 5YW, United Kingdom, School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, 106 91 Stockholm, Sweden, and ^¶Novozymes A/S, Brudelysvej 26, 1U1.23, DK-2880 Bagsvaerd, Denmark

The plant cell wall is a complex material in which the cellulose microfibrils are embedded within a mesh of other polysaccharides, some of which are loosely termed "hemicellulose." One such hemicellulose is xyloglucan, which displays a -1,4-linked D-glucose backbone substituted with xylose, galactose, and occasionally fucose moieties. Both xyloglucan and the enzymes responsible for its modification and degradation are finding increasing prominence, reflecting both the drive for enzymatic biomass conversion, their role in detergent applications, and the utility of modified xyloglucans for cellulose fiber modification. Here we present the enzymatic characterization and three-dimensional structures in ligand-free and xyloglucan-oligosaccharide complexed forms of two distinct xyloglucanases from glycoside hydrolase families GH5 and GH12. The enzymes, Paenibacillus pabuli XG5 and Bacillus licheniformis XG12, both display open active center grooves grafted upon their respective (/)₈ and -jelly roll folds, in which the side chain decorations of xyloglucan may be accommodated. For the -jelly roll enzyme topology of GH12, binding of xylosyl and pendant galactosyl moieties is tolerated, but the enzyme is similarly competent in the degradation of unbranched glucans. In the case of the (/)₈ GH5 enzyme, kinetically productive interactions are made with both xylose and galactose substituents, as reflected in both a high specific activity on xyloglucan and the kinetics of a series of aryl glycosides. The differential strategies for the accommodation of the side chains of xyloglucan presumably facilitate the action of these microbial hydrolases in milieus where diverse and differently substituted substrates may be encountered.

Received for publication, January 9, 2007 , and in revised form, March 9, 2007.

^* This work was supported by the Swedish Foundation for Strategic Research, the Swedish Research Council, and the Biotechnology and Biological Sciences Research Council. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ These authors contributed equally to this work.

² A Fellow (Rådsforskare) of the Swedish Research Council. To whom correspondence may be addressed. E-mail: harry{at}biotech.kth.se.

³ Recipient of a Royal Society-Wolfson Research Merit Award. To whom correspondence may be addressed. E-mail: davies{at}ysbl.york.ac.uk.

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