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Characterization and three-dimensional structures of two distinct bacterial xyloglucanases from families GH5 and GH12
KTH, School of Biotechnology (BIO), Glycoscience.
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2007 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 282, no 26, 19177-19189 p.Article in journal (Refereed) Published
Abstract [en]

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 beta-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 (beta/alpha)(8) and beta-jelly roll folds, in which the side chain decorations of xyloglucan may be accommodated. For the beta-jelly roll enzyme topology of GH12, binding of xylosyl and pendant galactosyl moieties is tolerated, but the enzymeis similarly competent in the degradation of unbranched glucans. In the case of the (beta/alpha)(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.

Place, publisher, year, edition, pages
2007. Vol. 282, no 26, 19177-19189 p.
Keyword [en]
plant-cell wall, carotovora subsp carotovora, angstrom resolution, cellulose surfaces, crystal-structures, endoglucanase, oligosaccharides, insights, cloning, enzyme
National Category
Biochemistry and Molecular Biology
URN: urn:nbn:se:kth:diva-16723DOI: 10.1074/jbc.M700224200ISI: 000247475300059ScopusID: 2-s2.0-34547134972OAI: diva2:334766
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-04-01Bibliographically approved
In thesis
1. Plant and microbial xyloglucanases: Function, Structure and Phylogeny
Open this publication in new window or tab >>Plant and microbial xyloglucanases: Function, Structure and Phylogeny
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, enzymes acting on the primary cell wall hemicellulose xyloglucan are studied.  Xyloglucans are ubiquitous in land plants which make them an important polysaccharide to utilise for microbes and a potentially interesting raw material for various industries.  The function of xyloglucans in plants is mainly to improve primary cell wall characteristics by coating and tethering cellulose microfibrils together.  Some plants also utilise xyloglucans as storage polysaccharides in their seeds.

In microbes, a variety of different enzymes for degrading xyloglucans have been found.  In this thesis, the structure-function relationship of three different microbial endo-xyloglucanases from glycoside hydrolase families 5, 12 and 44 are probed and reveal details of the natural diversity found in xyloglucanases.  Hopefully, a better understanding of how xyloglucanases recognise and degrade their substrate can lead to improved saccharification processes of plant matter, finding uses in for example biofuel production.

In plants, xyloglucans are modified in muro by the xyloglucan transglycosylase/hydrolase (XTH) gene products.  Interestingly, closely related XTH gene products catalyse either transglycosylation (XET activity) or hydrolysis (XEH activity) with dramatically different effects on xyloglucan and on cell wall characteristics.  The strict transglycosylases transfer xyloglucan segments between individual xyloglucan molecules while the hydrolases degrade xyloglucan into oligosaccharides.  Here, we describe and determine, a major determinant of transglycosylation versus hydrolysis in XTH gene products by solving and comparing the first 3D structure of an XEH, Tm-NXG1 and a XET, PttXET16-34.  The XEH activity was hypothesised, and later confirmed to be restricted to subset of the XTH gene products.  The in situ localisation of XEH activity in roots and hypocotyls of Arabidopsis was also visualised for the first time.  Furthermore, an evolutionary scheme for how XTH gene products developed from bacterial beta-1,3;1,4 glucanases was also presented based on the characterisation of a novel plant endo-glucanase, PtEG16-1. The EG16s are proposed to predate XTH gene products and are with activity on both xyloglucan and beta-1,3;1,4 glucans an “intermediate” in the evolution from beta-1,3;1,4 glucanases to XTH gene products.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 61 p.
Trita-BIO-Report, ISSN 1654-2312 ; 2011:07
xyloglucan, xyloglucanases, XTH, XET, XEH, endoglucanases, EG16
National Category
Biochemistry and Molecular Biology
urn:nbn:se:kth:diva-31677 (URN)978-91-7415-932-5 (ISBN)
Public defence
2011-04-15, FR4, Albanova Universitetscentrum, Stockholm, 10:00 (English)
QC 20110401Available from: 2011-04-01 Created: 2011-03-22 Last updated: 2011-11-03Bibliographically approved

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