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Structure and Activity of a Paenibacillus polymyxa Xyloglucanase from Glycoside Hydrolase Family 44
KTH, School of Biotechnology (BIO), Glycoscience.
KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
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2011 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 286, no 39, 33890-33900 p.Article in journal (Refereed) Published
Abstract [en]

The enzymatic degradation of plant polysaccharides is emerging as one of the key environmental goals of the early 21st century, impacting on many processes in the textile and detergent industries as well as biomass conversion to biofuels. One of the well known problems with the use of nonstarch (nonfood)-based substrates such as the plant cell wall is that the cellulose fibers are embedded in a network of diverse polysaccharides, including xyloglucan, that renders access difficult. There is therefore increasing interest in the "accessory enzymes," including xyloglucanases, that may aid biomass degradation through removal of "hemicellulose" polysaccharides. Here, we report the biochemical characterization of the endo-beta-1,4-(xylo)glucan hydrolase from Paenibacillus polymyxa with polymeric, oligomeric, and defined chromogenic aryl-oligosaccharide substrates. The enzyme displays an unusual specificity on defined xyloglucan oligosaccharides, cleaving the XXXG-XXXG repeat into XXX and GXXXG. Kinetic analysis on defined oligosaccharides and on aryl-glycosides suggests that both the -4 and +1 subsites show discrimination against xylose-appended glucosides. The three-dimensional structures of PpXG44 have been solved both in apo-form and as a series of ligand complexes that map the -3 to -1 and +1 to +5 subsites of the extended ligand binding cleft. Complex structures are consistent with partial intolerance of xylosides in the -4' subsites. The atypical specificity of PpXG44 may thus find use in industrial processes involving xyloglucan degradation, such as biomass conversion, or in the emerging exciting applications of defined xyloglucans in food, pharmaceuticals, and cellulose fiber modification.

Place, publisher, year, edition, pages
2011. Vol. 286, no 39, 33890-33900 p.
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:kth:diva-31964DOI: 10.1074/jbc.M111.262345ISI: 000295159200021Scopus ID: 2-s2.0-80053190600OAI: oai:DiVA.org:kth-31964DiVA: diva2:407920
Note
QC 20111103 Available from: 2011-04-01 Created: 2011-04-01 Last updated: 2017-12-11Bibliographically 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.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2011:07
Keyword
xyloglucan, xyloglucanases, XTH, XET, XEH, endoglucanases, EG16
National Category
Biochemistry and Molecular Biology
Identifiers
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)
Opponent
Supervisors
Note
QC 20110401Available from: 2011-04-01 Created: 2011-03-22 Last updated: 2011-11-03Bibliographically approved

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