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An endo β‐1,4 glucanse, PtEG16‐1 from black cottonwood (Populustrichocarpa) represents an evolutionary link between bacterial lichenases and XTH geneproducts
KTH, School of Biotechnology (BIO), Glycoscience.
KTH, School of Biotechnology (BIO), Glycoscience.
(English)Article in journal (Other academic) Submitted
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:kth:diva-31985OAI: oai:DiVA.org:kth-31985DiVA: diva2:407928
Note
QS 20120326Available from: 2011-04-01 Created: 2011-04-01 Last updated: 2012-03-26Bibliographically 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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CiteExportLink to record
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