title: Enzymic characterization of two recombinant xyloglucan endotransglucosylase/hydrolase (XTH) proteins of Arabidopsis and their effect on root growth and cell wall extension.
abstract: Xyloglucan endotransglucosylase/hydrolases (XTHs) are enzymes involved in the modification of load-bearing cell wall components. They cleave xyloglucan chains and, often, re-form bonds to the non-reducing ends of available xyloglucan molecules in plant primary cell walls. The enzymic properties and effects on root growth of two Arabidopsis thaliana XTHs belonging to subgroup I/II, that are predominantly expressed in root hairs and in non-elongating zones of the root, were analysed here. AtXTH14 and AtXTH26 were recombinantly produced in Pichia and subsequently purified. Both proteins were found to exhibit xyloglucan endotransglucosylase (XET; EC 2.4.1.207) but not xyloglucan endohydrolase (XEH; EC 3.2.1.151) activity. Their endotransglucosylase activity was at least 70x greater on xyloglucan rather than on mixed-linkage beta-glucan. Differences were found in pH- and temperature-dependence as well as in acceptor-substrate preferences. Furthermore, the specific activity of XET was approximately equal for the two enzymes. Removal of N-linked sugar residues by Endo H treatment reduced XET activity to 60%. Constant-load extensiometry experiments revealed that the enzymes reduce the extension in a model system of heat-inactivated isolated cell walls. When given to growing roots, either of these XTH proteins reduced cell elongation in a concentration-dependent manner and caused abnormal root hair morphology. This is the first time that recombinant and purified XTHs added to growing roots have exhibited a clear effect on cell elongation. It is proposed that these specific XTH isoenzymes play a role in strengthening the side-walls of root-hairs and cell walls in the root differentiation zone after the completion of cell expansion.
authors.affiliation: Department of Biology, University of Antwerp, Antwerpen, Belgium.
authors.forename: An
authors.initials: A
authors.lastname: Maris
authors.forename: Dmitry
authors.initials: D
authors.lastname: Suslov
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Fry
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Verbelen
authors.forename: Kris
authors.initials: K
authors.lastname: Vissenberg
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D002473:Cell Wall / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D004795:Enzyme Stability; D016695:Glycosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000737:chemistry / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D016695:Glycosyltransferases; C473049:xyloglucan - xyloglucosyltransferase