title: Mode of action of xylogalacturonan hydrolase towards xylogalacturonan and xylogalacturonan oligosaccharides.
abstract: XGH (xylogalacturonan hydrolase; GH 28) is an enzyme that is capable of degrading XGA (xylogalacturonan), which is a polymer of alpha-D-galacturonic acid, highly substituted with beta-D-xylose. XGA is present in cell walls of various plants and exudates, such as gum tragacanth. XGA oligosaccharides were derived from an XGH digestion of gum tragacanth, then fractionated, and analysed for their sugar composition and structure by matrix-assisted laser-desorption ionization-time-of-flight MS and nanospray MS. Several oligosaccharides from XGA were identified with different galacturonic acid/xylose ratios including five oligosaccharide isomers. Although XGH can act as an endo-enzyme, product-progression profiling showed that the disaccharide GalAXyl was predominantly produced from XGA by XGH, which indicated also an exolytic action. The latter was further supported by degradation studies of purified oligosaccharide GalA4Xyl3. It was shown that XGH acted from the non-reducing end towards the reducing end of this oligosaccharide, and showed the processive character of XGH. The results from this study further show that although XGH prefers to act between two xylosidated GalA units, it tolerates unsubstituted GalA units in its -1 and +1 subsites.
authors.affiliation: Laboratory of Food Chemistry, Department of Agrotechnology and Food Sciences, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
authors.forename: Joris
authors.initials: J
authors.lastname: Zandleven
authors.forename: Gerrit
authors.initials: G
authors.lastname: Beldman
authors.forename: Margaret
authors.initials: M
authors.lastname: Bosveld
authors.forename: Jaques
authors.initials: J
authors.lastname: Benen
authors.forename: Alphons
authors.initials: A
authors.lastname: Voragen
mesh_terms: D002236:Carbohydrate Conformation; D006603:Hexuronic Acids / Q000737:chemistry / Q000378:metabolism*; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity; D014995:Xylosidases / Q000378:metabolism*
chemical_list: D006603:Hexuronic Acids; D009844:Oligosaccharides; C465879:xylogalacturonan; D014995:Xylosidases