Zandleven Joris, Beldman Gerrit, Bosveld Margaret, Benen Jaques, Voragen Alphons
Laboratory of Food Chemistry, Department of Agrotechnology and Food Sciences, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
Biochem J. 2005 May 1;387(Pt 3):719-25. doi: 10.1042/BJ20041583.
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.
木糖半乳糖醛酸水解酶（XGH；糖基水解酶28家族）是一种能够降解木糖半乳糖醛酸（XGA）的酶，XGA是一种α-D-半乳糖醛酸的聚合物，被β-D-木糖高度取代。XGA存在于各种植物的细胞壁和渗出物中，如刺梧桐树胶。XGA寡糖由刺梧桐树胶经XGH消化产生，然后进行分级分离，并通过基质辅助激光解吸电离飞行时间质谱和纳米喷雾质谱分析其糖组成和结构。从XGA中鉴定出了几种具有不同半乳糖醛酸/木糖比例的寡糖，包括五种寡糖异构体。尽管XGH可以作为内切酶起作用，但产物进程分析表明，二糖GalAXyl主要是由XGH从XGA产生的，这也表明了其外切作用。对纯化的寡糖GalA4Xyl3的降解研究进一步支持了后者。结果表明，XGH从该寡糖的非还原端向还原端作用，显示出XGH的连续性特征。本研究结果进一步表明，尽管XGH更倾向于在两个木糖基化的GalA单元之间起作用，但它在其-1和+1亚位点能够耐受未取代的GalA单元。
