Enzymic characterization of two recombinant xyloglucan endotransglucosylase/hydrolase (XTH) proteins of Arabidopsis and their effect on root growth and cell wall extension
Enzymic characterization of two recombinant xyloglucan endotransglucosylase/hydrolase (XTH) proteins of Arabidopsis and their effect on root growth and cell wall extension
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DOI：
10.1093/jxb/erp229
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发表时间：
2009-09-01
影响因子：
6.9
通讯作者：
Vissenberg, Kris
中科院分区：
文献类型：
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作者：
Maris, An;Suslov, Dmitry;Vissenberg, Kris
木葡聚糖内切转葡糖基酶/水解酶（XTH）是参与承重细胞壁组分的修饰的酶。它们裂解木葡聚糖链，并且通常与植物初生细胞壁中可用的木葡聚糖分子的非还原末端重新形成键。本文分析了两种拟南芥XTH的酶学性质及其对根生长的影响，这两种XTH主要表达于根毛和根的非伸长区，属于亚组I/II。AtXTH 14和AtXTH 26在毕赤酵母中重组产生并随后纯化。发现两种蛋白质都表现出木葡聚糖内切转葡糖基酶（XET; EC 2.4.1.207）活性，但不表现出木葡聚糖内切水解酶（XEH; EC 3.2.1.151）活性。其内切转葡糖基酶活性对木葡聚糖的活性比对混合键β-葡聚糖的活性高至少70倍。差异被发现在pH值和温度的依赖性，以及在受体基板的喜好。此外，两种酶的XET比活性大致相等。通过Endo H处理去除N-连接的糖残基使XET活性降低至60%。恒载拉伸实验表明，酶减少热灭活孤立的细胞壁的模型系统中的扩展。当给予生长的根，这些XTH蛋白质中的任何一个以浓度依赖性的方式减少细胞伸长，并引起异常的根毛形态。这是第一次将重组和纯化的XTH添加到生长的根中，对细胞伸长表现出明显的作用。这些特异性XTH同工酶在细胞扩展完成后，对根毛侧壁和根分化区细胞壁的强化起作用。
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.