Trans-α-xylosidase, a widespread enzyme activity in plants, introduces (1→4)-α-D-xylobiose side-chains into xyloglucan structures
Trans-α-xylosidase, a widespread enzyme activity in plants, introduces (1→4)-α-D-xylobiose side-chains into xyloglucan structures
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DOI：
10.1016/j.phytochem.2012.02.003
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发表时间：
2012-06-01
期刊：
影响因子：
3.8
通讯作者：
Fry, Stephen C.
中科院分区：
文献类型：
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作者：
Frankova, Lenka;Fry, Stephen C.
被子植物具有保留的反式-α-木糖苷酶活性，可催化木糖残基在木葡聚糖结构之间的分子间转移。为了鉴定新转移的α-木糖残基的连接，我们使用[Xyl-H-3]XXXG（木葡聚糖七糖）作为供体底物，并使用还原胺化的木葡聚糖寡糖（XGO-NH2）作为受体。芦笋酶提取物产生阳离子放射性产物（[H-3]Xyl中心点XGO-NH2），该产物可被Driselase消化成含有α-[H-3]木糖残基的中性三糖。硼氢化物还原后，三聚体表现出高钼酸盐亲和力，表明木二糖基-(1→6)-山梨糖醇而不是二木糖基化山梨糖醇。因此，转木糖苷酶已将额外的α-[H-3]木糖残基接枝到异春木糖单元的木糖上。三糖被快速乙酰解成α-[H-3]木二糖，证实存在乙酰解不稳定的(1 -> 6)-键。通过还原该α-[H-3]木二糖形成的α-[H-3]木二糖醇具有低钼酸盐亲和力，表明是(1→2)或(1→4)键。在 NaOH 中，α-[H-3]木二糖以 (1 -> 4)-二糖的中等速率特征进行碱性剥离。最后，我们合成了八种非放射性木二糖[α和β； (1 1)、(1 -> 2)、(1 -> 3) 和 (1 -> 4)1 并发现 [H-3]木二糖仅与 (1 -> 4)-α-木二糖进行共色谱。我们得出结论，芦笋反式-α-木糖苷酶活性产生了一种新的木葡聚糖结构单元，α-D-Xylp-(1 -> 4)-α-D-Xylp-(1 -> 6)-D-Glc（缩写：“V”）。以这种方式修饰木葡聚糖结构可能会改变寡糖精活性，或改变其作为木葡聚糖内转葡糖基酶 (XET) 活性受体底物的适用性。 (C) 2012 Elsevier Ltd. 保留所有权利。
Angiosperms possess a retaining trans-a-xylosidase activity that catalyses the inter-molecular transfer of xylose residues between xyloglucan structures. To identify the linkage of the newly transferred a-xylose residue, we used [Xyl-H-3]XXXG (xyloglucan heptasaccharide) as donor substrate and reductively-aminated xyloglucan oligosaccharides (XGO-NH2) as acceptor. Asparagus officinalis enzyme extracts generated cationic radioactive products ([H-3]Xyl center dot XGO-NH2) that were Driselase-digestible to a neutral trisaccharide containing an alpha-[H-3]xylose residue. After borohydride reduction, the trimer exhibited high molybdate-affinity, indicating xylobiosyl-(1 -> 6)-glucitol rather than a di-xylosylated glucitol. Thus the trans-axylosidase had grafted an additional alpha-[H-3]xylose residue onto the xylose of an isoprimeverose unit. The trisaccharide was rapidly acetolysed to an alpha-[H-3]xylobiose, confirming the presence of an acetolysis-labile (1 -> 6)-bond. The alpha-[H-3]xylobiitol formed by reduction of this alpha-[H-3]xylobiose had low molybdate-affinity, indicating a (1 -> 2) or (1 -> 4) linkage. In NaOH, the alpha-[H-3]xylobiose underwent alkaline peeling at the moderate rate characteristic of a (1 -> 4)-disaccharide. Finally, we synthesised eight non-radioactive xylobioses [alpha and beta; (1 1), (1 -> 2), (1 -> 3) and (1 -> 4)1 and found that the [H-3]xylobiose co-chromatographed only with (1 -> 4)-alpha-xylobiose. We conclude that Asparagus trans-alpha-xylosidase activity generates a novel xyloglucan building block, alpha-D-Xylp-(1 -> 4)-alpha-D-Xylp-(1 -> 6)-D-Glc (abbreviation: 'V'). Modifying xyloglucan structures in this way may alter oligosaccharin activities, or change their suitability as acceptor substrates for xyloglucan endotransglucosylase (XET) activity. (C) 2012 Elsevier Ltd. All rights reserved.