植物细胞壁中的另一个组成部分：大麦木葡聚糖木葡糖基转移酶共价连接木葡聚糖和衍生自果胶的阴离子寡糖。,The Plant Journal

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植物细胞壁中的另一个组成部分：大麦木葡聚糖木葡糖基转移酶共价连接木葡聚糖和衍生自果胶的阴离子寡糖。
The Plant Journal ( IF 6.2 ) Pub Date : 2020-08-16 , DOI: 10.1111/tpj.14964
Barbora Stratilová _{1,

2} , Sergej Šesták ₁ , Jozef Mravec ₃ , Soňa Garajová _{1,

4} , Zuzana Pakanová ₁ , Kristína Vadinová ₁ , Danica Kučerová ₁ , Stanislav Kozmon ₁ , Julian G Schwerdt ₄ , Neil Shirley ₄ , Eva Stratilová ₁ , Maria Hrmova _{4,

5}

Affiliation

我们报道了来自大麦（Hordeum vulgare L.）的HvXET3和HvXET4木糖葡聚糖木糖基转移酶（XET; EC 2.4.1.207）的均基和异基糖基化活性，以及使用Alexa Fluor 488观察年轻大麦根中这些活性的可视化标记的低聚糖。我们发现这些同工酶催化与化学定义的供体和受体底物，特别是与木葡聚糖供体和五-半乳糖醛酸苷[α（1-4）GalA p ] ₅受体–同半乳糖醛酸聚糖（果胶）片段的转糖基反应。具有对接的XXXG供体和[α（1-4）GalA p ] ₅的HvXET3和HvXET4的3D分子模型支持了这种活性₅在活性位点的-4至+5个亚位点的受体底物。对金盏花（Tropaeolum majus L.）的大麦同工型和种子定位的TmXET6.3进行序列比较分析，可设计出可利用木葡聚糖/ [α（1-4）GalA催化异源糖基化反应的TmXET6.3突变体。p ] _5个底物对，而野生型TmXET6.3则缺乏这种活性。通过HvXET转录本的实时定量聚合酶链反应获得的表达数据和该基因家族表达谱的聚类热图显示，HvXET3和HvXET6共表达，但不具有单系起源。相反，HvXET3和当我们检查了419个糖苷水解酶16个家族成员（涵盖单子叶植物，双子叶植物和基础被子植物）的进化史时，HvXET4也具有这种关系。以木葡聚糖-果胶杂聚物的作用及其如何参与细胞壁的空间格局为背景，讨论了在具有木葡聚糖/ [α（1-4）GalA p ] ₅底物对的HvXET3和HvXET4中发现的异糖基转移活性。形成和重塑，并影响墙的结构特征。

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Another building block in the plant cell wall: Barley xyloglucan xyloglucosyl transferases link covalently xyloglucan and anionic oligosaccharides derived from pectin.

We report on the homo‐ and hetero‐transglycosylation activities of the HvXET3 and HvXET4 xyloglucan xyloglucosyl transferases (XET; EC 2.4.1.207) from barley (Hordeum vulgare L.), and the visualisation of these activities in young barley roots using Alexa Fluor 488‐labelled oligosaccharides. We discover that these isozymes catalyse the transglycosylation reactions with the chemically defined donor and acceptor substrates, specifically with the xyloglucan donor and the penta‐galacturonide [α(1‐4)GalAp]₅ acceptor – the homogalacturonan (pectin) fragment. This activity is supported by 3D molecular models of HvXET3 and HvXET4 with the docked XXXG donor and [α(1‐4)GalAp]₅ acceptor substrates at the −4 to +5 subsites in the active sites. Comparative sequence analyses of barley isoforms and seed‐localised TmXET6.3 from nasturtium (Tropaeolum majus L.) permitted the engineering of mutants of TmXET6.3 that could catalyse the hetero‐transglycosylation reaction with the xyloglucan/[α(1‐4)GalAp]₅ substrate pair, while wild‐type TmXET6.3 lacked this activity. Expression data obtained by real‐time quantitative polymerase chain reaction of HvXET transcripts and a clustered heatmap of expression profiles of the gene family revealed that HvXET3 and HvXET6 co‐expressed but did not share the monophyletic origin. Conversely, HvXET3 and HvXET4 shared this relationship, when we examined the evolutionary history of 419 glycoside hydrolase 16 family members, spanning monocots, eudicots and a basal Angiosperm. The discovered hetero‐transglycosylation activity in HvXET3 and HvXET4 with the xyloglucan/[α(1‐4)GalAp]₅ substrate pair is discussed against the background of roles of xyloglucan‐pectin heteropolymers and how they may participate in spatial patterns of cell wall formation and re‐modelling, and affect the structural features of walls.

更新日期：2020-08-16

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