Structural features conserved in subclass of type II arabinogalactan
Structural features conserved in subclass of type II arabinogalactan
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DOI：
10.5511/plantbiotechnology.20.0721a
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发表时间：
2020-12-01
影响因子：
1.6
通讯作者：
Kotake, Toshihisa
中科院分区：
文献类型：
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作者：
Ito, Kengo;Fukuoka, Kurumi;Kotake, Toshihisa
阿拉伯半乳糖蛋白(AGPs)是一种胞外蛋白多糖，被认为参与细胞形状的调节，从而对植物具有优异的力学性能起到重要作用。AGP由一个富含羟基脯氨酸的核心蛋白和大的阿拉伯半乳糖(AG)糖链组成，称为II型AG。这些AG具有β-1，3-半乳糖主链和β-1，6-半乳糖侧链，其他糖连接到这些侧链上。II型AG的结构因来源植物、组织和年龄的不同而不同。从以阿拉伯树胶和落叶松AG为代表的大量木本植物中获得的II型AGG，这里称为阿拉伯树胶亚类，具有β-1，3；1，6半乳聚糖结构，其中β-1，3-半乳聚糖主链被短的β-1，6-半乳聚糖侧链高度取代。另一方面，目前还不清楚从草本植物中发现的第二类AGs是否也具有保守的β-1，3：1，6-半乳聚糖的结构特征。在本研究中，我们探索了AGP-亚类中II型AG结构的相似性。从菠菜、西兰花、白菜、土豆和黄瓜中提取的级分中的II型AGs被特定的酶降解为半乳糖和β-1，6-低聚半乳糖。根据这些糖的比例，计算出这五种蔬菜中β-1，3-半乳糖主链的替代率为46%-58%，一直低于阿拉伯树胶和落叶松AG中的取代率。虽然大多数侧链是短的，但在这些蔬菜中也观察到了长链，如β-1，6-半乳六糖链。结果表明，AGP亚类中含有保守的β-1，3；1，6-半乳聚糖结构，区别于阿拉伯树胶亚类。
Arabinogalactan proteins (AGPs) are extracellular proteoglycans, which are presumed to participate in the regulation of cell shape, thus contributing to the excellent mechanical properties of plants. AGPs consist of a hydroxyprolinerich core-protein and large arabinogalactan (AG) sugar chains, called type II AGs. These AGs have a beta-1,3-galactan backbone and beta-1,6-galactan side chains, to which other sugars are attached. The structure of type II AG differs depending on source plant, tissue, and age. Type II AGs obtained from woody plants in large quantity as represented by gum arabic and larch AG, here designated gum arabic subclass, have a beta-1,3;1,6 galactan structure in which the beta-1,3-galactan backbone is highly substituted with short beta-1,6-galactan side chains. On the other hand, it is unclear whether type II AGs found as the glycan part of AGPs from herbaceous plants, here designated AGP-subclass, also have conserved beta-1,3:1,6-galactan structural features. In the present study we explore similarities of type II AG structures in the AGP-subclass. Type II AGs in fractions obtained from spinach, broccoli, bok choy, komatsuna, and cucumber were hydrolyzed into galactose and beta-1,6-galactooligosaccharides by specific enzymes. Based on the proportion of these sugars, the substitution ratio of the beta-1,3-galactan backbone was calculated as 46-58% in the five vegetables, which is consistently lower than what is seen in gum arabic and larch AG. Although most side chains were short, long chains such as beta-1,6-galactohexaose chains were also observed in these vegetables. The results suggest a conserved beta-1,3;1,6-galactan structure in the AGP-subclass that distinguishes it from the gum arabic-subclass.