Chen Yuning, Dong Wen, Tan Li, Held Michael A, Kieliszewski Marcia J
Department of Chemistry and Biochemistry, Ohio University, Athens, OH, USA.
Complex Carbohydrate Research Center, University of Georgia, Athens, GA, USA.
Biochem Insights. 2015 Sep 20;8(Supple 2):1-13. doi: 10.4137/BCI.S31353. eCollection 2015.
Extensins (EXTs) are hydroxyproline-rich glycoproteins (HRGPs) that are structural components of the plant primary cell wall. They are basic proteins and are highly glycosylated with carbohydrate accounting for >50% of their dry weight. Carbohydrate occurs as monogalactosyl serine and arabinosyl hydroxyproline, with arabinosides ranging in size from ~1 to 4 or 5 residues. Proposed functions of EXT arabinosylation include stabilizing the polyproline II helix structure and facilitating EXT cross-linking. Here, the involvement of arabinosylation in EXT cross-linking was investigated by assaying the initial cross-linking rate and degree of cross-linking of partially or fully de-arabinosylated EXTs using an in vitro cross-linking assay followed by gel permeation chromatography. Our results indicate that EXT arabinosylation is required for EXT cross-linking in vitro and the fourth arabinosyl residue in the tetraarabinoside chain, which is uniquely α-linked, may determine the initial cross-linking rate. Our results also confirm the conserved structure of the oligoarabinosides across species, indicating an evolutionary significance for EXT arabinosylation.
伸展蛋白（EXTs）是富含羟脯氨酸的糖蛋白（HRGPs），是植物初生细胞壁的结构成分。它们是碱性蛋白质，高度糖基化，碳水化合物占其干重的50%以上。碳水化合物以单半乳糖基丝氨酸和阿拉伯糖基羟脯氨酸的形式存在，阿拉伯糖苷的大小范围为~1至4或5个残基。EXT阿拉伯糖基化的推测功能包括稳定聚脯氨酸II螺旋结构和促进EXT交联。在此，通过使用体外交联测定法，随后进行凝胶渗透色谱法，测定部分或完全脱阿拉伯糖基化的EXTs的初始交联速率和交联程度，研究了阿拉伯糖基化在EXT交联中的作用。我们的结果表明，EXT阿拉伯糖基化是体外EXT交联所必需的，四阿拉伯糖苷链中唯一α连接的第四个阿拉伯糖基残基可能决定初始交联速率。我们的结果还证实了跨物种寡阿拉伯糖苷的保守结构，表明EXT阿拉伯糖基化具有进化意义。
