Laboratoire de Glycobiologie et Matrice Extracellulaire Végétale, UPRES EA 4358, Institut de Recherche et d'Innovation Biomédicale, Grand Réseau de Recherche-Végétal, Agronomie, Sol, Innovation, UFR des Sciences et Techniques, Normandie Université - Université de Rouen Mont-Saint-Aignan, France.
Laboratoire de Glycobiologie et Matrice Extracellulaire Végétale, UPRES EA 4358, Institut de Recherche et d'Innovation Biomédicale, Grand Réseau de Recherche-Végétal, Agronomie, Sol, Innovation, UFR des Sciences et Techniques, Normandie Université - Université de Rouen Mont-Saint-Aignan, France ; Institut Universitaire de France Paris, France.
Front Plant Sci. 2014 Oct 2;5:499. doi: 10.3389/fpls.2014.00499. eCollection 2014.
Cell wall O-glycoproteins and N-glycoproteins are two types of glycomolecules whose glycans are structurally complex. They are both assembled and modified within the endomembrane system, i.e., the endoplasmic reticulum (ER) and the Golgi apparatus, before their transport to their final locations within or outside the cell. In contrast to extensins (EXTs), the O-glycan chains of arabinogalactan proteins (AGPs) are highly heterogeneous consisting mostly of (i) a short oligo-arabinoside chain of three to four residues, and (ii) a larger β-1,3-linked galactan backbone with β-1,6-linked side chains containing galactose, arabinose and, often, fucose, rhamnose, or glucuronic acid. The fine structure of arabinogalactan chains varies between, and within plant species, and is important for the functional activities of the glycoproteins. With regards to N-glycans, ER-synthesizing events are highly conserved in all eukaryotes studied so far since they are essential for efficient protein folding. In contrast, evolutionary adaptation of N-glycan processing in the Golgi apparatus has given rise to a variety of organism-specific complex structures. Therefore, plant complex-type N-glycans contain specific glyco-epitopes such as core β,2-xylose, core α1,3-fucose residues, and Lewis(a) substitutions on the terminal position of the antenna. Like O-glycans, N-glycans of proteins are essential for their stability and function. Mutants affected in the glycan metabolic pathways have provided valuable information on the role of N-/O-glycoproteins in the control of growth, morphogenesis and adaptation to biotic and abiotic stresses. With regards to O-glycoproteins, only EXTs and AGPs are considered herein. The biosynthesis of these glycoproteins and functional aspects are presented and discussed in this review.
细胞壁 O-糖蛋白和 N-糖蛋白是两种糖分子，其聚糖结构复杂。它们都是在细胞内膜系统（内质网（ER）和高尔基体）内组装和修饰的，然后再运输到细胞内外的最终位置。与伸展蛋白（EXTs）不同，阿拉伯半乳聚糖蛋白（AGP）的 O-聚糖链高度异质，主要由（i）三到四个残基的短寡阿拉伯糖苷链和（ii）带有β-1,3 连接的半乳糖主链和β-1,6 连接的带有半乳糖、阿拉伯糖的侧链组成，通常还有岩藻糖、鼠李糖或葡萄糖醛酸。阿拉伯半乳聚糖链的精细结构在不同植物物种之间存在差异，并且对糖蛋白的功能活动很重要。关于 N-聚糖，迄今为止，在所有研究的真核生物中，ER 合成事件都高度保守，因为它们对蛋白质的有效折叠至关重要。相比之下，高尔基体中 N-聚糖加工的进化适应导致了各种具有生物体特异性的复杂结构。因此，植物复杂型 N-聚糖含有特定的糖基表位，如核心β,2-木糖、核心α1,3-岩藻糖残基，以及在天线末端位置的 Lewis(a)取代物。与 O-聚糖一样，蛋白质的 N-糖和 O-糖对其稳定性和功能至关重要。糖代谢途径中受影响的突变体为 N-/O-糖蛋白在控制生长、形态发生以及适应生物和非生物胁迫方面的作用提供了有价值的信息。关于 O-糖蛋白，本文仅考虑伸展蛋白（EXTs）和阿拉伯半乳聚糖蛋白（AGP）。本文介绍并讨论了这些糖蛋白的生物合成和功能方面。
