Lerouge P, Cabanes-Macheteau M, Rayon C, Fischette-Lainé A C, Gomord V, Faye L
Laboratoire des Transports Intracellulaires, CNRS-ESA 6037, IFRMP 23, Université de Rouen, Mont Saint Aignan, France.
Plant Mol Biol. 1998 Sep;38(1-2):31-48.
N-glycosylation is a major modification of proteins in plant cells. This process starts in the endoplasmic reticulum by the co-translational transfer of a precursor oligosaccharide to specific asparagine residues of the nascent polypeptide chain. Processing of this oligosaccharide into high-mannose-type, paucimannosidic-type, hybrid-type or complex-type N-glycans occurs in the secretory pathway as the glycoprotein moves from the endoplasmic reticulum to its final destination. At the end of their maturation, some plant N-glycans have typical structures that differ from those found in their mammalian counterpart by the absence of sialic acid and the presence of beta(1,2)-xylose and alpha( 1,3)-fucose residues. Glycosidases and glycosyltransferases that respectively catalyse the stepwise trimming and addition of sugar residues are generally considered as working in a co-ordinated and highly ordered fashion to form mature N-glycans. On the basis of this assembly line concept, fast progress is currently made by using N-linked glycan structures as milestones of the intracellular transport of proteins along the plant secretory pathway. Further developments of this approach will need to more precisely define the topological distribution of glycosyltransferases within a plant Golgi stack. In contrast with their acknowledged role in the targeting of lysosomal hydrolases in mammalian cells, N-glycans have no specific function in the transport of glycoproteins into the plant vacuole. However, the presence of N-glycans, regardless of their structures, is necessary for an efficient secretion of plant glycoproteins. In the biotechnology field, transgenic plants are rapidly emerging as an important system for the production of recombinant glycoproteins intended for therapeutic purposes, which is a strong motivation to speed up research in plant glycobiology. In this regard, the potential and limits of plant cells as a factory for the production of mammalian glycoproteins will be illustrated.
N-糖基化是植物细胞中蛋白质的一种主要修饰方式。该过程始于内质网，通过将前体寡糖共翻译转移至新生多肽链的特定天冬酰胺残基上。随着糖蛋白从内质网向其最终目的地移动，这种寡糖在内质网中被加工成高甘露糖型、寡甘露糖型、杂合型或复合型N-聚糖。在其成熟末期，一些植物N-聚糖具有典型结构，与哺乳动物对应物的结构不同之处在于缺乏唾液酸，以及存在β(1,2)-木糖和α(1,3)-岩藻糖残基。分别催化糖残基逐步修剪和添加的糖苷酶和糖基转移酶通常被认为是协同且高度有序地发挥作用以形成成熟的N-聚糖。基于这种装配线概念，目前通过将N-连接聚糖结构用作蛋白质沿着植物分泌途径进行细胞内运输的里程碑，已取得了快速进展。这种方法的进一步发展将需要更精确地定义植物高尔基体堆叠内糖基转移酶的拓扑分布。与它们在哺乳动物细胞中靶向溶酶体水解酶的公认作用不同，N-聚糖在植物糖蛋白运输到植物液泡中没有特定功能。然而，无论其结构如何，N-聚糖的存在对于植物糖蛋白的有效分泌都是必需的。在生物技术领域，转基因植物正迅速成为生产用于治疗目的的重组糖蛋白的重要系统，这是加速植物糖生物学研究的强大动力。在这方面，将说明植物细胞作为生产哺乳动物糖蛋白工厂的潜力和局限性。
