Table 1_An overview of protein N-glycosylation diversity in microalgae.docx

Microalgae are unicellular photosynthetic eukaryotic organisms that arose from distinct endosymbiotic events yielding a wide phylogenetic diversity. In contrast, a single lineage of green algae charophytes gives rise to all land plants. A large number of N-glycan structures were already characterized but the study of glycans N-linked to proteins in these unicellular organisms only recently begun and concerns a limited number of species. These structures differ to a large extent from known structures and exhibit various glycan decorations not reported so far in land plants. However, many pieces of the puzzle are still missing for a full understanding of the protein N-glycosylation biosynthesis in microalgae despite the structural elucidation of lipid-linked oligosaccharide precursors and the biochemical characterization of some Golgi glycosyltransferases. In the present review, we will give an overview of the recently published data on protein N-glycosylation in microalgae which enable to draw an updated picture of this sophisticated cellular process leading to a huge diversity of N-glycan structures. In this work, we will also highlight the arabinosylation and xylosylation of N-glycans in plants and microalgae.

微藻（Microalgae）是一类单细胞光合真核生物，其起源于多次独立的内共生事件，由此演化出丰富的系统发育多样性。与之相对，绿色藻类中的轮藻（charophytes）单一演化支孕育了所有陆生植物。尽管已有大量N-聚糖（N-glycan）结构得到解析，但针对这类单细胞生物中蛋白质N连接聚糖的研究直至近年才起步，且仅涉及有限的物种。这些聚糖结构与已知结构存在显著差异，且带有多种此前从未在陆生植物中报道过的聚糖修饰。尽管已完成脂连接寡糖前体的结构解析以及部分高尔基体糖基转移酶（Golgi glycosyltransferases）的生化特性表征，但要全面阐明微藻中蛋白质N-糖基化的生物合成过程，仍有诸多关键环节尚未明晰。在本综述中，我们将概述近期发表的微藻蛋白质N-糖基化相关研究数据，借此勾勒出这一复杂细胞过程的最新图景——该过程可产生种类极为丰富的N-聚糖结构。本研究还将重点介绍植物与微藻中N-聚糖的阿拉伯糖基化与木糖基化修饰。