State Key Laboratory of Pharmaceutical Biotechnology, NJU Advanced Institute for Life Sciences (NAILS), School of Life Sciences, Nanjing University, 163 Xianlin Avenue, Nanjing, 210046, Jiangsu, China.
Plant Mol Biol. 2020 Jul;103(4-5):581-596. doi: 10.1007/s11103-020-01012-z. Epub 2020 May 14.
N-glycans play a protective or monitoring role according to the folding state of associated protein or the distance from structural defects. Asparagine-linked (Asn/N-) glycosylation is one of the most prevalent and complex protein modifications and the associated N-glycans play crucial roles on protein folding and secretion. The studies have shown that many glycoproteins hold multiple N-glycans, yet little is known about the redundancy of N-glycans on a protein. In this study, we used BRI1 to decipher the roles of N-glycans on protein secretion and function. We found that all 14 potential N-glycosylation sites on BRI1 were occupied with oligosaccharides. The elimination of single N-glycan had no obvious effect on BRI1 secretion or function except N-glycan, which resulted in the retention of BRI1 in the endoplasmic reticulum (ER), similar to the loss of multiple highly conserved N-glycans. To misfolded bri1, the absence of N-glycans next to local structural defects enhanced the ER retention and the artificial addition of N-glycan could help the misfolded bri1-GFPs exiting from the ER, indicating that the N-glycans might serve as steric hindrance to protect the structure defects from ER recognition. We also found that the retention of misfolded bri1-9 by lectins and chaperones in the ER relied on the presence of multiple N-glycans distal to the local defects. Our findings revealed that the N-glycans might play a protective or monitoring role according to the folding state of associated protein or the distance from structural defects.
N-糖基化根据相关蛋白的折叠状态或与结构缺陷的距离发挥保护或监测作用。天冬酰胺连接（Asn/N-）糖基化是最普遍和复杂的蛋白修饰之一，相关的 N-聚糖在蛋白折叠和分泌中发挥关键作用。研究表明，许多糖蛋白含有多个 N-聚糖，但关于蛋白上 N-聚糖的冗余性知之甚少。在这项研究中，我们使用 BRI1 来破译 N-聚糖在蛋白分泌和功能中的作用。我们发现 BRI1 上的 14 个潜在 N-糖基化位点都被寡糖占据。除了导致 BRI1 在内质网（ER）中滞留的 N-聚糖外，单个 N-聚糖的消除对 BRI1 分泌或功能没有明显影响，这种情况类似于多个高度保守的 N-聚糖的缺失。对于错误折叠的 bri1，紧邻局部结构缺陷的 N-聚糖缺失会增强 ER 滞留，而人工添加 N-聚糖可以帮助错误折叠的 bri1-GFPs 从 ER 中逸出，这表明 N-聚糖可能作为空间位阻来保护结构缺陷免受 ER 识别。我们还发现，错误折叠的 bri1-9 在 ER 中被凝集素和伴侣蛋白滞留依赖于局部缺陷远端存在多个 N-聚糖。我们的发现表明，N-聚糖可能根据相关蛋白的折叠状态或与结构缺陷的距离发挥保护或监测作用。
