Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Muthgasse 18, Vienna, A-1190, Austria.
Plant J. 2018 Apr;94(2):246-259. doi: 10.1111/tpj.13851. Epub 2018 Mar 14.
Many soluble and integral membrane proteins fold in the endoplasmic reticulum (ER) with the help of chaperones and folding factors. Despite these efforts, protein folding is intrinsically error prone and amino acid changes, alterations in post-translational modifications or cellular stress can cause protein misfolding. Folding-defective non-native proteins are cleared from the ER and typically undergo ER-associated degradation (ERAD). Here, we investigated whether different misfolded glycoproteins require the same set of ERAD factors and are directed to HRD1 complex-mediated degradation in plants. We generated a series of glycoprotein ERAD substrates harboring a misfolded domain from Arabidopsis STRUBBELIG or the BRASSINOSTEROID INSENSITVE 1 receptor fused to different membrane anchoring regions. We show that single pass and multispanning ERAD substrates are subjected to glycan-dependent degradation by the HRD1 complex. However, the presence of a powerful ER exit signal in the multispanning ERAD substrates causes competition with ER quality control and targeting of misfolded glycoproteins to the vacuole. Our results demonstrate that the same machinery is used for degradation of topologically different misfolded glycoproteins in the ER of plants.
许多可溶性和整合膜蛋白在伴侣蛋白和折叠因子的帮助下在内质网（ER）中折叠。尽管有这些努力，蛋白质折叠本质上容易出错，并且氨基酸变化、翻译后修饰的改变或细胞应激会导致蛋白质错误折叠。折叠缺陷的非天然蛋白质从 ER 中清除，通常会经历 ER 相关降解（ERAD）。在这里，我们研究了不同的错误折叠糖蛋白是否需要相同的一组 ERAD 因子，并在植物中被定向到 HRD1 复合物介导的降解。我们生成了一系列糖蛋白 ERAD 底物，这些底物携带有来自拟南芥 STRUBBELIG 的错误折叠结构域或 BRASSINOSTEROID INSENSITIVE 1 受体，融合到不同的膜锚定区域。我们表明，单通道和多通道 ERAD 底物都受到 HRD1 复合物的糖依赖性降解。然而，多通道 ERAD 底物中存在强大的 ER 出口信号会导致与 ER 质量控制竞争，并将错误折叠的糖蛋白靶向液泡。我们的结果表明，在植物 ER 中，相同的机制用于降解拓扑结构不同的错误折叠糖蛋白。
