Yang Gege, Banfield David K
Division of Life Science, The Hong Kong University of Science and Technology, Kowloon, Hong Kong, SAR of China.
Mol Biol Cell. 2020 Dec 15;31(26):2883-2891. doi: 10.1091/mbc.E20-08-0539. Epub 2020 Oct 28.
Glycosylphosphatidylinositol-anchored proteins (GPI-APs) undergo extensive posttranslational modifications and remodeling, including the addition and subsequent removal of phosphoethanolamine (EtNP) from mannose 1 (Man1) and mannose 2 (Man2) of the glycan moiety. Removal of EtNP from Man1 is catalyzed by Cdc1p, an event that has previously been considered to occur in the endoplasmic reticulum (ER). We establish that Cdc1p is in fact a /medial Golgi membrane protein that relies on the COPI coatomer for its retention in this organelle. We also determine that Cdc1p does not cycle between the Golgi and the ER, and consistent with this finding, when expressed at endogenous levels ER-localized Cdc1p-HDEL is unable to support the growth of cells. Our temperature-sensitive alleles are defective in the transport of a prototypical GPI-AP-Gas1p to the cell surface, a finding we posit reveals a novel Golgi-localized quality control warrant. Thus, yeast cells scrutinize GPI-APs in the ER and also in the Golgi, where removal of EtNP from Man2 (via Ted1p in the ER) and from Man1 (by Cdc1p in the Golgi) functions as a quality assurance signal.
糖基磷脂酰肌醇锚定蛋白（GPI-APs）经历广泛的翻译后修饰和重塑，包括从聚糖部分的甘露糖1（Man1）和甘露糖2（Man2）添加并随后去除磷酸乙醇胺（EtNP）。从Man1上去除EtNP由Cdc1p催化，这一事件以前被认为发生在内质网（ER）中。我们确定Cdc1p实际上是一种/高尔基体中间膜蛋白，它依赖于COPI衣被蛋白复合物保留在这个细胞器中。我们还确定Cdc1p不会在高尔基体和内质网之间循环，与此发现一致，当以内源水平表达时，内质网定位的Cdc1p-HDEL无法支持细胞生长。我们的温度敏感等位基因在典型的GPI-AP-Gas1p向细胞表面的转运中存在缺陷，我们认为这一发现揭示了一种新的高尔基体定位的质量控制保证。因此，酵母细胞在内质网和高尔基体中都对GPI-APs进行检查，其中从Man2（通过内质网中的Ted1p）和Man1（通过高尔基体中的Cdc1p）去除EtNP作为一种质量保证信号。
