Department of Biochemistry, University of Geneva, Sciences II, 30 quai Ernest-Ansermet, CH-1211 Geneva, Switzerland.
Traffic. 2010 Aug;11(8):1017-33. doi: 10.1111/j.1600-0854.2010.01081.x. Epub 2010 May 11.
Previous studies have shown that yeast glycosylphosphatidylinositol-anchored proteins (GPI-APs) and other secretory proteins are preferentially incorporated into distinct coat protein II (COPII) vesicle populations for their transport from the endoplasmic reticulum (ER) to the Golgi apparatus, and that incorporation of yeast GPI-APs into COPII vesicles requires specific lipid interactions. We compared the ER exit mechanism and segregation of GPI-APs from other secretory proteins in mammalian and yeast cells. We find that, unlike yeast, ER-to-Golgi transport of GPI-APs in mammalian cells does not depend on sphingolipid synthesis. Whereas ER exit of GPI-APs is tightly dependent on Sar1 in mammalian cells, it is much less so in yeast. Furthermore, in mammalian cells, GPI-APs and other secretory proteins are not segregated upon COPII vesicle formation, in contrast to the remarkable segregation seen in yeast. These findings suggest that GPI-APs use different mechanisms to concentrate in COPII vesicles in the two organisms, and the difference might explain their propensity to segregate from other secretory proteins upon ER exit.
先前的研究表明，酵母糖基磷脂酰肌醇锚定蛋白（GPI-APs）和其他分泌蛋白优先被整合到不同的衣壳蛋白 II（COPII）小泡中，以便从内质网（ER）运输到高尔基体，并且酵母 GPI-APs 整合到 COPII 小泡中需要特定的脂质相互作用。我们比较了哺乳动物和酵母细胞中 GPI-APs 从其他分泌蛋白中分离出来的 ER 出口机制。我们发现，与酵母不同，哺乳动物细胞中 GPI-APs 的 ER 到高尔基体的运输不依赖于神经鞘脂的合成。虽然在哺乳动物细胞中，GPI-APs 的 ER 出口严格依赖于 Sar1，但在酵母中则不然。此外，在哺乳动物细胞中，GPI-APs 和其他分泌蛋白在 COPII 小泡形成时并未分离，与酵母中观察到的明显分离形成鲜明对比。这些发现表明，GPI-APs 在这两种生物中使用不同的机制来浓缩在 COPII 小泡中，这种差异可能解释了它们在 ER 出口时从其他分泌蛋白中分离出来的倾向。
