Role of deubiquitinating enzymes (DUBs) in Protein trafficking

真核细胞内化细胞表面蛋白的命运是由它们的泛素化程度决定的。在胞吞途径中泛素化依赖性分选的机制将以酵母abc转运蛋白Ste6为模型蛋白进行更密切的研究。在早期内体水平，泛素化的Ste6被分类到溶酶体/空泡途径降解，而未泛素化的Ste6被循环回细胞表面。在之前的实验中，我们发现非泛素化Ste6的再循环依赖于分选连接蛋白（Snx） 4和单体网格蛋白接头Gga2。我们的目标将是研究在Ste6泛素化依赖的分类中，分类连接蛋白、网格蛋白接头和网格蛋白是如何合作的。我们将定义Ste6中的循环信号，并寻找与这些信号相互作用的蛋白质。当然，分选连接蛋白和网格蛋白接头是这种分析的主要候选者。分选连接蛋白在以管为基础的内体分选中的作用现在变得越来越清楚。然而，目前尚不清楚有多少不同的分选途径在早期内体水平上起作用，以及货物是如何被特异性识别的。我们建立了一个工作模型，整合了大多数关于Ste6和其他酵母膜蛋白分类的已知数据。这个模型将通过不同的实验进行检验。

The fate of internalized cell surface proteins in eukaryotic cells is determined by their degree of ubiquitination. The mechanisms underlying ubiquitination-dependent sorting in the endocytic pathway will be examined more closely using the yeast ABC-transporter Ste6 as a model protein. At the level of early endosomes, ubiquitinated Ste6 is sorted into the lysosomal/vacuolar pathway for degradation, while non-ubiquitinated Ste6 is recycled back to the cell surface. In previous experiments, we found that recycling of non-ubiquitinated Ste6 is dependent on sorting nexin (Snx) 4 and on the monomeric clathrin adaptor Gga2. Our goal will be to examine how sorting nexins, clathrin adaptors and clathrin cooperate in ubiquitination-dependent sorting of Ste6. We will define recycling signals in Ste6 and look for proteins interacting with these signals. Of course, sorting nexins and clathrin adaptors are prime candidates for this analysis. The role of sorting nexins in tubular-based endosomal sorting is now becoming increasingly clear. At present, however, it is unclear how many distinct sorting pathways operate at the level of early endosomes and how cargo is specifically recognized. We established a working model that integrates most of the known data about the sorting of Ste6 and other yeast membrane proteins. This model will be tested by different experiments.