Raiborg Camilla, Wesche Jørgen, Malerød Lene, Stenmark Harald
Department of Biochemistry, Institute for Cancer Research, The Norwegian Radium Hospital and The University of Oslo, Montebello, N-0310 Oslo, Norway.
J Cell Sci. 2006 Jun 15;119(Pt 12):2414-24. doi: 10.1242/jcs.02978. Epub 2006 May 23.
Endocytosed membrane proteins that are destined for degradation in lysosomes are ubiquitylated and recognised by sorting complexes on endosome membranes. The ubiquitin-binding sorting component Hrs as well as ubiquitylated cargo are enriched in a characteristic flat clathrin coat on the endosome membrane. The function of clathrin within this coat has not been investigated. Here, we show that both clathrin and the clathrin-box motif of Hrs are required for the clustering of Hrs into restricted microdomains. The C-terminus of Hrs, which contains the clathrin-box, is sufficient to redirect a phosphatidylinositol(3)-phosphate-binding protein into the Hrs- and clathrin-containing microdomains. Although these microdomains show little lateral diffusion in the membrane, they are dynamic structures that exchange Hrs and clathrin with similar kinetics, and acquire the downstream sorting component Tsg101. The clathrin-mediated clustering is essential for the function of Hrs in degradative protein sorting. We conclude that clathrin is responsible for concentrating Hrs in endosomal microdomains specialised for recognition of ubiquitylated membrane proteins, thus enabling efficient sorting of cargo into the degradative pathway.
注定要在溶酶体中降解的内吞膜蛋白会被泛素化，并被内体膜上的分选复合物识别。泛素结合分选成分Hrs以及泛素化的货物在内体膜上的特征性扁平网格蛋白包被中富集。网格蛋白在这个包被中的功能尚未得到研究。在这里，我们表明，网格蛋白和Hrs的网格蛋白盒基序都是将Hrs聚集到受限微结构域所必需的。Hrs的C末端包含网格蛋白盒，足以将磷脂酰肌醇(3)-磷酸结合蛋白重定向到含有Hrs和网格蛋白的微结构域中。尽管这些微结构域在膜中几乎没有横向扩散，但它们是动态结构，以相似的动力学交换Hrs和网格蛋白，并获得下游分选成分Tsg101。网格蛋白介导的聚集对于Hrs在降解性蛋白质分选中的功能至关重要。我们得出结论，网格蛋白负责将Hrs集中在内体微结构域中，这些微结构域专门用于识别泛素化膜蛋白，从而使货物能够有效地分选到降解途径中。
