Polo Simona, Sigismund Sara, Faretta Mario, Guidi Monica, Capua Maria Rosaria, Bossi Giovanna, Chen Hong, De Camilli Pietro, Di Fiore Pier Paolo
Department of Experimental Oncology, European Institute of Oncology, Via Ripamonti 435, 20141, Milan, Italy.
Nature. 2002 Mar 28;416(6879):451-5. doi: 10.1038/416451a.
Ubiquitination is a post-translation modification in which ubiquitin chains or single ubiquitin molecules are appended to target proteins, giving rise to poly- or monoubiquitination, respectively. Polyubiquitination targets proteins for destruction by the proteasome. The role of monoubiquitination is less understood, although a function in membrane trafficking is emerging, at least in yeast. Here we report that a short amino-acid stretch at the carboxy-termini of the monoubiquitinated endocytic proteins Eps15 and eps15R is indispensable for their monoubiquitination. A similar sequence, also required for this modification, is found in other cytosolic endocytic proteins, such as epsins and Hrs. These sequences comprise a protein motif, UIM (ref. 6), which has been proposed to bind to ubiquitin. We confirm this for the UIMs of eps15, eps15R, epsins and Hrs. Thus, the same motif in several endocytic proteins is responsible for ubiquitin recognition and monoubiquitination. Our results predict the existence of a UIM:ubiquitin-based intracellular network. Eps15/eps15R, epsins and Hrs may function as adaptors between ubiquitinated membrane cargo and either the clathrin coat or other endocytic scaffolds. In addition, through their own ubiquitination, they may further contribute to the amplification of this network in the endocytic pathway.
泛素化是一种翻译后修饰，其中泛素链或单个泛素分子被附加到靶蛋白上，分别产生多泛素化或单泛素化。多泛素化将蛋白质靶向蛋白酶体进行降解。单泛素化的作用尚不太清楚，尽管至少在酵母中，其在膜运输中的功能正在显现。在这里，我们报告单泛素化的内吞蛋白Eps15和eps15R的羧基末端的短氨基酸片段对其单泛素化是必不可少的。在其他胞质内吞蛋白如epsin和Hrs中也发现了这种修饰所需的类似序列。这些序列包含一个蛋白质基序，即泛素相互作用基序（UIM，参考文献6），有人提出它可与泛素结合。我们证实了eps15、eps15R、epsin和Hrs的UIM确实如此。因此，几种内吞蛋白中的相同基序负责泛素识别和单泛素化。我们的结果预示着存在一个基于UIM：泛素的细胞内网络。Eps15/eps15R、epsin和Hrs可能作为泛素化膜货物与网格蛋白包被或其他内吞支架之间的衔接蛋白发挥作用。此外，通过自身的泛素化，它们可能进一步促进该网络在内吞途径中的扩增。
