Matic Ivan, Macek Boris, Hilger Maximiliane, Walther Tobias C, Mann Matthias
Department of Proteomics and Signal Transduction, Max Planck Institute for Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany.
J Proteome Res. 2008 Sep;7(9):4050-7. doi: 10.1021/pr800368m. Epub 2008 Aug 16.
Protein dynamics is regulated by an elaborate interplay between different post-translational modifications. Ubiquitin and ubiquitin-like proteins (Ubls) are small proteins that are covalently conjugated to target proteins with important functional consequences. One such modifier is SUMO, which mainly modifies nuclear proteins. SUMO contains a unique N-terminal arm not present in ubiquitin and other Ubls, which functions in the formation of SUMO polymers. Here, we unambiguously show that serine 2 of the endogenous SUMO-1 N-terminal protrusion is phosphorylated in vivo using very high mass accuracy mass spectrometry at both the MS and the MS/MS level and complementary fragmentation techniques. Strikingly, we detected the same phosphorylation in yeast, Drosophila and human cells, suggesting an evolutionary conserved function for this modification. The nearly identical human SUMO-2 and SUMO-3 isoforms differ in serine 2; thus, only SUMO-3 could be phosphorylated at this position. Our finding that SUMO can be modified may point to an additional level of complexity through modifying a protein-modifier.
蛋白质动力学受不同翻译后修饰之间复杂的相互作用调控。泛素和类泛素蛋白（Ubls）是小蛋白，它们与靶蛋白共价结合，具有重要的功能影响。其中一种修饰因子是SUMO，它主要修饰核蛋白。SUMO含有一个泛素和其他Ubls中不存在的独特N端臂，其在SUMO聚合物形成中起作用。在此，我们使用非常高质量精度的质谱仪在MS和MS/MS水平以及互补碎裂技术，明确表明内源性SUMO-1 N端突出部分的丝氨酸2在体内被磷酸化。引人注目的是，我们在酵母、果蝇和人类细胞中检测到相同的磷酸化，表明这种修饰具有进化保守功能。几乎相同的人类SUMO-2和SUMO-3亚型在丝氨酸2上存在差异；因此，只有SUMO-3能在此位置被磷酸化。我们发现SUMO可以被修饰，这可能通过修饰一种蛋白修饰因子指向了一个额外的复杂层面。
