Department of Neurology and 2 Department of Biochemistry I, University of Göttingen, 37073 Göttingen, Germany.
J Cell Biol. 2011 Jul 11;194(1):49-60. doi: 10.1083/jcb.201010117.
Posttranslational modification of proteins by attachment of small ubiquitin-related modifier (SUMO) contributes to numerous cellular phenomena. Sumoylation sometimes creates and abolishes binding interfaces, but increasing evidence points to another role for sumoylation in promoting the solubility of aggregation-prone proteins. Using purified α-synuclein, an aggregation-prone protein implicated in Parkinson's disease that was previously reported to be sumoylated upon overexpression, we compared the aggregation kinetics of unmodified and modified α-synuclein. Whereas unmodified α-synuclein formed fibrils, modified α-synuclein remained soluble. The presence of as little as 10% sumoylated α-synuclein was sufficient to delay aggregation significantly in vitro. We mapped SUMO acceptor sites in α-synuclein and showed that simultaneous mutation of lysines 96 and 102 to arginine significantly impaired α-synuclein sumoylation in vitro and in cells. Importantly, this double mutant showed increased propensity for aggregation and cytotoxicity in a cell-based assay and increased cytotoxicity in dopaminergic neurons of the substantia nigra in vivo. These findings strongly support the model that sumoylation promotes protein solubility and suggest that defects in sumoylation may contribute to aggregation-induced diseases.
蛋白质的翻译后修饰通过连接小泛素相关修饰物（SUMO）来实现，这有助于许多细胞现象的发生。SUMO 修饰有时会创建和取消结合界面，但越来越多的证据表明，SUMO 修饰在促进易于聚集的蛋白质的可溶性方面具有另一种作用。我们使用纯化的α-突触核蛋白（一种先前报道在过表达时会发生 SUMO 修饰的、与帕金森病有关的易于聚集的蛋白质），比较了未经修饰和修饰的α-突触核蛋白的聚集动力学。未修饰的α-突触核蛋白形成纤维，而修饰的α-突触核蛋白保持可溶性。即使只有 10%的 SUMO 修饰的α-突触核蛋白存在，也足以显著延迟体外聚集。我们在α-突触核蛋白中定位了 SUMO 接受位点，并表明同时将赖氨酸 96 和 102 突变为精氨酸，会显著损害α-突触核蛋白在体外和细胞中的 SUMO 修饰。重要的是，这种双突变体在基于细胞的测定中显示出更高的聚集倾向和细胞毒性，并且在体内黑质多巴胺能神经元中显示出更高的细胞毒性。这些发现强烈支持 SUMO 修饰促进蛋白质可溶性的模型，并表明 SUMO 修饰缺陷可能导致聚集诱导疾病。
