Abstract：
Alpha-synuclein (a-Syn) is a presynaptic protein, the misfolding of which is associated with Parkinson\'s disease. Rab GTPases are small guanine nucleotide binding proteins that play key roles in vesicle trafficking and have been associated with a-Syn function and dysfunction. a-Syn is enriched on synaptic vesicles, where it has been reported to interact with GTP-bound Rab3a, a master regulator of synaptic vesicle trafficking. a-Syn is known to bind weakly to Rab8a in solution via a positively charged patch, but the physiological implications of such interactions have not been explored. Here, we investigate direct interactions between a-Syn and Rab3a in solution and on lipid membranes using NMR spectroscopy. We find that the C terminus of a-Syn interacts with Rab3a in a manner similar to its previously reported interaction with Rab8a. While weak in solution, we demonstrate that this interaction becomes stronger when the proteins are bound to a membrane surface. The Rab3a binding site for a-Syn is similar to the surface that contacts the Rab3a effector rabphilin-3A, which modulates the enzymatic activity of Rab3a. Accordingly, we show that a-Syn inhibits GTP hydrolysis by Rab3a and that inhibition is more potent on the membrane surface, suggesting that their interaction may be functionally relevant. Finally, we show that phosphorylation of a-Syn residue Ser 129, a modification associated with Parkinson\'s disease pathology, enhances its interactions with Rab3a and increases its ability to inhibit Rab3a GTP hydrolysis. These results represent the first observation of a functional role for synuclein-Rab interactions and for a-Syn Ser 129 phosphorylation.
摘要：
α-突触核蛋白（a-Syn）是一种突触前蛋白，其中的错误折叠与帕金森病有关。RabGTP酶是小鸟嘌呤核苷酸结合蛋白，在囊泡运输中起关键作用，并与a-Syn功能和功能障碍有关。a-Syn富含突触小泡，据报道，它与GTP结合的Rab3a相互作用，突触小泡运输的主要调节因子。已知a-Syn通过带正电荷的贴片与溶液中的Rab8a弱结合，但是这种相互作用的生理意义尚未被探索。这里,我们使用NMR光谱研究了溶液中和脂质膜上的a-Syn和Rab3a之间的直接相互作用。我们发现a-Syn的C末端与Rab3a的相互作用方式类似于先前报道的与Rab8a的相互作用。虽然溶液很弱，我们证明，当蛋白质结合到膜表面时，这种相互作用变得更强。a-Syn的Rab3a结合位点与接触Rab3a效应rabphilin-3A的表面相似，其调节Rab3a的酶活性。因此，我们表明，a-Syn抑制GTP水解Rab3a和抑制是更有效的膜表面，这表明它们的相互作用可能在功能上相关。最后,我们显示a-Syn残基Ser129的磷酸化，一种与帕金森病病理相关的修饰，增强其与Rab3a的相互作用并增强其抑制Rab3aGTP水解的能力。这些结果代表了对突触核蛋白-Rab相互作用和a-SynSer129磷酸化的功能作用的首次观察。
