Serine-129 phosphorylation of a-synuclein is an activity-dependent trigger for physiologic protein-protein interactions and synaptic function

Phosphorylation of a-synuclein at the Serine-129 site (a-syn Ser129P) is an established pathologic hallmark of synucleinopathies and a therapeutic target. In physiologic states, only a small fraction of a-syn is phosphorylated at this site, and most studies have focused on the pathologic roles of this post-translational modification. We found that unlike wild-type (WT) a-syn which is widely expressed throughout the brain, the overall pattern of a-syn Ser129P is restricted, suggesting intrinsic regulation. Surprisingly, preventing Ser129P blocked activity-dependent synaptic attenuation by a-syn – thought to reflect its normal function. Exploring mechanisms, we found that neuronal activity augments Ser129P, which is a trigger for protein-protein interactions that are necessary for mediating a-syn function at the synapse. AlphaFold2-driven modeling and membrane-binding simulations suggest a scenario where Ser129P induces conformational changes that facilitate interactions with binding partners. Our experiments offer a new conceptual platform for investigating the role of Ser129 in synucleinopathies, with implications for drug-development.α-突触核蛋白（α-synuclein）在丝氨酸129位点的磷酸化（α-syn Ser129P）是突触核蛋白病公认的病理标志，同时也是治疗靶点。在生理状态下，仅有少量α-突触核蛋白在此位点发生磷酸化，既往多数研究均聚焦于该翻译后修饰的病理作用。我们的研究发现，与在全脑广泛表达的野生型（WT）α-突触核蛋白不同，α-syn Ser129P的整体分布模式具有局限性，提示其存在内在调控机制。令人意外的是，阻断Ser129位点磷酸化可阻断α-突触核蛋白介导的活动依赖性突触衰减——这一过程此前被认为是α-突触核蛋白的正常生理功能。在探索其作用机制的过程中，我们发现神经元活动可增强Ser129位点磷酸化，而该修饰可作为触发蛋白质相互作用的诱因，而这些相互作用正是α-突触核蛋白在突触处发挥功能所必需的。AlphaFold2驱动的建模与膜结合模拟实验提示，Ser129位点磷酸化可诱导构象变化，进而促进其与结合伴侣发生相互作用。本研究为探究Ser129在突触核蛋白病中的作用提供了全新的概念研究平台，同时对药物开发具有重要指导意义。