The aberrant aggregation of the presynaptic protein α-synuclein (α-syn) is a hallmark of synucleinopathies, which include Parkinson’s disease, dementia with Lewy bodies, and multiple system atrophy. Previous studies have suggested that α-syn can undergo liquid–liquid phase separation (LLPS) and transition from a liquid to a solid state, which contributes to aggregation and fibril formation. However, the factors that instigate α-syn LLPS have remained unclear. Now, Matsuo et al. have discovered that the cytoplasmic Ca²⁺ influx triggers the assembly of RNA G-quadruplexes (rG4s), which bind to α-syn and facilitate its LLPS and gelation.

The team also developed a light-induced assembly system called optoG4. This system includes an RNA component with rG4-forming repeats and MS2 RNA hairpin repeats, and a protein component that combines the MS2-binding protein MCP with mCherry and CRY2, a protein capable of oligomerization upon exposure to blue light. Using the optoG4 system, the team were able to control the formation and dissolution of rG4 condensates in cultured neurons and in mice. They observed that rG4 assembly led to the aggregation of endogenous α-syn and induced Parkinson’s disease-like phenotypes, such as neuron death and motor dysfunction. Furthermore, oral administration of 5-aminolevulinic acid, a prodrug of protoporphyrin IX that binds to rG4, reduced α-syn aggregation and alleviated Parkinson’s disease-like phenotypes in mice treated with α-syn preformed fibrils.

突触前蛋白 α-突触核蛋白 （α-syn） 的异常聚集是突触核蛋白病的标志，包括帕金森病、路易体痴呆和多系统萎缩。先前的研究表明，α-syn 可以经历液-液相分离 （LLPS） 并从液态转变为固态，这有助于聚集和原纤维形成。然而，引发 α-syn LLPS 的因素仍不清楚。现在，Matsuo 等人发现，细胞质 Ca²⁺ 内流触发了 RNA G 四链体 （rG4） 的组装，这些四链体与 α-syn 结合并促进其 LLPS 和凝胶化。

该团队还开发了一种名为 optoG4 的光诱导组装系统。该系统包括一个具有 rG4 形成重复序列和 MS2 RNA 发夹重复序列的 RNA 组分，以及一个将 MS2 结合蛋白 MCP 与 mCherry 和 CRY2 相结合的蛋白质组分，CRY2 是一种在蓝光下能够寡聚化的蛋白质。使用 optoG4 系统，该团队能够控制培养神经元和小鼠中 rG4 凝聚物的形成和溶解。他们观察到 rG4 组装导致内源性 α-syn 聚集并诱导帕金森病样表型，例如神经元死亡和运动功能障碍。此外，口服 5-氨基乙酰丙酸（一种与 rG4 结合的原卟啉 IX 的前药）减少了 α-syn 聚集并减轻了用 α-syn 预制原纤维治疗的小鼠的帕金森病样表型。