盐浓度对FUS蛋白相分离的调控研究

Regulation Study of FUS Protein Phase Separation by Salt Concentration

摘要: 肉瘤融合蛋白(Fused in sarcoma, FUS)是来自异质核糖核蛋白家族的RNA结合蛋白。FUS在细胞内参与了DNA损伤修复，RNA剪接、转录、翻译等多种生理过程，这些过程与其生理条件下通过液液相分离(liquid-liquid phase separation, LLPS)形成的类液滴状无膜细胞结构密切相关。在这个过程中FUS通过LLPS形成的生理性液滴状结构可能会老化成为病理性的聚集体，如水凝胶、包涵体和淀粉样纤维等。并且这些病理性聚集体被发现与肌萎缩性侧索硬化症(Amyotrophic lateral sclerosis, ALS)、额颞叶变性(Frontotemporal lobe degeneration, FTLD)等多种神经退行性疾病相关。本文进一步研究了影响FUS发生LLPS和病理性沉淀的相关因素，我们发现FUS蛋白LLPS和形成病理性聚集体是蛋白质浓度依赖的。在低蛋白浓度下FUS不会发生相分离，随着蛋白浓度的升高FUS蛋白开始发生LLPS现象，但是当蛋白浓度继续升高时则会形成淀粉样纤维聚集体。值得注意的是，这个过程受到盐浓度的显著影响，无盐和低盐浓度下发生LLPS的FUS蛋白，却在中、高盐浓度时迅速形成病理性的不规则聚集体。在FUS蛋白的LLPS过程中随着时间的变化液滴会不断变大，液滴在不同溶液中的生长效率为：无盐 > KCl > NaCl。

Abstract: Fused in sarcoma (FUS) is an RNA-binding protein from the heterogeneous nuclear ribonucleoprotein family. FUS is involved in various physiological processes in cells, including DNA damage repair, RNA splicing, transcription, and translation. It is worth noting that during this process, these physiological droplets may age and transform into pathological aggregates, such as hydrogels, inclusions, and amyloid-like fibers. Moreover, pathological aggregates have been found to be associated with various neurodegenerative diseases like amyotrophic lateral sclerosis (ALS) and Frontotemporal lobe degeneration (FTLD). This study further investigates the factors influencing the occurrence of LLPS and pathological precipitation of FUS. We found that LLPS and the formation of pathological aggregates of FUS protein are dependent on protein concentration. Under low protein concentrations, FUS does not undergo phase separation; as the protein concentration increases, the FUS protein begins to exhibit liquid-liquid phase separation (LLPS), but with further increase in protein concentration, it will form amyloid-like fiber aggregates. It is worth noting that this process is significantly influenced by salt concentration. FUS protein undergoes LLPS at no or low salt concentrations, but rapidly forms pathological irregular aggregates at medium to high salt concentrations. Droplets continuously grow larger over time during the LLPS process of FUS protein. The growth efficiency of droplets in different solutions is: no salt > KCl > NaCl.