Aberrant liquid-to-solid phase transitions of biomolecular condensates have been linked to various neurodegenerative diseases. However, the underlying molecular interactions that drive aging remain enigmatic. Here, we develop quantitative time-resolved crosslinking mass spectrometry to monitor protein interactions and dynamics inside condensates formed by the protein fused in sarcoma (FUS). We identify misfolding of the RNA recognition motif (RRM) of FUS as a key driver of condensate ageing. We demonstrate that the small heat shock protein HspB8 partitions into FUS condensates via its intrinsically disordered domain and prevents condensate hardening via condensate-specific interactions that are mediated by its α-crystallin domain (αCD). These αCD-mediated interactions are altered in a disease-associated mutant of HspB8, which abrogates the ability of HspB8 to prevent condensate hardening. We propose that stabilizing aggregation-prone folded RNA-binding domains inside condensates by molecular chaperones may be a general mechanism to prevent aberrant phase transitions.

中文翻译：

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HspB8 通过陪伴其折叠的 RNA 结合域来防止 FUS 的异常相变

生物分子凝聚物的异常液固相变与各种神经退行性疾病有关。然而，驱动衰老的潜在分子相互作用仍然是个谜。在这里，我们开发了定量时间分辨交联质谱来监测蛋白质相互作用和由肉瘤 (FUS) 中融合的蛋白质形成的凝聚物内的动力学。我们确定 FUS 的 RNA 识别基序 (RRM) 的错误折叠是冷凝物老化的关键驱动因素。我们证明小热休克蛋白 HspB8 通过其固有的无序结构域划分为 FUS 冷凝物，并通过其 α-晶状体蛋白结构域 (αCD) 介导的冷凝物特异性相互作用防止冷凝物硬化。这些 αCD 介导的相互作用在 HspB8 的疾病相关突变体中发生了改变，这消除了 HspB8 防止冷凝物硬化的能力。我们建议通过分子伴侣稳定缩合物内易于聚集的折叠 RNA 结合域可能是防止异常相变的一般机制。