Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 201210, China.
University of the Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China.
Proc Natl Acad Sci U S A. 2020 Dec 8;117(49):31123-31133. doi: 10.1073/pnas.2002437117. Epub 2020 Nov 23.
Membraneless organelles contain a wide spectrum of molecular chaperones, indicating their important roles in modulating the metastable conformation and biological function of membraneless organelles. Here we report that class I and II Hsp40 (DNAJ) proteins possess a high ability of phase separation rendered by the flexible G/F-rich region. Different Hsp40 proteins localize in different membraneless organelles. Specifically, human Hdj1 (DNAJB1), a class II Hsp40 protein, condenses in ubiquitin (Ub)-rich nuclear bodies, while Hdj2 (DNAJA1), a class I Hsp40 protein, condenses in nucleoli. Upon stress, both Hsp40 proteins incorporate into stress granules (SGs). Mutations of the G/F-rich region not only markedly impaired Hdj1 phase separation and SG involvement and disrupted the synergistic phase separation and colocalization of Hdj1 and fused in sarcoma (FUS) in cells. Being cophase separated with FUS, Hdj1 stabilized the liquid phase of FUS against proceeding into amyloid aggregation in vitro and alleviated abnormal FUS aggregation in cells. Moreover, Hdj1 uses different domains to chaperone FUS phase separation and amyloid aggregation. This paper suggests that phase separation is an intrinsic property of Hsp40 proteins, which enables efficient incorporation and function of Hsp40 in membraneless organelles and may further mediate the buildup of chaperone network in membraneless organelles.
无膜细胞器包含广泛的分子伴侣，表明它们在调节无膜细胞器的亚稳态构象和生物学功能方面发挥着重要作用。在这里，我们报告说，I 类和 II 类 Hsp40（DNAJ）蛋白具有由柔性 G/F 丰富区域赋予的高相分离能力。不同的 Hsp40 蛋白定位于不同的无膜细胞器中。具体而言，人类 Hdj1（DNAJB1），一种 II 类 Hsp40 蛋白，凝聚在富含泛素（Ub）的核体内，而 Hdj2（DNAJA1），一种 I 类 Hsp40 蛋白，凝聚在核仁中。在应激下，两种 Hsp40 蛋白都被纳入应激颗粒（SGs）。G/F 丰富区域的突变不仅显著削弱了 Hdj1 的相分离和 SG 参与，并破坏了 Hdj1 和融合肉瘤（FUS）在细胞中的协同相分离和共定位。与 FUS 共相分离，Hdj1 稳定了 FUS 的液相，防止其在体外进行淀粉样聚集，并减轻了细胞中异常 FUS 聚集。此外，Hdj1 使用不同的结构域来伴侣 FUS 的相分离和淀粉样聚集。本文表明，相分离是 Hsp40 蛋白的固有特性，这使得 Hsp40 在无膜细胞器中的有效掺入和功能成为可能，并可能进一步介导无膜细胞器中伴侣网络的构建。
