Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA.
Cell. 2020 Apr 16;181(2):325-345.e28. doi: 10.1016/j.cell.2020.03.046.
The mechanisms underlying ribonucleoprotein (RNP) granule assembly, including the basis for establishing and maintaining RNP granules with distinct composition, are unknown. One prominent type of RNP granule is the stress granule (SG), a dynamic and reversible cytoplasmic assembly formed in eukaryotic cells in response to stress. Here, we show that SGs assemble through liquid-liquid phase separation (LLPS) arising from interactions distributed unevenly across a core protein-RNA interaction network. The central node of this network is G3BP1, which functions as a molecular switch that triggers RNA-dependent LLPS in response to a rise in intracellular free RNA concentrations. Moreover, we show that interplay between three distinct intrinsically disordered regions (IDRs) in G3BP1 regulates its intrinsic propensity for LLPS, and this is fine-tuned by phosphorylation within the IDRs. Further regulation of SG assembly arises through positive or negative cooperativity by extrinsic G3BP1-binding factors that strengthen or weaken, respectively, the core SG network.
核糖核蛋白 (RNP) 颗粒组装的机制尚不清楚，包括建立和维持具有不同成分的 RNP 颗粒的基础。一种突出的 RNP 颗粒是应激颗粒 (SG)，这是真核细胞在应激反应中形成的动态且可逆的细胞质组装。在这里，我们表明 SG 通过液-液相分离 (LLPS) 组装，这种分离源自核心蛋白-RNA 相互作用网络中不均匀分布的相互作用。该网络的中心节点是 G3BP1，它作为分子开关，在细胞内游离 RNA 浓度升高时，触发 RNA 依赖性 LLPS。此外，我们表明，G3BP1 中三个不同的无规卷曲区域 (IDR) 之间的相互作用调节其内在的 LLPS 倾向，并且这可以通过 IDR 内的磷酸化来精细调节。SG 组装的进一步调节是通过外在的 G3BP1 结合因子的正或负协同作用产生的，这些因子分别增强或削弱核心 SG 网络。
