Biomolecules can be sequestered into membrane-less compartments, referred to as biomolecular condensates. Experimental and computational methods have helped define the physical-chemical properties of condensates. Less is known about how the high macromolecule concentrations in condensed phases contribute “solvent” interactions that can remodel the free-energy landscape of other condensate-resident proteins, altering thermally accessible conformations and, in turn, modulating function. Here, we use solution NMR spectroscopy to obtain atomic resolution insights into the interactions between the immature form of superoxide dismutase 1 (SOD1), which can mislocalize and aggregate in stress granules, and the RNA-binding protein CAPRIN1, a component of stress granules. NMR studies of CAPRIN1:SOD1 interactions, focused on both unfolded and folded SOD1 states in mixed phase and demixed CAPRIN1-based condensates, establish that CAPRIN1 shifts the SOD1 folding equilibrium toward the unfolded state through preferential interactions with the unfolded ensemble, with little change to the structure of the folded conformation. Key contacts between CAPRIN1 and the H80-H120 region of unfolded SOD1 are identified, as well as SOD1 interaction sites near both the arginine-rich and aromatic-rich regions of CAPRIN1. Unfolding of immature SOD1 in the CAPRIN1 condensed phase is shown to be coupled to aggregation, while a more stable zinc-bound, dimeric form of SOD1 is less susceptible to unfolding when solvated by CAPRIN1. Our work underscores the impact of the condensate solvent environment on the conformational states of resident proteins and supports the hypothesis that ALS mutations that decrease metal binding or dimerization function as drivers of aggregation in condensates.

中文翻译：

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驱动 CAPRIN1 缩合物中 SOD1 展开的溶剂相互作用的原子分辨率图


生物分子可以被隔离在无膜隔室中，称为生物分子凝聚物。实验和计算方法有助于定义冷凝物的物理化学性质。人们对凝聚相中的高大分子浓度如何促进“溶剂”相互作用知之甚少，这种相互作用可以重塑其他凝聚态蛋白质的自由能景观，改变热可接近的构象，进而调节功能。在这里，我们使用溶液核磁共振波谱来获得原子分辨率的见解，以了解未成熟形式的超氧化物歧化酶 1 (SOD1) 与 RNA 结合蛋白 CAPRIN1（应激颗粒的一个组成部分）之间的相互作用，超氧化物歧化酶 1 (SOD1) 可能在应激颗粒中错误定位和聚集。 CAPRIN1:SOD1 相互作用的 NMR 研究，重点关注混合相中的未折叠和折叠 SOD1 状态以及基于 CAPRIN1 的分层缩合物，确定 CAPRIN1 通过与未折叠整体的优先相互作用，将 SOD1 折叠平衡向未折叠状态转变，几乎没有改变折叠构象的结构。确定了 CAPRIN1 和未折叠 SOD1 的 H80-H120 区域之间的关键接触，以及 CAPRIN1 富含精氨酸和富含芳香族区域附近的 SOD1 相互作用位点。 CAPRIN1 凝聚相中未成熟 SOD1 的解折叠与聚集相关，而更稳定的锌结合二聚体形式的 SOD1 在被 CAPRIN1 溶剂化时不易解折叠。我们的工作强调了冷凝液溶剂环境对常驻蛋白构象状态的影响，并支持这样的假设：减少金属结合或二聚化的 ALS 突变是冷凝液中聚集的驱动因素。