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Abstract：
Eukaryotic cells form condensates to sense and adapt to their environment [S. F. Banani, H. O. Lee, A. A. Hyman, M. K. Rosen, Nat. Rev. Mol. Cell Biol. 18, 285-298 (2017), H. Yoo, C. Triandafillou, D. A. Drummond, J. Biol. Chem. 294, 7151-7159 (2019)]. Poly(A)-binding protein (Pab1), a canonical stress granule marker, condenses upon heat shock or starvation, promoting adaptation [J. A. Riback et al., Cell 168, 1028-1040.e19 (2017)]. The molecular basis of condensation has remained elusive due to a dearth of techniques to probe structure directly in condensates. We apply hydrogen-deuterium exchange/mass spectrometry to investigate the mechanism of Pab1\'s condensation. Pab1\'s four RNA recognition motifs (RRMs) undergo different levels of partial unfolding upon condensation, and the changes are similar for thermal and pH stresses. Although structural heterogeneity is observed, the ability of MS to describe populations allows us to identify which regions contribute to the condensate\'s interaction network. Our data yield a picture of Pab1\'s stress-triggered condensation, which we term sequential activation (Fig. 1A), wherein each RRM becomes activated at a temperature where it partially unfolds and associates with other likewise activated RRMs to form the condensate. Subsequent association is dictated more by the underlying free energy surface than specific interactions, an effect we refer to as thermodynamic specificity. Our study represents an advance for elucidating the interactions that drive condensation. Furthermore, our findings demonstrate how condensation can use thermodynamic specificity to perform an acute response to multiple stresses, a potentially general mechanism for stress-responsive proteins.
摘要：
真核细胞形成凝聚体以感知和适应环境[S.F.Banani,H.O.Lee,A.A.海曼，M.K.Rosen,纳特。Rev.Mol.细胞生物。18,285-298(2017),H.Yoo,C.Triandafillou,D.A.德拉蒙德,J、生物。Chem.294,7151-7159（2019年）]。Poly(A)-结合蛋白(Pab1),典型的应力颗粒标记，在热休克或饥饿时凝结，促进适应[J.A.Riback等人。,168号牢房，1028-1040。e19(2017)]。由于缺乏直接在缩合物中探测结构的技术，缩合的分子基础仍然难以捉摸。我们应用氢-氘交换/质谱来研究Pab1的缩合机理。Pab1的四个RNA识别基序（RRM）在凝聚时经历不同水平的部分解折叠，对于热应力和pH值的变化是相似的。尽管观察到结构异质性，MS描述种群的能力使我们能够确定哪些区域对凝析油的相互作用网络有贡献。我们的数据显示了Pab1的应力触发冷凝，我们称之为顺序激活(图。1A),其中每个RRM在其部分展开并与其他同样活化的RRM缔合以形成冷凝物的温度下被活化。随后的缔合更多地取决于潜在的自由能表面，而不是特定的相互作用，我们称之为热力学特异性的效应。我们的研究代表了阐明驱动冷凝的相互作用的进步。此外，我们的研究结果证明了冷凝如何利用热力学特异性来对多种应力进行急性反应，一个潜在的一般机制的应激反应蛋白。
