Phase separation as a survival strategy: stress protection by translation factor condensates

蛋白质凝聚的概念提供了一种新的方式来思考细胞如何感知压力并为生存做出适当的反应。到目前为止，我们的工作几乎没有触及这个新原理的表面，我们还没有了解它对理解压力反应以及生物进化和生态学的贡献。我们最近发现，酵母翻译因子Ded1p组装成冷凝物，以应对热应激。这使其解旋酶活性失活，从而促进从管家翻译到应激蛋白质生产的转换。然而，重要的问题仍然没有答案：Ded1p热诱导冷凝的分子事件是什么，具体的生理益处是什么？翻译因子的浓缩对调节热应激期间的翻译至关重要吗？如果是这样的话，除了Ded1p之外，还有哪些翻译因子通过热诱导凝聚组装？最近的证据表明，Ded1p在翻译起始过程中与翻译起始复合物eIF4F相互作用。与Ded1p一样，我们发现eIF4F以热依赖的方式组装成冷凝物。我们假设eIF4F通过缩合失活促进了翻译中的额外开关，其用于下调特定的mRNA组。因此，该工作计划的目的是揭示Ded1p和eIF4F形成热诱导冷凝物的分子事件，并确定与冷凝相关的自适应功能。更具体地说，我们将1）研究热诱导冷凝的分子事件，2）确定热敏性的关键氨基酸基序，并分析进化如何调整蛋白质冷凝到不同的热环境，3）研究冷凝物组装和拆卸如何调节，以及冷凝物动力学和性质如何影响应激反应，以及4）建立翻译因子缩合物的生理功能并确定缩合物如何促进应激存活。我们设想，这个研究项目将提供一个急需的更深入的分子热诱导冷凝的理解，从而为其他基本的细胞过程，如转录和信号的温度调节提供一个模板。

The concept of protein condensation provides a novel way to think about how cells sense stress and mount an appropriate response for survival. Work so far has barely touched the surface of this novel principle and we have yet to learn of the contributions it can make to understanding stress responses and the evolution and ecology of organisms. We recently showed that the yeast translation factor Ded1p assembles into condensates in response to heat stress. This inactivates its helicase activity thereby promoting a switch in translation from housekeeping to stress protein production. However, important questions remain unanswered: what are the molecular events underlying heat-induced condensation by Ded1p and what are the specific physiological benefits? Is the condensation of translation factors crucial for regulating translation during heat stress? And if so, which other translation factors besides Ded1p assemble by heat-induced condensation? Recent evidence suggests that Ded1p interacts with the translation initiation complex eIF4F during translation initiation. Like for Ded1p, we have found that eIF4F assembles into condensates in a heat-dependent manner. We hypothesize that eIF4F inactivation by condensation promotes an additional switch in translation which serves to downregulate specific sets of mRNAs. The purpose of the work program is therefore to uncover the molecular events underlying the formation of heat-induced condensates by Ded1p and eIF4F and to pinpoint the adaptive functions that are associated with condensation. More specifically, we will 1) study the molecular events underlying heat-induced condensation, 2) determine critical amino acid motifs underlying thermal sensitivity and analyze how evolution has tuned protein condensation to different thermal environments, 3) study how condensate assembly and disassembly is regulated and how condensate dynamics and properties affect the stress response, and 4) establish the physiological function of translation factor condensates and determine how condensation promotes stress survival. We envisage that this research project will provide a much-needed deeper molecular understanding of heat-induced condensation, thus providing a template for temperature regulation of other fundamental cellular processes such as transcription and signaling.