Yang Zhi, Haakonsen Diane L, Heider Michael, Witus Samuel R, Zelter Alex, Beschauner Tobias, MacCoss Michael J, Rapé Michael
Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA, USA.
Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA, USA.
Nature. 2025 May 6. doi: 10.1038/s41586-025-09074-z.
Chronic stress response activation impairs cell survival and causes devastating degenerative diseases. Organisms accordingly deploy silencing factors, such as the E3 ubiquitin ligase silencing factor of the integrated stress response (SIFI), to terminate stress response signalling and ensure cellular homeostasis. How a silencing factor can sense stress across cellular scales to elicit timely stress response inactivation is poorly understood. Here we combine cryo-electron microscopy analysis of endogenous SIFI with AlphaFold modelling and biochemical studies to report the structural and mechanistic basis of the silencing of the integrated stress response. SIFI detects both stress indicators and stress response components through flexible domains within an easily accessible scaffold, before building linkage-specific ubiquitin chains at separate, sterically restricted elongation modules. Ubiquitin handover by a ubiquitin-like domain couples versatile substrate modification to linkage-specific ubiquitin polymer formation. Stress response silencing therefore exploits a catalytic mechanism that is geared towards processing many diverse proteins and therefore allows a single enzyme to monitor and, if needed, modulate a complex cellular state.
慢性应激反应激活会损害细胞存活并导致毁灭性的退行性疾病。因此，生物体部署了沉默因子，如综合应激反应的E3泛素连接酶沉默因子（SIFI），以终止应激反应信号并确保细胞内稳态。目前人们对沉默因子如何在细胞尺度上感知应激以引发及时的应激反应失活知之甚少。在这里，我们将内源性SIFI的冷冻电子显微镜分析与AlphaFold建模和生化研究相结合，以报告综合应激反应沉默的结构和机制基础。SIFI通过一个易于接近的支架内的柔性结构域检测应激指标和应激反应成分，然后在单独的、空间受限的延伸模块上构建连接特异性泛素链。一个类泛素结构域的泛素传递将通用的底物修饰与连接特异性泛素聚合物形成耦合起来。因此，应激反应沉默利用了一种催化机制，该机制旨在处理多种不同的蛋白质，从而使单一酶能够监测并在需要时调节复杂的细胞状态。
