The chemistry and physics of cellular shutdown: unraveling how and why cells enter into a hypometabolic state
Biophysics
Final Report Abstract
Single-celled organisms such as Saccharomyces cerevisiae are frequently exposed to unfavorable environmental conditions. The ability of these organisms to effectively respond to stressful conditions is fundamental for their survival. As a response to unfavorable conditions such as starvation cells often enter into a dormant state. This dormant state is characterized by downregulated metabolism, changes in protein synthesis and alterations in the dynamics of the cytoplasm. However, how cells enter into and recover from a dormant state is still poorly understood. In this project, we studied dormancy in "Saccharomyces cerevisiae" and other single-celled organism and found it to be associated with a significant decrease in the mobility of organelles and foreign tracer particles. We showed that this reduced mobility is caused by an influx of protons and a marked acidification of the cytoplasm, which leads to widespread higher-order assembly of proteins and triggers a transition of the cytoplasm to a solid-like state with increased mechanical stability. We further demonstrated that this transition is required for cellular survival under conditions of starvation. These findings create a new view of the cytoplasm as an adaptable fluid that can reversibly transition into a protective solid-like state. We next went on to study the function of these higher order assemblies that form in the cytoplasm starved cells. We focused on assemblies that regulate the process of protein synthesis, which is one of the major energy-consuming processes in starved cells. We found that the essential translation initiation factor eIF2B forms filaments in starved budding yeast cells. Filamentation was triggered by starvation-induced acidification of the cytosol, which was caused by an influx of protons from the extracellular environment. We showed that filament assembly by eIF2B is necessary for rapid and efficient downregulation of translation. Importantly, this mechanism did not require the kinase Gcn2. Furthermore, analysis of site-specific variants of eIF2B suggested that eIF2B assembly resulted in enzymatically inactive filaments that promoted stress survival and fast recovery of cells from starvation. We propose that translation regulation through protein assembly is a widespread mechanism that allows cells to enter into a dormant state and adapt to fluctuating environments.
Publications
- Adaptive reorganization of the cytoplasm upon stress in budding yeast
G. Marini, E. Nüske, W. Leng, S. Alberti, G Pigino
(See online at https://doi.org/10.1101/468454) - Filament formation by the translation factor eIF2B regulates protein synthesis in starved cells
E. Nüske, G. Marini, D. Richter, W. Leng, A. Bogdanova, T. M. Franzmann, G. Pigino, S. Alberti
(See online at https://doi.org/10.1101/467829) - (2016). A pH-driven transition of the cytoplasm from a fluid- to a solid-like state promotes entry into dormancy. eLife, 5:e09347
M. C. Munder, D. Midtvedt, T. Franzmann, E. Nüske, O. Otto, M. Herbig, E. Ulbricht, P. Müller, A. Taubenberger, S. Maharana, L. Malinovska, D. Richter, J. Guck, V. Zaburdaev, S. Alberti
(See online at https://doi.org/10.7554/eLife.09347) - (2017). Cell adaptation upon stress: the emerging role of membrane-less compartments. Current Opinions in Cell Biology, 47, 34-42
C. Rabouille and S. Alberti
(See online at https://doi.org/10.1016/j.ceb.2017.02.006) - (2018). Phase separation of a yeast prion protein promotes cellular fitness. Science, 359, eaao5654
T. M. Franzmann, M. Jahnel, A. Pozniakovsky, J. Mahamid, A. S. Holehouse, E. Nüske, D. Richter, W. Baumeister, S. W. Grill, R. V. Pappu, A. A. Hyman, S. Alberti
(See online at https://doi.org/10.1126/science.aao5654) - Different Material States of Pub1 Condensates Define Distinct Modes of Stress Adaptation and Recovery (2018). Cell Reports, 23(11) 3327-3339
S. Kroschwald, M. C. Munder, S. Maharana, T. Franzmann, D. Richter, M. Ruer, A. Hyman, S. Alberti
(See online at https://doi.org/10.1016/j.celrep.2018.05.041)
