Cellular stress sensing via biomolecular condensation

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Project Summary Background: Cells experience a wide array of environmental stresses, and must be able to sense and respond to changes in order to survive. The sensing process which occurs depends on the stress itself, and we have identified over 150 heat-sensitive proteins in S. cerevisiae which exhibit biomolecular condensation after temperature increase. Within this group, a conserved set of GTPases displays significant aggregation without the requirement of any other cellular components, opening up the possibility that these proteins have the ability to sense heat shock. Further, this set of proteins is connected to two fundamental functional responses which occur under heat stress -- transcriptional upregulation of heat shock genes and shutoff of ribosome biogenesis. Proteins that are highly sensitive to heat may act as long-unidentified sensors upstream of massive functional changes within the cell, and serve as heat sensing candidates for this proposal. Long viewed as a toxic consequence of harsh environmental conditions, recent work has shown that biomolecular condensate formation is non-random, adaptive, and reversible. With this emerging view, diseases like dementia and ALS which are associated with the accumulation of non-membrane bound protein aggregates might be the result of an aberrant activation of stress sensing pathways, indicating that our understanding of the disease pathology may need to be reevaluated. Specific Aims: 1: Are candidates sufficient to induce the transcriptional response in vivo? 2: What is the mechanism for heat sensing? 3: What is the functional relevance of candidate condensation on ribosome production? Study Design: I will take advantage of a cryophilic yeast which execute their heat-induced cellular responses at lower temperatures than S. cerevisiae. The cryophilic yeast likely contain homologous sensor proteins with increased sensitivity at lower temperatures. I will replace the endogenous sensor candidate genes with their cryophilic homologs and assay the ability of the recombinant S. cerevisiae to upregulate the production of heat- specific transcripts and attenuate ribosome biogenesis. I will reconstitute the components of these functional responses in vitro and test whether the condensation of candidate sensors can affect either response. Condensation of candidate sensors will also be studied in vitro using biochemical and biophysical assays to investigate their intrinsic ability to sense heat to describe the mechanistic underpinnings of sensing. Training: This research will be performed with Dr. D. Allan Drummond at the University of Chicago and will build upon my experimental skills by first characterizing the functional relevance of biomolecular condensation in environmental stress sensing and further expanding into understanding the biophysical mechanism. This training will prepare me for a future career studying how environmental stresses shape cellular behavior.