Viscoadaptation Controls Diffusion and Intracellular Reaction Rates in Response to Heat and Energy Availability

Abstract

Cells must precisely orchestrate thousands of reactions in both time and space. Yet reaction kinetics are highly dependent on uncontrollable environmental conditions such as temperature and energy availability. Here, we uncover a mechanism by which budding yeast counteract these environmental fluctuations by modulating viscosity to control the rate of cellular processes. This “viscoadaptation” is achieved via two carbohydrates, trehalose and glycogen, whose regulated production varies the viscosity of the intracellular environment, slowing the motion of individual proteins while maintaining their solubility. Viscoadaptation functions as both an acute stress response and a homeostatic mechanism, allowing cells growing from 22°C to 40°C to maintain constant rates of intracellular diffusion and diffusion-controlled chemical reactions. Multiple conditions that lower ATP trigger viscoadaptation, linking energy availability to reaction rate control. Viscoadaptation reveals viscosity to be a tunable property by which cells regulate diffusion-controlled processes dynamically in response to a changing environment.