Macromolecular condensation buffers intracellular water potential.
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Abstract
Optimum protein function and biochemical activity critically depends on water availability because solvent thermodynamics drive protein folding and macromolecular interactions1. Reciprocally, macromolecules restrict the movement of 'structured' water molecules within their hydration layers, reducing the available 'free' bulk solvent and therefore the total thermodynamic potential energy of water, or water potential. Here, within concentrated macromolecular solutions such as the cytosol, we found that modest changes in temperature greatly affect the water potential, and are counteracted by opposing changes in osmotic strength. This duality of temperature and osmotic strength enables simple manipulations of solvent thermodynamics to prevent cell death after extreme cold or heat shock. Physiologically, cells must sustain their activity against fluctuating temperature, pressure and osmotic strength, which impact water availability within seconds. Yet, established mechanisms of water homeostasis act over much slower timescales2,3; we therefore postulated the existence of a rapid compensatory response. We find that this function is performed by water potential-driven changes in macromolecular assembly, particularly biomolecular condensation of intrinsically disordered proteins. The formation and dissolution of biomolecular condensates liberates and captures free water, respectively, quickly counteracting thermal or osmotic perturbations of water potential, which is consequently robustly buffered in the cytoplasm. Our results indicate that biomolecular condensation constitutes an intrinsic biophysical feedback response that rapidly compensates for intracellular osmotic and thermal fluctuations. We suggest that preserving water availability within the concentrated cytosol is an overlooked evolutionary driver of protein (dis)order and function.
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Acknowledgements: The order of the second and corresponding authors is arbitrary and these authors can change the order of their respective names to suit their own interests. This work has been supported by the Medical Research Council, as part of United Kingdom Research and Innovation (MC_UP_1201/13 to E.D.; MC_UP_1201/4 to J.S.O. and MCMB MR/V028669/1 to J.E.C.), the Human Frontier Science Program (Career Development Award CDA00034/2017 to E.D.), a Versus Arthritis Senior Research Fellowship Award (20875 to Q.-J.M.) and an MRC project grant (MR/K019392/1 to Q.-J.M.), a Grifols ‘ALTA’ Alpha-1-Antitrypsin Laurell’s Training Award and an Alpha-1-Foundation (grant number 614939) to J.E.C., and by a Wellcome Trust Sir Henry Dale Fellowship (208790/Z/17/Z to R.S.E.). N.M.R. is supported by a Medical Research Council Clinician Scientist Fellowship (MR/S022023/1). L.K.K. and V.J.P.-H. are recipients of EMBO Postdoctoral fellowships (ALTF 876-2021 and ALTF 577-2018, respectively). K.E.M. is supported by the Wellcome Trust through a Sir Henry Wellcome Postdoctoral Fellowship (220480/Z/20/Z). P.M.M. and J.B. were supported by Volkswagen ‘Life’ grant number 96827 and the DFG Excellence Cluster Physics of Life. We thank H. Andreas for frog maintenance; C. Godlee and M. Kaksonen for the gift of unpublished S. cerevisiae yeast strains and initial discussion of yeast experiments about temperature; P. Tran for S. pombe yeast strains; L. Miller for help with yeast work; A. Bertolotti for the kind gift of SH-SY5Y cells; and C. Russo, F. Jülicher, M. Gonzalez-Gaitan, K. Kruse, L. Blanchoin, J. Löwe, R. Hegde, P. Farrell and P. Crosby for discussion and suggestions; the staff at the companies Cherry Biotech and Elvesys, in particular T. Guérinier, for their help in designing and assembling the custom microfluidics system required for this project; the members of the Electronics and Mechanical workshops of the LMB for key support; the staff at the LMB Mass Spectrometry facility for performing and analysing MS data; and A. Prasad and T. Stevens for sharing the scripts for protein disorder and kinase motif predictions, respectively. Cartoons were created using BioRender. For the purpose of open access, the MRC Laboratory of Molecular Biology has applied a CC BY public copyright licence to any author accepted manuscript version arising.
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1476-4687
