Natural multi-osmolyte cocktails form deep eutectic systems of unprecedented complexity: discovery, affordances and perspectives

Abstract

While exaptation is most impressive when links between very dissimilar contexts are established, it can be even more pervasive when the previously unestablished connection seems surprisingly obvious in retrospect. We herein established such a connection between two major research fields previously advancing in parallel: osmolytes and deep eutectic solvents. Osmolytes are small molecules produced in cells as a response to external stimuli. Based on their individual interaction with macromolecules, single osmolytes are currently categorized as “kosmotropes” (stabilizing proteins) and “chaotropes” (destabilizing them). However, with two or more osmolytes, synergistic effects were also observed on top of cumulative ones. All current attempts to explain these synergistic effects have been studying osmolyte–osmolyte interactions in aqueous solutions, but none has been generally applicable so far, indicating that a new model “beyond kosmotropes and chaotropes” is needed to understand the function of osmolytes. We have gathered enough evidence to formulate a hypothesis of such a new model. First, inspired by patterns frequently observed in nature, five major stabilizing osmolytes (kosmotropes) prominent across kingdoms (trimethylamine N-oxide, sarcosine, glycerophosphorylcholine, dimethylsulfoniopropionate and ectoine) were for the first time employed to form novel two- and three-component DESs with all known natural perturbants/chaotropes (urea, guanidine hydrochloride and arginine). Going beyond the current three-component barrier, we mimicked the exact composition of multi-osmolyte cocktails widely observed in nature and we here report the rapid and consistent formation of deep eutectic systems of unprecedented complexity and the tunable potential of these new systems to stabilize a template protein. Based on these observations, we postulate that, in vivo, osmolytes form deep eutectic systems featuring new, emergent and synergistic properties which govern their interaction with macromolecules. We believe that such bio-inspired, osmolyte-based DESs can be a remarkable new tool to study complex natural systems in higher granularity and to engineer their microenvironment towards efficient and sustainable processes at scale.