Allostery in Biomolecular Condensates.

Allosteric proteins and membrane-less biomolecular condensates are physics-governed pivotal functional components. Allosteric regulation is an inherent physical property of dynamic proteins, and dynamic proteins are allosteric. Thus, in biomolecular condensates (like everywhere else in the cell), allostery is at play, and often missing in condensate descriptions is that the cooperative transitions can involve allosteric effects. The condensate environment can be especially conducive to allostery. Condensed settings can increase the chance of protein interaction and allosteric encounters in function-specific condensates. Specific protein-protein interactions provide the structural framework for signals to transmit cooperatively and dynamically, ultimately modulating cell activity. Their interfaces are commonly enriched in nonpolar (hydrophobic) surface. With abundant functionally specific proteins, and surfaces accommodating multiple hydrophobic patches, interconnected multivalent molecular networks are expected. Lacking hydrophobic cores, disordered proteins' folding-upon-binding scenarios often form strong hydrophobic interfaces, and cooperative (partially disordered) multimers are also common. Repelling water is a major force in condensate formation, albeit not the sole. Here we emphasize dilution as functional and allosteric determinant. Extremely high dilution in rapidly growing proliferating cells can stimulate senescence; lower dilution increases concentration, thus, higher probability of increased proximity and reduced separation, driving protein-protein interactions, and allostery. Is there then effective allostery in condensates? We believe that it depends on the cell state. Under normal physiological conditions, with condensates water content around 40% of total cell mass-yes; over 70% could be too diluted. If too low-it can become function-poor aggregate-like. Effective allostery and signaling require specific interactions, extending from clustered receptors to the cytoskeleton.