Mapping and Moving Through Intracellular Phase Space using Photo-induced Protein Condensates

Cells compartmentalize their heterogenous intracellular environment to efficiently orchestrate diverse intracellular tasks, many of which rely on membrane-less compartments, dynamic multicomponent condensates that assemble by concentration-dependent liquid-liquid phase separation. However, whether and how cellular condensates can be found in coexistence at the nonequilibrium cellular environment are still largely unclear, including the biophysical principles by which phase separation can be precisely localized within subregions of the cell, particularly in the case of law abundance proteins. In this talk I’ll introduce a novel photo-activatable platform designed for spatiotemporally nucleating intracellular condensates by tuning the molecular driving forces of phase separation. Using this quantitative system, we were able to map, for the first time, full intracellular phase diagrams of phase separating proteins, both under native conditions and under specific post translational modifications or point mutations. We find that while intracellular protein concentration may be insufficient for global phase separation, sequestering protein ligands to slowly diffusing nucleation centers can move the cell into different regions of the phase diagram, resulting in localized phase separation. This diffusive capture mechanism may nucleate liquid phases and stabilize coexistence while liberating the cell from the constraint of global protein abundance.