BPS2026 – Biomolecules compete or cooperate to determine condensate partitioning

In cells, condensates act to compartmentalize biomolecules, organizing their concentrations to control structure and function. Here, using fluorescent microscopy, we study the partitioning of client biomolecules in condensates. We use two model systems: one disordered and without specific binding, one partially ordered and with specific binding. We find that some client combinations in the disordered system result in competition, where one client displaces the other from the interior of the droplet. In the partially ordered system we observe cooperation, where one client recruits another. In both model systems, we measure accumulation of clients at the interface of droplets in the special case where they have weak interactions with the droplet bulk. Our findings show how cells can regulate the spatial distribution of biomolecules in condensates by controlling client concentrations.