Directed Movement of Condensates by Reaction-driven Assembly*

The cellular environment, characterized by its intricate composition and spatial organization, hosts a variety of organelles, ranging from membrane-bound ones to membraneless structures that are formed through liquid-liquid phase separation. Cells show precise control over the position of such condensates. We demonstrate that organelle movement within cellular domains can naturally arise from biochemical reactions, which are driven by a chemical fuel and produce waste. Simulations and analytical arguments within a minimal model of phase separation and reaction cycles reveal that the directed movement stems from two contributions: fuel and waste are refilled or extracted locally, resulting in concentration gradients, which (i) induce product fluxes via incompressibility and (ii) results in an asymmetric production in the organelle's surroundings and thereby shifts its position. We show that the former contribution dominates and sets the direction of the movement, away from or towards fuel source and waste sink, depending on the product molecules' affinity towards fuel and waste, respectively. The mechanism thus provides a simple means to organize condensates with different compositions. Particle-based simulations as a control and systems with more complex reaction cycles underline the universality of this mechanism.