Clathrin adaptors drive phase separation in endocytosis and trafficking.

Liquid-liquid phase separation (LLPS) underlies the formation of biomolecular condensates that organize processes, including endocytosis and membrane trafficking. Although LLPS has been implicated in clathrin-mediated pathways, the contribution of adaptor proteins to condensate formation and function remains unclear. Here we show that two yeast adaptors, Ent5 and Sla2, undergo LLPS in vitro and this property correlates with their roles in membrane trafficking and condensate recruitment in vivo. Ent5 condensation is driven by a dynamic helix within its disordered region that acts as a molecular "sticker". Deletion of this 249-287 helix disrupts membrane-associated condensation and leads to altered coating dynamics in vivo, with Ent5-dependent transport events becoming delayed. In contrast, Sla2 behaves as a driver and as a client of LLPS, with its coiled-coil (CC) region mediating condensation. Together, these findings reveal that endocytic adaptors can promote condensate formation through distinct structural features, coupling clathrin binding and membrane association through phase separation.