BPS2026 – Reciprocal regulation of clathrin assembly and the growth of protein networks

Clathrin-mediated endocytosis plays a vital role in membrane trafficking, influencing diverse cellular processes, such as signaling homeostasis, cell adhesion, and receptor recycling. The plasma membrane invaginates through coordinated actions of multiple proteins that recruit and organize the clathrin coat. Recent studies reveal that early-arriving clathrin accessory proteins, including Eps15 and Fcho2, form phase-separated condensates that facilitate recruitment of downstream components, thereby supporting clathrin-coated vesicle assembly and maturation. However, the mechanisms by which protein condensates regulate and are regulated by clathrin assembly remain unclear. Through in vitro reconstitution combined with nuclear magnetic resonance spectroscopy, we show that these condensates serve as platforms for the recruitment and assembly of clathrin triskelia. This condensate driven assembly is enhanced in the presence of the accessory protein, AP2, which is readily incorporated within condensates. In turn, clathrin assembly restricted the growth of condensates, exhibiting surfactant-like behavior that stabilized protein-protein interactions while imposing the preferred curvature of the clathrin lattice. This mutual regulation ensures efficient formation of clathrin-coated vesicles while preventing unchecked condensate expansion. More generally, these findings illuminate how intrinsically disordered and structured proteins cooperate to build complex cellular architectures.