Eps15 membrane-binding and -bending activity acts redundantly with Fcho1 during clathrin-mediated endocytosis

Clathrin coat assembly on membranes requires cytosolic adaptors and accessory proteins, which bridge triskeleons with the lipid bilayer and stabilize lattice architecture throughout the process of vesicle formation. In Caenorhabditis elegans, the prototypical AP-2 adaptor complex, which is activated by the accessory factor Fcho1 at the plasma membrane, is dispensable during embryogenesis, enabling us to define alternative mechanisms that facilitate clathrin-mediated endocytosis. Here we uncover a synthetic genetic interaction between C. elegans Fcho1 (FCHO-1) and Eps15 (EHS-1), suggesting that they function in a parallel and potentially redundant manner. Consistent with this idea, we find that the FCHO-1 EFC/F-BAR domain and the EHS-1 EH domains exhibit highly similar membrane-binding and -bending characteristics in vitro. Furthermore, we demonstrate a critical role for EHS-1 when FCHO-1 membrane-binding and -bending activity is specifically eliminated in vivo. Taken together, our data highlight Eps15 as an important membrane-remodeling factor, which acts in a partially redundant manner with Fcho proteins during the earliest stages of clathrin-mediated endocytosis.