Abstract

The heterotetrameric AP2 adaptor (, 2, 2 and 2 subunits) plays a central role in clathrin-mediated endocytosis. We present the protein recruitment function and 1.7 Å resolution structure of its 2-appendage domain to complement those previously determined for the 2 subunit and appendage. Using structure-directed mutagenesis, we demonstrate the ability of the 2 appendage alone to bind directly to clathrin and the accessory proteins AP180, epsin and eps15 at the same site. Clathrin polymerization is promoted by binding of clathrin simultaneously to the 2-appendage site and to a second site on the adjacent 2 hinge. This results in the displacement of the other ligands from the 2 appendage. Thus clathrin binding to an AP2–accessory protein complex would cause the controlled release of accessory proteins at sites of vesicle formation.