Dual interaction of synaptotagmin with mu 2-and alpha-adaptin facilitates clathrin-coated pit nucleation

The synaptic vesicle protein synaptotagmin was proposed to act as a major d ocking site for the recruitment of clathrin coats implicated in endocytosis , including the recycling of synaptic vesicles. We show here that the C2B d omain of synaptotagmin binds mu2- and alpha -adaptin, two of the four subun its of the endocytic adaptor complex AP-2, mu2 represents the major interac ting subunit of AP-2 within this complex. Its binding to synaptotagmin is m ediated by a site in subdomain B that is distinct from the binding site for tyrosine-based sorting motifs located in subdomain A. The presence of the C2B domain of synaptotagmin at the surface of liposomes enhances the recrui tment of AP-2 and clathrin, Conversely, perturbation of the interaction bet ween synaptotagmin and AP-2 by synprint, the cytoplasmic synaptotagmin-bind ing domain of N-type calcium channels, inhibits transferrin internalization in living cells. We conclude that a dual interaction of synaptotagmin with the clathrin adaptor AP-2 plays a key physiological role in the nucleation of endocytic clathrin-coated pits.