Assembly protein recruiting clathrin and adaptor protein complex 2 (AP2) to cell membranes at sites of coated-pit formation and clathrin-vesicle assembly. May be required to determine the amount of membrane to be recycled, possibly by regulating the size of the clathrin cage. Involved in AP2-dependent clathrin-mediated endocytosis at the neuromuscular junction. Required for the efficient targeting of the synaptic vesicle protein synaptobrevin. Binds clathrin and phosphatidylinositol 4,5-bisphosphate. Colocalized with clathrin in the Golgi area. High levels in the nervous system and at lower levels in other tissues. In neurons, enriched at presynaptic terminals and is also present in cell bodies. Belongs to the PICALM/SNAP91 family.