α-Synuclein interacts directly with AP2 and regulates its binding to synaptic membranes.

α-Synuclein mutation and aggregation are associated with several neurodegenerative disorders, including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. It is expressed in the presynaptic compartment where it regulates clathrin mediated synaptic vesicle endocytosis. We have shown that α-synuclein regulates clathrin lattice size and curvature in vitro. However, the molecular mechanism by which this occurs remains unknown. Here, we show a strong colocalization between the heterotetrametric clathrin adaptor protein-2 (AP2) and α-synuclein at presynapses. Moreover, we report a direct biochemical interaction between the AP2 core domain and the C-terminal domain of α-synuclein. We further show that α-synuclein binds to isolated synaptic membranes in an ATP-dependent manner, similar to AP2 and the monomeric adaptor protein, 180 KDa (AP180), suggesting that α-synuclein, AP2, and AP180 share a common synaptic membrane binding pathway. In contrast, other endocytic proteins, such as clathrin heavy chain and the large GTPase dynamin-1, bind to synaptic membranes independent of ATP. After immunodepleting α-synuclein, we observed a specific reduction in AP2 binding to synaptic membranes, indicating that α-synuclein interaction with AP2 is necessary to maintain normal levels of AP2 on synaptic membranes. These findings demonstrate that α-synuclein plays a critical role in stabilizing AP2 on synaptic membranes, an event that is required for initiation of clathrin-mediated synaptic vesicle endocytosis.