The calcium chelator BAPTA affects the binding of assembly protein AP-2 to membranes

Clathrin coated vesicles are involved in receptor-mediated transport. The coat of these vesicles is constituted mostly of clathrin and the assembly proteins AP-1 or AP-2. In the present study using an in vitro binding system, we found that the interaction of AP-2 but not AP-1 with membranes diminished when the calcium chelating agent BAPTA was added. The maximal inhibitory effect was observed with 10 mM of the chelating agent. Binding of AP-2 to membranes was recovered by adding calcium in a concentration-dependent fashion. Binding was also affected when the membranes were previously treated with BAPTA and then washed. However, other chelating agents such as EDTA or EGTA, as well as the zinc chelating TPEN, did not have any effect on the binding. From these results we postulate a role for calcium in regulating the assembly-disassembly cycle of adaptors in the formation of clathrin coated vesicles.