ATPase activity associated with the uncoating of clathrin baskets by Hsp70

In the presence of ATP, bovine brain hsp70 has been shown to remove clathrin from bovine brain clathrin-coated vesicles in a rapid stoichiometric initial burst followed by slow steady-state uncoating. In addition, it has been found recently that a 100-kDa cofactor is required for hsp70 to uncoat clathrin baskets prepared with the assembly protein AP-2. In this study the ATPase activity associated with uncoating was investigated, with baskets formed from clathrin and assembly proteins. Mixed assembly proteins or assembly protein AP-2 could not be used in ATPase studies because they activated the hsp70 ATPase activity even in the absence of clathrin. However, this was not the case with assembly protein AP180. A stoichiometric initial burst of ATP hydrolysis was found to accompany the initial burst of uncoating of AP180-clathrin baskets by hsp70, with 1 mol of hydrolyzed ATP/mol of released clathrin heavy chain. Furthermore, the presence of a 100-kDa cofactor was needed for both processes. These results suggest that an initial burst of uncoating occurs with all clathrin baskets, that an initial burst of ATP hydrolysis accompanies this initial burst of uncoating, and that a 100-kDa cofactor is required for both.