Polypeptide release by Hsp90 involves ATP hydrolysis and is enhanced by the co-chaperone p23

The molecular chaperone Hsp90 binds and hydrolyses ATP, but how this ATPase activity regulates the interaction of Hsp90 with a polypeptide substrate is not yet understood. Using the glucocorticoid receptor ligand binding domain as a substrate, we show that dissociation of Hsp90 from bound polypeptide depends on the Hsp90 ATPase and is blocked by geldanamycin, a specific ATPase inhibitor. The co-chaperone p23 greatly stimulates Hsp90 substrate release with ATP, but not with the non-hydrolysable nucleotides ATP gammaS or AMP-PNP. Point mutants of Hsp90 with progressively lower ATPase rates are progressively slower in ATP-dependent substrate release but are still regulated by p23. In contrast, ATPase-inactive Hsp90 mutants release substrate poorly and show no p23 effect. These results outline an ATP-driven cycle of substrate binding and release for Hsp90 which differs from that of other ATP-driven chaperones. Conversion of the ATP state of Hsp90 to the ADP state through hydrolysis is required for efficient release of substrate polypeptide. p23 couples the ATPase activity to polypeptide dissociation and thus can function as a substrate release factor for Hsp90.