A Mutation in the Catalytic Loop of Hsp90 Specifically Impairs ATPase Stimulation by Aha1p, But Not Hch1p

Heat shock protein 90 (Hsp90) is a molecular chaperone that plays a central role in maintaining cellular homeostasis by facilitating activation of a large number of client proteins. ATP-dependent client activation by Hsp90 is tightly regulated by a host of co-chaperone proteins that control progression through the activation cycle. ATPase stimulation of Hsp90 by Ahal p requires a conserved RKxK motif that interacts with the catalytic loop of Hsp90. In this study, we explore the role of this RKxK motif in the biological and biochemical properties of Hchl p. We found that this motif is required for Hchl p-mediated ATPase stimulation in vitro, but mutations that block stimulation do not impair the action of Hchl p in vivo. This suggests that the biological function of Hchl p is not directly linked to ATPase stimulation. Moreover, a mutation in the catalytic loop of Hsp90 specifically impairs ATPase stimulation by Ahal p but not by Hchl p. Our work here suggests that both Hchl p and Ahal p regulate Hsp90 function through interaction with the catalytic loop but do so in different ways. (C) 2014 Elsevier Ltd. All rights reserved.