Structure of Hsp90-p23-GR reveals the Hsp90 client-remodelling mechanism

Hsp90 is a conserved and essential molecular chaperone responsible for the folding and activation of hundreds of 'client' proteins^1-3. The glucocorticoid receptor (GR) is a model client that constantly depends on Hsp90 for activity^4-9. GR ligand binding was previously shown to nr inhibited by Hsp70 and restored by Hsp90, aided by the co-chaperone p23¹⁰. However, a molecular understanding of the chaperone-mediated remodelling that occurs between the inactive Hsp70-Hsp90 'client-loading complex' and an activated Hsp90-p23 'client-maturation complex' is lacking for any client, including GR. Here we present a cryo-electron microscopy (cryo-EM) structure of the human GR-maturation complex (GR-Hsp90-p23), revealing that the GR ligand-binding domain is restored to a folded, ligand-bound conformation, while being simultaneously threaded through the Hsp90 lumen. In addition, p23 directly stabilizes native GR using a C-terminal helix, resulting in enhanced ligand binding. This structure of a client bound to Hsp90 in a native conformation contrasts sharply with the unfolded kinase-Hsp90 structure¹¹. Thus, aided by direct co-chaperone-client interactions, Hsp90 can directly dictate client-specific folding outcomes. Together with the GR-loading complex structure¹², we present the molecular mechanism of chaperone-mediated GR remodelling, establishing the first, to our knowledge, complete chaperone cycle for any Hsp90 client.