Structural Basis for Recognition of the Hsp90 Closed, ATP State by the TPR-Containing Co-Chaperone FKBP51

Abstract

Molecular chaperones Hsp90 and Hsp70 are critical in protein homeostasis (proteostasis), interacting directly with many “client” proteins to promote ATP-driven remodeling and activation. Co-chaperones bind Hsp90 and Hsp70 forming dynamic chaperone complexes which specify the client folding pathway. Many interact via their tetratricopeptide repeat (TPR) domain, which binds the EEVD motif at the flexible carboxyl-terminus of Hsp90 and Hsp70. However, for many TPR cochaperones, the protein:protein interactions and mechanisms which enable Hsp70/Hsp90 specificity and regulation in the folding pathway remain unclear. The peptidyl-prolyl isomerase FK506-binding protein 51 (FKBP51) interacts specifically with Hsp90 (and not Hsp70) to promote the folding of key client proteins including kinases, steroid hormone receptors, and Tau. Here we have determined a cryo-EM structure of the human Hsp90:FKBP51:p23 complex to 3.3 Å resolution, revealing a distinct TPR interaction mechanism which enables recognition of the Hsp90 closed, ATP state via binding to the C-terminal Hsp90 dimer. Moreover, this interaction positions the FK1 domain of FKBP51 close to the middle domain of Hsp90 revealing a potential mechanism for isomerase activity targeted to distinct sites of Hsp90-bound clients. Together with biochemical analysis to probe interactions, these results reveal how the immunophilin class of TPR co-chaperones may act on specific client regulation and folding steps of the Hsp90-driven chaperone pathway.