Exploring protein kinase regulation by HSP90 through cryo-EM

Activation of client protein kinases by the Heat shock protein 90 (HSP90) molecular chaperone system is affected by phosphorylation at multiple sites on HSP90, on the kinase specific co-chaperone CDC37, and the kinase client itself. Removal of regulatory phosphorylation from client kinases and their release from the HSP90-CDC37 system depends on a Ser/Thr phosphatase PP5, which associates with HSP90 via its N-terminal TPR domain. Using cryo-EM, Dr. Pearl identifies the structure of the oncogenic protein kinase client BRAFV600E bound to HSP90-CDC37, showing how the V600E mutation favours BRAF association with HSP90-CDC37. Structures of HSP90-CDC37-BRAFV600E complexes with PP5, in autoinhibited and activated conformations, together with proteomic analysis of its phosphatase activity on BRAFV600E and CRAF, reveal how PP5 is activated by recruitment to HSP90 complexes to comprehensively dephosphorylate client proteins, removing interaction sites for regulatory partners such as 14-3-3 proteins, and performing a ‘factory reset’ of the kinase prior to release. These basic studies enable the discovery and development of novel small-molecule inhibitors with application as drugs for the treatment of cancer and other diseases.