Recognition, activation and targeted degradation of protein kinases clients by the HSP90-molecular chaperone

Many oncogenic protein kinases depend on interaction with the HSP90 molecular chaperone, mediated by the co-chaperone CDC37, for their cellular stability and oncogenic activity. Inhibition of HSP90's conformationally-coupled ATPase mechanism leads to the ubiqtuitylation and degradation of these protein kinase 'clients'. Consequently HSP90 is an important target for therapeutic intervention in cancer. Although there has been substantial progress in this field, important issues remain unresolved. In particular we wish to understand : 1. How protein kinase clients are specifically and selectively recognised by the CDC37 co-chaperone, and recruited to HSP90 ? 2. What structural and biochemical changes are elicited in the client protein by recruitment to HSP90 and by its conformationally-coupled ATPase cycle ? 3. How dephosphorylation of CDC37 by the HSP90-targeted protein phosphatase PP5 regulates client protein release ? 4. How protein kinase clients are targeted for proteasomal degradation when HSP90's ATPase is inhibited ? To address these questions we will use cryoelectron microscopy, X-ray crystallography, NMR spectroscopy, and a range of biochemical and biophysical approaches, to determine structures of key complexes along the pathway from initial client recognition to release or ubiquitylation, and define the structural and biochemical transitions that connect them.