Cell 150, 987–1001 (2012)

HSP90 is a chaperone that interacts with a diverse group of substrate proteins or clients, but the rules that govern client selection and HSP90-client interactions are unclear. Taipale et al. now report 'LUMIER with BACON', an assay involving a bait protein tagged with a Flag epitope and a prey protein tagged with Renilla luciferase. The proteins are coexpressed, and bait and prey are quantified by ELISA and luminescence, respectively, in high-throughput format after immunoprecipitation. Using their assay, the authors evaluated several client classes for interaction with HSP90 and found that ∼60% of human kinases interacted with HSP90. The authors next showed that the majority of kinases but not other client types also interacted with the cochaperone CDC37, suggesting that CDC37 mediates kinase-HSP90 interaction. Chemical inhibition of HSP90 with a diverse set of inhibitors generally decreased HSP90-kinase interactions but with client-specific dissociation rates. Analysis of functional and structural databases suggested that HSP90 clients might be less stable than nonclients. The authors showed that stabilization of the kinase domain of clients with small molecules that bind the ATP-binding pocket decreased the kinase-HSP90 interaction. Taken together, the data indicate that the CDC37 cochaperone is an adaptor for protein kinases and that, within this class of proteins, HSP90 clients are intrinsically unstable compared to nonclients.