The synergistic roles of the Hsp90-Cdc37 chaperone machinery and protein kinases in biology and disease have stimulated extensive structural and functional studies of regulatory mechanisms underlying the Hsp90-kinase interactions.  The recent cryo-electron microscopy structure of the Hsp90-Cdc37-Cdk4 kinase complex has provided a framework for dissecting regulatory principles underlying recruitment of kinase clients to the chaperone system. We  examined these mechanisms at the molecular level by combining multiscale modeling of conformational landscapes for the protein kinases clients with systems biology analysis and biophysical characterization of the chaperone-kinase interactions. Our study provides evidence that the Hsp90-Cdc37 chaperone machinery can promote conformational instability of the client kinases through a mechanism of reciprocal dynamic exchange, in which protection of the partially unfolded kinase by Hsp90 may spatially confine client ensemble and accelerate refolding. Network modelling and percolation analysis approaches were used to emulate thermal unfolding and characterize conformational landscapes of a wide range of protein kinases, revealing that chaperone dependency of protein kinase clients may be linked with the elevated conformational mobility of their inactive states induced by dynamic and energetic polarization of kinase lobes. By showcasing a family of cyclin-dependent (CDK) kinases that display a broad repertoire of chaperone dependencies, we discovered that unique functional dynamics signatures and chaperone addiction of CDK4 and CDK7 client proteins can explain divergences in their regulatory mechanisms. We have analyzed mechanisms by which kinase inhibitors and allosteric Hsp90 modulators that may act synergistically and exert their pharmacological effect by depriving the client kinase of access to the molecular chaperone. We discuss structure-based design studies of conformation-specific BRAF modulators that modulate regulatory mechanisms by which oncogenic BRAF mutants rely on the Hsp90 dependence for the accumulation of the constitutively active form. By integrating computational systems biology analysis of Hsp90-BRAF binding and biophysical experiments, we discovered novel allosteric modulators of Hsp90 and BRAF kinase that act synergistically by antagonizing the Hsp90-BRAF interactions and depriving the client kinase of access to the molecular chaperone.

Multiscale modeling and network-based systems biology analysis of protein kinase regulation by the Hsp90-Cdc37 chaperone system: Towards discovery of synergistic allosteric modulators targeting Hsp90-kinase interactions and evading drug resistance

255th National Meeting (2018)

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