Functional Role and Hierarchy of the Intermolecular Interactions in Binding of Protein Kinase Clients to the Hsp90-Cdc37 Chaperone: Structure-Based Network Modeling of Allosteric Regulation.

A fundamental role of the Hsp90-Cdc37 chaperone machinery in mediating conformational development and activation of diverse protein kinase clients is essential for signal transduction. Structural and biochemical studies have demonstrated that characterization of global conformational changes and allosteric interactions in the Hsp90-Cdc37-kinase complexes are central to our understanding of the mechanisms underlying kinase recruitment and processing by the Hsp90-Cdc37 chaperone. The recent cryo-electron microscopy structure of the Hsp90-Cdc37-Cdk4 kinase complex has provided a framework for dissecting regulatory principles underlying differentiation and recruitment of protein kinase clients to the chaperone machinery. In this work, we have characterized functional role and hierarchy of the intermolecular interactions in binding of protein kinase clients to the Hsp90-Cdc37 system. The network analysis revealed important relationships between structural stability, global centrality, and functional significance of regulatory hotspots in chaperone regulation and client recognition. A unique asymmetric topography of the intermolecular communities in the chaperone-kinase complex has quantified a central mediating role of Cdc37 in client recognition and allosteric regulation of the chaperone-kinase complex. Modeling of allosteric pathways in the chaperone complex has further clarified structural and energetic signatures of allosteric hotspots, particularly linking sites of post-translational modifications in Hsp90 with their role in allosteric interactions and client regulation. The results of this integrative computational study are compared with a wide range of structural, biochemical, and cell-based experiments, offering a robust network-centric model of allosteric regulation and client kinase recognition by the Hsp90-Cdc37 chaperone machine.