Structural characterization of the N-terminal kinase-interacting domain of an Hsp90-cochaperone Cdc37 by CD and solution NMR spectroscopy

Exploring Mechanisms of Communication Switching in the Hsp90-Cdc37 Regulatory Complexes with Client Kinases through Allosteric Coupling of Phosphorylation Sites: Perturbation-Based Modeling and Hierarchical Community Analysis of Residue Interaction Networks

Understanding molecular principles underlying chaperone-based modulation of kinase client activity is critically important to dissect functions and activation mechanisms of many oncogenic proteins. The recent experimental studies have suggested that phosphorylation sites in the Hsp90 and Cdc37 proteins can serve as conformational communication switches of chaperone regulation and kinase interactions. However, a mechanism of allosteric coupling between phosphorylation sites in the Hsp90 and Cdc37 during client binding is poorly understood, and the molecular signatures underpinning specific roles of phosphorylation sites in the Hsp90 regulation remain unknown. In this work, we employed a combination of evolutionary analysis, coarse-grained molecular simulations together with perturbation-based network modeling and scanning of the unbound and bound Hsp90 and Cdc37 structures to quantify allosteric effects of phosphorylation sites and identify unique signatures that are characteristic for communication switches of kinase-specific client binding. By using network-based metrics of the dynamic intercommunity bridgeness and community centrality, we characterize specific signatures of phosphorylation switches involved in allosteric regulation. Through perturbation-based analysis of the dynamic residue interaction networks, we show that mutations of kinase-specific phosphorylation switches can induce long-range effects and lead to a global rewiring of the allosteric network and signal transmission in the Hsp90-Cdc37-kinase complex. We determine a specific group of phosphorylation sites in the Hsp90 where mutations may have a strong detrimental effect on allosteric interaction network, providing insight into the mechanism of phosphorylation-induced communication switching. The results demonstrate that kinase-specific phosphorylation switches of communications in the Hsp90 may be partly predisposed for their regulatory role based on preexisting allosteric propensities.

Discovery and Optimization of Small Molecules Targeting the Protein-Protein Interaction of Heat Shock Protein 90 (Hsp90) and Cell Division Cycle 37 as Orally Active Inhibitors for the Treatment of Colorectal Cancer

Cell division cycle 37 (Cdc37) is known to work as a kinase-specific cochaperone, which selectively regulates the maturation of kinases through protein-protein interaction (PPI) with Hsp90. Directly disrupting the Hsp90-Cdc37 PPI is emerging as an alternative strategy to develop anticancer agents through a specific inhibition manner of kinase clients of Hsp90. Based on a first specific small-molecule inhibitor targeting Hsp90-Cdc37 PPI (DDO-5936), which was previously reported by our group, we conducted a preliminary investigation of the structure-activity relationships and pharmacodynamic evaluations to improve the potency and drug-like properties. Here, our efforts resulted in the currently best inhibitor 18h with improved binding affinity (K_d = 0.5 μM) and cellular inhibitory activity (IC₅₀ = 1.73 μM). Both in vitro and in vivo assays revealed that 18h could efficiently block the Hsp90-Cdc37 interaction to specifically inhibit kinase clients of Hsp90. Furthermore, 18h showed ideal physiochemical properties with favorable stability, leading to an oral efficacy in vivo.