Ligand-driven modulation of chaperone-cochaperone networks shapes proteostasis outcomes.

Protein homeostasis depends on a delicate interplay between folding and degradation, orchestrated by molecular chaperones. Among them, Hsp90 is a central hub, regulating nearly 10% of the proteome through ATP-driven conformational cycles and selective interactions with cochaperones. The glucocorticoid receptor (GR) represents a paradigmatic Hsp90 client, whose maturation requires sequential remodeling steps involving multi-protein assemblies. While cryo-EM provided snapshots of these complexes, the dynamic determinants of GR activation and the antagonistic roles of cochaperones FKBP51 and FKBP52 remain poorly understood. Here, we integrate unbiased equilibrium atomistic molecular dynamics with nonequilibrium simulations of four different Hsp90-cochaperone-client assemblies that oversee distinct steps of GR maturation to elucidate how finely tuned dynamics and coordination/communication mechanisms determine functional emergence. Perturbations encoded by ligand insertion or removal reveal steroid binding as critical for both structural stability and inter-component communication. Ligand engagement not only stabilizes GR's active conformation but also feeds back to reshape chaperone and cochaperone dynamics, thereby modulating progression through the folding pathway. Steroid binding reinforces the interface in the Hsp90-p23-GR assembly, positioning cochaperone p23 as a molecular sensor for ligand occupancy. Comparative analyses of post-maturation complexes further uncover how immunophilins FKBP51 and FKBP52, despite structural similarity, elicit divergent allosteric effects on GR conformation and Hsp90-ATPase, determining opposing client fates. Our results establish ligand binding as an active modulator of chaperone-mediated folding, linking metabolic cues (ligand presence and levels) to client maturation. More broadly, they highlight cochaperones as dynamic checkpoints that selectively bias client outcomes, revealing generalizable principles of proteostasis regulation and opportunities for therapeutic intervention.