Structural Rigidity Regulates Functional Interactions in the Hsp40-Hsp70 Molecular Machine

Protein interactions commonly involve lock-and-key associations between interacting domains. Structural features of these binding partners regulate the nature and extent of their interactions. We report our investigations on specific physical characteristics required of the Hsp40 J-domain to stimulate ATP hydrolysis in the Hsp40-Hsp70 molecular chaperone machine. Characterization of functional and dysfunctional Hsp40-Hsp70 interactions using isothermal titration calorimetry (ITC), and nuclear magnetic resonance (NMR) spectroscopy reveals the importance of structural rigidity for Hsp40 function. Our results suggest that the functional J-domain acts like a semi-elliptical spring, whose resistance to bending in Hsp40-Hsp70 interactions modulates the ATPase domain conformational change and promotes ATP hydrolysis.