An Interdomain Energetic Tug-of-War Creates the Allosterically Active State in Hsp70 Molecular Chaperones

The allosteric mechanism of Hsp70 molecular chaperones enables ATP binding to the N-terminal nucleotide-binding domain (NBD) to alter substrate affinity to the C-terminal substrate-binding domain (SBD) and substrate binding to enhance ATP hydrolysis. Cycling between ATP-bound and ADP/substrate-bound states requires Hsp70s to visit a state with high ATPase activity and fast on/off kinetics of substrate binding. We have trapped this allosterically active'' state for the E. coli Hsp70, DnaK, and identified how interactions among the NBD, the beta subdomain of the SBD, the SBD alpha-helical lid, and the conserved hydrophobic interdomain linker enable allosteric signal transmission between ligand-binding sites. Allostery in Hsp70s results from an energetic tug-of-war between domain conformations and formation of two orthogonal interfaces: between the NBD and SBD, and between the helical lid and the beta subdomain of the SBD. The resulting energetic tension underlies Hsp70 functional properties and enables them to be modulated by ligands and cochaperones and tuned'' through evolution.