Mutations in the DnaK chaperone affecting interaction with the DnaJ cochaperone

Hsp70 chaperones assist protein folding by ATP-controlled cycles of substra te binding and release. ATP hydrolysis is the rate-limiting step of the ATP ase cycle that causes locking in of substrates into the substrate-binding c avity of Hsp70. This key step is strongly stimulated by DnaJ cochaperones. We show for the Escherichia coli Hsp70 homolog, DnaK, that stimulation by D naJ requires the linked ATPase and substrate-binding domains of DnaK. Funct ional interaction with DnaJ is affected by mutations in an exposed channel located in the ATPase domain of DnaK. It is proposed that binding to this c hannel, possibly involving the J-domain, allows DnaJ to couple substrate bi nding with ATP hydrolysis by DnaK, Evolutionary conservation of the channel and the J-domain suggests conservation of the mechanism of action of DnaJ proteins.