Balance of ATPase stimulation and nucleotide exchange is not required for efficient refolding activity of the DnaK chaperone

The DnaK system from Thermus thermophilus (DnaKTth) exhibits pronounced differences in organisation and regulation to its mesophile counterpart from Escherichia coli (DnaKEco). While the ATPase cycle of DnaKEco is tightly regulated by the concerted action of the two cofactors DnaJEco and GrpEEco, the DnaKTth system features an imbalance in this cochaperone mediated regulation. GrpETth considerably accelerates the ATP/ADP exchange, but DnaJTth only slightly stimulates ATPase activity, believed to be a key step for chaperone activity of DnaKEco. By in vitro complementation assays, we could not detect significant ATPase-stimulation of orthologous DnaJTth · DnaKEco or DnaJEco · DnaKTth-complexes as compared to the DnaKEco system, although they were nevertheless active in luciferase refolding experiments. Assistance of protein recovery by DnaK thus seems to be uncoupled of the magnitude of DnaJ mediated ATPase-stimulation.