We describe importance of the characteristic segment in ATPase domain of DnaK chaperone which is present in all gram-negative bacteria but is absent in all gram-positive bacteria. In vitro studies, ATPase activity, luciferase-refolding activity, and surface plasmon resonance analyses, demonstrated that a segment-deletion mutant DnaKΔ74-96 became defective in the cooperation with the co-chaperones DnaJ and GrpE. In addition, in vivo complementation assay showed that expression of DnaKΔ74-96 could not rescue the viability of Escherichia coli ΔdnaK mutant at 43 °C. Consequently, we suggest evolutionary significance for this DnaK ATPase domain segment in gram-negative bacteria towards the DnaK chaperone system.
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