A molecular chaperone, ClpA, functions like DnaK and DnaJ

The two major molecular chaperone families that mediate ATP-dependent protein folding and refolding are the heat shock proteins Hsp60s (GroEL) and Hsp70s (DnaK). Clp proteins, like chaperones, are highly conserved, present in all organisms, and contain ATP and polypeptide binding sites. We discovered that ClpA, the ATPase component of the ATP-dependent ClpAP protease, is a molecular chaperone. ClpA performs the ATP-dependent chaperone function of DnaK and DnaJ in the in vitro activation of the plasmid P1 RepA replication initiator protein. RepA is activated by the conversion of dimers to monomers. We show that ClpA targets RepA for degradation by ClpP, demonstrating a direct link between the protein unfolding function of chaperones and proteolysis. In another chaperone assay, ClpA protects luciferase from irreversible heat inactivation but is unable to reactivate luciferase.