The E. coli IbpA/B proteins belong to a group of molecular chaperones which under heat shock protect polypeptides from irreversible denaturation and facilitate their refolding to the native structure in cooperation with the ATP-dependent chaperones: DnaK/DnaJ/GrpE and ClpB. Several data suggest that IbpA/B participate in the protection of E. coli cells against oxidative stress: IbpA/B inhibits inactivation of some E. coli enzymes by superoxide radicals in vitro. Furthermore, overproduced IbpA/B increase E. coli resistance to superoxide stress. We demonstrate that the IbpA/B participate in the protection of E. coli against oxidative stress induced by copper ions. The transition metal copper is essential to a variety of cellular functions, however even moderately increased level of copper may be toxic for the cell. The toxicity results from the Fenton or Haber-Weiss reaction in which copper ions catalyze the production of OH radicals from hydroperoxide. We show that the lack of IbpA/B causes increased E. coli sensitivity to copper ions. IbpA/B proteins inhibited copper-catalyzed oxidation of a model enzyme – alcohol dehydrogenase (AdhE) both in vivo and in vitro. We demonstrated that IbpA/B in cooperation with DnaK system prevented heat - inactivation and aggregation of AdhE under anaerobic conditions, both in vitro and in vivo. We suggest that the overall ability of IbpA/B to protect cells from copper -induced damage may result from the metal chelation and direct binding to the protected proteins.

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