Biochemical characterization of CopA, the Escherichia coli Cu(I)-translocating P-type ATPase

Abstract

Escherichia coli CopA is a copper ion-translocating P-type ATPase that confers copper resistance. CopA formed a phosphorylated intermediate with [γ-32P]ATP. Phosphorylation was inhibited by vanadate and sensitive to KOH and hydroxylamine, consistent with acylphosphate formation on conserved Asp-523. Phosphorylation required a monovalent cation, either Cu(I) or Ag(I). Divalent cations Cu(II), Zn(II), or Co(II) could not substitute, signifying that the substrate of this copper-translocating P-type ATPase is Cu(I) and not Cu(II). CopA purified from dodecylmaltoside-solubilized membranes similarly exhibited Cu(I)/Ag(I)-stimulated ATPase activity, with a Km for ATP of 0.5 mM. CopA has two N-terminal Cys(X)2Cys sequences, Gly-Leu-Ser-Cys14-Gly-His-Cys17, and Gly-Met-Ser-Cys110-Ala-Ser-Cys113, and a Cys479-Pro-Cys481 motif in membrane-spanning segment six. The requirement of these cysteine residues was investigated by the effect of mutations and deletions. Mutants with substitutions of the N-terminal cysteines or deletion of the first Cys-(X)2-Cys motif formed acylphosphate intermediates. From the copper dependence of phosphoenzyme formation, the mutants appear to have 2-3 fold higher affinity for Cu(I) than wild type CopA. In contrast, substitutions in Cys479 or Cys481 resulted in loss of copper resistance, transport and phosphoenzyme formation. These results imply that the cysteine residues of the Cys-Pro-Cys motif (but not the N-terminal cysteine residues) are required for CopA function.