Interaction kinetics of the copper-responsive CopY repressor with the cop promoter of Enterococcus hirae

In Enterococcus hirae, copper homeostasis is controlled by the cop operon, which encodes the copper-responsive repressor CopY, the copper chaperone CopZ, and two copper ATPases, CopA and CopB. The four genes are under control of CopY, which is a homodimeric zinc protein, [Zn(II)CopY]2. It acts as a copper-responsive repressor: when media copper is raised, CopY is released from the DNA, allowing transcription to proceed. This involves the conversion of [Zn(II)CopY]2 to [Cu(I)2CopY]2, which is no longer able to bind to the promoter. Binding analysis of [Zn(II)CopY]2 to orthologous promoters and to control DNA by surface plasmon resonance analysis defined the consensus sequence TACAnnTGTA as the repressor binding element, or “cop box”, of Gram-positive bacteria. Association and dissociation rates for the CopY–DNA interaction in the absence and presence of added copper were determined. The dissociation rate of [Zn(II)CopY]2 from the promoter was 7.3×10-6 s-1 and was increased to 5×10-5 s-1 in the presence of copper. This copper-induced change may be the underlying mechanism of copper induction. Induction of the cop operon was also assessed in vivo with a biosensor containing a lux reporter system under the control of the E. hirae cop promoter. Half-maximal induction of this biosensor was observed at 5 μM media copper, which delineates the ambient copper concentration to which the cop operon responds in vivo.