CopY-like copper inducible repressors are putative 'winged helix' proteins

CopY of Enterococcus hirae is a well characterized copper-responsive repressor involved in copper homeostasis. In the absence of copper, it binds to the promoter. In high copper, the CopZ copper chaperone donates copper to CopY, thereby releasing it from the promoter and allowing transcription of the downstream copper homeostatic genes of the cop operon. We here show that the CopY-like repressors from E. hirae, Lactococcus lactis, and Streptococcus mutans have similar affinities not only for their native promoters, but also for heterologous cop promoters. CopZ of L. lactis accelerated the release of CopY from the promoter, suggesting that CopZ of L. lactis acts as copper chaperone, similar to CopZ in E. hirae. The consensus binding motif of the CopY-like repressors was shown to be TACAxxTGTA. The same binding motif is present in promoters controlled by BlaI of Bacillus licheniformis, MecI of Staphylococcus aureus and related repressors. BlaI and MecI have known structures and belong to the family of 'winged helix' proteins. In the N- terminal domain, they share significant sequence similarity with CopY of E. hirae. Moreover, they bind to the same TACAxxTGTA motif. NMR analysis of the N-terminal DNA binding domain of CopY of L. lactis showed that it contained the same alpha-helical content like the same regions of BlaI and MecI. These findings suggest that the DNA binding domains of CopY-like repressors are also of the 'winged helix' type.