Regulation of the Staphylococcus aureus stress response pathway by copper ions.

The CtsR transcriptional repressor is essential for Staphylococcus aureus stress adaptation through its regulation of protein quality control systems. Here, we demonstrate that copper-associated oxidative perturbation modulates the DNA-binding activity of CtsR through a conserved cysteine residue. In vitro biochemical assays showed that Cu2+ promotes Cys37-dependent disulfide-linked dimer formation, weakens CtsR binding to the clpC promoter. A heterologous dual-plasmid GFP reporter assay further showed that copper can derepress a CtsR-controlled reporter in cells, while the CtsRC37A mutant largely abolished this response. In S. aureus, direct copper perturbation induced copper homeostasis genes and activated the endogenous CtsR-controlled clpC operon. In addition, antibiotic-induced oxidative stress was associated with intracellular ROS accumulation, copper homeostasis perturbation, and activation of protein quality control genes. Transcriptomic analysis further linked antibiotic-induced stress to copper detoxification, redox adaptation, and proteostasis responses. Together, these findings are consistent with a copper-associated Cys37-dependent redox mechanism potentially coupling metal homeostasis, oxidative stress, and proteostasis regulation in S. aureus, which could advance understanding of bacterial stress adaptation and merit investigation for therapeutic applications.