A novel OxyR sensor and regulator of hydrogen peroxide stress with one cysteine residue in Deinococcus radiodurans.

In bacteria, OxyR is a peroxide sensor and transcription regulator, which can sense the presence of reactive oxygen species and induce antioxidant system. When the cells are exposed to H(2)O(2), OxyR protein is activated via the formation of a disulfide bond between the two conserved cysteine residues (C199 and C208). In Deinococcus radiodurans, a previously unreported special characteristic of DrOxyR (DR0615) is found with only one conserved cysteine. dr0615 gene mutant is hypersensitive to H(2)O(2), but only a little to ionizing radiation. Site-directed mutagenesis and subsequent in vivo functional analyses revealed that the conserved cysteine (C210) is necessary for sensing H(2)O(2), but its mutation did not alter the binding characteristics of OxyR on DNA. Under oxidant stress, DrOxyR is oxidized to sulfenic acid form, which can be reduced by reducing reagents. In addition, quantitative real-time PCR and global transcription profile results showed that OxyR is not only a transcriptional activator (e.g., katE, drb0125), but also a transcriptional repressor (e.g., dps, mntH). Because OxyR regulates Mn and Fe ion transporter genes, Mn/Fe ion ratio is changed in dr0615 mutant, suggesting that the genes involved in Mn/Fe ion homeostasis, and the genes involved in antioxidant mechanism are highly cooperative under extremely oxidant stress. In conclusion, these findings expand the OxyR family, which could be divided into two classes: typical 2-Cys OxyR and 1-Cys OxyR.