Redox Regulation Gets More Complicated

Abstract

Gene expression is regulated in response to changes in cellular redox status. Kim et al. provide evidence that not all agents that alter redox status are perceived as identical. Using biochemical analysis of the bacterial transcription factor OxyR, which has a cysteine redox center, the authors analyzed the accessibility of the six cysteines, the structural changes associated with cysteine modification, and finally the effect of various oxidants on DNA-binding and transcription activation. Only one cysteine (C 199 ) was accessible and reacted with peroxide to form OxyR-SOH, with S-nitrosoglutathione to form OxyR-SNO, or with glutathione disulfide to form OxyR-SSG. In vivo, OxyR was fully reduced under nonstimulated conditions. Peroxide treatment of the bacteria to oxidize OxyR led to the production of OxyR-SSG. In vitro transcription assays demonstrated that OxyR-SOH, OxyR-SNO, and OxyR-SSG stimulated transcription from both the katG and OxyS promoters. Each of the modified forms of OxyR exhibited different DNA-binding characteristics at the katG and OxyS promoters. However, the DNA-binding affinity did not correlate with transactivating potential. Cystine modification altered DNA-binding and transcriptional activation capability independently. These results provide an initial answer to how gene regulation can be tuned to the specific redox stress and suggest that the redox center in OxyR is not a simple on-off switch, but is a more selective and specific sensor for redox changes. S. O. Kim, K. Merchant, R. Nudelman, W. F. Beyer, Jr., T. Keng, J. DeAngelo, A. Hausladen, J. S. Stamler, OxyR: A molecular code for redox-related signaling. Cell 109 , 383-396 (2002). [Online Journal]