Analysis of the Nitric Oxide-sensing Non-heme Iron Center in the NorR Regulatory Protein*
- Nicholas P. Tucker‡,1,
- Benoît D'Autréaux‡,1,2,
- Faridoon K. Yousafzai‡,
- Shirley A. Fairhurst‡,
- Stephen Spiro§ and
- Ray Dixon‡,3
- ‡Department of Molecular Microbiology, John Innes Centre, Colney, Norwich Research Park, Norwich NR4 7UH, United Kingdom and the §Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75083-0688
- ↵3 To whom correspondence should be addressed: Tel.: 44-160-3045-0747; Fax: 44-160-3450-778; E-mail: ray.dixon{at}bbsrc.ac.uk.
Abstract
The NorR regulatory protein senses nitric oxide (NO) to activate genes required for NO detoxification under anaerobic and microaerobic conditions in Escherichia coli. NorR belongs to the σ54-dependent family of transcriptional activators and contains an N-terminal regulatory GAF (cGMP phosphodiesterase, adenylate cyclase, FhlA) domain that controls the ATPase activity of the central AAA+ domain to regulate productive interactions with σ54. Binding of NO to a non-heme iron center in the GAF domain results in the formation of a mononitrosyl-iron complex and releases intramolecular repression of the AAA+ domain to enable activation of transcription. In this study, we have further characterized NorR spectroscopically and substituted conserved residues in the GAF domain. This analysis, in combination with structural modeling of the GAF domain, has identified five candidate ligands to the non-heme iron and suggests a model in which the metal ion is coordinated in a pseudo-octahedral environment by three aspartate residues, an arginine, and a cysteine.
- Received July 17, 2007.
- Revision received November 14, 2007.
- The American Society for Biochemistry and Molecular Biology, Inc.
