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J. Biol. Chem., Vol. 283, Issue 2, 908-918, January 11, 2008

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Analysis of the Nitric Oxide-sensing Non-heme Iron Center in the NorR Regulatory Protein^*

Nicholas P. Tucker¹, Benoît D'Autréaux¹², Faridoon K. Yousafzai, Shirley A. Fairhurst, Stephen Spiro, and Ray Dixon³

From the 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

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 ⁵⁴-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 ⁵⁴. 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 for publication, July 17, 2007 , and in revised form, November 14, 2007.

^* This work was supported by the Biotechnology and Biological Sciences and Research Council (Grant BB/D009588/1 to R. D.) and National Science Foundation Grant MCB-0702858 (to S. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Both authors contributed equally to this work.

² Current address: Laboratoire Stress Oxydant et Cancer, SBIGeM, iBiTec-S, CEA-Saclay, Gif-sur-Yvette 91191, Cedex, France.

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.

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