NorR, NO reduction and detoxification Regulator, is one of several regulatory proteins, such as Fur, SoxR, and OxyR, that are involved in the response to reactive nitrogen species. Under anaerobic and microaerobic conditions it activates transcription of the norVW operon, encoding a nitric oxide (NO)-reducing flavorubredoxin that detoxifies NO [5, 6, 7, 8, 9].
A norR mutant is completely defective with respect to anaerobic NO detoxification  and is sensitive to reactive nitrogen intermediates generated from nitroprusside. The norR gene is transcribed divergently from norVW and autoregulated . It is activated in the absence of oxygen and by nitrite under anaerobic conditions .
NorR is a σ54-dependent transcriptional activator .
It contains three domains: an N-terminal GAF (cGMP phosphodiesterase, adenylate cyclase, FhlA) domain that is involved in signal sensing [5, 12, 13]; a central catalytic AAA+ domain that is required for interacting with σ54 and for coupling ATP hydrolysis to promoter DNA melting by RNA polymerase; and a C-terminal domain that contains a helix-turn-helix DNA-binding motif .Read more >
In the absence of NO, the activity of the central catalytic AAA+ domain of NorR is repressed by direct interaction between the GAF domain and the σ54-interacting region of the AAA+ domain. This interaction prevents access to the σ54-RNA polymerase complex . Binding of NO relieves intramolecular repression and activates the ATPase activity of the central AAA+ domain [12, 16]. The GAF domain contains a mononuclear nonheme iron center that binds NO reversibly . Spectroscopy studies and structural modeling of the GAF domain identified five candidate ligands for the nonheme iron and suggested a model in which it is coordinated in a pseudo-octahedral environment by three aspartate residues, an arginine, and a cysteine . The iron oxidation state influences the activation of NorR .
The intergenic region of norR and norVW carries three binding sites for NorR with a symmetrical 11-bp consensus sequence . These sites act as enhancer-binding sites for transcriptional activation by NorR [3, 18]. All three sites are required for the stimulation of the ATPase activity in vitro and activation of norV expression in vivo .
Based on biochemical experiments and electron micrographs using a norR mutant carrying a deletion of the N-terminal domain, it has been proposed that NorR binds as a hexameric ring to DNA . The data further suggest that in contrast to other enhancer-binding proteins the DNA binding per se induces a conformational change in NorR that promotes hexameric ring formation. Presumably the hexamer is further stabilized by additional DNA wrapped around the ring. Binding of NO to the GAF domain relieves intramolecular repression of the central domain, leading to the activation of the ATPase activity and interaction with σ54 RNA polymerase .
Reviews: [4, 16, 20]br>
|Connectivity class:||Local Regulator|
|Length:||1515 bp / 504 aa|
|TU(s) encoding the TF:||
|Regulated gene(s)||norR, norV, norW|
|Multifun term(s) of regulated gene(s)||
MultiFun Term (List of genes associated to the multifun term)
electron carriers (2)
Transcription related (1)
|Regulated operon(s)||norR, norVW|
|First gene in the operon(s)||norR, norV|
|Simple and complex regulons|
|Simple and complex regulatory phrases||
Regulatory phrase (List of promoters regulated by the phrase)
|Functional conformation||Function||Promoter||Sigma factor||Central Rel-Pos||Distance to first Gene||Genes||Sequence||LeftPos||RightPos||Evidence (Confirmed, Strong, Weak)||References|
|2832346||2832358||[AIBSCS], [BPP], [GEA]||, , , |
|2832322||2832334||[AIBSCS], [BPP], [GEA]||, , , |
|2832301||2832313||[AIBSCS], [BPP], [GEA]||, , , |
|2832301||2832313||[AIBSCS], [BPP], [GEA]||, , , , , , |
|2832322||2832334||[AIBSCS], [BPP], [GEA]||, , , , , , |
|2832346||2832358||[AIBSCS], [BPP], [GEA]||, , , , , , |
|Evolutionary conservation of regulatory elements|
 Justino MC., Goncalves VM., Saraiva LM., 2005, Binding of NorR to three DNA sites is essential for promoter activation of the flavorubredoxin gene, the nitric oxide reductase of Escherichia coli., Biochem Biophys Res Commun. 328(2):540-4
 Tucker N., D'autreaux B., Spiro S., Dixon R., 2005, DNA binding properties of the Escherichia coli nitric oxide sensor NorR: towards an understanding of the regulation of flavorubredoxin expression., Biochem Soc Trans. 33(Pt 1):181-3
 Tucker NP., D'Autr?aux B., Studholme DJ., Spiro S., Dixon R., 2004, DNA binding activity of the Escherichia coli nitric oxide sensor NorR suggests a conserved target sequence in diverse proteobacteria., J Bacteriol. 186(19):6656-60
 Gardner AM., Gessner CR., Gardner PR., 2003, Regulation of the nitric oxide reduction operon (norRVW) in Escherichia coli. Role of NorR and sigma54 in the nitric oxide stress response., J Biol Chem. 278(12):10081-6
 Hutchings MI., Mandhana N., Spiro S., 2002, The NorR protein of Escherichia coli activates expression of the flavorubredoxin gene norV in response to reactive nitrogen species., J Bacteriol. 184(16):4640-3
 Vicente JB., Teixeira M., 2005, Redox and spectroscopic properties of the Escherichia coli nitric oxide-detoxifying system involving flavorubredoxin and its NADH-oxidizing redox partner., J Biol Chem. 280(41):34599-608
 Mukhopadhyay P., Zheng M., Bedzyk LA., LaRossa RA., Storz G., 2004, Prominent roles of the NorR and Fur regulators in the Escherichia coli transcriptional response to reactive nitrogen species., Proc Natl Acad Sci U S A. 101(3):745-50
 da Costa PN., Teixeira M., Saraiva LM., 2003, Regulation of the flavorubredoxin nitric oxide reductase gene in Escherichia coli: nitrate repression, nitrite induction, and possible post-transcription control., FEMS Microbiol Lett. 218(2):385-93
 Tucker NP., D'Autreaux B., Yousafzai FK., Fairhurst SA., Spiro S., Dixon R., 2008, Analysis of the nitric oxide-sensing non-heme iron center in the NorR regulatory protein., J Biol Chem. 283(2):908-18
 Bush M., Ghosh T., Tucker N., Zhang X., Dixon R., 2010, Nitric oxide-responsive interdomain regulation targets the ¿¿54-interaction surface in the enhancer binding protein NorR., Mol Microbiol. 77(5):1278-88
 Baptista JM., Justino MC., Melo AM., Teixeira M., Saraiva LM., 2012, Oxidative stress modulates the nitric oxide defense promoted by Escherichia coli flavorubredoxin., J Bacteriol. 194(14):3611-7
 Busch A., Pohlmann A., Friedrich B., Cramm R., 2004, A DNA region recognized by the nitric oxide-responsive transcriptional activator NorR is conserved in beta- and gamma-proteobacteria., J Bacteriol. 186(23):7980-7
 Tucker NP., Ghosh T., Bush M., Zhang X., Dixon R., 2010, Essential roles of three enhancer sites in sigma54-dependent transcription by the nitric oxide sensing regulatory protein NorR., Nucleic Acids Res. 38(4):1182-94