Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.7.1.4 (nitrite reductase)
1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A gene, designated dnr, was identified in the vicinity of the structural genes for nitrite reductase (nirS) and nitric oxide reductase (norCB), and the gene for activation of the reductases (nirQ) from Pseudomonas aeruginosa. It encodes a protein of 227 amino acids homologous with the CRP/FNR-family transcriptional regulators. Promoter activities for nirS, nirQ and norCB were considerably reduced in the dnr mutant as well as in the mutant of anr, the other fnr-like regulatory gene from P. aeruginosa. This is the first finding that two CRP/FNR-related regulators are involved in denitrification in one strain.
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PMID:Expression of the nir and nor genes for denitrification of Pseudomonas aeruginosa requires a novel CRP/FNR-related transcriptional regulator, DNR, in addition to ANR. 766 87

The expression of denitrification by a facultatively anaerobic bacterium requires as exogenous signals a low oxygen tension concomitant with an N oxide. We have studied the role of nitric oxide (NO), nitrous oxide (N2O), and nitrite as signal molecules for the expression of the denitrification apparatus of Pseudomonas stutzeri. Transcriptional kinetics of structural genes were monitored by Northern blot analysis in a 60-min time frame after cells were exposed to an N oxide signal. To differentiate the inducer role of NO from that of nitrite, mRNA kinetics were monitored under anoxic conditions in a nirF strain, where NO generation from nitrite is prevented because of a defect in heme D(1) biosynthesis. NO-triggered responses were monitored from the nirSTB operon (encoding cytochrome cd(1) nitrite reductase), the norCB operon (encoding NO reductase), nosZ (encoding nitrous oxide reductase), and nosR (encoding a putative regulator). Transcription of nirSTB and norCB was activated by 5 to 50 nM NO, whereas the nosZ promoter required about 250 nM. Nitrite at 5 to 50 nM elicited no response. At a threshold concentration of 650 nM N2O, we observed in the anoxic cell the transient appearance of nosZ and nosR transcripts. Constant levels of transcripts of both genes were observed in an anoxic cell sparged with N2O. NO at 250 nM stimulated in this cell type the expression of nos genes severalfold. The transcription factor DnrD, a member of the FNR-CRP family, was found to be part of the NO-triggered signal transduction pathway. However, overexpression of dnrD in an engineered strain did not result in NirS synthesis, indicating a need for activation of DnrD. NO modified the transcriptional pattern of the dnrD operon by inducing the transcription of dnrN and dnrO, located upstream of dnrD. Insertional mutagenesis of dnrN altered the kinetic response of the nirSTB operon towards nitrite. Our data establish NO and DnrD as key elements in the regulatory network of denitrification in P. stutzeri. The NO response adds to the previously identified nitrate-nitrite response mediated by the NarXL two-component system for the expression of respiratory nitrate reductase encoded by the narGHJI operon.
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PMID:Nitric oxide signaling and transcriptional control of denitrification genes in Pseudomonas stutzeri. 1127 11

Shewanella oneidensis is a metal reducer that can use several terminal electron acceptors for anaerobic respiration, including fumarate, nitrate, dimethyl sulfoxide (DMSO), trimethylamine N-oxide (TMAO), nitrite, and insoluble iron and manganese oxides. Two S. oneidensis mutants, SR-558 and SR-559, with Tn5 insertions in crp, were isolated and analyzed. Both mutants were deficient in Fe(III) and Mn(IV) reduction. They were also deficient in anaerobic growth with, and reduction of, nitrate, fumarate, and DMSO. Although nitrite reductase activity was not affected by the crp mutation, the mutants failed to grow with nitrite as a terminal electron acceptor. This growth deficiency may be due to the observed loss of cytochromes c in the mutants. In contrast, TMAO reduction and growth were not affected by loss of cyclic AMP (cAMP) receptor protein (CRP). Fumarate and Fe(III) reductase activities were induced in rich medium by the addition of cAMP to aerobically growing wild-type S. oneidensis. These results indicate that CRP and cAMP play a role in the regulation of anaerobic respiration, in addition to their known roles in catabolite repression and carbon source utilization in other bacteria.
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PMID:Involvement of cyclic AMP (cAMP) and cAMP receptor protein in anaerobic respiration of Shewanella oneidensis. 1277 5

In Bradyrhizobium japonicum, a gene named nnrR was identified which encodes a protein with high similarity to FNR/CRP-type transcriptional regulators. Mutant strains carrying an nnrR null mutation were unable to grow anaerobically in the presence of nitrate or nitrite, and they lacked both nitrate and nitrite reductase activities. Anaerobic activation of an nnrR'-'lacZ fusion required FixLJ and FixK(2). In turn, N oxide-mediated induction of nir and nor genes encoding nitrite and nitric oxide reductase, respectively, depended on NnrR. Thus, NnrR expands the FixLJ-FixK(2) regulatory cascade by an additional control level which integrates the N oxide signal required for maximal induction of the denitrification genes.
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PMID:Bradyrhizobium japonicum NnrR, a denitrification regulator, expands the FixLJ-FixK2 regulatory cascade. 1281 94

NnrR, a transcriptional activator and member of the CRP/FNR family of regulators, is responsible for controlling the expression of a number of denitrification genes in Rhodobacter sphaeroides 2.4.3. The apparent effector for NnrR is nitric oxide, and in its presence NnrR activates expression of the nirK gene and the nor operon, encoding nitrite reductase and nitric oxide reductase, respectively. Whether nitric oxide directly interacts with NnrR to activate transcription is unknown. Other denitrifiers carry putative orthologs of NnrR. To gain insight into NnrR function, a number of conserved residues were mutagenized. The impact of these changes on NnrR function was assessed by monitoring expression of a nirK-lacZ fusion. In this way a region spanning from Tyr93 to Cys103 that contains residues critical for NnrR activity was identified.
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PMID:Site-directed mutagenesis of NnrR: a transcriptional regulator of nitrite and nitric oxide reductase in Rhodobacter sphaeroides. 1468 Jun 95

The nitrite reductase and nitric oxide reductase regulator (NNR) from Paracoccus denitrificans activates transcription in response to nitric oxide (NO). The mechanism of NO sensing has not been elucidated for NNR, or for any of its orthologues from the FNR/CRP family of transcriptional regulators. Using regulated expression of the nnr gene in Escherichia coli, evidence has now been obtained to indicate that activation of NNR by NO does not require de novo synthesis of the NNR polypeptide. In anaerobic cultures, NNR is inactivated slowly following removal of the source of NO. In contrast, exposure of anaerobically grown cultures to oxygen causes rapid inactivation of NNR, suggesting that the protein is inactivated directly by oxygen. By random and site-directed mutagenesis, two variants of NNR were isolated (with substitutions of arginine at position 80) that show high levels of activity in anaerobic cultures in the absence of NO. These proteins remain substantially inactive in aerobic cultures, suggesting that the substitutions uncouple the NO- and oxygen-signalling mechanisms, thus providing further evidence that NNR senses both molecules. Structural modelling suggested that Arg-80 is close to the C-helix that forms the monomer-monomer interface in other members of the FNR/CRP family and plays an important role in transducing the activating signal between the regulatory and DNA binding domains. Assays of NNR activity in a haem-deficient mutant of E. coli provided preliminary evidence to indicate that NNR activity is haem dependent.
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PMID:Transcription factor NNR from Paracoccus denitrificans is a sensor of both nitric oxide and oxygen: isolation of nnr* alleles encoding effector-independent proteins and evidence for a haem-based sensing mechanism. 1662 62

Denitrification in the soybean endosymbiont Bradyrhizobium diazoefficiens is controlled by a complex regulatory network composed of two hierarchical cascades, FixLJ-FixK₂-NnrR and RegSR-NifA. In the former cascade, the CRP/FNR-type transcription factors FixK₂ and NnrR exert disparate control on expression of core denitrifying systems encoded by napEDABC, nirK, norCBQD, and nosRZDFYLX genes in response to microoxia and nitrogen oxides, respectively. To identify additional genes controlled by NnrR and involved in the denitrification process in B. diazoefficiens, we compared the transcriptional profile of an nnrR mutant with that of the wild type, both grown under anoxic denitrifying conditions. This approach revealed more than 170 genes were simultaneously induced in the wild type and under the positive control of NnrR. Among them, we found the cycA gene which codes for the c ₅₅₀ soluble cytochrome (CycA), previously identified as an intermediate electron donor between the bc ₁ complex and the denitrifying nitrite reductase NirK. Here, we demonstrated that CycA is also required for nitrous oxide reductase activity. However, mutation in cycA neither affected nosZ gene expression nor NosZ protein steady-state levels. Furthermore, cycA, nnrR and its proximal divergently oriented nnrS gene, are direct targets for FixK₂ as determined by in vitro transcription activation assays. The dependence of cycA expression on FixK₂ and NnrR in anoxic denitrifying conditions was validated at transcriptional level, determined by quantitative reverse transcription PCR, and at the level of protein by performing heme c-staining of soluble cytochromes. Thus, this study expands the regulon of NnrR and demonstrates the role of CycA in the activity of the nitrous oxide reductase, the key enzyme for nitrous oxide mitigation.
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PMID:Expanding the Regulon of the Bradyrhizobium diazoefficiens NnrR Transcription Factor: New Insights Into the Denitrification Pathway. 3148 51

Shewanella oneidensis, a metal reducer and facultative anaerobe, expresses a large number of c-type cytochromes, many of which function as anaerobic reductases. All of these proteins contain the typical heme-binding motif CXXCH and require the Ccm proteins for maturation. Two c-type cytochrome reductases also possess atypical heme-binding sites, the NrfA nitrite reductase (CXXCK) and the SirA sulfite reductase (CX₁₂NKGCH). S. oneidensis MR-1 encodes two cytochrome c synthetases (CcmF and SirE) and two apocytochrome c chaperones (CcmI and SirG). SirE located in the sir gene cluster is required for the maturation of SirA, but not NrfA. Here we show that maturation of SirA requires the combined function of the two apocytochrome c chaperones CcmI and SirG. Loss of either protein resulted in decreased sulfite reductase. Furthermore, SirA was not detected in a mutant that lacked both chaperones, perhaps due to misfolding or instability. These results suggest that CcmI interacts with SirEFG during SirA maturation, and with CcmF during maturation of NrfA. Additionally, we show that CRP regulates expression of sirA via the newly identified transcriptional regulatory protein, SirR.
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PMID:Regulation and Maturation of the Shewanella oneidensis Sulfite Reductase SirA. 3196 87

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