norR2 encodes a nitric oxide-responsive sigma-54-dependent transcriptional activator in Cupriavidus necator H16. It is the chromosomal paralog of the megaplasmid-encoded NorR1 and has the conserved NorR GAF, AAA+ ATPase, and Fis-family helix-turn-helix DNA-binding architecture.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0005524
ATP binding
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: NorR2 contains the conserved sigma-54-interaction/AAA+ ATPase region of NorR-family bacterial enhancer-binding proteins. ATP binding is plausible, but ATP hydrolysis is the more informative molecular function.
Reason: The InterPro evidence identifies the sigma-54 interaction ATP-binding region, while NorR-family biochemical work shows that NO binding stimulates ATPase activity to activate transcription by RNA polymerase.
Proposed replacements:
ATP hydrolysis activity
Supporting Evidence:
file:CUPNH/norR2/norR2-uniprot.txt
InterPro; IPR002078; Sigma_54_int.
PMID:16193057
Binding of NO stimulates the ATPase activity of NorR, enabling the activation of transcription by RNA polymerase.
|
|
GO:0006355
regulation of DNA-templated transcription
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: NorR2 positively activates NO-responsive transcription of nitric oxide reductase genes through the NorR/sigma-54 regulatory system.
Reason: The existing term is correct but too broad. Ralstonia studies show NorR is required for transcriptional activation of the norA/norB nitric oxide reductase operon in response to NO.
Proposed replacements:
positive regulation of DNA-templated transcription
Supporting Evidence:
PMID:11069685
The regulator gene maps adjacent to norAB, is divergently transcribed and present in two copies on the megaplasmid pHG1 (norR1) and the chromosome (norR2).
PMID:15667304
norB and the adjacent norA form an operon that is controlled by the sigma(54)-dependent transcriptional activator NorR in response to NO.
|
|
GO:0043565
sequence-specific DNA binding
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: NorR2 has a Fis-family helix-turn-helix DNA-binding domain, but generic sequence-specific DNA binding misses its NO-responsive transcriptional activator function.
Reason: NorR proteins bind upstream activator sequences and activate sigma-54-dependent transcription in response to NO. GO:0141097 captures this ligand-modulated activator activity more precisely than generic DNA binding.
Proposed replacements:
ligand-modulated transcription activator activity
Supporting Evidence:
PMID:15667304
A NorR derivative containing MalE in place of the N-terminal domain binds to a 73 bp region upstream of norA that includes three copies of the putative upstream activator sequence GGT-(N(7))-ACC.
PMID:16193057
Here we show that the regulatory domain of NorR contains a mononuclear non-haem iron centre, which reversibly binds NO.
|
|
GO:0019333
denitrification pathway
|
IEA
GO_REF:0000041 |
MARK AS OVER ANNOTATED |
Summary: NorR2 controls expression of NO reductase but is not itself a denitrification enzyme. The UniPathway row imports pathway context too directly for a regulator.
Reason: Species-specific evidence supports NorR2 as the chromosomal copy of an NO-responsive regulator of nitric oxide reductase expression. UniProt records denitrification as regulatory context, and the Ralstonia NorR study states that other denitrification-chain steps are independent of NorR.
Supporting Evidence:
file:CUPNH/norR2/norR2-uniprot.txt
PATHWAY: Nitrogen metabolism; nitrate reduction (denitrification) [regulation].
PMID:11069685
This reaction is not strictly co-ordinated on the regulatory level with the other nitrogen oxide-reducing steps of the denitrification chain that are independent of NorR.
|
|
GO:0141097
ligand-modulated transcription activator activity
|
ISS
PMID:11069685 A novel NO-responding regulator controls the reduction of ni... |
NEW |
Summary: NorR2 is the chromosomal copy of the NO-responsive NorR transcriptional activator system in C. necator H16.
Reason: The existing sequence-specific DNA-binding annotation is too narrow for NorR2. Direct mutant evidence in this organism was generated mainly for norR1, so this NEW term is treated as ISS for norR2 based on the chromosomal paralog relationship, conserved GAF/AAA+/Fis-domain NorR architecture, and NorR-family biochemical evidence for NO sensing and ATPase-stimulated sigma-54 activation.
Supporting Evidence:
PMID:11069685
The regulator gene maps adjacent to norAB, is divergently transcribed and present in two copies on the megaplasmid pHG1 (norR1) and the chromosome (norR2).
PMID:15667304
The N-terminal domain of NorR contains a GAF module and is hypothesized to interact with a signal molecule.
PMID:16193057
Binding of NO stimulates the ATPase activity of NorR, enabling the activation of transcription by RNA polymerase.
file:CUPNH/norR2/norR2-deep-research-falcon.md
Falcon synthesis treats NorR2 as the chromosomal NorR paralog in the norR2A2B2 locus, with conserved GAF, AAA+ ATPase, and DNA-binding architecture supporting NO-responsive sigma-54 transcriptional activation by homology and locus context.
file:interpro/panther/PTHR32071/PTHR32071-deep-research-falcon.md
PTHR32071 family research supports sigma-54 enhancer-binding proteins as conserved AAA+ transcriptional activators with pathway-specific sensory-domain inputs.
|
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The target protein specified by UniProt accession Q9K4U8 is annotated as “Nitric oxide reductase transcription regulator NorR2”, encoded by norR2 with ordered locus name H16_B2325 in Cupriavidus necator strain H16 (historically Ralstonia eutropha). The literature retrieved in this run supports that C. necator H16 contains a chromosome 2 nitric-oxide-reductase locus organized as norR2A2B2 (i.e., regulator plus structural genes), consistent with Q9K4U8 being the transcriptional regulator controlling the chromosomal NOR2 system. (kohlmann2014copingwithanoxia pages 5-6, kohlmann2014copingwithanoxia pages 9-11)
Important limitation: no primary paper retrieved here explicitly names UniProt Q9K4U8 or H16_B2325; the mapping of Q9K4U8↔norR2↔chromosome-2 norR2A2B2 is therefore supported indirectly through the C. necator H16 locus naming/organization reported in omics and review sources rather than via a dedicated biochemical characterization of Q9K4U8 itself. (kohlmann2014copingwithanoxia pages 5-6, zumft2008chapter13– pages 20-23)
NorR-family regulators are NtrC-like enhancer-binding proteins that activate transcription from σ54 (RpoN)-dependent promoters. Mechanistically, σ54-dependent activation typically requires an ATPase activator (an EBP) bound at an upstream enhancer site, which contacts the σ54-RNA polymerase closed complex and uses ATP hydrolysis to promote open-complex formation. (cadby2014theregulationof pages 59-63)
In C. necator (described under its historical name R. eutropha), NorR is described as a σ54-dependent enhancer-binding regulator that activates norA-linked promoters controlling functional nitric oxide reductase (NOR) systems. (zumft2008chapter13– pages 20-23)
Across bacteria, NorR is described as a three-domain protein comprising:
- an N-terminal GAF domain (signal/cofactor binding),
- a central AAA+ ATPase domain (the σ54-EBP motor), and
- a C-terminal helix-turn-helix (HTH) DNA-binding domain. (cadby2014theregulationof pages 59-63)
For C. necator/R. eutropha, the same architecture is described for its NorR regulator(s), aligning with UniProt’s domain summary for Q9K4U8 (GAF + AAA+ ATPase + DNA-binding fold). (zumft2008chapter13– pages 20-23)
Nitric oxide (NO) is a reactive intermediate produced during denitrification (e.g., during nitrite reduction). NorR-controlled NOR systems reduce NO and are therefore part of NO homeostasis and anaerobic respiration physiology. In C. necator H16, denitrification genes (including NOR components) are strongly induced under oxygen-limited/denitrifying conditions. (kohlmann2014copingwithanoxia pages 5-6, kohlmann2014copingwithanoxia pages 4-5)
Direct C. necator H16 evidence supports that the organism encodes two functional NOR loci:
- norR1A1B1 on megaplasmid pHG1, and
- norR2A2B2 on chromosome 2.
These loci encode transcriptional regulators (NorR1/NorR2) controlling their respective structural operons (norA1B1 and norA2B2). (kohlmann2014copingwithanoxia pages 5-6)
The chromosomal structural genes include norB2 and norA2 (locus IDs reported as H16_B2323 = norB2 and H16_B2324 = norA2), placing norR2 (H16_B2325) immediately in the expected regulatory position for the NOR2 operon. (kohlmann2014copingwithanoxia pages 5-6)
The C. necator H16 NOR structural genes norB1/norB2 encode quinol-oxidizing nitric oxide reductases (qNOR subtype). Thus, NorR2’s functional consequence is to control expression of a membrane-associated respiratory NO reductase system used during denitrification. (kohlmann2014copingwithanoxia pages 6-7)
For R. eutropha/C. necator, NorR is described as activating σ54-dependent norA-linked promoters and targeting partially palindromic enhancer sequences with a consensus GGT-(N7)-ACC. (zumft2008chapter13– pages 20-23)
A key mechanistic element of NorR-family regulators is NO sensing through a metal cofactor. The reviewed sources describe NorR as NO-responsive, sensing NO via a non-heme iron cofactor in the N-terminal GAF domain, with NO functioning as an allosteric effector. (cadby2014theregulationof pages 59-63)
Detailed biochemical evidence summarized for E. coli NorR indicates the GAF domain contains a mononuclear non-heme Fe center that binds NO to form an {Fe(NO)}7 mononitrosyl complex, thereby activating the AAA+ ATPase domain; ATP hydrolysis then drives σ54-RNA polymerase open-complex formation and transcriptional activation. (zumft2008chapter13– pages 20-23)
Interpretation for norR2/Q9K4U8: Given the conserved NorR domain architecture described for C. necator/R. eutropha and the explicit statement that NorR activation by NO explains NOR operon induction in C. necator H16 denitrification, the simplest functional annotation is that NorR2 is an NO-responsive σ54 EBP that couples NO (likely via a GAF-associated metal center) to ATPase-driven transcriptional activation of the NOR2 operon. Direct biochemical validation of the Fe–NO adduct in Q9K4U8 itself was not retrieved here, so this should be treated as inference based on strong homology/mechanistic conservation. (zumft2008chapter13– pages 20-23, kohlmann2014copingwithanoxia pages 5-6)
In the multi-omics study of denitrification in C. necator H16, denitrification-related reductase clusters form genomic “hot spots,” including an NAR2/NIR/NOR2 cluster on chromosome 2 (region III) and a separate set on plasmid pHG1 (region VI) containing additional denitrification modules (including NOR1 and NOS). This establishes the chromosome 2 norR2A2B2 system as part of the core denitrification response. (kohlmann2014copingwithanoxia pages 9-11)
The same dataset detected other denitrification regulators, including an FNR-like regulator (Fnr3) and a DNR-like regulator (DnrD, located in the pHG1 NIR/nor/nos cluster), with DnrD strongly induced during denitrification (32-fold at T|SP-D). This indicates NorR2 operates within a broader anaerobic regulatory program coordinating expression of reductases across denitrification stages. (kohlmann2014copingwithanoxia pages 7-8)
No direct subcellular localization experiment for NorR2/Q9K4U8 was retrieved. However, as a DNA-binding transcriptional regulator activating σ54-dependent promoters, its site of action is expected to be the cytosol/nucleoid-associated (i.e., interacting with chromosomal DNA and σ54-RNA polymerase). This is a functional inference consistent with the NorR paradigm and not a demonstrated localization for Q9K4U8. (cadby2014theregulationof pages 59-63)
Proteomics from denitrifying C. necator H16 shows that NorB1/NorB2 (qNOR catalytic subunits) are strongly enriched in membrane fractions, reported as ~20–30-fold higher abundance in membrane vs soluble fraction. NorA1/NorA2, described as soluble NO-binding partners, were also detected in membrane fractions, consistent with placing NO binding near the membrane (NO is hydrophobic) to support efficient reduction by the membrane-associated NorB complex. (kohlmann2014copingwithanoxia pages 6-7)
The most directly relevant quantitative dataset retrieved is the comprehensive denitrification proteomic/transcriptomic survey in C. necator H16 (published 2014; still widely used as a reference framework for this organism’s denitrification physiology).
Key statistics from this study:
- 2261 proteins identified (~34% of the genome). (kohlmann2014copingwithanoxia pages 4-5)
- Using p ≤ 0.05 and ≥4-fold change cutoffs, 324 proteins were differentially expressed (174 preferentially aerobic; 150 preferentially oxygen-deficient). (kohlmann2014copingwithanoxia pages 4-5)
- The chromosomal NOR2 genes showed strong induction under denitrifying conditions, with example reported log2-scale induction values for norB2 (H16_B2323) around ~7.2–7.3 and ~6.3–6.6, and for norA2 (H16_B2324) around ~7.8, 7.3, 7.1, 6.3, 4.8, 5.4 across the study’s contrasts, consistent with strong anaerobic activation attributed to NO/NorR activation. (kohlmann2014copingwithanoxia pages 5-6)
Within the literature successfully retrieved and read in this run, no 2023–2024 primary research articles were found that directly characterize norR2 (Q9K4U8/H16_B2325) in C. necator H16 at the level of regulon mapping, promoter binding, NO/metal biochemistry, or phenotype of a norR2 knockout.
Accordingly, the most authoritative mechanistic interpretation for NorR2 in C. necator H16 must still rely on:
- the organism-specific denitrification expression/regional context from the C. necator H16 omics survey (2014), and (kohlmann2014copingwithanoxia pages 5-6, kohlmann2014copingwithanoxia pages 4-5)
- authoritative synthesis of NorR/NOR regulation in R. eutropha/C. necator and NorR mechanistic chemistry from E. coli as summarized in a respiratory NOR chapter/review. (zumft2008chapter13– pages 20-23)
Because NorR2 is a transcriptional regulator of NO reductase genes, its real-world relevance is linked to control of NO toxicity and denitrification efficiency under low-oxygen conditions.
No directly retrieved applied study (2023–2024 or otherwise) explicitly deploys norR2 as an engineering target in C. necator H16; therefore, application statements above should be treated as pathway-driven implications rather than demonstrated implementations. (kohlmann2014copingwithanoxia pages 5-6, kohlmann2014copingwithanoxia pages 6-7)
An authoritative synthesis of respiratory nitric oxide reductase systems describes R. eutropha/C. necator as having σ54-dependent norA promoters activated by NorR and highlights NorR as the cognate regulator with recognizable upstream enhancer sites; it further integrates biochemical understanding from E. coli NorR (non-heme Fe–NO chemistry in the GAF domain) to explain NorR-family NO sensing and transcriptional control. (zumft2008chapter13– pages 20-23)
| Claim/feature | Evidence type | Key details | Source (first author year) | DOI/URL |
|---|---|---|---|---|
| Gene identity and locus context | C. necator direct | UniProt Q9K4U8 corresponds to norR2 / H16_B2325 in Cupriavidus necator H16. In the denitrification dataset, chromosome 2 carries a norR2A2B2 locus; H16_B2323 = norB2 and H16_B2324 = norA2, with NOR2 located in the chromosome-2 denitrification hot spot / region III. This supports assignment of H16_B2325 as the upstream regulator for the NOR2 operon (kohlmann2014copingwithanoxia pages 5-6, kohlmann2014copingwithanoxia pages 9-11). | Kohlmann 2014 | https://doi.org/10.1021/pr500491r |
| Domain architecture | Mixed: C. necator direct for NorR assignment; other-species general for detailed domain model | NorR in R. eutropha/C. necator is described as an NtrC-like, sigma54-dependent enhancer-binding regulator with N-terminal GAF, central AAA+ ATPase, and C-terminal DNA-binding domain architecture; this matches the domain annotation supplied for Q9K4U8 (zumft2008chapter13– pages 20-23, cadby2014theregulationof pages 59-63). | Zumft 2008; Cadby 2014 | https://doi.org/10.1016/b978-044452839-1.50014-0 |
| Mechanism of action | Mixed: C. necator direct for sigma54 / NorR-linked regulation; other-species general for sensing chemistry | In R. eutropha/C. necator, NorR activates sigma54-dependent norA-linked promoters and recognizes enhancer-like partially palindromic sites with consensus GGT-(N7)-ACC (zumft2008chapter13– pages 20-23). Detailed biochemical mechanism is from E. coli NorR: the GAF domain binds a mononuclear non-heme Fe center that forms an {Fe(NO)}7 mononitrosyl upon NO binding, which activates the AAA+ ATPase to drive open-complex formation by sigma54-RNA polymerase (zumft2008chapter13– pages 20-23, cadby2014theregulationof pages 59-63). | Zumft 2008; Cadby 2014 | https://doi.org/10.1016/b978-044452839-1.50014-0 |
| Regulatory targets | C. necator direct | The direct target is the norA2B2 promoter / operon on chromosome 2, part of the two functional NOR systems norR1A1B1 on pHG1 and norR2A2B2 on chromosome 2. Under denitrifying conditions, NOR2 genes are strongly induced: norB2 (H16_B2323) reported around log2 7.2-7.3 and 6.3-6.6 in dataset comparisons; norA2 (H16_B2324) around log2 7.8, 7.3, 7.1, 6.3, 4.8, and 5.4 across transcript / protein contrasts, consistent with NO-responsive NorR activation (kohlmann2014copingwithanoxia pages 5-6, kohlmann2014copingwithanoxia pages 6-7). | Kohlmann 2014 | https://doi.org/10.1021/pr500491r |
| Subcellular localization inference | Mixed: C. necator direct for NOR subunits; inferred for NorR2 | NorR2 is most plausibly a soluble cytosolic DNA-binding transcription regulator acting on chromosome 2 promoters; no direct localization experiment for NorR2 was reported in the gathered evidence (cadby2014theregulationof pages 59-63). For its regulated enzyme system, NorB1 / NorB2 were 20-30-fold more abundant in membrane fractions than soluble fractions, while NorA1 / NorA2, though considered soluble NO-binding partners, were also detected in membrane fractions, plausibly to bind hydrophobic NO near the membrane (kohlmann2014copingwithanoxia pages 6-7). | Cadby 2014; Kohlmann 2014 | https://doi.org/10.1021/pr500491r |
| Quantitative denitrification dataset statistics | C. necator direct | Combined proteomics / transcriptomics identified 2261 proteins, about 34 percent of the genome. Using p less than or equal to 0.05 and at least 4-fold change cutoffs, 324 proteins were differentially expressed: 174 enriched aerobically and 150 under oxygen deficiency; 20 and 55 proteins reached up to 16-fold overexpression in aerobic and anaerobic conditions, respectively. The denitrification regulator DnrD was strongly induced at T | SP-D: 32-fold (kohlmann2014copingwithanoxia pages 7-8, kohlmann2014copingwithanoxia pages 4-5). | Kohlmann 2014 |
Table: This table summarizes the strongest gathered evidence for functional annotation of Cupriavidus necator H16 norR2 (Q9K4U8/H16_B2325), separating direct organism-specific findings from inferences based on NorR-family studies in other bacteria. It is useful for distinguishing what is experimentally supported in C. necator from what is inferred from conserved NorR mechanism.
References
(kohlmann2014copingwithanoxia pages 5-6): Yvonne Kohlmann, Anne Pohlmann, Edward Schwartz, Daniela Zühlke, Andreas Otto, Dirk Albrecht, Christina Grimmler, Armin Ehrenreich, Birgit Voigt, Dörte Becher, Michael Hecker, Bärbel Friedrich, and Rainer Cramm. Coping with anoxia: a comprehensive proteomic and transcriptomic survey of denitrification. Journal of proteome research, 13 10:4325-38, Sep 2014. URL: https://doi.org/10.1021/pr500491r, doi:10.1021/pr500491r. This article has 15 citations and is from a peer-reviewed journal.
(kohlmann2014copingwithanoxia pages 9-11): Yvonne Kohlmann, Anne Pohlmann, Edward Schwartz, Daniela Zühlke, Andreas Otto, Dirk Albrecht, Christina Grimmler, Armin Ehrenreich, Birgit Voigt, Dörte Becher, Michael Hecker, Bärbel Friedrich, and Rainer Cramm. Coping with anoxia: a comprehensive proteomic and transcriptomic survey of denitrification. Journal of proteome research, 13 10:4325-38, Sep 2014. URL: https://doi.org/10.1021/pr500491r, doi:10.1021/pr500491r. This article has 15 citations and is from a peer-reviewed journal.
(zumft2008chapter13– pages 20-23): Walter G. Zumft. Chapter 13 – respiratory nitric oxide reductases, norb and norz, of the heme–copper oxidase type. ArXiv, pages 327-353, Jan 2008. URL: https://doi.org/10.1016/b978-044452839-1.50014-0, doi:10.1016/b978-044452839-1.50014-0. This article has 5 citations.
(cadby2014theregulationof pages 59-63): IT Cadby. The regulation of gene expression in sulphate reducing bacteria. Unknown journal, 2014.
(kohlmann2014copingwithanoxia pages 4-5): Yvonne Kohlmann, Anne Pohlmann, Edward Schwartz, Daniela Zühlke, Andreas Otto, Dirk Albrecht, Christina Grimmler, Armin Ehrenreich, Birgit Voigt, Dörte Becher, Michael Hecker, Bärbel Friedrich, and Rainer Cramm. Coping with anoxia: a comprehensive proteomic and transcriptomic survey of denitrification. Journal of proteome research, 13 10:4325-38, Sep 2014. URL: https://doi.org/10.1021/pr500491r, doi:10.1021/pr500491r. This article has 15 citations and is from a peer-reviewed journal.
(kohlmann2014copingwithanoxia pages 6-7): Yvonne Kohlmann, Anne Pohlmann, Edward Schwartz, Daniela Zühlke, Andreas Otto, Dirk Albrecht, Christina Grimmler, Armin Ehrenreich, Birgit Voigt, Dörte Becher, Michael Hecker, Bärbel Friedrich, and Rainer Cramm. Coping with anoxia: a comprehensive proteomic and transcriptomic survey of denitrification. Journal of proteome research, 13 10:4325-38, Sep 2014. URL: https://doi.org/10.1021/pr500491r, doi:10.1021/pr500491r. This article has 15 citations and is from a peer-reviewed journal.
(kohlmann2014copingwithanoxia pages 7-8): Yvonne Kohlmann, Anne Pohlmann, Edward Schwartz, Daniela Zühlke, Andreas Otto, Dirk Albrecht, Christina Grimmler, Armin Ehrenreich, Birgit Voigt, Dörte Becher, Michael Hecker, Bärbel Friedrich, and Rainer Cramm. Coping with anoxia: a comprehensive proteomic and transcriptomic survey of denitrification. Journal of proteome research, 13 10:4325-38, Sep 2014. URL: https://doi.org/10.1021/pr500491r, doi:10.1021/pr500491r. This article has 15 citations and is from a peer-reviewed journal.
id: Q9K4U8
gene_symbol: norR2
product_type: PROTEIN
status: DRAFT
taxon:
id: NCBITaxon:381666
label: Cupriavidus necator (strain ATCC 17699 / DSM 428 / KCTC 22496 / NCIMB 10442 / H16 / Stanier 337)
description: >-
norR2 encodes a nitric oxide-responsive sigma-54-dependent transcriptional
activator in Cupriavidus necator H16. It is the chromosomal paralog of the
megaplasmid-encoded NorR1 and has the conserved NorR GAF, AAA+ ATPase, and
Fis-family helix-turn-helix DNA-binding architecture.
existing_annotations:
- term:
id: GO:0005524
label: ATP binding
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
NorR2 contains the conserved sigma-54-interaction/AAA+ ATPase region of
NorR-family bacterial enhancer-binding proteins. ATP binding is plausible,
but ATP hydrolysis is the more informative molecular function.
action: MODIFY
reason: >-
The InterPro evidence identifies the sigma-54 interaction ATP-binding
region, while NorR-family biochemical work shows that NO binding
stimulates ATPase activity to activate transcription by RNA polymerase.
proposed_replacement_terms:
- id: GO:0016887
label: ATP hydrolysis activity
additional_reference_ids:
- PMID:16193057
supported_by:
- reference_id: file:CUPNH/norR2/norR2-uniprot.txt
supporting_text: InterPro; IPR002078; Sigma_54_int.
- reference_id: PMID:16193057
supporting_text: Binding of NO stimulates the ATPase activity of NorR, enabling the activation of transcription by RNA polymerase.
- term:
id: GO:0006355
label: regulation of DNA-templated transcription
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
NorR2 positively activates NO-responsive transcription of nitric oxide
reductase genes through the NorR/sigma-54 regulatory system.
action: MODIFY
reason: >-
The existing term is correct but too broad. Ralstonia studies show NorR
is required for transcriptional activation of the norA/norB nitric oxide
reductase operon in response to NO.
proposed_replacement_terms:
- id: GO:0045893
label: positive regulation of DNA-templated transcription
additional_reference_ids:
- PMID:11069685
- PMID:15667304
supported_by:
- reference_id: PMID:11069685
supporting_text: The regulator gene maps adjacent to norAB, is divergently transcribed and present in two copies on the megaplasmid pHG1 (norR1) and the chromosome (norR2).
- reference_id: PMID:15667304
supporting_text: norB and the adjacent norA form an operon that is controlled by the sigma(54)-dependent transcriptional activator NorR in response to NO.
- term:
id: GO:0043565
label: sequence-specific DNA binding
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
NorR2 has a Fis-family helix-turn-helix DNA-binding domain, but generic
sequence-specific DNA binding misses its NO-responsive transcriptional
activator function.
action: MODIFY
reason: >-
NorR proteins bind upstream activator sequences and activate
sigma-54-dependent transcription in response to NO. GO:0141097 captures
this ligand-modulated activator activity more precisely than generic DNA
binding.
proposed_replacement_terms:
- id: GO:0141097
label: ligand-modulated transcription activator activity
additional_reference_ids:
- PMID:15667304
- PMID:16193057
supported_by:
- reference_id: PMID:15667304
supporting_text: A NorR derivative containing MalE in place of the N-terminal domain binds to a 73 bp region upstream of norA that includes three copies of the putative upstream activator sequence GGT-(N(7))-ACC.
- reference_id: PMID:16193057
supporting_text: Here we show that the regulatory domain of NorR contains a mononuclear non-haem iron centre, which reversibly binds NO.
- term:
id: GO:0019333
label: denitrification pathway
evidence_type: IEA
original_reference_id: GO_REF:0000041
review:
summary: >-
NorR2 controls expression of NO reductase but is not itself a
denitrification enzyme. The UniPathway row imports pathway context too
directly for a regulator.
action: MARK_AS_OVER_ANNOTATED
reason: >-
Species-specific evidence supports NorR2 as the chromosomal copy of an
NO-responsive regulator of nitric oxide reductase expression. UniProt
records denitrification as regulatory context, and the Ralstonia NorR
study states that other denitrification-chain steps are independent of
NorR.
additional_reference_ids:
- PMID:11069685
supported_by:
- reference_id: file:CUPNH/norR2/norR2-uniprot.txt
supporting_text: 'PATHWAY: Nitrogen metabolism; nitrate reduction (denitrification) [regulation].'
- reference_id: PMID:11069685
supporting_text: This reaction is not strictly co-ordinated on the regulatory level with the other nitrogen oxide-reducing steps of the denitrification chain that are independent of NorR.
- term:
id: GO:0141097
label: ligand-modulated transcription activator activity
evidence_type: ISS
original_reference_id: PMID:11069685
review:
summary: >-
NorR2 is the chromosomal copy of the NO-responsive NorR transcriptional
activator system in C. necator H16.
action: NEW
reason: >-
The existing sequence-specific DNA-binding annotation is too narrow for
NorR2. Direct mutant evidence in this organism was generated mainly for
norR1, so this NEW term is treated as ISS for norR2 based on the
chromosomal paralog relationship, conserved GAF/AAA+/Fis-domain NorR
architecture, and NorR-family biochemical evidence for NO sensing and
ATPase-stimulated sigma-54 activation.
additional_reference_ids:
- PMID:15667304
- PMID:16193057
supported_by:
- reference_id: PMID:11069685
supporting_text: The regulator gene maps adjacent to norAB, is divergently transcribed and present in two copies on the megaplasmid pHG1 (norR1) and the chromosome (norR2).
- reference_id: PMID:15667304
supporting_text: The N-terminal domain of NorR contains a GAF module and is hypothesized to interact with a signal molecule.
- reference_id: PMID:16193057
supporting_text: Binding of NO stimulates the ATPase activity of NorR, enabling the activation of transcription by RNA polymerase.
- reference_id: file:CUPNH/norR2/norR2-deep-research-falcon.md
supporting_text: >-
Falcon synthesis treats NorR2 as the chromosomal NorR paralog in the
norR2A2B2 locus, with conserved GAF, AAA+ ATPase, and DNA-binding
architecture supporting NO-responsive sigma-54 transcriptional
activation by homology and locus context.
- reference_id: file:interpro/panther/PTHR32071/PTHR32071-deep-research-falcon.md
supporting_text: >-
PTHR32071 family research supports sigma-54 enhancer-binding proteins
as conserved AAA+ transcriptional activators with pathway-specific
sensory-domain inputs.
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings: []
- id: GO_REF:0000041
title: Gene Ontology annotation based on UniPathway vocabulary mapping
findings: []
- id: PMID:11069685
title: A novel NO-responding regulator controls the reduction of nitric oxide in Ralstonia eutropha.
findings:
- statement: Ralstonia has two NorR copies, norR1 and norR2, that control NO-responsive nitric oxide reductase transcription.
supporting_text: The regulator gene maps adjacent to norAB, is divergently transcribed and present in two copies on the megaplasmid pHG1 (norR1) and the chromosome (norR2).
reference_section_type: ABSTRACT
full_text_unavailable: true
- statement: NorR does not coordinate all denitrification steps.
supporting_text: This reaction is not strictly co-ordinated on the regulatory level with the other nitrogen oxide-reducing steps of the denitrification chain that are independent of NorR.
reference_section_type: ABSTRACT
full_text_unavailable: true
- id: PMID:15667304
title: Transcriptional regulation of nitric oxide reduction in Ralstonia eutropha H16.
findings:
- statement: NorR is an NO-responsive sigma-54-dependent activator that binds upstream activator sequences.
supporting_text: norB and the adjacent norA form an operon that is controlled by the sigma(54)-dependent transcriptional activator NorR in response to NO.
reference_section_type: ABSTRACT
full_text_unavailable: true
- id: PMID:16193057
title: A non-haem iron centre in the transcription factor NorR senses nitric oxide.
findings:
- statement: NorR-family proteins couple NO binding to ATPase-dependent transcription activation.
supporting_text: Binding of NO stimulates the ATPase activity of NorR, enabling the activation of transcription by RNA polymerase.
reference_section_type: ABSTRACT
full_text_unavailable: true
- id: file:CUPNH/norR2/norR2-uniprot.txt
title: UniProt record for norR2
findings:
- statement: >-
UniProt describes NorR2 as required for NO-induced NO reductase expression
and not required for nitrous oxide reductase expression.
- id: file:CUPNH/norR2/norR2-deep-research-falcon.md
title: Falcon deep research for norR2
findings:
- statement: >-
Deep research supports NorR2 as an NO-responsive sigma-54 enhancer-binding
regulator of the chromosomal NOR2 system and explicitly marks detailed
Fe-NO/GAF chemistry as family-level inference rather than direct
biochemical evidence for Q9K4U8.
- id: file:interpro/panther/PTHR32071/PTHR32071-deep-research-falcon.md
title: Falcon family deep research for PTHR32071 sigma-54-dependent transcriptional regulators
findings:
- statement: >-
Family research found that the conserved sigma-54/AAA+ activation module
is reused in many bacterial regulators, while N-terminal sensory domains
define the regulated pathway and signal.
core_functions:
- description: >-
Activates sigma-54-dependent nitric oxide reductase transcription in
response to nitric oxide through a conserved NorR regulatory architecture.
molecular_function:
id: GO:0141097
label: ligand-modulated transcription activator activity
directly_involved_in:
- id: GO:0045893
label: positive regulation of DNA-templated transcription
supported_by:
- reference_id: PMID:11069685
supporting_text: >-
The regulator gene maps adjacent to norAB, is divergently transcribed and
present in two copies on the megaplasmid pHG1 (norR1) and the chromosome
(norR2).
- reference_id: PMID:15667304
supporting_text: >-
norB and the adjacent norA form an operon that is controlled by the
sigma(54)-dependent transcriptional activator NorR in response to NO.
- reference_id: file:CUPNH/norR2/norR2-uniprot.txt
supporting_text: >-
FUNCTION: Required for the nitric oxide (NO) induced expression of NO
reductase. Not required for expression of nitrate reductase or nitrous
oxide reductase.
- reference_id: file:CUPNH/norR2/norR2-deep-research-falcon.md
supporting_text: >-
The simplest functional annotation is that NorR2 is an NO-responsive
sigma-54 bacterial enhancer-binding protein that couples NO sensing to
ATPase-driven transcriptional activation of the NOR2 operon.
- reference_id: file:interpro/panther/PTHR32071/PTHR32071-deep-research-falcon.md
supporting_text: >-
Sigma-54 enhancer-binding proteins conserve AAA+ transcriptional
activation but differ in sensory wiring, supporting NorR2 as an
NO-responsive regulator rather than a direct denitrification enzyme.