OhrR (PA2849) is the organic hydroperoxide-sensing transcriptional repressor of Pseudomonas aeruginosa, a 151-residue MarR/OhrR-family protein with a winged-helix DNA-binding region. It binds the operators of the thiol peroxidase gene ohr (PA2850) and of its own gene and represses their transcription. Oxidation of OhrR by an organic hydroperoxide changes its structure so that it releases the operators, which induces ohr and ohrR expression; the regulator therefore couples organic hydroperoxide sensing to the peroxide-detoxifying response. An ohrR mutant is more resistant to organic hydroperoxides, consistent with de-repressed ohr, and is attenuated in the Caenorhabditis elegans infection model.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000976 transcription cis-regulatory region binding | IMP PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | ACCEPT | Summary: CollecTF IMP for the same operator-binding claim. Reason: Same claim as the IPI row; the rows reinforce each other. Supporting Evidence: PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes |
| GO:0000976 transcription cis-regulatory region binding | IPI PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | ACCEPT | Summary: CollecTF IPI; OhrR binds the ohr and ohrR operators directly. Reason: Direct operator binding is the central result of the paper (abstract read) and is the basis of the CollecTF site records. Supporting Evidence: PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes file:PSEAE/ohrR/ohrR-uniprot.txt DNA_BIND 61..84 |
| GO:0001217 DNA-binding transcription repressor activity | IMP PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | ACCEPT | Summary: CollecTF IMP for the same repressor activity. Reason: Consistent with the IPI row; the ohrR mutant de-represses ohr and becomes organic hydroperoxide resistant. Supporting Evidence: PMID:20139188 ohrR and ohr mutants show increased and decreased resistance to organic hydroproxides, respectively, compared to a parental strain |
| GO:0001217 DNA-binding transcription repressor activity | IPI PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | ACCEPT | Summary: CollecTF IPI; repressor activity on the ohr and ohrR promoters. Reason: Operator binding plus loss of repression on oxidation establishes a DNA-binding transcription repressor activity. Supporting Evidence: PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes PMID:20139188 Exposure to an organic hydroperoxide leads to oxidation of OhrR and to subsequent structural changes that result in the loss of the repressor's ability to bind to the operators that allow expression of the target genes |
| GO:0003677 DNA binding | IEA GO_REF:0000104 | TOO GENERAL | Summary: Rule-based IEA, DNA binding, from the MarR-type HTH signature. Reason: Entailed by GO:0000976 transcription cis-regulatory region binding, accepted here. |
| GO:0003700 DNA-binding transcription factor activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO, DNA-binding transcription factor activity. Reason: GO:0001217 DNA-binding transcription repressor activity, accepted here, is_a descendant of it. |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location keyword mapping, cytoplasm. Reason: The only location consistent with a DNA-binding repressor of a bacterial chromosomal operon. The underlying UniProt statement is ARBA-derived rather than experimental, so this is accepted on biological grounds, not on the keyword. Supporting Evidence: PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes |
| GO:0006351 DNA-templated transcription | IEA GO_REF:0000104 | REMOVE | Summary: Rule-based IEA, DNA-templated transcription. Reason: OhrR is a repressor: it does not perform transcription, it controls it. The process term for its activity is GO:0045892 negative regulation of DNA-templated transcription, which it already carries with experimental evidence. A mapping from an HTH signature to the transcription process itself is an electronic over-reach. Supporting Evidence: PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes |
| GO:0006355 regulation of DNA-templated transcription | IBA GO_REF:0000033 | TOO GENERAL | Summary: PAINT IBA from PTN002109389 (MarR-family regulators); OhrR is one of eight seeds, with B. subtilis OhrR and ScoC, E. coli MarR, SlyA and MprA, S. oneidensis OhrR and PA0942. Reason: The IBD is well founded: B. subtilis OhrR (IMP/IDA GO:0045892, IMP GO:0001227), E. coli MarR (IDA GO:0003677, IMP GO:0045892) and MprA (IDA GO:0000976) all have experimental transcription-regulation annotations, so it stands without this seed, and regulation of transcription suits the whole MarR clade. For OhrR the more specific GO:0045892, held with experimental evidence, entails it. Supporting Evidence: PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000120 | TOO GENERAL | Summary: Combined automated IEA, regulation of DNA-templated transcription. Reason: Entailed by the accepted GO:0045892. |
| GO:0006950 response to stress | IBA GO_REF:0000033 | MODIFY | Summary: PAINT IBA from PTN002109389 for response to stress; seeded by B. subtilis OhrR and E. coli MarR (OhrR is not a seed of this IBD). Reason: Correct but general. OhrR is itself oxidised by organic hydroperoxides and sets the level of the Ohr peroxidase, so the specific response it takes part in is the response to hydroperoxide. The regulation term GO:1900407 held elsewhere in this review is a regulation class, not a descendant of response to stress, so it does not entail this row. The IBD itself is sound: B. subtilis OhrR carries IMP GO:0042542 response to hydrogen peroxide and E. coli MarR IMP GO:0071236/GO:0009408 stress responses, so it stands without OhrR, which is not among its two seeds. Propagation Review Root cause: NO FAILURE CORE Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002109389 · PTN002109389 SUPPORTS TRANSFER MarR-family node (229 leaf IBAs, 33 taxa). A generic stress-response term is appropriate for a node that mixes peroxide, antibiotic-efflux and sporulation regulators; for OhrR the hydroperoxide-specific child is supported. UniProtKB:O34777 · ohrR (B. subtilis; IBD seed) SUPPORTS TRANSFER Carries IMP GO:0042542 response to hydrogen peroxide; an organic hydroperoxide sensor like the target. UniProtKB:P27245 · marR (E. coli; IBD seed) SUPPORTS TRANSFER Carries IMP GO:0071236 response to antibiotic and GO:0009408 response to heat, i.e. stress responses of a different kind, which is why the node term stops at the root. Proposed replacements: response to hydroperoxide Supporting Evidence: PMID:20139188 ohrR and ohr mutants show increased and decreased resistance to organic hydroproxides, respectively, compared to a parental strain PMID:20139188 Exposure to an organic hydroperoxide leads to oxidation of OhrR and to subsequent structural changes that result in the loss of the repressor's ability to bind to the operators that allow expression of the target genes |
| GO:0032993 protein-DNA complex | IMP PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | KEEP AS NON CORE | Summary: CollecTF IMP for the same protein-DNA complex claim. Reason: Consistent with the IPI row (the same call was made for fleQ in this repository). Supporting Evidence: PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes |
| GO:0032993 protein-DNA complex | IPI PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | KEEP AS NON CORE | Summary: CollecTF IPI; OhrR in complex with its operator DNA. Reason: A restatement of operator binding as a component term; true but adds nothing beyond the accepted MF rows. Supporting Evidence: PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes |
| GO:0045892 negative regulation of DNA-templated transcription | EXP PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | ACCEPT | Summary: CollecTF EXP for the same repression claim. Reason: Same claim, independent evidence line in the same paper (binding plus expression). Supporting Evidence: PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes |
| GO:0045892 negative regulation of DNA-templated transcription | IEP PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | ACCEPT | Summary: CollecTF IEP; differential induction of ohr and ohrR by tert-butyl hydroperoxide. Reason: Expression-pattern evidence for the same repression, consistent with the IMP and EXP rows. Supporting Evidence: PMID:20139188 Exposure to an organic hydroperoxide leads to oxidation of OhrR and to subsequent structural changes that result in the loss of the repressor's ability to bind to the operators that allow expression of the target genes |
| GO:0045892 negative regulation of DNA-templated transcription | IMP PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | ACCEPT | Summary: PseudoCAP IMP (and the IBD seed row); ohrR mutant de-represses ohr and gains organic hydroperoxide resistance. Reason: Mutant and operator-binding data agree: OhrR represses ohr and its own gene, and the repression is relieved on oxidation. This is the gene's core function and the seed is sound. Supporting Evidence: PMID:20139188 ohrR encodes an organic hydroperoxide sensor and a transcriptional repressor that regulates organic hydroperoxide-inducible expression of a thiol peroxidase gene, ohr, and itself PMID:20139188 OhrR binds directly to the operators and represses transcription of these genes PMID:20139188 ohrR and ohr mutants show increased and decreased resistance to organic hydroproxides, respectively, compared to a parental strain |
| GO:1900407 regulation of cellular response to oxidative stress | IMP PMID:20139188 Analyses of the regulatory mechanism and physiological roles... | ACCEPT | Summary: PseudoCAP IMP; the ohrR mutant is more resistant to organic hydroperoxides and the ohr mutant less so. Reason: OhrR sets the level of the Ohr thiol peroxidase and is itself the hydroperoxide sensor, so it regulates the cellular response to this oxidative stress. The mutant phenotype is direct evidence. Supporting Evidence: PMID:20139188 ohrR and ohr mutants show increased and decreased resistance to organic hydroproxides, respectively, compared to a parental strain PMID:20139188 Exposure to an organic hydroperoxide leads to oxidation of OhrR and to subsequent structural changes that result in the loss of the repressor's ability to bind to the operators that allow expression of the target genes |
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Download this section (compressed HTML)Q: Which cysteine chemistry does P. aeruginosa OhrR use: the one-cysteine sulfenamide route of B. subtilis OhrR, or a two-cysteine disulfide switch as in Xanthomonas OhrR?
Experiment: Mass spectrometry and cysteine-substitution analysis of purified OhrR after tert-butyl hydroperoxide treatment, with operator-binding assays, to define the redox switch.
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The oxidation chemistry that switches P. aeruginosa OhrR off its operators, and whether a low-molecular-weight thiol partner is involved, is undetermined.
BIOLOGY
What is known: It is established that organic hydroperoxide exposure oxidises OhrR and abolishes operator binding, and that the protein belongs to the one-cysteine/two-cysteine OhrR subfamily.
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