Tpx (PA2532) is the atypical 2-Cys thiol peroxidase (peroxiredoxin, EC 1.11.1.24) of Pseudomonas aeruginosa. Its peroxidatic cysteine (Cys60) reduces hydrogen peroxide and organic hydroperoxides (cumene and tert-butyl hydroperoxide) and forms an intramolecular disulfide with the resolving cysteine (Cys94), which is reduced by thioredoxin and thioredoxin reductase with NADPH. Tpx has a low Km for organic hydroperoxides and a Km for H2O2 in the submillimolar range, and a tpx deletion mutant is more sensitive to 0.5 mM H2O2 but not to high H2O2 concentrations, so Tpx protects against moderate peroxide stress. Unlike E. coli Tpx it lacks a typical periplasmic signal sequence and appears to be cytoplasmic. tpx is strongly induced by redox-cycling agents and diamide and is repressed by IscR.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0008379 obsolete thioredoxin peroxidase activity | IBA GO_REF:0000033 | MODIFY | Summary: Thioredoxin-dependent peroxidase activity is the core function of Tpx; the term GO:0008379 is now obsolete and its replacement is GO:0140824 thioredoxin-dependent peroxiredoxin activity. Reason: The IBD at PTN002454730 is sound: it is seeded by E. coli Tpx (P0A862, IDA PMID:7499381) and by P. aeruginosa Tpx (PseudoCAP IDA), and it stands on the E. coli seed alone. GOA now labels GO:0008379 obsolete. The P. aeruginosa enzyme was shown to reduce organic hydroperoxides as well as H2O2 with thioredoxin, which is exactly GO:0140824 (hydroperoxide-general), so that is the replacement. Propagation Review Root cause: SOURCE STALE OR MISSING Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002454730 Β· PTN002454730 SOURCE STALE OR MISSING Thiol peroxidase clade (32 leaves, 30 taxa). The function placed is correct for the clade, but the node term GO:0008379 has been obsoleted; it should be updated to GO:0140824. UniProtKB:P0A862 Β· E. coli Tpx SUPPORTS TRANSFER IDA GO:0008379 (PMID:7499381) and EXP GO:0140824 (PMID:12514184); supports the IBD independently of the P. aeruginosa seed. UniProtKB:P57668 Β· tpx (PA2532) SUPPORTS TRANSFER PseudoCAP IDA seed (PMID:22609922): purified Tpx coupled to TrxA/TrxB/NADPH reduces H2O2, CHP and BHP. Sound. Proposed replacements: thioredoxin-dependent peroxiredoxin activity Supporting Evidence: PMID:22609922 The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. PMID:22609922 When the assays were carried out in the absence of either TrxA or TrxB, no oxidation of NADPH to NADP + occurred |
| GO:0008379 obsolete thioredoxin peroxidase activity | IDA PMID:22609922 Pseudomonas aeruginosa thiol peroxidase protects against hyd... | MODIFY | Summary: PseudoCAP seed row: purified recombinant Tpx reduces H2O2 and organic hydroperoxides in a TrxA/TrxB/NADPH-coupled assay, with no activity when either Trx component is omitted. Sound; refine the obsolete term to GO:0140824. Reason: Full text read: the coupled assay and kinetic parameters for H2O2, CHP and BHP directly show thioredoxin-dependent peroxiredoxin activity. The only change is the obsolete term; GO:0140824 covers all three substrates shown. Proposed replacements: thioredoxin-dependent peroxiredoxin activity Supporting Evidence: PMID:22609922 The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. PMID:22609922 Tpx contains thiol-dependent peroxidase activity and is capable of reducing either organic hydroperoxides or H 2 O 2 by using reduced thioredoxin (Trx) as an electron donor. PMID:22609922 When the assays were carried out in the absence of either TrxA or TrxB, no oxidation of NADPH to NADP + occurred |
| GO:0008379 obsolete thioredoxin peroxidase activity | IEA GO_REF:0000120 | MODIFY | Summary: Obsolete term; replace with GO:0140824. Reason: Same function as the IDA row, which the gene also carries as GO:0140824 (IEA, from EC 1.11.1.24). Proposed replacements: thioredoxin-dependent peroxiredoxin activity Supporting Evidence: file:PSEAE/tpx/tpx-uniprot.txt Reaction=a hydroperoxide + [thioredoxin]-dithiol = an alcohol + [thioredoxin]-disulfide + H2O file:PSEAE/tpx/tpx-uniprot.txt IPR002065; TPX. |
| GO:0016209 antioxidant activity | IEA GO_REF:0000120 | TOO GENERAL | Summary: True but entailed by thioredoxin-dependent peroxiredoxin activity. Reason: GO:0140824, accepted here, is_a peroxidase activity, which is_a GO:0016209 antioxidant activity. Supporting Evidence: PMID:22609922 The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: True but entailed by thioredoxin-dependent peroxiredoxin activity. Reason: GO:0140824, accepted here, is a descendant of GO:0016491 oxidoreductase activity. Supporting Evidence: PMID:22609922 The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. |
| GO:0016684 oxidoreductase activity, acting on peroxide as acceptor | IEA GO_REF:0000002 | TOO GENERAL | Summary: True but entailed by thioredoxin-dependent peroxiredoxin activity. Reason: GO:0140824, accepted here, is_a GO:0016684 oxidoreductase activity, acting on peroxide as acceptor (via peroxidase activity). Supporting Evidence: PMID:22609922 The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. |
| GO:0034599 cellular response to oxidative stress | IBA GO_REF:0000033 | TOO GENERAL | Summary: True; Tpx protects against peroxide stress. Entailed by cellular response to hydrogen peroxide, which Tpx carries from its own mutant data. IBD sound. Reason: GO:0070301 cellular response to hydrogen peroxide, accepted here from the tpx mutant and complementation data, is_a GO:0034599. The IBD at PTN002454730 is seeded by E. coli Tpx (IMP, PMID:8824604) and P. aeruginosa Tpx (PseudoCAP IMP of GO:0070301) and stands on either seed. Supporting Evidence: PMID:22609922 The Ξ tpx mutant was more than 10-fold more sensitive to 0.5 mM H 2 O 2 than the PAO1 wild type PMID:22609922 This altered phenotype could be complemented in the Ξ tpx mutant carrying pTrxA for trans -expression of tpx from the pUFR047 plasmid |
| GO:0034599 cellular response to oxidative stress | IEA GO_REF:0000117 | TOO GENERAL | Summary: Entailed by cellular response to hydrogen peroxide. Reason: Same as the IBA row; GO:0070301 is_a GO:0034599. Supporting Evidence: PMID:22609922 The Ξ tpx mutant was more than 10-fold more sensitive to 0.5 mM H 2 O 2 than the PAO1 wild type |
| GO:0070301 cellular response to hydrogen peroxide | IMP PMID:22609922 Pseudomonas aeruginosa thiol peroxidase protects against hyd... | ACCEPT | Summary: PseudoCAP seed row: a tpx deletion mutant is more than 10-fold more sensitive to 0.5 mM H2O2, complemented by tpx in trans. Sound. Reason: Full text read. The mutant phenotype is directly explained by the loss of the gene's own peroxidase activity (Km for H2O2 in the submillimolar range), so this is participation, not an indirect phenotype. The row seeds the PTN002454730 IBD of GO:0034599 and is sound. Supporting Evidence: PMID:22609922 The Ξ tpx mutant was more than 10-fold more sensitive to 0.5 mM H 2 O 2 than the PAO1 wild type PMID:22609922 This altered phenotype could be complemented in the Ξ tpx mutant carrying pTrxA for trans -expression of tpx from the pUFR047 plasmid PMID:22609922 It can be envisaged that Tpx is the main enzyme that defends against H 2 O 2 at βΌ0.5 mM because its K m value is in this range. |
| GO:0098869 cellular oxidant detoxification | IEA GO_REF:0000120 | ACCEPT | Summary: Tpx detoxifies H2O2 and organic hydroperoxides. Reason: Peroxide reduction by Tpx is the detoxification step itself, and the mutant shows reduced protection against H2O2. Supporting Evidence: PMID:22609922 The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. PMID:22609922 The Ξ tpx mutant was more than 10-fold more sensitive to 0.5 mM H 2 O 2 than the PAO1 wild type |
| GO:0140824 thioredoxin-dependent peroxiredoxin activity | IEA GO_REF:0000120 | ACCEPT | Summary: Thioredoxin-dependent peroxiredoxin activity; the core molecular function, shown directly for this protein. Reason: Supported by the IDA data on purified P. aeruginosa Tpx with H2O2, cumene and tert-butyl hydroperoxide. Supporting Evidence: PMID:22609922 The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. PMID:22609922 When the assays were carried out in the absence of either TrxA or TrxB, no oxidation of NADPH to NADP + occurred file:PSEAE/tpx/tpx-uniprot.txt Reaction=a hydroperoxide + [thioredoxin]-dithiol = an alcohol + [thioredoxin]-disulfide + H2O |
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Download this section (compressed HTML)Q: Is P. aeruginosa Tpx cytoplasmic, as the PhoA/LacZ fusions suggest, unlike periplasmic E. coli Tpx, and does that location explain its preference for moderate H2O2 levels?
Experiment: Fractionate PAO1 cells expressing native Tpx and immunoblot cytoplasmic and periplasmic fractions with marker controls to establish its compartment.
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