PA2078 is the (7S,10S)-hydroperoxide diol synthase (7,10-DS) of the oleate-diol synthase pathway of Pseudomonas aeruginosa. It converts 10-H(P)OME, the hydroperoxide made from oleic acid by its operon partner PA2077, into the oxylipin 7,10-DiHOME, which accumulates outside the cell. PA2078 is a periplasmic protein of the di-heme cytochrome c peroxidase family (FadCcp subfamily, an in-paralog of PA2077), but neither of its heme sites is required for diol synthase activity, so its catalytic site lies elsewhere. Its co-expression relieves the toxicity of PA2077-derived hydroperoxide.
Definition: Catalysis of the reaction (10S)-hydroperoxy-(8E)-octadecenoate = (7S,10S)-dihydroxy-(8E)-octadecenoate.
Justification: PA2078 performs this reaction; GO has only the analogous fungal linoleate 8-hydroperoxide isomerase term and the general intramolecular hydroxytransferase parent.
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004130 cytochrome-c peroxidase activity | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: IBA from the family-level Ccp node PTN000779264, seeded by P. aeruginosa CcpA and E. coli YhjA. PA2078 is a FadCcp-subfamily diol synthase whose heme sites are not required for its known activity. Reason: Ancestral family activity never tested for PA2078; its characterized activity is a heme-independent hydroperoxide-to-diol conversion. Same call as on PA2077. Propagation Review Root cause: PROPAGATION BAD Failure modes: FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN000779264 · PTN000779264 SUPPORTS SOURCE BUT NOT TARGET Family-level di-heme Ccp node; sound for classical peroxidases, but PA2078 has a different activity that does not use its hemes. UniProtKB:P14532 · ccpA (P. aeruginosa cytochrome c551 peroxidase) SUPPORTS SOURCE BUT NOT TARGET Classical bacterial Ccp in the main peroxidase branch. UniProtKB:P37197 · yhjA (E. coli) SUPPORTS SOURCE BUT NOT TARGET Classical bacterial Ccp in the main peroxidase branch. Supporting Evidence: PMID:26154497 These results indicate that neither the proximal or distal heme groups, nor the cysteine putatively related to P450 enzymes are involved in the catalytic activity of PA2078. |
| GO:0009055 electron transfer activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: InterPro2GO from the cytochrome c domain. No electron-carrier role is known for PA2078. Reason: Domain-based; PA2078 is an enzyme whose activity does not even need its hemes, so an electron carrier function is unsupported. Supporting Evidence: PMID:26154497 These results indicate that neither the proximal or distal heme groups, nor the cysteine putatively related to P450 enzymes are involved in the catalytic activity of PA2078. |
| GO:0020037 heme binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: PA2078 keeps two CXXCH heme c attachment motifs, but neither heme site is needed for diol synthase activity. Reason: Heme attachment is likely from the motifs, but the hemes appear to be an inherited, non-catalytic feature; non-core. Supporting Evidence: PMID:26154497 These results indicate that neither the proximal or distal heme groups, nor the cysteine putatively related to P450 enzymes are involved in the catalytic activity of PA2078. |
| GO:0031408 oxylipin biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN002826263, seeded by PA2078 itself and PA2077. True for PA2078, which has its own IMP evidence. Reason: Correct for this leaf. The node term over-reaches for the other five leaves; that GO_CENTRAL defect is recorded once on the PA2077 IBA row (genes/PSEAE/PA2077/PA2077-ai-review.yaml). Supporting Evidence: PMID:24980978 whereas PA2078 encodes for the (7S,10S)-hydroperoxide diol synthase enzyme (7,10-DS) which allows the conversion of 10-H(P)OME into 7,10-DiHOME. |
| GO:0031408 oxylipin biosynthetic process | IMP PMID:24980978 Unveiling the genes responsible for the unique Pseudomonas a... | ACCEPT | Summary: PseudoCAP IMP and a seed of the PTN002826263 IBD. The PA2078 mutant releases no hydroxylated fatty acids; complementation assigns it the second step. Reason: PA2078 catalyses the second step of 7,10-DiHOME synthesis. Seed verdict SOUND. Supporting Evidence: PMID:24980978 whereas PA2078 encodes for the (7S,10S)-hydroperoxide diol synthase enzyme (7,10-DS) which allows the conversion of 10-H(P)OME into 7,10-DiHOME. |
| GO:0098869 cellular oxidant detoxification | IEA GO_REF:0000108 | MARK AS OVER ANNOTATED | Summary: Logical inference from the cytochrome-c peroxidase IBA. PA2078 does consume the hydroperoxide made by PA2077, and its co-expression relieves PA2077 toxicity. Reason: The row rests on an untested peroxidase activity. The real activity converts a toxic hydroperoxide intermediate within a biosynthetic pathway; describing that as oxidant detoxification is the authors' interpretation, not a demonstrated role. Supporting Evidence: PMID:26154497 Normal growth rates and full activity were achieved in both mutants, indicating that when the two enzymes are co-expressed in trans, both maintain their respective functions, with PA2078 abolishing toxicity. |
| GO:0050486 intramolecular hydroxytransferase activity | IMP PMID:24980978 Unveiling the genes responsible for the unique Pseudomonas a... | NEW | Summary: Proposed MF. PA2078 converts (10S)-hydroperoxy-octadecenoate into (7S,10S)-dihydroxy-octadecenoate, an isomerization; GO places the analogous fungal reaction (GO:0052879, 8-hydroperoxide 8S-isomerase) under this term. Reason: The activity is shown by complementation and separate heterologous expression; no MF is annotated at present. A reaction-specific child term is proposed. Supporting Evidence: PMID:24980978 whereas PA2078 encodes for the (7S,10S)-hydroperoxide diol synthase enzyme (7,10-DS) which allows the conversion of 10-H(P)OME into 7,10-DiHOME. |
| GO:0042597 periplasmic space | IC PMID:26154497 In Silico/In Vivo Insights into the Functional and Evolution... | NEW | Summary: Signal peptide (SignalP 1-23) and PhoA fusion screening place PA2078 in the periplasm. Reason: Two independent lines agree; no cellular component is annotated at present. Supporting Evidence: PMID:26154497 both proteins display type I signal export sequences that allow transport of the synthesized products to the periplasm, a fact experimentally confirmed by PhoA fusion screening |
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Download this section (compressed HTML)Q: If neither heme site of PA2078 is catalytic, which residues form its active site, and does the reaction proceed by intramolecular oxygen transfer as in fungal diol synthases?
Experiment: Use 18O-labelled 10-H(P)OME with purified PA2078 to test whether the 7-hydroxyl oxygen comes from the hydroperoxide (intramolecular transfer) or from water.
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