FabA (PA1610) is the beta-hydroxydecanoyl-ACP dehydratase/isomerase of the dissociated type II fatty acid synthase of Pseudomonas aeruginosa, a hot-dog-fold enzyme of the FabA subfamily. It has two activities: it dehydrates (3R)-hydroxyacyl-ACP intermediates to (2E)-enoyl-ACP (EC 4.2.1.59) during each round of elongation, and, uniquely for this subfamily, it isomerises (2E)-decenoyl-ACP to (3Z)-decenoyl-ACP (EC 5.3.3.14), the committed branch point that introduces the cis double bond into unsaturated fatty acids. The cis-3-decenoyl-ACP it makes is then elongated by FabB. fabA is cotranscribed with fabB as the fabAB operon, and fabA mutants are auxotrophic for unsaturated fatty acids. FabA is a soluble cytosolic enzyme.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | TOO GENERAL | Summary: UniProt subcellular-location mapping. True, but GO:0005829 cytosol, accepted above, is part_of cytoplasm and is already asserted here. Reason: Entailed by the accepted cytosol row. |
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN002824827 (bacterial-restricted node, seeded by E. coli FabA) placing the enzyme in the cytosol. The dissociated type II FAS is a soluble cytosolic system. Reason: Correct location for a soluble type II FAS enzyme and where its activity acts. |
| GO:0006633 fatty acid biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from the eight-node PTN008624492 GO:0006633 IBD, which this gene's own PseudoCAP row helped seed (expected self-appearance in WITH/FROM). FabA performs the dehydration step of each elongation round, so it does part of the process. Reason: Core and directly performed. Not marked too general despite the accepted GO:0006636 descendant - FabA's dehydratase acts on saturated acyl-ACPs too, so the general term covers work the unsaturated-specific term does not. Supporting Evidence: PMID:9286984 Chromosomal fabA and fabB mutants were isolated; the mutants were auxotrophic for unsaturated fatty acids. |
| GO:0006633 fatty acid biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: InterPro/UniPathway mapping of the same process claim as the IBA row. Reason: Consistent with the accepted IBA row. |
| GO:0006636 unsaturated fatty acid biosynthetic process | IEA GO_REF:0000104 | ACCEPT | Summary: UniRule mapping of the unsaturated fatty acid biosynthetic process, matching the PseudoCAP IMP row. Reason: Core process - FabA's isomerase activity commits carbon to the unsaturated branch. |
| GO:0006636 unsaturated fatty acid biosynthetic process | IMP PMID:9286984 Fatty acid biosynthesis in Pseudomonas aeruginosa: cloning a... | ACCEPT | Summary: PseudoCAP row and the seed of the GO:0006633 IBD at PTN008624492. The evidence is the unsaturated-fatty-acid auxotrophy of chromosomal fabA mutants, but for fabA phenotype and catalysis coincide: FabA's isomerase makes the cis-3-decenoyl-ACP intermediate, the committed step of UFA synthesis. This is participation, not mere necessity. Reason: Core process, performed by this enzyme's own isomerase step. The seeded node term is the parent GO:0006633, so the specific term stays on the gene. Supporting Evidence: PMID:9286984 Chromosomal fabA and fabB mutants were isolated; the mutants were auxotrophic for unsaturated fatty acids. |
| GO:0019171 (3R)-hydroxyacyl-[acyl-carrier-protein] dehydratase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from the PTN008624492 IBD (FabA/FabZ dehydratase node, seeded by E. coli FabA P0A6Q3, E. coli FabZ P0A6Q6 and an Arabidopsis homolog). The (3R)-hydroxyacyl-ACP dehydratase activity is the family-defining activity and is directly supported for PAO1 FabA by its UniProt-curated catalytic activities. Reason: Sound node assertion at the right level; core activity of the enzyme. Supporting Evidence: file:PSEAE/fabA/fabA-uniprot.txt Reaction=a (3R)-hydroxyacyl-[ACP] = a (2E)-enoyl-[ACP] + H2O; |
| GO:0019171 (3R)-hydroxyacyl-[acyl-carrier-protein] dehydratase activity | IEA GO_REF:0000120 | ACCEPT | Summary: InterPro/RHEA/EC 4.2.1.59 mapping of the same dehydratase activity, agreeing with the IBA row and the UniProt catalytic activity. Reason: Consistent electronic assertion of the demonstrated activity. |
| GO:0034017 trans-2-decenoyl-acyl-carrier-protein isomerase activity | IEA GO_REF:0000120 | ACCEPT | Summary: RHEA/EC 5.3.3.14 mapping of the trans-2-decenoyl-ACP isomerase activity, the UFA-committing activity of the FabA subfamily. Reason: Core activity; UniProt curates this reaction for the enzyme and it is the step that introduces cis unsaturation. Supporting Evidence: file:PSEAE/fabA/fabA-uniprot.txt Reaction=(2E)-decenoyl-[ACP] = (3Z)-decenoyl-[ACP]; |
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Download this section (compressed HTML)Q: Over what range of acyl chain lengths does P. aeruginosa FabA act as a dehydratase versus an isomerase, and how is the partition with FabZ (if present) organised in this organism?
Experiment: Assay purified PAO1 FabA for dehydratase and isomerase activities on a graded set of (3R)-hydroxyacyl-ACP and (2E)-enoyl-ACP substrates to define the chain-length dependence of each activity.
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