FabB is the 3-oxoacyl-ACP synthase I of Pseudomonas putida KT2440 type-II fatty-acid synthesis. It performs decarboxylative condensations between malonyl-ACP and acyl-ACP substrates and is especially important for extending the cis-3-decenoyl-ACP intermediate generated by FabA in unsaturated fatty-acid synthesis.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004315 3-oxoacyl-[acyl-carrier-protein] synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Correct core molecular function for FabB. Reason: UniProt records both general acyl-ACP elongation and the cis-unsaturated substrate reaction. Supporting Evidence: file:PSEPK/fabB/fabB-uniprot.txt Reaction=(3Z)-decenoyl-[ACP] + malonyl-[ACP] + H(+) = 3-oxo-(5Z)- file:PSEPK/fabB/fabB-deep-research-openscientist.md it elongates an ACP-bound acyl chain by two carbons per cycle. |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Cytoplasm is plausible for this soluble enzyme but is not supported by a direct KT2440 localization experiment. Reason: Retain the localization annotation without using it to define the catalytic core function. Supporting Evidence: file:PSEPK/fabB/fabB-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0005829 cytosol | IEA GO_REF:0000118 | MARK AS OVER ANNOTATED | Summary: Redundant child localization alongside the broader cytoplasm annotation. Reason: Cytosol adds no useful distinction for this bacterial soluble enzyme. |
| GO:0006633 fatty acid biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: Correct core pathway assignment. Reason: UniProt places FabB in fatty-acid biosynthesis. Supporting Evidence: file:PSEPK/fabB/fabB-uniprot.txt PATHWAY: Lipid metabolism; fatty acid biosynthesis. |
| GO:0006636 unsaturated fatty acid biosynthetic process | ISS PMID:34181948 A cryptic long-chain 3-ketoacyl-ACP synthase in the Pseudomo... | NEW | Summary: Add the unsaturated-fatty-acid branch process supported by the FabB ortholog's committed cis-unsaturated-chain elongation role. Reason: Deleting fabB in P. putida F1 caused unsaturated-fatty-acid auxotrophy, and purified F1 FabB elongated the FabA-derived cis-unsaturated intermediate. This is strong close-strain comparative support for the orthologous KT2440 protein, but it is not a direct KT2440 experiment. Supporting Evidence: PMID:34181948 The resulting ΞfabB mutant strain was a UFA (oleic acid) auxotroph demonstrating the importance of the gene in P. putida F1 UFA synthesis PMID:34181948 PpFabB and PpFabF2 both produce the same products as E. coli FabB |
| GO:0016746 acyltransferase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Correct parent activity but redundant with the specific KAS term. Reason: The 3-oxoacyl-ACP synthase term captures FabB substrate and chemistry. |
| GO:0016747 acyltransferase activity, transferring groups other than amino-acyl groups | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: Correct parent activity but redundant with the specific KAS term. Reason: The 3-oxoacyl-ACP synthase term captures FabB substrate and chemistry. |
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Download this section (compressed HTML)Q: What is the division of substrate range between KT2440 FabB and the two KAS-II paralogs?
Q: Does KT2440 FabB itself generate acetyl-ACP from malonyl-ACP, as shown for the FabB ortholog in P. putida strain F1, or does KT2440 rely on MadB for that primer-forming chemistry?
Experiment: Compare purified FabB, FabF, and PP_3303 against saturated and cis-unsaturated acyl-ACP chain lengths using product-resolved LC-MS.
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