fabD (PA2968) encodes malonyl-CoA:acyl carrier protein transacylase (MCAT, FabD), the enzyme that transfers the malonyl group of malonyl-CoA to the phosphopantetheine arm of holo-ACP. Malonyl-ACP is the two-carbon extender substrate for every elongation cycle of type II fatty acid synthesis and for FabH initiation, so FabD is an essential entry point of the pathway. In P. aeruginosa fabD lies in the plsX-fabD-fabG-acpP-fabF cluster, which lacks fabH. His6-tagged FabD, purified together with native P. aeruginosa ACP, has malonyl-CoA:ACP transacylase activity in vitro, and a site-directed chromosomal W258Q allele gives a temperature-sensitive mutant, consistent with the gene being essential. FabD is a soluble cytoplasmic enzyme with the catalytic serine and histidine of the FabD acyltransferase fold.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004314 [acyl-carrier-protein] S-malonyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: MCAT activity by IBA from PTN002448244 (E. coli FabD, M. tuberculosis FabD, human MCAT, yeast MCT1). Reason: Agrees with the in vitro transacylase activity of purified P. aeruginosa FabD; the seeds are characterised MCATs and the FabD family (TIGR00128) is functionally uniform. Supporting Evidence: PMID:10464226 In an in vitro system, purified ACP functioned as acyl acceptor and H(6)-FabD exhibited malonyl-CoA:ACP transacylase activity. |
| GO:0004314 [acyl-carrier-protein] S-malonyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: EC 2.3.1.39 / InterPro mapping; consistent with experiment. Reason: Same claim as the IBA row, supported by the purified-enzyme assay. Supporting Evidence: file:PSEAE/fabD/fabD-uniprot.txt TIGR00128; fabD; 1. |
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: Cytosol by IBA from E. coli FabD. Reason: Bacterial type II FAS enzymes are soluble cytoplasmic proteins; FabD has no signal peptide or transmembrane segment. Supporting Evidence: file:PSEAE/fabD/fabD-uniprot.txt Reaction=holo-[ACP] + malonyl-CoA = malonyl-[ACP] + CoA; |
| GO:0006633 fatty acid biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: Fatty acid biosynthesis by IBA from PTN002448244, seeded by E. coli and M. tuberculosis FabD, human MCAT, Arabidopsis MCAT and this gene. Reason: MCAT makes the malonyl-ACP consumed in every FAS II elongation cycle, a step of the pathway; the node term suits the clade. G3XCZ6 in WITH/FROM reflects its own IDA. Supporting Evidence: PMID:10464226 In an in vitro system, purified ACP functioned as acyl acceptor and H(6)-FabD exhibited malonyl-CoA:ACP transacylase activity. |
| GO:0006633 fatty acid biosynthetic process | IDA PMID:10464226 Characterization of a Pseudomonas aeruginosa fatty acid bios... | ACCEPT | Summary: PseudoCAP IDA, one of five seeds of the PTN002448244 IBD. Purified H6-FabD transferred malonyl from malonyl-CoA to purified P. aeruginosa ACP. Reason: Abstract only, but the abstract reports the purified-enzyme reaction outright. Transfer of malonyl to ACP is the committed loading step for FAS II elongation, so the enzyme performs a step of fatty acid biosynthesis. Seed verdict SOUND. Supporting Evidence: PMID:10464226 In an in vitro system, purified ACP functioned as acyl acceptor and H(6)-FabD exhibited malonyl-CoA:ACP transacylase activity. |
| GO:0016740 transferase activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: Generic transferase activity from the acyltransferase domain InterPro entry. Reason: Entailed by the accepted [acyl-carrier-protein] S-malonyltransferase activity. |
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Download this section (compressed HTML)Q: Does FabD also supply malonyl-ACP to the P. aeruginosa pathways that branch from FAS II (for example the 3-hydroxyacyl precursors of rhamnolipids and the acyl chains of acyl-homoserine lactones), and is there any FabD paralog that can substitute at the restrictive temperature?
Experiment: Measure fatty acid, rhamnolipid and AHL output in the fabD(W258Q) temperature-sensitive strain after a shift to the restrictive temperature.
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