FogD is a short-chain dehydrogenase/reductase in the flavoglaucin biosynthetic cluster of Aspergillus ruber. It acts with the polyketide synthase FogA and oxidoreductases FogB and FogC during formation of the aromatic core of prenylated salicylaldehyde metabolites. FogD is proposed to contribute reductive release of the nascent polyketide as a salicyl alcohol, but its isolated catalytic reaction has not been established. The alcohol intermediate permits subsequent hydroxylation and prenylation before oxidation to the aldehyde end products. Functional evidence comes from reconstruction and deletion experiments with an A. ruber cluster in A. nidulans; the source strain was QEN-0407-G2 and the cluster was mapped against the CBS 135680 reference genome. FogD subcellular localization and possible additional substrates remain unresolved.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000140 acylglycerone-phosphate reductase (NADP+) activity | IEA GO_REF:0000118 | MODIFY | Summary: The propagated acylglycerone-phosphate reductase (NADP+) activity claim is too specific for FogD. Reason: The focused OpenScientist report supports functional divergence from Ayr1: FogD retains the SDR fold and participates in flavoglaucin polyketide redox chemistry, while UniProt records EC 1.1.1.- for CH-OH donor/NAD(P) acceptor chemistry. FogD is only 39.5% identical to yeast Ayr1 and sits in the distinct PANTHER PTHR44169:SF3 SRDE subfamily, so no target assay supports transfer of the Ayr1-specific acyl-DHAP substrate. Keep the CH-OH/NAD(P) parent rather than this Ayr1-derived glycerolipid-substrate assertion. Proposed replacements: oxidoreductase activity, acting on the CH-OH group of donors, NAD or NADP as acceptor Supporting Evidence: file:ASPRC/fogD/fogD-uniprot.txt involved in the reductive release of the modified PKS products file:ASPRC/fogD/fogD-notes.md The current PAINT slice records experimentally grounded Ayr1-seeded IBDs, but does not contain historical node PTN001211783. file:ASPRC/fogD/fogD-hypotheses/sdr-lipid-functions-and-polyketide-release/openscientist.md No FogD-specific assay, localization experiment, or mutant supports any of these six terms. |
| GO:0004806 triacylglycerol lipase activity | IEA GO_REF:0000118 | MARK AS OVER ANNOTATED | Summary: The propagated triacylglycerol lipase activity claim is Ayr1-specific and unsupported for FogD. Reason: PMID:24187129 validates triacylglycerol lipase activity for the Ayr1 source, so the source annotation is sound. The focused report found no FogD hydrolase assay and placed FogD in a distinct PTHR44169:SF3 secondary-metabolite SDR subfamily only 39.5% identical to Ayr1, making wholesale transfer of Ayr1 moonlighting unsupported while not logically impossible. Supporting Evidence: file:ASPRC/fogD/fogD-uniprot.txt involved in the reductive release of the modified PKS products file:ASPRC/fogD/fogD-notes.md The current PAINT slice records experimentally grounded Ayr1-seeded IBDs, but does not contain historical node PTN001211783. PMID:24187129 These investigations led to the identification of Ayr1p as a novel triacylglycerol lipase of yeast lipid droplets file:ASPRC/fogD/fogD-hypotheses/sdr-lipid-functions-and-polyketide-release/openscientist.md conserved fold and cofactor chemistry transfer, whereas Ayr1's **specific substrate identities and dual moonlighting functions do not** |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: The propagated endoplasmic reticulum localization remains an unsupported Ayr1 transfer. Reason: Ayr1 was experimentally localized to the ER, but the focused report found no FogD localization evidence and the demonstrated flavoglaucin-cluster role does not require this compartment. FogD is only 39.5% identical to Ayr1 and falls in the distinct PTHR44169:SF3 subfamily, so the existing row should be treated as a low-confidence non-core Ayr1 homology transfer rather than as an established FogD localization. Supporting Evidence: file:ASPRC/fogD/fogD-uniprot.txt involved in the reductive release of the modified PKS products file:ASPRC/fogD/fogD-notes.md The current PAINT slice records experimentally grounded Ayr1-seeded IBDs, but does not contain historical node PTN001211783. file:ASPRC/fogD/fogD-hypotheses/sdr-lipid-functions-and-polyketide-release/openscientist.md No FogD-specific assay, localization experiment, or mutant supports any of these six terms. |
| GO:0005811 lipid droplet | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: The propagated lipid-droplet localization remains an unsupported Ayr1 transfer. Reason: The Ayr1 source has experimentally supported lipid-droplet association, but the focused report found no target localization assay for FogD. A flavoglaucin biosynthetic role does not formally exclude a lipid-droplet pool, yet Ayr1's specific localization is not portable across 39.5% identity and the distinct PTHR44169:SF3 subfamily without supporting targeting evidence. Supporting Evidence: file:ASPRC/fogD/fogD-uniprot.txt involved in the reductive release of the modified PKS products file:ASPRC/fogD/fogD-notes.md The current PAINT slice records experimentally grounded Ayr1-seeded IBDs, but does not contain historical node PTN001211783. PMID:24187129 These investigations led to the identification of Ayr1p as a novel triacylglycerol lipase of yeast lipid droplets file:ASPRC/fogD/fogD-hypotheses/sdr-lipid-functions-and-polyketide-release/openscientist.md No FogD-specific assay, localization experiment, or mutant supports any of these six terms. |
| GO:0006654 phosphatidic acid biosynthetic process | IEA GO_REF:0000118 | MARK AS OVER ANNOTATED | Summary: The propagated phosphatidic acid biosynthetic process claim is an unsupported Ayr1 transfer. Reason: Ayr1's phosphatidic-acid-pathway role is real, but it derives from a yeast primary lipid enzyme rather than a FogD-specific phenotype. PMID:32134669 and the PTHR44169:SF3 placement support flavoglaucin biosynthesis for FogD, and the focused report found no evidence that the target also participates in Ayr1-like glycerophospholipid biosynthesis. Supporting Evidence: file:ASPRC/fogD/fogD-uniprot.txt involved in the reductive release of the modified PKS products file:ASPRC/fogD/fogD-notes.md The current PAINT slice records experimentally grounded Ayr1-seeded IBDs, but does not contain historical node PTN001211783. file:ASPRC/fogD/fogD-hypotheses/sdr-lipid-functions-and-polyketide-release/openscientist.md No FogD-specific assay, localization experiment, or mutant supports any of these six terms. |
| GO:0019433 triglyceride catabolic process | IEA GO_REF:0000118 | MARK AS OVER ANNOTATED | Summary: The propagated triglyceride catabolic process claim is Ayr1-specific and unsupported for FogD. Reason: Ayr1 demonstrates SDR reductase/lipase bifunctionality in the source family, but the focused report supports divergence of FogD's specific substrate scope across the distinct, 39.5%-identical PTHR44169:SF3 subfamily. No FogD-specific evidence places the flavoglaucin-cluster reductase in triglyceride hydrolysis or turnover, so this BP row is an over-propagated Ayr1 lipid-metabolism claim. Supporting Evidence: file:ASPRC/fogD/fogD-uniprot.txt involved in the reductive release of the modified PKS products file:ASPRC/fogD/fogD-notes.md The current PAINT slice records experimentally grounded Ayr1-seeded IBDs, but does not contain historical node PTN001211783. PMID:24187129 These investigations led to the identification of Ayr1p as a novel triacylglycerol lipase of yeast lipid droplets file:ASPRC/fogD/fogD-hypotheses/sdr-lipid-functions-and-polyketide-release/openscientist.md conserved fold and cofactor chemistry transfer, whereas Ayr1's **specific substrate identities and dual moonlighting functions do not** |
| GO:0044550 secondary metabolite biosynthetic process | IEA GO_REF:0000117 | ACCEPT | Summary: FogD belongs to the experimentally reconstructed flavoglaucin cluster and contributes to formation of its polyketide-derived metabolites. RETIRED - this ARBA row is no longer present in the current GOA snapshot (2026-10 refresh). Reason: Retain the broad secondary-metabolite process. The published supplementary methods map FogD to EYE95338/EURHEDRAFT_455854 and document its deletion in the heterologous A. nidulans cluster strain; Figure S8 shows low accumulation of the FogA-derived intermediate. The phenotype is from a reconstructed A. ruber QEN-0407-G2 cluster, not a directly assayed deletion in native CBS 135680. UniProt maps these findings to this reference-genome protein. Precise reaction specificity remains provisional. Supporting Evidence: PMID:32134669 The polyketide skeleton was released as alkylated salicyl alcohols file:ASPRC/fogD/fogD-notes.md The supplement identifies JN009 as the fogD deletion strain in the reconstructed A. nidulans JN004 cluster background. |
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Download this section (compressed HTML)Q: What is the exact catalytic mechanism of fogD? Does it perform a true NADPH-dependent reductive release of the thioester-bound polyketide from fogA, or does it catalyze a different modification of the PKS-bound intermediate?
Suggested experts: Shu-Ming Li (Philipps-Universitat Marburg, senior author of PMID:32134669), Jonas Nies (first author of PMID:32134669)
Q: Does fogD interact directly with the fogA polyketide synthase via protein-protein interaction, and if so, which domains mediate this interaction?
Suggested experts: Shu-Ming Li (Philipps-Universitat Marburg)
Q: Does FogD retain any of the experimentally grounded Ayr1 lipid activities or localizations, and can historical TreeGrafter node PTN001211783 be mapped onto the current PTHR44169 PAINT tree? A different biosynthetic role and a short source list do not themselves establish an erroneous graft.
Q: Which exact reaction and cofactor does isolated FogD use? GO:0016616 is adopted provisionally on UniProt's ECO:0000305 EC=1.1.1.- placement; a direct reductive-thioester-release result would move the molecular function to the aldehyde/oxo donor branch instead.
Q: Would a flavoglaucin-specific GO process add useful coverage beyond polyketide biosynthetic process? The former proposal is withheld pending ontology review; the ancestor/descendant secondary-metabolite and polyketide proposals must not both be added.
Experiment: Express and purify recombinant fogD, then test its ability to release polyketide intermediates from purified fogA-bound substrates in vitro. Measure NADPH consumption and product formation (salicyl alcohols) by LC-MS. Include controls without NADPH and with a predicted catalytic-site mutant (Y147F; inactivity to be measured) to test the proposed reductive mechanism.
Hypothesis: fogD catalyzes the NADPH-dependent reductive release of polyketide intermediates from the fogA PKS, generating salicyl alcohol products.
Type: in vitro biochemical assay
Experiment: Perform co-immunoprecipitation or pull-down assays using tagged fogD and fogA expressed in A. nidulans. Alternatively, use bacterial two-hybrid or yeast two-hybrid assays to test for direct protein-protein interaction between fogD and specific domains of fogA (KS, ACP, or thioesterase-like domains).
Hypothesis: fogD forms a direct physical interaction with the fogA polyketide synthase to perform trans-acting reductive release.
Type: protein-protein interaction assay
Experiment: Generate site-directed mutants of fogD at predicted active site residues (Y147F, K151A) and cofactor binding residues. Express these in a fogD-deletion background in A. ruber or heterologously in A. nidulans with fogA/B/C, and measure flavoglaucin and salicyl alcohol production by HPLC/LC-MS. Loss of pathway products would test their requirement in this pathway; purified-protein assays would be needed to distinguish catalysis from stability.
Hypothesis: Specific active site residues (Tyr-147, Lys-151) are essential for fogD catalytic activity in the fog pathway.
Type: site-directed mutagenesis with metabolite profiling
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