PP_3199 encodes a predicted FAD-dependent monooxygenase in the KT2440 flavonoid-degradation locus. Sequence similarity and conserved locus context identify it as an FdeE-like enzyme predicted to hydroxylate naringenin and related flavonoids before A-ring cleavage. The target protein has not been characterized directly, so its substrate range, C-8 regioselectivity, and pyridine-nucleotide preference remain unverified in P. putida.
Definition: Catalysis of the C-8 hydroxylation of a flavonoid using reduced pyridine nucleotide and molecular oxygen, with incorporation of one oxygen atom into the flavonoid and reduction of the other oxygen atom to water.
Justification: The characterized Hsero_1007/FdeE enzyme performs C-8 hydroxylation across several flavonoid classes, whereas GO:0016709 captures only the general monooxygenase reaction class.
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004497 monooxygenase activity | IEA GO_REF:0000118 | MODIFY | Summary: Correct but general: PP_3199 has the architecture of an FAD-dependent aromatic monooxygenase, captured more specifically by GO:0016709 in this review. Reason: The monooxygenase-family assignment is supported by the target's FAD-binding domain architecture and similarity to experimentally characterized Hsero_1007/FdeE, whose purified enzyme shows the more specific NAD(P)H-dependent single-oxygen-incorporating reaction class. The row is therefore refined to GO:0016709, which the gene already carries, as for the Hsero_1007 review. Proposed replacements: oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen, NAD(P)H as one donor, and incorporation of one atom of oxygen Supporting Evidence: file:PSEPK/PP_3199/PP_3199-uniprot.txt InterPro; IPR050493; FAD-dep_Monooxygenase_BioMet. PMID:39107441 Like LjF8H33 and RgF8H25, it showed an absolute requirement for NADPH, while the addition of FAD to the reaction mixture containing the NADPH coenzyme did not result in changes in activity, as also was described for LjF8H33. |
| GO:0016709 oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen, NAD(P)H as one donor, and incorporation of one atom of oxygen | IEA GO_REF:0000117 | ACCEPT | Summary: PP_3199 is predicted to use reduced pyridine nucleotide and oxygen for aromatic hydroxylation. Reason: This term captures the supported reaction class without asserting the untested target-specific substrate, regioselectivity, or NADH-versus-NADPH preference. Supporting Evidence: file:PSEPK/PP_3199/PP_3199-bioinformatics/RESULTS.md Reciprocal best-hit relationship: true PMID:39107441 Like LjF8H33 and RgF8H25, it showed an absolute requirement for NADPH, while the addition of FAD to the reaction mixture containing the NADPH coenzyme did not result in changes in activity, as also was described for LjF8H33. |
| GO:0071949 FAD binding | IEA GO_REF:0000002 | ACCEPT | Summary: PP_3199 contains the conserved FAD-binding architecture of flavoprotein monooxygenases. Reason: InterPro identifies an FAD-binding domain, and the experimentally studied Hsero_1007 ortholog is a flavin-dependent monooxygenase. Supporting Evidence: file:PSEPK/PP_3199/PP_3199-uniprot.txt InterPro; IPR002938; FAD-bd. |
| GO:0046275 flavonoid catabolic process | ISS file:PSEPK/PP_3199/PP_3199-deep-research-openscientist.md | NEW | Summary: PP_3199 is predicted to catalyze the initiating hydroxylation in bacterial naringenin degradation. Reason: PP_3199 and the experimentally characterized Hsero_1007/FdeE monooxygenase are reciprocal proteome best hits, share 40.4% global identity, and occur in conserved fde loci. GO:0046275 flavonoid catabolic process is used; GO has no naringenin-specific catabolic child. Supporting Evidence: file:PSEPK/PP_3199/PP_3199-deep-research-openscientist.md The direct enzymatic characterization derives from the *Herbaspirillum* ortholog; the KT2440 assignment rests on strong orthology, conserved gene-cluster synteny, and a conserved regulator (see Limitations). file:PSEPK/PP_3199/PP_3199-bioinformatics/RESULTS.md Pairwise identity over aligned residue pairs: 40.4% file:PSEPK/PP_3199/PP_3199-bioinformatics/RESULTS.md Reciprocal best-hit relationship: true PMID:27059806 naringenin remained unaltered, suggesting that the FdeE protein is involved in the initial step of naringenin degradation. |
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Download this section (compressed HTML)Q: Does PP_3199 catalyze C-8 hydroxylation of naringenin in KT2440, and does it use NADPH, NADH, or both?
Experiment: Purify PP_3199 and assay naringenin, flavones, isoflavones, and flavonols with FAD, oxygen, and each reduced pyridine nucleotide, identifying products by LC-MS/MS and NMR.
Type: biochemical reconstitution and product identification
Experiment: Compare wild type, a PP_3199 deletion, and a complemented strain during growth on naringenin, measuring substrate loss and hydroxylated-intermediate accumulation.
Type: genetics and targeted metabolomics
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: PP_3199's physiological substrate range, hydroxylation position, and NADH-versus-NADPH preference have not been measured directly in KT2440.
OPEN BIOLOGYCURATION
What is known: Reciprocal best-hit orthology supports an FdeE-like flavonoid monooxygenase, but 40.4% identity is insufficient to assume identical specificity without target assays.
Significance: Direct evidence is required before assigning a future C-8 flavonoid-monooxygenase term experimentally to PP_3199.
What would resolve it: Purify PP_3199 and identify products from naringenin and representative flavonoids using NADH and NADPH separately.
Provenance (the field's own admissions):
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