PqsH (PA2587) is a FAD-dependent class A aromatic hydroxylase (3-hydroxybenzoate 6-hydroxylase family) that catalyses the last step of Pseudomonas quinolone signal (PQS) biosynthesis. It hydroxylates 2-heptyl-4(1H)-quinolone (HHQ) at C3 to give 2-heptyl-3-hydroxy-4(1H)-quinolone (PQS), using NADH (NADPH less efficiently) and O2 (EC 1.14.13.182). The purified enzyme has high-nanomolar apparent Km values for HHQ and O2 and a turnover of about 2.5 per min. It accepts C7 and C9 alkyl-chain HHQ analogues equally well and shorter chains poorly. Because O2 is a substrate, PqsH cannot make PQS anaerobically, so oxygen availability directly gates PQS production and PQS-controlled behaviours such as membrane vesicle formation, iron chelation and virulence factor expression. Converting HHQ to PQS raises the potency of the quinolone quorum-sensing signal acting through PqsR (MvfR). pqsH transcription depends on the LasR quorum-sensing regulator, which links the Las and PQS systems.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000117 | TOO GENERAL | Summary: ARBA root-level catalytic activity. True, but GO:0102164 HHQ synthase activity, accepted below, entails it. Reason: Uninformative root-of-MF term; the accepted specific activity GO:0102164 already implies it. |
| GO:0004497 monooxygenase activity | IBA GO_REF:0000033 | MODIFY | Summary: IBA from the PAINT IBD on PTN008173107, the PTHR45934 family root. PqsH's own PseudoCAP IDA is the only seed, so the appearance of Q9I0Q0 in WITH/FROM is expected and not circular. PqsH is inside the clade, on the horizontal-transfer branch shared with Streptomyces SCO1338 and the plant clade. Generic monooxygenase activity is a sound node-level claim for a family of FAD_binding_3 class A aromatic hydroxylases, and it is true of PqsH. Reason: Correct for PqsH and appropriate at the family-root node, but for this gene the evidence supports the more specific GO:0102164 (is_a GO:0016709 is_a GO:0004497), which the gene already carries; the action matches the IDA row on the same term. The phylogenetic claim itself is not disputed: generic monooxygenase activity is the right level for the node, and GO:0102164 must not be pushed up to it (see notes, PseudoCAP IBA-seed assessment). Propagation Review Root cause: NO FAILURE CORE Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN008173107 · PTN008173107 SUPPORTS TRANSFER Family root of PTHR45934 (297 leaves); PqsH sits on the horizontal-transfer child PTN005262028 together with Streptomyces SCO1338 and a 294-leaf plant clade. The generic node term is appropriate; the gene-level term is GO:0102164. UniProtKB:Q9I0Q0 · pqsH (self; sole IBD seed, IDA PMID:20662781) SUPPORTS TRANSFER Expected self-seed reflecting the target's own purified-enzyme evidence. Proposed replacements: 2-heptyl-3-hydroxy-4(1H)-quinolone synthase activity Supporting Evidence: PMID:20662781 Steady state kinetic analysis confirmed HHQ, NADH, and oxygen as substrates of MBP-PqsH, consistent with its predicted role as an HHQ hydroxylating monooxygenase file:PSEAE/pqsH/pqsH-bioinformatics/RESULTS.md So 294 of the 297 leaves are green-plant proteins |
| GO:0004497 monooxygenase activity | IDA PMID:20662781 Oxygen levels rapidly modulate Pseudomonas aeruginosa social... | MODIFY | Summary: PseudoCAP IDA and the sole seed of the PTN008173107 IBD. The paper purified MBP-PqsH and showed NADH- and O2-dependent hydroxylation of HHQ to PQS. The product was confirmed by TLC, spectra and ESI-MS, and kinetics were measured for all three substrates. This is direct evidence for monooxygenase activity, and more precisely for the exact reaction of GO:0102164 2-heptyl-3-hydroxy-4(1H)-quinolone synthase activity (RHEA:37871). Reason: The seed is sound but under-specific. The paper directly supports the specific term GO:0102164, which the gene already carries by IEA. Refining the IDA would not affect the IBD, because GO:0102164 is a descendant of GO:0004497 and remains valid evidence for the generic node term. Proposed replacements: 2-heptyl-3-hydroxy-4(1H)-quinolone synthase activity Supporting Evidence: PMID:20662781 we show that PqsH catalyses the terminal step in PQS production, synthesizing PQS in vitro using the substrates 2-heptyl-4-quinolone (HHQ), NADH and oxygen |
| GO:0044550 secondary metabolite biosynthetic process | IDA PMID:20662781 Oxygen levels rapidly modulate Pseudomonas aeruginosa social... | ACCEPT | Summary: PqsH itself catalyses the final step of PQS biosynthesis, as the in vitro reconstitution of HHQ to PQS shows, so this is participation and not an indirect requirement. GO has no specific 2-alkyl-4-quinolone/PQS biosynthesis term, so this is the most specific available BP. Reason: Direct participation (catalytic step) in PQS secondary metabolite biosynthesis, shown with purified enzyme; consistent with pathway partners pqsB/pqsC, which carry the same term. Supporting Evidence: PMID:20662781 we show that PqsH catalyses the terminal step in PQS production, synthesizing PQS in vitro using the substrates 2-heptyl-4-quinolone (HHQ), NADH and oxygen PMID:12426334 Since pqsH is required for PQS synthesis, this finding accounts for a previous observation that PQS production requires LasR function |
| GO:0071949 FAD binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro FAD-binding domain (Pfam FAD_binding_3) mapping. PqsH is a class A flavoprotein hydroxylase. FAD is the cofactor its NAD(P)H/O2 hydroxylation chemistry requires, though no study in the cache measured bound FAD directly. Reason: Domain-based cofactor binding consistent with family membership and with the NADH/O2-dependent hydroxylation chemistry. Supporting Evidence: PMID:20662781 PqsH is a member of a family of flavin-dependent monooxygenases that utilize NAD(P)H and oxygen to catalyze hydroxylation of aromatic substrates |
| GO:0102164 2-heptyl-3-hydroxy-4(1H)-quinolone synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: The EC/Rhea mapping gives the exact HHQ 3-monooxygenase (PQS synthase) activity, which purified-enzyme assays support directly. Reason: Core molecular function with direct biochemical support; the more specific replacement for the IDA monooxygenase activity row. Supporting Evidence: PMID:20662781 we show that PqsH catalyses the terminal step in PQS production, synthesizing PQS in vitro using the substrates 2-heptyl-4-quinolone (HHQ), NADH and oxygen PMID:33452035 Hydroxylation of the PQS precursor 2-heptylquinolin-4(1H)-one (HHQ) by the signal synthase PqsH boosts AQ quorum sensing |
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Download this section (compressed HTML)Q: GO:0009372 quorum sensing is defined to include producing the signal molecule. Should signal synthases such as PqsH (and PqsABCD, LasI, RhlI) be annotated involved_in quorum sensing? None of the comparators in this pathway (pqsB, pqsC) carry the term, which suggests a convention to restrict it to signal perception and response.
Q: The PTN008173107 IBD (monooxygenase activity) at the PTHR45934 root propagates to about 294 plant proteins (Arabidopsis MO1/MO2/MO3, CTF2A/B and orthologs). Its only experimental seed is PqsH, on a horizontally transferred bacterial branch. Do any plant members have experimental evidence that could act as additional seeds? Are the FAD- and NAD(P)H-binding and catalytic motifs conserved across the plant clade?
Q: Does PqsH also 3-hydroxylate HQNO to PQS-N-oxide in P. aeruginosa, as comparative work on AQ 3-monooxygenases suggests?
Experiment: Determine the flavin content and reductive/oxidative half-reactions of tag-free PqsH (stopped-flow), and test HQNO as a substrate, to confirm the class A flavoprotein mechanism and the substrate range.
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