pqqC (PP_0378) encodes pyrroloquinoline-quinone synthase (EC 1.3.3.11), the terminal enzyme of the PQQ biosynthetic pathway. It catalyzes the final ring-closure plus multi-electron (eight-electron) oxidation of the late precursor AHQQ to form mature pyrroloquinoline quinone, a reaction that consumes molecular oxygen and is cofactor-independent. In P. putida KT2440, pqqC is part of the conserved pqqF-A-B-C-D-E-G cluster and is cotranscribed with pqqD-E-G; PQQ synthesis is cytosolic and supplies mature PQQ to periplasmic PQQ-dependent dehydrogenases (e.g. glucose dehydrogenase).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0018189 pyrroloquinoline quinone biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: This biological-process annotation is correct because PqqC is the terminal pyrroloquinoline-quinone synthase in the PQQ biosynthetic pathway. Falcon deep research independently confirms PqqC catalyzes the final step of PQQ biosynthesis and places pqqC within the conserved KT2440 pqqF-A-B-C-D-E-G biosynthetic cluster, cotranscribed with pqqD-E-G. Reason: PqqC directly produces mature PQQ from the late pathway intermediate AHQQ, and is embedded in the coordinated terminal module of the KT2440 PQQ biosynthesis operon. Supporting Evidence: file:PSEPK/pqqC/pqqC-uniprot.txt PATHWAY: Cofactor biosynthesis; pyrroloquinoline quinone biosynthesis. file:PSEPK/pqqC/pqqC-goa.tsv GO:0018189 pyrroloquinoline quinone biosynthetic process file:PSEPK/pqqC/pqqC-deep-research-falcon.md **PqqC** is widely described as the enzyme catalyzing the **final step** of PQQ biosynthesis file:PSEPK/pqqC/pqqC-deep-research-falcon.md **pqqC** is a core member of the conserved PQQ-biosynthesis gene cluster that includes **pqqF-A-B-C-D-E-G file:PSEPK/pqqC/pqqC-deep-research-falcon.md RT-PCR evidence that **pqqC–pqqD–pqqE–pqqG** are **cotranscribed on one transcript** |
| GO:0033732 pyrroloquinoline-quinone synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is the exact core molecular function for PqqC. UniProt assigns EC 1.3.3.11 and describes ring cyclization plus eight-electron oxidation generating PQQ. Falcon deep research independently confirms the reaction (AHQQ to PQQ via ring closure coupled to multi-electron oxidation using molecular oxygen), the O2/peroxide stoichiometry (3 O2 consumed, yielding 2 H2O2 + 2 H2O), and describes PqqC as a cofactorless oxidase. These details are inferred by homology/mechanistic conservation, as the catalytic step and active-site residues are strongly conserved across the PqqC family. Reason: The enzyme name, EC 1.3.3.11 mapping, and the conserved AHQQ-to-PQQ oxidative ring-closure reaction directly support pyrroloquinoline-quinone synthase activity. Supporting Evidence: file:PSEPK/pqqC/pqqC-uniprot.txt RecName: Full=Pyrroloquinoline-quinone synthase file:PSEPK/pqqC/pqqC-uniprot.txt Ring cyclization and eight-electron oxidation file:PSEPK/pqqC/pqqC-goa.tsv GO:0033732 pyrroloquinoline-quinone synthase activity file:PSEPK/pqqC/pqqC-deep-research-falcon.md via **ring closure** coupled to a **multi-electron oxidation** using molecular oxygen file:PSEPK/pqqC/pqqC-deep-research-falcon.md **3 equivalents of O\_2 consumed**, producing **2 equivalents H\_2O\_2** and **2 equivalents H\_2O** during conversion of AHQQ to PQQ file:PSEPK/pqqC/pqqC-deep-research-falcon.md PqqC as a **cofactorless oxidase** |
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Download this section (compressed HTML)Q: Which late PQQ precursor accumulates in a KT2440 pqqC mutant, and does it match the inferred PqqC substrate (AHQQ) from characterized homologs?
Experiment: Purify KT2440 PqqC and assay conversion of the late PQQ precursor AHQQ under oxygenated conditions, using LC-MS to track substrate depletion and PQQ formation, and quantify O2 consumption and H2O2 production to confirm the family-conserved stoichiometry.
Hypothesis: PqqC catalyzes the final oxidative cyclization step in KT2440 PQQ biosynthesis.
Type: enzyme assay and LC-MS metabolite tracking
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