PqqC (pyrroloquinoline-quinone synthase, VPARA_00940, A0A0H2MDI9) in Variovorax paradoxus is a 254-amino-acid cofactor-less oxidase (EC 1.3.3.11; HAMAP MF_00654, InterPro IPR011845, NCBIfam TIGR02111) encoded in the pqqBCDE (VPARA_00950-VPARA_00920) gene cluster. It catalyzes the terminal step of pyrroloquinoline quinone (PQQ) biosynthesis: the ring cyclization and eight-electron, eight-proton oxidation of 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid (AHQQ) to mature PQQ using three equivalents of molecular oxygen (producing two equivalents of H2O2 and two equivalents of H2O, RHEA:10692) without requiring a metal or organic prosthetic group.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0033732 pyrroloquinoline-quinone synthase activity | IEA GO_REF:0000120 | ACCEPT | Reason: PqqC (VPARA_00940, A0A0H2MDI9) is the canonical pyrroloquinoline-quinone synthase (EC 1.3.3.11, RHEA:10692; HAMAP MF_00654, InterPro IPR011845) that catalyzes the terminal ring cyclization and eight-electron oxidation of AHQQ to mature PQQ. Supporting Evidence: UniProtKB:A0A0H2MDI9 CC -!- FUNCTION: Ring cyclization and eight-electron oxidation of 3a-(2-amino- CC 2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9- CC dicarboxylic-acid to PQQ. {ECO:0000256|HAMAP-Rule:MF_00654}. PMID:32731194 PqqC catalyzes an overall eight-electron and eight-proton oxidation on AHQQ in the absence of any organic/metal cofactor, consuming three equivalents of O2 in a single turnover manner. |
| GO:0018189 pyrroloquinoline quinone biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Reason: PqqC (VPARA_00940) catalyzes the final committed oxidative step of the pyrroloquinoline quinone biosynthetic pathway in Variovorax paradoxus. Supporting Evidence: UniProtKB:A0A0H2MDI9 CC -!- PATHWAY: Cofactor biosynthesis; pyrroloquinoline quinone biosynthesis. CC {ECO:0000256|HAMAP-Rule:MF_00654}. PMID:22324760 A total of five gene products, PqqA, PqqB, PqqC, PqqD, and PqqE, are identified as being obligatory for PQQ production. |
| GO:0005829 cytosol | IC UniProtKB:A0A0H2MDI9 | NEW | Reason: Inferred by curator (IC) because V. paradoxus PqqC (A0A0H2MDI9) is a soluble 254-residue enzyme lacking signal peptides or transmembrane domains that synthesizes mature PQQ in the bacterial cytosol prior to cofactor export to periplasmic quinoproteins. Supporting Evidence: UniProtKB:A0A0H2MDI9 FT DOMAIN 31..243 FT /note="Thiaminase-2/PQQC" FT /evidence="ECO:0000259|Pfam:PF03070" |
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Download this section (compressed HTML)Q: How is mature PQQ released from the closed product-bound conformation of Variovorax paradoxus PqqC (VPARA_00940) and exported across the inner membrane to load periplasmic quinoproteins such as Gcd (VPARA_65850) and VPARA_00790?
Experiment: Purify recombinant Variovorax paradoxus PqqC (A0A0H2MDI9) and measure single- and multiple-turnover oxidation of AHQQ to PQQ under aerobic conditions, quantifying O2 consumption and H2O2 production by Clark electrode oximetry and Amplex Red assays.
Hypothesis: V. paradoxus PqqC converts AHQQ to PQQ with a 3 O2 : 2 H2O2 : 1 PQQ stoichiometry in a single-turnover reaction whose rate-limiting step is product release.
Type: In vitro enzyme kinetics and oxygen/peroxide stoichiometry assay
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