Curation Notes for Variovorax paradoxus `pqqC` (`A0A0H2MDI9`, `VPARA_00940`)

Overview

UniProt Accession: A0A0H2MDI9 (A0A0H2MDI9_VARPD)
Ordered Locus Name: VPARA_00940 (encoded between pqqB [VPARA_00950] and pqqD [VPARA_00930] in the pqqBCDE cluster)
Gene Symbol: pqqC
Organism: Variovorax paradoxus (NCBITaxon:34073, strain TBEA6)
Protein Function: 254-amino-acid pyrroloquinoline-quinone synthase (PqqC, EC 1.3.3.11, RHEA:10692; HAMAP-Rule:MF_00654, InterPro:IPR011845, NCBIfam:TIGR02111) that catalyzes the terminal ring cyclization and eight-electron, eight-proton oxidation of AHQQ to mature PQQ (UniProtKB:A0A0H2MDI9).

PqqC is one of the five obligatory gene products (PqqA-E) for bacterial PQQ biosynthesis ([PMID:22324760 Distribution and properties of the genes encoding the biosynthesis of the bacterial cofactor, pyrroloquinoline quinone., "A total of five gene products, PqqA, PqqB, PqqC, PqqD, and PqqE, are identified as being obligatory for PQQ production."]).
Catalyzes a cofactor-independent 8-electron, 8-proton oxidation of 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid (AHQQ) to PQQ, consuming 3 equivalents of $\text{O}_2$ and yielding 2 $\text{H}_2\text{O}_2$ and 2 $\text{H}_2\text{O}$ ([PMID:32731194 Biogenesis of the peptide-derived redox cofactor pyrroloquinoline quinone., "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."]).
Pathway context is modeled in MODULE:pqq_biosynthesis.

GO:0033732 (pyrroloquinoline-quinone synthase activity, IEA via EC:1.3.3.11 / RHEA:10692) -> ACCEPT (exact core catalytic function).
GO:0018189 (pyrroloquinoline quinone biosynthetic process, IEA via UniProtKB-UniRule:UR000098301) -> ACCEPT (core biological process).

GO:0005829 (cytosol, IC, located_in) — soluble 254-residue cytoplasmic enzyme lacking signal peptides or transmembrane helices.