So far only a single turnover of the enzyme has been observed, and the pyrroloquinoline quinone remains bound to it. It is not yet known what releases the product in the bacterium.
PqqC is part of a complex of six enzymes that act together in pyrroloquinoline-quinone synthesis: PqqA serves as a complex precursor for for pyrroloquinoline-quinone synthesis, PqqB is not directly required for pyrroloquinoline-quinone biosynthesis, but a carrier and responsible for its transport across the plasma-membrane into the periplasm, PqqC does not contain a redox-active metal or other cofactor and is responsible for the last cyclization and oxidation steps in pyrroloquinoline-quinone synthesis, PqqD has three possible functions: first, it could play a role in the release of pyrroloquinoline-quinone from PqqC, second it could be involved in binding of PqqB to PqqC, third it could function as the dioxygenase in the pathway, PqqE is a family member of radical S-adenosylmethionine enzymes and catalyzes a radical driven C-C bond formation required to link the glutamate and tyrosine moieties at atoms C9 and C9a of pyrroloquinoline-quinone, PqqF recognizes and cleaves all four peptide bonds in PqqA
So far only a single turnover of the enzyme has been observed, and the pyrroloquinoline quinone remains bound to it. It is not yet known what releases the product in the bacterium.
catalyzes the final step of PQQ formation, which involves a ring closure and an overall eight-electron oxidation of 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid in the absence of a redox-active metal or cofactor
catalyzes the final step of PQQ formation, which involves a ring closure and an overall eight-electron oxidation of 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid in the absence of a redox-active metal or cofactor
PqqC catalyzes the last step of pyrroloquinoline quinone biogenesis which involves a ring closure and an eight-electron oxidation of the substrate 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid
pyrroloquinoline quinone, i.e. 4,5-dihydro-4,5-dioxo-1Hpyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, PQQ, synthesized by the enzyme, is a bacterial cofactor in numerous alcohol dehydrogenases including methanol dehydrogenase and glucose dehydrogenase
an all atom model of the quinoprotein dehydrogenase PqqC in complex with 4,5-dihydro-4,5-dioxo-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid (PQQ) and O2, solvated with TIP3 water in periodic boxes, is subjected to random-acceleration molecular dynamics (RAMD) showing that O2 leaves the active binding pocket, in front of PQQ, to get to the solvent, as easily as with a variety of other O2-activating enzymes, O2 carriers, and gas-sensing proteins. The shortest pathway, orthogonal to the center of the mean plane of PQQ, is largely preferred by O2 over pathways slightly deviating from this line. These observations challenge the interpretation of an impermeable active binding pocket of PqqC-PQQ, as drawn from both X-ray diffraction data of the crystal at low temperature and physiological experimentation. Key residues for the minor O2 gates are 1. Q155, L158, R177, and R17, 2. E188, and L191, and 3. D83 and Q182, or the main O2 egress involving residues P151, L180, and A183, modeling, overview
the enzyme has 14 conserved active site residues, which are in close contact with bound substrate pyrroloquinoline quinone. It exhibits a stepwise process in which substrate binding leads to the generation of the closed protein conformation, with the latter playing a critical role in O2 binding and catalysis
purified recombinant enzyme mutants H154S/PQQ Y175F/PQQ Y175S/R179S in complex with intermediate 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid, sitting drop-vapor diffusion method, optimized conditions for each mutant: 0.1 M HEPES, pH 7.0, 0.5% w/v PEG 8000 for mutant H154S/PQQ complex, 0.2 M ammonium sulfate, 0.1 M Bis-Tris, pH 6.5, 25% w/v PEGl 3350 for mutant Y175F/PQQ complex, and 0.2 M sodium chloride, 0.1 M Tris, pH 8.5, 25% w/v PEG 3350 for mutant R179S/Y175S/intermediate complex, all at 20°C, X-ray diffraction structure determination and analysis at 1.3-2.35 A resolution
site-directed mutagenesis, active site mutant, even with substrate PQQ bound, the enzyme is still in the open conformation with helices alpha5b and alpha6 unfolded and the active site solvent accessible, no product formation
site-directed mutagenesis, active site mutant, the mutant shows an open conformation with a reaction intermediate trapped in the active site, the intermediate is tricyclic but nonplanar, implying that it has not undergone oxidatio, R179S/Y175S shows acceptable substrate complex crystals
site-directed mutagenesis, active site mutant, the mutant shows a closed conformation indicating that Y175 is not required for the conformational change, no product formation