menaquinone-6 and quinone

Topics: Anaerobiosis; Bacteroides fragilis; Cytochromes; Electron Transport; Fumarates; Humans; NAD; Oxygen; Quinones; Respiration; Succinate Dehydrogenase; Vitamin K 2

Type III polyketide synthases (PKSs) found across

Topics: Polyketides; Quinones; Streptomyces; Vitamin K 2

Diverse aerobic bacteria use atmospheric H

Topics: Atmosphere; Cryoelectron Microscopy; Hydrogen; Hydrogenase; Hydrogenation; Mycobacterium smegmatis; Oxidation-Reduction; Oxygen; Vitamin K 2

Aerobic respiration metabolism in Group B Streptococcus (GBS) is activated by exogenous heme and menaquinone. This capacity enhances resistance of GBS to acid and oxidative stress and improves its survival. In this work, we discovered that GBS is able to respire in the presence of heme and 1,4-dihydroxy-2-naphthoic acid (DHNA). DHNA is a biosynthetic precursor of demethylmenaquinone (DMK) in many bacterial species. A GBS gene (gbs1789) encodes a homolog of the MenA 1,4-dihydroxy-2-naphthoate prenyltransferase enzyme, involved in the synthesis of demethylmenaquinone. In this study, we showed that gbs1789 is involved in the biosynthesis of long-chain demethylmenaquinones (DMK-10). The Δgbs1789 mutant cannot respire in the presence of heme and DHNA, indicating that endogenously synthesized DMKs are cofactors of the GBS respiratory chain. We also found that isoprenoid side chains from GBS DMKs are produced by the protein encoded by the gbs1783 gene, since this gene can complement an Escherichia coli ispB mutant defective for isoprenoids chain synthesis. In the gut or vaginal microbiote, where interspecies metabolite exchanges occur, this partial DMK biosynthetic pathway can be important for GBS respiration and survival in different niches.

Topics: Benzoquinones; Biosynthetic Pathways; Heme; Metabolic Networks and Pathways; Naphthols; Streptococcus agalactiae; Vitamin K 2

Naturally synthesized quinones perform a variety of important cellular functions. Escherichia coli produce both ubiquinone and menaquinone, which are involved in electron transport. However, semiquinone intermediates produced during the one-electron reduction of these compounds, as well as through auto-oxidation of the hydroxyquinone product, generate reactive oxygen species that stress the cell. Here, we present the crystal structure of YgiN, a protein of hitherto unknown function. The three-dimensional fold of YgiN is similar to that of ActVA-Orf6 monooxygenase, which acts on hydroxyquinone substrates. YgiN shares a promoter with "modulator of drug activity B," a protein with activity similar to that of mammalian DT-diaphorase capable of reducing mendione. YgiN was able to reoxidize menadiol, the product of the "modulator of drug activity B" (MdaB) enzymatic reaction. We therefore refer to YgiN as quinol monooxygenase. Modulator of drug activity B is reported to be involved in the protection of cells from reactive oxygen species formed during single electron oxidation and reduction reactions. The enzymatic activities, together with the structural characterization of YgiN, lend evidence to the possible existence of a novel quinone redox cycle in E. coli.

Topics: Benzoquinones; Binding Sites; Crystallography, X-Ray; Dimerization; Drug Resistance, Neoplasm; Electron Transport; Electrons; Escherichia coli; Escherichia coli Proteins; Mixed Function Oxygenases; Models, Chemical; Models, Molecular; Oxidation-Reduction; Promoter Regions, Genetic; Protein Conformation; Protein Folding; Protein Structure, Secondary; Quinones; Reactive Oxygen Species; Recombinant Proteins; Spectrophotometry; Time Factors; Ubiquinone; Vitamin K 2

DsbB is a disulfide oxidoreductase present in the Escherichia coli plasma membrane. Its cysteine pairs, Cys41-Cys44 and Cys104-Cys130, facing the periplasm, as well as the bound quinone molecules play crucial roles in oxidizing DsbA, the protein dithiol oxidant in the periplasm. In this study, we characterized quinone-free forms of DsbB prepared from mutant cells unable to synthesize ubiquinone and menaquinone. While such preparations lacked detectable quinones, previously reported lauroylsarcosine treatment was ineffective in removing DsbB-associated quinones. Moreover, DsbB-bound quinone was shown to contribute to the redox-dependent fluorescence changes observed with DsbB. Now we reconfirmed that redox potentials of cysteine pairs of quinone-free DsbB are lower than that of DsbA, as far as determined in dithiothreitol redox buffer. Nevertheless, the quinone-free DsbB was able to oxidize approximately 40% of DsbA in a 1:1 stoichiometric reaction, in which hemi-oxidized forms of DsbB having either disulfide are generated. It was suggested that the DsbB-DsbA system is designed in such a way that specific interaction of the two components enables the thiol-disulfide exchanges in the "forward" direction. In addition, a minor fraction of quinone-free DsbB formed the DsbA-DsbB disulfide complex stably. Our results show that the rapid and the slow pathways of DsbA oxidation can proceed up to significant points, after which these reactions must be completed and recycled by quinones under physiological conditions. We discuss the significance of having such multiple reaction pathways for the DsbB-dependent DsbA oxidation.

Topics: Bacterial Proteins; Benzoquinones; Cell Membrane; Chromatography, High Pressure Liquid; Cysteine; Disulfides; Dithiothreitol; Dose-Response Relationship, Drug; Escherichia coli; Kinetics; Mass Spectrometry; Membrane Proteins; Microscopy, Fluorescence; Models, Biological; Mutation; Oxidants; Oxidation-Reduction; Oxygen; Protein Folding; Protein Structure, Tertiary; Sarcosine; Time Factors; Tryptophan; Vitamin K 2