The ubiK protein is an accessory factor necessary for bacterial Ubiquinone (UQ) biosynthesis and forms a complex with the UQ biogenesis factor UbiJ

Ubiquinone (UQ), also referred to as coenzyme Q, is a widespread lipophilic molecule in both prokaryotes and eukaryotes in which it primarily acts as an electron carrier. Eleven proteins are known to participate in UQ biosynthesis in Escherichia coli, and we recently demonstrated that UQ biosynthesis requires additional, nonenzymatic factors, some of which are still unknown. Here, we report on the identification of a bacterial gene, yqiC, which is required for efficient UQ biosynthesis, and which we have renamed ubiK. Using several methods, we demonstrated that the UbiK protein forms a complex with the C-terminal part of UbiJ, another UQ biogenesis factor we previously identified. We found that both proteins are likely to contribute to global UQ biosynthesis rather than to a specific biosynthetic step, because both ubiK and ubiJ mutants accumulated octaprenylphenol, an early intermediate of the UQ biosynthetic pathway. Interestingly, we found that both proteins are dispensable for UQ biosynthesis under anaerobiosis, even though they were expressed in the absence of oxygen. We also provide evidence that the UbiK-UbiJ complex interacts with palmitoleic acid, a major lipid in E. coli. Last, in Salmonella enterica, ubiK was required for proliferation in macrophages and virulence in mice. We conclude that although the role of the UbiK-UbiJ complex remains unknown, our results support the hypothesis that UbiK is an accessory factor of Ubi enzymes and facilitates UQ biosynthesis by acting as an assembly factor, a targeting factor, or both.Agence Nationale de la Recherche ANR-15-CE11-0001-02Centre National de la Recherche Scientifique PICS07279French State Program "Investissements d'Avenir" ANR-11-LABX-001

Biosynthesis and physiology of coenzyme Q in bacteria.

International audienceUbiquinone, also called coenzyme Q, is a lipid subject to oxido-reduction cycles. It functions in the respiratory electron transport chain and plays a pivotal role in energy generating processes. In this review, we focus on the biosynthetic pathway and physiological role of ubiquinone in bacteria. We present the studies which, within a period of five decades, led to the identification and characterization of the genes named ubi and involved in ubiquinone production in Escherichia coli. When available, the structures of the corresponding enzymes are shown and their biological function is detailed. The phenotypes observed in mutants deficient in ubiquinone biosynthesis are presented, either in model bacteria or in pathogens. A particular attention is given to the role of ubiquinone in respiration, modulation of two-component activity and bacterial virulence. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference

ubiJ, a New Gene Required for Aerobic Growth and Proliferation in Macrophage, Is Involved in Coenzyme Q Biosynthesis in Escherichia coli and Salmonella enterica Serovar Typhimurium.

International audienceUbiquinone (coenzyme Q or Q8) is a redox active lipid which functions in the respiratory electron transport chain and plays a crucial role in energy-generating processes. In both Escherichia coli and Salmonella enterica serovar Typhimurium, the yigP gene is located between ubiE and ubiB, all three being likely to constitute an operon. In this work, we showed that the uncharacterized yigP gene was involved in Q8 biosynthesis in both strains, and we have renamed it ubiJ. Under aerobic conditions, an ubiJ mutant was found to be impaired for Q8 biosynthesis and for growth in rich medium but did not present any defect anaerobically. Surprisingly, the C-terminal 50 amino acids, predicted to interact with lipids, were sufficient to restore Q8 biosynthesis and growth of the ubiJ mutant. Salmonella ubiE and ubiB mutants were impaired in Q8 biosynthesis and in respiration using different electron acceptors. Moreover, ubiE, ubiJ, and ubiB mutants were all impaired for Salmonella intracellular proliferation in macrophages. Taken together, our data establish an important role for UbiJ in Q8 biosynthesis and reveal an unexpected link between Q8 and virulence. They also emphasize that Salmonella organisms in an intracellular lifestyle rely on aerobic respiration to survive and proliferate within macrophages

30 ans de publication dans Mappemonde

En juin 2018, nous avons organisé une journée d’études à l’université Paris 1 Panthéon-Sorbonne pour fêter, avec des lecteurs et des membres passés et présents du comité de rédaction, les 30 ans de publication de la revue Mappemonde avec quelques mois de retard, le tout premier numéro de la revue ayant été publié en 1986. En cette fin d’année 2019, alors que nous approchons déjà des 34 ans de publication, nous proposons dans ce numéro l’ouverture d’un dossier spécial qui rassemble certaines d..

Iron-Sulfur (Fe/S) Protein Biogenesis: Phylogenomic and Genetic Studies of A-Type Carriers

Iron sulfur (Fe/S) proteins are ubiquitous and participate in multiple biological processes, from photosynthesis to DNA repair. Iron and sulfur are highly reactive chemical species, and the mechanisms allowing the multiprotein systems ISC and SUF to assist Fe/S cluster formation in vivo have attracted considerable attention. Here, A-Type components of these systems (ATCs for A-Type Carriers) are studied by phylogenomic and genetic analyses. ATCs that have emerged in the last common ancestor of bacteria were conserved in most bacteria and were acquired by eukaryotes and few archaea via horizontal gene transfers. Many bacteria contain multiple ATCs, as a result of gene duplication and/or horizontal gene transfer events. Based on evolutionary considerations, we could define three subfamilies: ATC-I, -II and -III. Escherichia coli, which has one ATC-I (ErpA) and two ATC-IIs (IscA and SufA), was used as a model to investigate functional redundancy between ATCs in vivo. Genetic analyses revealed that, under aerobiosis, E. coli IscA and SufA are functionally redundant carriers, as both are potentially able to receive an Fe/S cluster from IscU or the SufBCD complex and transfer it to ErpA. In contrast, under anaerobiosis, redundancy occurs between ErpA and IscA, which are both potentially able to receive Fe/S clusters from IscU and transfer them to an apotarget. Our combined phylogenomic and genetic study indicates that ATCs play a crucial role in conveying ready-made Fe/S clusters from components of the biogenesis systems to apotargets. We propose a model wherein the conserved biochemical function of ATCs provides multiple paths for supplying Fe/S clusters to apotargets. This model predicts the occurrence of a dynamic network, the structure and composition of which vary with the growth conditions. As an illustration, we depict three ways for a given protein to be matured, which appears to be dependent on the demand for Fe/S biogenesis

Prix de thèse 2019

Après délibération lors de la réunion du comité de rédaction de la revue du 20 septembre 2019 à l’Institut de Géographie, le Prix de Thèse Mappemonde 2019 a été décerné. Ce prix récompense, rappelons-le, « une thèse de doctorat de qualité, où l’image géographique (prise au sens large : cartes, photographies, modèles, croquis et cartogrammes, représentation de données satellitaires, SIG, animations) aura été mobilisée de manière particulièrement pertinente dans le raisonnement scientifique ». ..

Quinolinate synthase, an iron-sulfur enzyme in NAD biosynthesis

International audienceNicotinamide adenine dinucleotide (NAD) plays a crucial role as a cofactor in numerous essential redox biological reactions. NAD derives from quinolinic acid which is synthesized in E. coli from L-aspartate and dihydroxyacetone phosphate (DHAP) as the result of the concerted action of two enzymes, L-aspartate oxidase (NadB) and quinolinate synthetase (NadA). We report here the characterization of NadA protein from E. coli. When anaerobically purified, the isolated soluble protein contains 3-3.5 iron and 3-3.5 sulfide/ polypeptide chain. Mössbauer spectra of the 57Fe-protein revealed that the majority of the iron is in the form of a (4Fe-4S)2+ cluster. An enzymatic assay for quinolinate synthetase activity was set up and allowed to demonstrate that the cluster is absolutely required for NadA activity. Exposure to air leads to degradation of the cluster and inactivate enzyme

X-ray spectral curvature of High Frequency Peaked BL Lacs: a predictor for the TeV flux

Most of the extragalactic sources detected at TeV energies are BL Lac objects. They belong to the subclass of "high frequency peaked BL Lacs" (HBLs) exhibiting spectral energy distributions with a lower energy peak in the X-ray band; this is widely interpreted as synchrotron emission from relativistic electrons. The X-ray spectra are generally curved, and well described in terms of a log-parabolic shape. In a previous investigation of TeV HBLs (TBLs) we found two correlations between their spectral parameters. (1) The synchrotron peak luminosity L_p increases with its peak energy E_p; (2) the curvature parameter b decreases as E_p increases. The first is consistent with the synchrotron scenario, while the second is expected from statistical/stochastic acceleration mechanisms for the emitting electrons. Here we present an extensive X-ray analysis of a sample of HBLs observed with XMM-Newton and SWIFT but undetected at TeV energies (UBLs), to compare their spectral behavior with that of TBLs. Investigating the distributions of their spectral parameters and comparing the TBL X-ray spectra with that of UBLs, we develop a criterion to select the best HBLs candidates for future TeV observations.Comment: 25 pages, 6 figures, Astrophysical Journal publishe

Redox controls reca protein activity via reversible oxidation of its methionine residues

Reactive oxygen species (ROS) cause damage to DNA and proteins. Here we report that the RecA recombinase is itself oxidized by ROS. Genetic and biochemical analyses revealed that oxidation of RecA altered its DNA repair and DNA recombination activities. Mass spectrometry analysis showed that exposure to ROS converted 4 out of 9 Met residues of RecA to methionine sulfoxide. Mimicking oxidation of Met35 by changing it for Gln caused complete loss of function whereas mimicking oxidation of Met164 resulted in constitutive SOS activation and loss of recombination activity. Yet, all ROS-induced alterations of RecA activity were suppressed by methionine sulfoxide reductases MsrA and MsrB. These findings indicate that under oxidative stress, MsrA/B is needed for RecA homeostasis control. The implication is that, besides damaging DNA structure directly, ROS prevent repair of DNA damage by hampering RecA activity.Agence Nationale de la Re-cherche ANR-10-LABX-62-IBEIDFondation pour la Recherche Medicale FRM - FDT20150532554National Institute of General Medical Sciences GM3233

A new gene involved in coenzyme Q biosynthesis in Escherichia coli: UbiI functions in aerobic C5-hydroxylation

International audienceCoenzyme Q (ubiquinone or Q) is a redox-active lipid found in organisms ranging from bacteria to mammals in which it plays a crucial role in energy-generating processes. Q biosynthesis is a complex pathway that involves multiple proteins. In this work, we show that the uncharacterized conserved visC gene is involved in Q biosynthesis in Escherichia coli, and we have renamed it ubiI. Based on genetic and biochemical experiments, we establish that the UbiI protein functions in the C5-hydroxylation reaction. A strain deficient in ubiI has a low level of Q and accumulates a compound derived from the Q biosynthetic pathway, which we purified and characterized. We also demonstrate that UbiI is only implicated in aerobic Q biosynthesis and that an alternative enzyme catalyzes the C5-hydroxylation reaction in the absence of oxygen. We have solved the crystal structure of a truncated form of UbiI. This structure shares many features with the canonical FAD-dependent para-hydroxybenzoate hydroxylase and represents the first structural characterization of a monooxygenase involved in Q biosynthesis. Site-directed mutagenesis confirms that residues of the flavin binding pocket of UbiI are important for activity. With our identification of UbiI, the three monooxygenases necessary for aerobic Q biosynthesis in E. coli are known