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Accueil > Départements > Microbiologie > Soufian OUCHANE : Adaptation Bactérienne aux changements environnementaux

Publications de l’équipe

2017


  • A. Durand, M. - L. Bourbon, A. - S. Steunou, B. Khalfaoui-Hassani, C. Legrand, A. Guitton, C. Astier, et S. Ouchane, « Biogenesis of the bacterial cbb3 cytochrome c oxidase: active subcomplexes support a sequential assembly model », The Journal of Biological Chemistry, 2017.
    Résumé : The cbb3 oxidase has a high affinity for oxygen and is required for growth of bacteria, including pathogens, in oxygen-limited environments. However, the assembly of this oxidase is poorly understood. Most cbb3 are composed of four subunits: the catalytic CcoN subunit, the two cytochromes c subunits (CcoO and CcoP) involved in electron transfer and the small CcoQ subunit with an unclear function. Here, we address the role of these four subunits in cbb3 biogenesis in the purple bacterium Rubrivivax gelatinosus Analyses of membrane proteins from different mutants revealed the presence of active CcoNQO and CcoNO subcomplexes and also showed that the CcoP subunit is not essential for their assembly. However, CcoP was required for the oxygen reduction activity in the absence of CcoQ. We also found that CcoQ is dispensable for forming an active CcoNOP subcomplex in membranes. CcoNOP exhibited oxygen reductase activity, indicating that the cofactors (hemes b and copper for CcoN, cytochromes c for CcoO and CcoP) were present within the subunits. Finally, we discovered the presence of a CcoNQ subcomplex and showed that CcoN is the required anchor for the assembly of the full CcoNQOP complex. On the basis of these findings, we propose a sequential assembly model in which the CcoQ subunit is required for the early maturation step: CcoQ first associates with CcoN before the CcoNQ-CcoO interaction. CcoP associates to CcoNQO subcomplex in the late maturation step and once the CcoNQOP complex is fully formed, CcoQ is released for degradation by the FtsH protease. This model could be conserved in other bacteria including the pathogenic bacteria lacking the assembly factor CcoH as in R. gelatinosus.
    Mots-clés : BACADA, bacteria, cbb3 cytochrome c oxidase biogenesis, cytochrome oxidase, membrane protein, membrane sub-complexes assembly, MICROBIO, PDC, protein assembly, respiration, subunit inteactions.

2015


  • A. Durand, A. Azzouzi, M. - L. Bourbon, A. - S. Steunou, S. Liotenberg, A. Maeshima, C. Astier, M. Argentini, S. Saito, et S. Ouchane, « c-Type Cytochrome Assembly Is a Key Target of Copper Toxicity within the Bacterial Periplasm », mBio, vol. 6, nᵒ 5, p. e01007-01015, 2015.
    Résumé : In the absence of a tight control of copper entrance into cells, bacteria have evolved different systems to control copper concentration within the cytoplasm and the periplasm. Central to these systems, the Cu(+) ATPase CopA plays a major role in copper tolerance and translocates copper from the cytoplasm to the periplasm. The fate of copper in the periplasm varies among species. Copper can be sequestered, oxidized, or released outside the cells. Here we describe the identification of CopI, a periplasmic protein present in many proteobacteria, and show its requirement for copper tolerance in Rubrivivax gelatinosus. The ΔcopI mutant is more susceptible to copper than the Cu(+) ATPase copA mutant. CopI is induced by copper, localized in the periplasm and could bind copper. Interestingly, copper affects cytochrome c membrane complexes (cbb3 oxidase and photosystem) in both ΔcopI and copA-null mutants, but the causes are different. In the copA mutant, heme and chlorophyll synthesis are affected, whereas in ΔcopI mutant, the decrease is a consequence of impaired cytochrome c assembly. This impact on c-type cytochromes would contribute also to the copper toxicity in the periplasm of the wild-type cells when they are exposed to high copper concentrations. IMPORTANCE: Copper is an essential cation required as a cofactor in enzymes involved in vital processes such as respiration, photosynthesis, free radical scavenging, and pathogenesis. However, copper is highly toxic and has been implicated in disorders in all organisms, including humans, because it can catalyze the production of toxic reactive oxygen species and targets various biosynthesis pathways. Identifying copper targets, provides insights into copper toxicity and homeostatic mechanisms for copper tolerance. In this work, we describe for the first time a direct effect of excess copper on cytochrome c assembly. We show that excess copper specifically affects periplasmic and membrane cytochromes c, thus suggesting that the copper toxicity targets c-type cytochrome biogenesis.
    Mots-clés : BACADA, Betaproteobacteria, Copper, Cytochromes c, Gene Deletion, MICROBIO, Molecular Sequence Data, Periplasm, Periplasmic Proteins, Protein Multimerization, Sequence Analysis, DNA.

  • S. Liotenberg, A. - S. Steunou, A. Durand, M. - L. Bourbon, D. Bollivar, M. Hansson, C. Astier, et S. Ouchane, « Oxygen-dependent copper toxicity: targets in the chlorophyll biosynthesis pathway identified in the copper efflux ATPase CopA deficient mutant », Environmental Microbiology, vol. 17, nᵒ 6, p. 1963-1976, 2015.
    Résumé : Characterization of a copA(-) mutant in the purple photosynthetic bacterium Rubrivivax gelatinosus under low oxygen or anaerobic conditions, as well as in the human pathogen Neisseria gonorrhoeae identified HemN as a copper toxicity target enzyme in the porphyrin synthesis pathway. Heme synthesis is, however, unaffected by copper under high oxygen tension because of the aerobic coproporphyrinogen III oxidase HemF. Nevertheless, in the copA(-) mutant under aerobiosis, we show that the chlorophyll biosynthesis pathway is affected by excess copper resulting in a substantial decrease of the photosystem. Analyses of pigments and enzyme activity showed that under low copper concentrations, the mutant accumulated protochlorophyllide, suggesting that the protochlorophyllide reductase activity is affected by excess copper. Increase of copper concentration led to a complete lack of chlorophyll synthesis as a result of the loss of Mg-chelatase activity. Both enzymes are widely distributed from bacteria to plants; both are [4Fe-4S] proteins and oxygen sensitive; our data demonstrate their in vivo susceptibility to copper in the presence of oxygen. Additionally, our study provides the understanding of molecular mechanisms that may contribute to chlorosis in plants when exposed to metals. The role of copper efflux systems and the impact of copper on heme and chlorophyll biosynthesis in phototrophs are addressed.
    Mots-clés : Adenosine Triphosphatases, Aerobiosis, BACADA, Bacterial Proteins, Betaproteobacteria, Cation Transport Proteins, Chlorophyll, Copper, Coproporphyrinogen Oxidase, Coproporphyrinogens, Humans, Lyases, MICROBIO, Neisseria gonorrhoeae, Oxidoreductases Acting on CH-CH Group Donors, Oxygen, Protochlorophyllide.
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Publications Principales avant 2015

1 - Azzouzi, A., Steunou AS, Durand A, Khalfaoui-Hassani B, Bourbon ML, Astier C, Bollivar DW, Ouchane S. (2013) Coproporphyrin III excretion identifies the anaerobic coproporphyrinogen III oxidase HemN as a copper target in the Cu+-ATPase mutant copA- of Rubrivivax gelatinosus. Mol. Microbiol 88(2):339-51.

2 - Steunou, A.S, Liotenberg, S., Soler, M., Briandet , R., Barbe, V., Astier, C. and Ouchane, S. (2013) EmbRS a new two-component system that inhibits biofilm formation and saves Rubrivivax gelatinosus from sinking. MicrobiologyOpen 2(3):431-46.

3 - Khalfaoui Hassani, B., Steunou, AS., Liotenberg, S., Reiss-Husson, F., Astier, C., Ouchane, S. (2010 b) Adaptation to oxygen : Role of terminal oxidases in photosynthesis initiation in the purple photosynthetic bacterium, Rubrivivax gelatinosus. J Biol Chem, 285 (26) 19891-9.

4 - Khalfaoui Hassani, B., Astier, C., Nitschke, W., Ouchane, S. (2010 a) CtpA a copper-translocating P-type ATPase involved in the biogenesis of multiple copper-requiring enzymes. J Biol Chem, 285 (25) 19330-7.

5 - Liotenberg, S., Steunou, A.S., Picaud, M., Reiss-Husson, F., Astier, C., Ouchane, S. (2008). Organization and expression of photosynthesis genes and operons in anoxygenic photosynthetic proteobacteria. Env. Microbiol, 10 (9) 2267-76.

6 - Ducluzeau, A.L., Ouchane S., Nitschke W. (2008). cbb3 Oxidases are an Ancient Innovation of the Domain Bacteria. Mol Biol Evol, 25 (6) 1158-1166

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