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      Hierarchical regulation of the NikR-mediated nickel response in Helicobacter pylori

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          Nickel is an essential metal for Helicobacter pylori, as it is the co-factor of two enzymes crucial for colonization, urease and hydrogenase. Nickel is taken up by specific transporters and its intracellular homeostasis depends on nickel-binding proteins to avoid toxicity. Nickel trafficking is controlled by the Ni(II)-dependent transcriptional regulator NikR. In contrast to other NikR proteins, NikR from H. pylori is a pleiotropic regulator that depending on the target gene acts as an activator or a repressor. We systematically quantified the in vivo Ni 2+-NikR response of 11 direct NikR targets that encode functions related to nickel metabolism, four activated and seven repressed genes. Among these, four targets were characterized for the first time ( hpn, hpn-like, hydA and hspA) and NikR binding to their promoter regions was demonstrated by electrophoretic mobility shift assays. We found that NikR-dependent repression was generally set up at higher nickel concentrations than activation. Kinetics of the regulation revealed a gradual and temporal NikR-mediated response to nickel where activation of nickel-protection mechanisms takes place before repression of nickel uptake. Our in vivo study demonstrates, for the first time, a chronological hierarchy in the NikR-dependent transcriptional response to nickel that is coherent with the control of nickel homeostasis in H. pylori.

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          Most cited references 48

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          Helicobacter pylori persistence: biology and disease.

          Helicobacter pylori are bacteria that have coevolved with humans to be transmitted from person to person and to persistently colonize the stomach. Their population structure is a model for the ecology of the indigenous microbiota. A well-choreographed equilibrium between bacterial effectors and host responses permits microbial persistence and health of the host but confers risk of serious diseases, including peptic ulceration and gastric neoplasia.
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            Molecular hydrogen as an energy source for Helicobacter pylori.

            The gastric pathogen Helicobacter pylori is known to be able to use molecular hydrogen as a respiratory substrate when grown in the laboratory. We found that hydrogen is available in the gastric mucosa of mice and that its use greatly increased the stomach colonization by H. pylori. Hydrogenase activity in H. pylori is constitutive but increased fivefold upon incubation with hydrogen. Hydrogen concentrations measured in the stomachs of live mice were found to be 10 to 50 times as high as the H. pylori affinity for hydrogen. A hydrogenase mutant strain is much less efficient in its colonization of mice. Therefore, hydrogen present in animals as a consequence of normal colonic flora is an energy-yielding substrate that can facilitate the maintenance of a pathogenic bacterium.
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              Ribbon-helix-helix transcription factors: variations on a theme.

              The ribbon-helix-helix (RHH) superfamily of transcription factors uses a conserved three-dimensional structural motif to bind to DNA in a sequence-specific manner. This functionally diverse protein superfamily regulates the transcription of genes that are involved in the uptake of metals, amino-acid biosynthesis, cell division, the control of plasmid copy number, the lytic cycle of bacteriophages and, perhaps, many other cellular processes. In this Analysis, the structures of different RHH transcription factors are compared in order to evaluate the sequence motifs that are required for RHH-domain folding and DNA binding, as well as to identify conserved protein-DNA interactions in this superfamily.

                Author and article information

                Nucleic Acids Res
                Nucleic Acids Research
                Oxford University Press
                September 2011
                September 2011
                11 June 2011
                11 June 2011
                : 39
                : 17
                : 7564-7575
                1Département de Microbiologie, Institut Pasteur, Unité Pathogenèse de Helicobacter, 75724 Paris Cedex 15 and 2UMR 5249 CEA-CNRS-UJF iRTSV/Laboratoire de Chimie et Biologie des Métaux, 38054 Grenoble Cedex 09, France
                Author notes
                *To whom correspondence should be addressed. Tel: +33 1 40 61 36 41; Fax: +33 1 40 61 36 40; Email: hdereuse@

                Present addresses: Cécile Muller, USC INRA 2017, Microbiologie de l’Environnement, EA 956, IRBA, Université de Caen, 14032 Caen cedex, France.

                Christelle Bahlawane, Institute for Medical Microbiology and Hospital Epidemiology Hannover Medical School, Carl-Neuberg-Str. 1 D-30625 Hannover, Germany.

                Kristine Schauer, Mécanismes Moléculaires du Transport Intracellulaire, UMR 144 CNRS/Institut Curie, 75248 Paris Cedex 05, France.

                © The Author(s) 2011. Published by Oxford University Press.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Page count
                Pages: 12
                Molecular Biology



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