246 research outputs found
Metal ion selectivity and homeostasis: nickel sensing in the human pathogen Helicobacter pylori
No full textHomeostasis of transition metals is crucial for cellular life and is related to the use of metals as cofactors of many enzymes that catalyze an enormous variety of biological reactions. Living organisms elaborated complex and tightly regulated mechanisms to correctly acquire, utilize and allocate metals, neutralizing their harmful potential. In these processes, a fundamental role is played by metal sensor proteins, which are metal-dependent transcription factors that can select, among several intracellular metal ions, the correct metal cofactor, and mediate the specific cellular response by regulating protein expression. Due to the critical function that metal ion homeostasis generally plays in host-pathogen interactions, metal-sensors are considered fundamental virulence factors, because their deletion diminishes or abrogates the survival and colonization of many pathogens. A paradigmatic example is represented by the human pathogen Helicobacter pylori, which relies on the activity of the nickel-dependent enzymes urease and hydrogenase to survive in the acidic stomach mucosa, where it is responsible of several diseases, such as gastric ulcer and cancer. In this bacterium, nickel homeostasis is governed by NikR, a widespread homo-tetrameric transcription factor controlling the expression of proteins involved in nickel trafficking and/or nickel enzymes, in response to different concentrations of intracellular nickel.
In the present study, the modulation of the interaction between Helicobacter pylori NikR (HpNikR) and DNA, exerted by different concentrations of Ni2+ and/or other metal ions, is investigated. In particular, the thermodynamic parameters of the interaction between Ni2+, or other divalent metal ions, and HpNikR are determined by using isothermal titration calorimetry (ITC). The metal ion-dependent capability of HpNikR to bind PureA, the promoter of the urease operon, was investigated by using mobility shift assays, DNAse footprinting and ITC. The results provide a congruent description of the parameters that determine HpNikR binding to metal ions and DNA and yield clear proofs for activation of HpNikR selectively driven by Ni2+, through a protein conformational rearrangement specifically induced by Ni2+ binding (1-2). A general scheme (see Figure) for the nickel selective HpNikR–DNA interaction is proposed.
(1) B. Zambelli, M. Bellucci, A. Danielli, V. Scarlato, S. Ciurli
The Ni2+ binding properties of Helicobacter pylori NikR
Chem. Commun., 2007, 35, pp. 3649 - 3651
(2) B. Zambelli, A. Danielli, S. Romagnoli, P. Neyroz, S. Ciurli, V. Scarlato
High-affinity Ni2+ binding selectively promotes binding of Helicobacter pylori NikR to its target urease promoter
J. Mol. Biol., 2008, 383, pp. 1129 - 114
Selectivity of Metal Ion Binding Specifically Drives the Interaction of a Ni2+-sensor with its operator DNA
No full textTransition metal ions are essential micronutrient for living organisms, being fundamental cofactors of many enzymes that catalyze an enormous variety of biological reactions. At the same time, several metal ions are toxic in their free form for cellular life, demanding a tight regulation of their intracellular trafficking and homeostasis. A paradigmatic example is represented by the human pathogen Helicobacter pylori, which relies on the activity of the nickel-dependent enzymes urease and hydrogenase to survive in the acidic stomach mucosa, where it is responsible of several diseases, such as gastric ulcer and cancer. In this bacterium, homeostasis of essential Ni2+ ions should be tightly controlled to allow growth and colonization. In this processes, NikR, a widespread homo-tetrameric transcription factor controlling the expression of proteins involved in nickel trafficking and/or nickel enzymes, plays a crucial role. The present study investigates the modulation of the interaction between Helicobacter pylori NikR (HpNikR) and DNA, exerted by different concentrations of Ni2+ and/or other metal ions. In particular, the thermodynamic parameters of the interaction between Ni2+, or other divalent metal ions, and HpNikR are determined by using isothermal titration calorimetry (ITC). The metal-dependent capability of HpNikR to bind PureA, the promoter of the urease operon, was determined by using mobility shift assays, DNAse footprinting and ITC. The results provide a congruent description of the factors that determine HpNikR binding to metal ions and DNA and yield clear proofs for activation of HpNikR selectively driven by Ni2+, through a protein conformational rearrangement specifically induced by Ni2+ binding (1-2).
(1) B. Zambelli, M. Bellucci, A. Danielli, V. Scarlato, S. Ciurli; The Ni2+ binding properties of Helicobacter pylori NikR. Chem. Commun., 2007, 35, pp. 3649 - 3651
(2) B. Zambelli, A. Danielli, S. Romagnoli, P. Neyroz, S. Ciurli, V. Scarlato; High-affinity Ni2+ binding selectively promotes binding of Helicobacter pylori NikR to its target urease promoter. J. Mol. Biol., 2008, 383, pp. 1129 - 114
Bioinorganic chemistry of nickel
No full textFollowing the discovery of the first specific and essential role of nickel in biology in 1975 (the dinuclear active site of the enzyme urease) [1], nickel has become a major player in bioinorganic chemistry, particularly in microorganisms, having impacts on both environmental settings and human pathologies. At least nine classes of enzymes are now known to require nickel in their active sites, including catalysis of redox [(Ni,Fe) hydrogenases, carbon monoxide dehydrogenase, methyl coenzyme M reductase, acetyl coenzyme A synthase, superoxide dismutase] and nonredox (glyoxalase I, acireductone dioxygenase, lactate isomerase, urease) chemistries. In addition, the dark side of nickel has been illuminated in regard to its participation in microbial pathogenesis, cancer, and immune responses. Knowledge gleaned from the investigations of inorganic chemists into the coordination and redox chemistry of this element have boosted the understanding of these biological roles of nickel in each context. In this issue, eleven contributions, including four original research articles and seven critical reviews, will update the reader on the broad spectrum of the role of nickel in biology
Holo- Helicobacter pylori NikR contains four square-planar nickel-binding sites at physiological pH
No full textThe crystal structure of Helicobacter pylori holo-NikR, a Ni(2+)-dependent transcription factor, determined at pH 7.3, shows four square-planar nickel-binding sites, involving one cysteinate and three histidine ligands. This observation reconciles previous inconsistencies among calorimetric data, structural information at non-physiological pH, and computational studies
Nickel as a virulence factor in the Class I bacterial carcinogen, Helicobacter pylori
No full textHelicobacter pylori is a human bacterial pathogen that causes peptic ulcers and has been designated a Class I carcinogen by the International Agency for Research on Cancer (IARC). Its ability to survive in the acid environment of the stomach, to colonize the stomach mucosa, and to cause cancer, are linked to two enzymes that require nickel—urease and hydrogenase. Thus, nickel is an important virulence factor and the proteins involved in nickel trafficking are potential antibiotic targets. This review summarizes the nickel biochemistry of H. pylori with a focus on the roles of nickel in virulence, nickel homeostasis, maturation of urease and hydrogenase, and the unique nickel trafficking that occurs between the hydrogenase maturation pathway and urease nickel incorporation that is mediated by the metallochaperone HypA and its partner, HypB
Metallo-chaperones and active-site assembly of metallo-enzymes: the case of nickel in urease
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