The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Vincent Mejean - One of the best experts on this subject based on the ideXlab platform.
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genes regulated by Torr the trimethylamine oxide response regulator of shewanella oneidensis
Journal of Bacteriology, 2004Co-Authors: Christophe Bordi, Mireille Ansaldi, Cecile Jourlincastelli, Chantal Iobbinivol, Vincent MejeanAbstract:The torECAD operon encoding the trimethylamine oxide (TMAO) respiratory system of Shewanella oneidensis is positively controlled by the TorS/Torr two-component system when TMAO is available. Activation of the tor operon occurs upon binding of the phosphorylated response regulator Torr to a single operator site containing the direct repeat nucleotide sequence TTCATAN4TTCATA. Here we show that the replacement of any nucleotide of one TTCATA hexamer prevented Torr binding in vitro, meaning that Torr specifically interacts with this DNA target. Identical direct repeat sequences were found in the promoter regions of Torr and of the new gene torF (SO4694), and they allowed Torr binding to both promoters. Real-time PCR experiments revealed that Torr is negatively autoregulated, whereas torF is strongly induced by Torr in response to TMAO. Transcription start site location and footprinting analysis indicate that the operator site at Torr overlaps the promoter −10 box, whereas the operator site at torF is centered at −74 bp from the start site, in agreement with the opposite role of Torr in the regulation of the two genes. Since torF and torECAD are positively coregulated by Torr, we propose that the TorF protein plays a role related to TMAO respiration.
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An unsuspected autoregulatory pathway involving apocytochrome TorC and sensor TorS in Escherichia coli.
Proceedings of the National Academy of Sciences of the United States of America, 2001Co-Authors: Shoko Gon, C Jourlin-castelli, Laurence Theraulaz, Vincent MejeanAbstract:Trimethylamine N-oxide (TMAO) respiration is carried out mainly by the Tor system in Escherichia coli. This system is encoded by the torCAD operon and comprises a periplasmic TMAO reductase (TorA) and a c-type cytochrome (TorC), which shuttles electrons to TorA. Expression of the tor operon is positively controlled by the TorS/Torr phosphorelay system in response to TMAO availability and negatively regulated by apocytochrome TorC. Interaction studies showed that, when immature, TorC can no longer bind TorA efficiently but can bind the periplasmic detector region of sensor TorS. ApoTorC negative autoregulation and TMAO induction are thus mediated by the same sensor protein. As apocytochromes related to TorC could not down-regulate the tor operon, we concluded that this negative control is highly specific. Moreover, the N-terminal half of apoTorC played no role in this control but the immature C-terminal domain of TorC strongly down-regulated the tor operon and interacted with the TorS detector region. This sophisticated autoregulatory pathway thus involves the C-terminal domain of apoTorC and allows optimal TorC biogenesis by preventing from saturation the c-type cytochrome maturation machinery.
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Rapid dephosphorylation of the Torr response regulator by the TorS unorthodox sensor in Escherichia coli
Journal of Bacteriology, 2001Co-Authors: Mireille Ansaldi, C Jourlin-castelli, Michèle Lepelletier, Laurence Theraulaz, Vincent MejeanAbstract:Induction of the torCAD operon, encoding the trimethylamine N-oxide (TMAO) respiratory system, is tightly controlled by the TorS-Torr phosphorelay system in response to TMAO availability. TorS is an unorthodox sensor that contains three phosphorylation sites and transphosphorylates Torr via a four-step phosphorelay, His443-->Asp723-->His850-->Asp(Torr). In this study, we provide genetic evidence that TorS can dephosphorylate phospho-Torr when TMAO is removed. Dephosphorylation probably occurs by a reverse phosphorelay, Asp(Torr)-->His850-->Asp723, since His850 and Asp723 are both essential in this process. By using reverse transcriptase PCR, we also show that TMAO removal results in shutoff of tor operon transcription in less than 2 min. Based on our results and on analogy to other phosphorelay signal transduction systems, we propose that reverse phosphotransfer could be a rapid and efficient mechanism to inactivate response regulators.
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The Torr high-affinity binding site plays a key role in both Torr autoregulation and torCAD operon expression in Escherichia coli
Journal of Bacteriology, 2000Co-Authors: Mireille Ansaldi, Gwénola Simon, Michèle Lepelletier, Vincent MejeanAbstract:In the presence of trimethylamine N-oxide (TMAO), the TorS-Torr two-component regulatory system induces the torCAD operon, which encodes the TMAO respiratory system of Escherichia coli. The sensor protein TorS detects TMAO and transphosphorylates the response regulator Torr which, in turn, activates transcription of torCAD. The Torr gene and the torCAD operon are divergently transcribed, and the short Torr-torC intergenic region contains four direct repeats (the tor boxes) which proved to be Torr binding sites. The tor box 1-box 2 region covers the Torr transcription start site and constitutes a Torr high-affinity binding site, whereas box 3 and box 4 correspond to low-affinity binding sites. By using Torr-lacZ operon fusions in different genetic backgrounds, we showed that the Torr gene is negatively autoregulated. Surprisingly, Torr autoregulation is TMAO independent and still occurs in a torS mutant. In addition, this negative regulation involves only the Torr high-affinity binding site. Together, these data suggest that phosphorylated as well as unphosphorylated Torr binds the box 1-box 2 region in vivo, thus preventing RNA polymerase from binding to the Torr promoter whatever the growth conditions. By changing the spacing between box 2 and box 3, we demonstrated that the DNA motifs of the high- and low-affinity binding sites must be close to each other and located on the same side of the DNA helix to allow induction of the torCAD operon. Thus, prior Torr binding to the box 1-box 2 region seems to allow cooperative binding of phosphorylated Torr to box 3 and box 4.
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Transphosphorylation of the Torr response regulator requires the three phosphorylation sites of the TorS unorthodox sensor in Escherichia coli
Journal of Molecular Biology, 1997Co-Authors: Cécile Jourlin, Mireille Ansaldi, Vincent MejeanAbstract:Two-component regulatory systems allow cells to adapt to environmental changes. In Escherichia coli, the TorS/Torr two-component system induces the expression of the tor structural operon encoding the trimethylamine N-oxide reductase respiratory system in response to substrate availability. TorS belongs to a sensor subfamily that includes a classical transmitter domain, a receiver, and a C-terminal alternative transmitter domain. The histidine phosphorylation sites of each TorS transmitter domain and the aspartate phosphorylation site of the TorS receiver were individually changed by site-directed mutagenesis. All three phosphorylation sites proved essential for in vivo induction of the tor structural operon and for in vitro transphosphorylation of the cognate Torr response regulator. The His to Gln change in the classical transmitter domain abolished TorS autophosphorylation, whereas TorS underwent significant autophosphorylation when the phosphorylation site of its receiver or alternative transmitter was changed. Complementation between pairs of defective TorS proteins was achieved in vitro, allowing Torr transphosphorylation. This strongly suggests that TorS is a multimer in which intermolecular phosphorylation occurs. The wild-type alternative transmitter domain alone was shown to complement a TorS protein mutated in its C-terminal alternative transmitter. Interestingly, overproduction of the alternative transmitter domain led to in vivo Torr-dependent constitutive expression of the tor operon in a torS+or torS context. Hence, the TorS alternative transmitter contains the phosphodonor site for Torr. Taken together, our results support a TorS phosphorylation cascade from the classical transmitter to the sensor receiver and the alternative transmitter phosphorylation sites.
Mireille Ansaldi - One of the best experts on this subject based on the ideXlab platform.
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genes regulated by Torr the trimethylamine oxide response regulator of shewanella oneidensis
Journal of Bacteriology, 2004Co-Authors: Christophe Bordi, Mireille Ansaldi, Cecile Jourlincastelli, Chantal Iobbinivol, Vincent MejeanAbstract:The torECAD operon encoding the trimethylamine oxide (TMAO) respiratory system of Shewanella oneidensis is positively controlled by the TorS/Torr two-component system when TMAO is available. Activation of the tor operon occurs upon binding of the phosphorylated response regulator Torr to a single operator site containing the direct repeat nucleotide sequence TTCATAN4TTCATA. Here we show that the replacement of any nucleotide of one TTCATA hexamer prevented Torr binding in vitro, meaning that Torr specifically interacts with this DNA target. Identical direct repeat sequences were found in the promoter regions of Torr and of the new gene torF (SO4694), and they allowed Torr binding to both promoters. Real-time PCR experiments revealed that Torr is negatively autoregulated, whereas torF is strongly induced by Torr in response to TMAO. Transcription start site location and footprinting analysis indicate that the operator site at Torr overlaps the promoter −10 box, whereas the operator site at torF is centered at −74 bp from the start site, in agreement with the opposite role of Torr in the regulation of the two genes. Since torF and torECAD are positively coregulated by Torr, we propose that the TorF protein plays a role related to TMAO respiration.
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Rapid dephosphorylation of the Torr response regulator by the TorS unorthodox sensor in Escherichia coli
Journal of Bacteriology, 2001Co-Authors: Mireille Ansaldi, C Jourlin-castelli, Michèle Lepelletier, Laurence Theraulaz, Vincent MejeanAbstract:Induction of the torCAD operon, encoding the trimethylamine N-oxide (TMAO) respiratory system, is tightly controlled by the TorS-Torr phosphorelay system in response to TMAO availability. TorS is an unorthodox sensor that contains three phosphorylation sites and transphosphorylates Torr via a four-step phosphorelay, His443-->Asp723-->His850-->Asp(Torr). In this study, we provide genetic evidence that TorS can dephosphorylate phospho-Torr when TMAO is removed. Dephosphorylation probably occurs by a reverse phosphorelay, Asp(Torr)-->His850-->Asp723, since His850 and Asp723 are both essential in this process. By using reverse transcriptase PCR, we also show that TMAO removal results in shutoff of tor operon transcription in less than 2 min. Based on our results and on analogy to other phosphorelay signal transduction systems, we propose that reverse phosphotransfer could be a rapid and efficient mechanism to inactivate response regulators.
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The Torr high-affinity binding site plays a key role in both Torr autoregulation and torCAD operon expression in Escherichia coli
Journal of Bacteriology, 2000Co-Authors: Mireille Ansaldi, Gwénola Simon, Michèle Lepelletier, Vincent MejeanAbstract:In the presence of trimethylamine N-oxide (TMAO), the TorS-Torr two-component regulatory system induces the torCAD operon, which encodes the TMAO respiratory system of Escherichia coli. The sensor protein TorS detects TMAO and transphosphorylates the response regulator Torr which, in turn, activates transcription of torCAD. The Torr gene and the torCAD operon are divergently transcribed, and the short Torr-torC intergenic region contains four direct repeats (the tor boxes) which proved to be Torr binding sites. The tor box 1-box 2 region covers the Torr transcription start site and constitutes a Torr high-affinity binding site, whereas box 3 and box 4 correspond to low-affinity binding sites. By using Torr-lacZ operon fusions in different genetic backgrounds, we showed that the Torr gene is negatively autoregulated. Surprisingly, Torr autoregulation is TMAO independent and still occurs in a torS mutant. In addition, this negative regulation involves only the Torr high-affinity binding site. Together, these data suggest that phosphorylated as well as unphosphorylated Torr binds the box 1-box 2 region in vivo, thus preventing RNA polymerase from binding to the Torr promoter whatever the growth conditions. By changing the spacing between box 2 and box 3, we demonstrated that the DNA motifs of the high- and low-affinity binding sites must be close to each other and located on the same side of the DNA helix to allow induction of the torCAD operon. Thus, prior Torr binding to the box 1-box 2 region seems to allow cooperative binding of phosphorylated Torr to box 3 and box 4.
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Transphosphorylation of the Torr response regulator requires the three phosphorylation sites of the TorS unorthodox sensor in Escherichia coli
Journal of Molecular Biology, 1997Co-Authors: Cécile Jourlin, Mireille Ansaldi, Vincent MejeanAbstract:Two-component regulatory systems allow cells to adapt to environmental changes. In Escherichia coli, the TorS/Torr two-component system induces the expression of the tor structural operon encoding the trimethylamine N-oxide reductase respiratory system in response to substrate availability. TorS belongs to a sensor subfamily that includes a classical transmitter domain, a receiver, and a C-terminal alternative transmitter domain. The histidine phosphorylation sites of each TorS transmitter domain and the aspartate phosphorylation site of the TorS receiver were individually changed by site-directed mutagenesis. All three phosphorylation sites proved essential for in vivo induction of the tor structural operon and for in vitro transphosphorylation of the cognate Torr response regulator. The His to Gln change in the classical transmitter domain abolished TorS autophosphorylation, whereas TorS underwent significant autophosphorylation when the phosphorylation site of its receiver or alternative transmitter was changed. Complementation between pairs of defective TorS proteins was achieved in vitro, allowing Torr transphosphorylation. This strongly suggests that TorS is a multimer in which intermolecular phosphorylation occurs. The wild-type alternative transmitter domain alone was shown to complement a TorS protein mutated in its C-terminal alternative transmitter. Interestingly, overproduction of the alternative transmitter domain led to in vivo Torr-dependent constitutive expression of the tor operon in a torS+or torS context. Hence, the TorS alternative transmitter contains the phosphodonor site for Torr. Taken together, our results support a TorS phosphorylation cascade from the classical transmitter to the sensor receiver and the alternative transmitter phosphorylation sites.
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Binding of the Torr regulator to cis‐acting direct repeats activates tor operon expression
Molecular Microbiology, 1995Co-Authors: G Simon, Cécile Jourlin, Mireille Ansaldi, Marie-claire Pascal, Marc Chippaux, Vincent MejeanAbstract:The expression of the Escherichia coli torCAD operon, which encodes the anaerobically expressed trimethylamine N-oxide (TMAO) reductase respiratory system, requires the presence of TMAO in the medium. The response regulator, Torr, has recently been identified as the regulatory protein that controls the expression of the torCAD operon in response to TMAO. The torC regulatory region contains four direct repeats of a decameric consensus motif designated the tor boxes. Alteration by base substitutions of any of the four tor boxes in a plasmid containing a torC′-lacZ fusion dramatically reduces Torr-dependent torC expression. In addition, deletion of the distal tor box (box1) abolishes torC induction whereas the presence of a DNA fragment starting three bases upstream from box1 suffices for normal torC expression. Footprinting and gel-retardation experiments unambiguously demonstrated that Torr binds to the torC regulatory region. Three distinct regions are protected by Torr binding. One of approximately 24 nucleotides covers the first two tor boxes (box1 and box2); the second is located upstream from the −35 promoter sequence and includes the third tor box (box3); the last is found downstream from the −35 sequence and corresponds to the fourth tor box (box4). Binding to the upstream tor boxes (box1 and box2) appears to be stronger than binding to the downstream tor boxes (box3 and box4) since only the upstream region is protected at the lower concentration of Torr used in the footprinting experiments. We propose a model in which multiple binding sites (i.e. the tor boxes) contribute to the formation of a nucleoprotein complex, but only one particular proximal site positions Torr properly so that it interacts with RNA polymerase.
K.d. Wise - One of the best experts on this subject based on the ideXlab platform.
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Batch-processed vacuum-sealed capacitive pressure sensors
Journal of Microelectromechanical Systems, 2001Co-Authors: A.v. Chavan, K.d. WiseAbstract:This paper reports two multitransducer vacuum-sealed capacitive barometric pressure sensors, one using single-lead and the other using multiple-leads to transfer the electrical signal out of the vacuum-sealed reference cavity. The first device operates with a resolution of 37 mTorr over a pressure range from 600 to 800 Torr. The sensitivity is 27 fF/Torr (3000 ppm/Torr). The TCO at 750 Torr is 3900 ppm//spl deg/C and the TCS is 1000 ppm//spl deg/C. The second device has a resolution of 25 mTorr over a range from 500 to 800 Torr, with individual transducer sensitivity of 39 fF/Torr. The TCO at 750 Torr is 1350 ppm//spl deg/C and TCS is 1000 ppm//spl deg/C. Both devices have an on-chip compensation capacitor and are read out using an electronically-trimmed switched-capacitor charge integrator.
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An ultrasensitive silicon pressure-based microflow sensor
IEEE Transactions on Electron Devices, 1992Co-Authors: S.t. Cho, K. Najafi, C.e. Lowman, K.d. WiseAbstract:An ultrasensitive silicon pressure-based flowmeter has been developed for use in measuring sub-SCCM gas flow in semiconductor process equipment. The device utilizes a capacitive pressure sensor to measure the pressure drop induced by flow across a micromachined silicon flow channel. The flowmeter is fabricated using a single-sided dissolved-wafer process and requires only six masks. The capacitive pressure sensor uses a thin (2.9 mu m) stress-compensated membrane, which enables the sensor to monitor differential pressures as low as 1 mTorr while withstanding overpressures greater than 700 Torr. Creep and fatigue change the offset by
S.t. Cho - One of the best experts on this subject based on the ideXlab platform.
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An ultrasensitive silicon pressure-based microflow sensor
IEEE Transactions on Electron Devices, 1992Co-Authors: S.t. Cho, K. Najafi, C.e. Lowman, K.d. WiseAbstract:An ultrasensitive silicon pressure-based flowmeter has been developed for use in measuring sub-SCCM gas flow in semiconductor process equipment. The device utilizes a capacitive pressure sensor to measure the pressure drop induced by flow across a micromachined silicon flow channel. The flowmeter is fabricated using a single-sided dissolved-wafer process and requires only six masks. The capacitive pressure sensor uses a thin (2.9 mu m) stress-compensated membrane, which enables the sensor to monitor differential pressures as low as 1 mTorr while withstanding overpressures greater than 700 Torr. Creep and fatigue change the offset by
Selim Alayoglu - One of the best experts on this subject based on the ideXlab platform.
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co oxidation on ptsn nanoparticle catalysts occurs at the interface of pt and sn oxide domains formed under reaction conditions
Journal of Catalysis, 2014Co-Authors: William D Michalak, James M Krier, Selim Alayoglu, Jaeyoon Shin, Kwangjin An, K Komvopoulos, G A SomorjaiAbstract:The barrier to CO oxidation on Pt catalysts is the strongly bound adsorbed CO, which inhibits O2 adsorption and hinders CO2 formation. Using reaction studies and in situ X-ray spectroscopy with colloidally prepared, monodisperse 2 nm Pt and PtSn nanoparticle catalysts, we show that the addition of Sn to Pt provides distinctly different reaction sites and a more efficient reaction mechanism for CO oxidation compared to pure Pt catalysts. To probe the influence of Sn, we intentionally poisoned the Pt component of the nanoparticle catalysts using a CO-rich atmosphere. With a reaction environment comprised of 100 Torr CO and 40 Torr O2 and a temperature range between 200 and 300 C, Pt and PtSn catalysts exhibited activation barriers for CO2 formation of 133 kJ/mol and 35 kJ/mol, respectively. While pure Sn is readily oxidized and is not active for CO oxidation, the addition of Sn to Pt provides an active site for O2 adsorption that is important when Pt is covered with CO. Sn oxide was identified as the active Sn species under reaction conditions by in situ ambient pressure X-ray photoelectron spectroscopy measurements. While chemical signatures of Pt and Sn indicated intermixed metallic components under reducing conditions, Pt and Sn were found to reversibly separate into isolated domains of Pt and oxidic Sn on the nanoparticle surface under reaction conditions of 100 mTorr CO and 40 mTorr O2 between temperatures of 200–275 C. Under these conditions, PtSn catalysts exhibited apparent reaction orders in O2 for CO2 production that were 0.5 and lower with increasing partial pressures. These reaction orders contrast the first-order dependence in O2 known for pure Pt. The differences in activation barriers, non-first-order dependence in O2, and the presence of a partially oxidized Sn indicate that the enhanced activity is due to a reaction mechanism that occurs at a Pt/Sn oxide interface present at the nanoparticle surface.
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Surface Composition and Catalytic Evolution of Au_ x Pd_1−x (x = 0.25, 0.50 and 0.75) Nanoparticles Under CO/O_2 Reaction in Torr Pressure Regime and at 200 °C
Catalysis Letters, 2011Co-Authors: Selim Alayoglu, Virginia Altoe, Colin Specht, Funda Aksoy, Derek R. Butcher, Russ J. Renzas, Gabor A. SomorjaiAbstract:Au_ x Pd_1− x ( x = 0, 0.25, 0.5, 0.75, 1) nanoparticle (NP) catalysts (8–11 nm) were synthesized by a one-pot reaction strategy using colloidal chemistry. XPS depth profiles with variable X-ray energies and scanning transmission electron microscopy (STEM) analyses show that the as-synthesized Au_ x Pd_1− x ( x = 0.25 and 0.5) bimetallic NPs have gradient alloy structures with Au-rich cores and Pd-rich shells. The evolution of composition and structure in the surface region corresponding to a mean free path of 0.6–0.8 nm (i.e., 2–3 layers to the bulk from the particle surface) was studied with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) under CO/O_2 reaction in the Torr pressure regime. Under the reaction conditions of 80 mTorr CO and 200 mTorr O_2 at 200 °C, the surface region of Au_0.75Pd_0.25 NP is Au-rich (~70% by Au). All Au_ x Pd_1− x ( x = 0.25, 0.5, 0.75) NP catalysts have higher turnover rates for the model CO/O_2 reaction than pure Pd and pure Au NPs. The Pd-rich Au_0.25Pd_0.75 NPs show the highest turnover rates and the Pd-rich Au_0.5Pd_0.5 NPs the lowest turnover rates at 200 °C. Interestingly, the Au-rich Au_0.75Pd_0.25 NPs exhibit steady-state turnover rates which are intermediate to those of the Pd-rich bimetallic nanoparticles. Graphical Abstract
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surface composition and catalytic evolution of auxpd1 x x 0 25 0 50 and 0 75 nanoparticles under co o2 reaction in Torr pressure regime and at 200 c
Catalysis Letters, 2011Co-Authors: Selim Alayoglu, Virginia Altoe, Colin Specht, Funda Aksoy, Derek R. Butcher, Russ J. RenzasAbstract:AuxPd1-x (x = 0, 0.25, 0.5, 0.75, 1) nanopar- ticle (NP) catalysts (8-11 nm) were synthesized by a one- pot reaction strategy using colloidal chemistry. XPS depth profiles with variable X-ray energies and scanning trans- mission electron microscopy (STEM) analyses show that the as-synthesized AuxPd1-x (x = 0.25 and 0.5) bimetallic NPs have gradient alloy structures with Au-rich cores and Pd-rich shells. The evolution of composition and structure in the surface region corresponding to a mean free path of 0.6-0.8 nm (i.e., 2-3 layers to the bulk from the particle surface) was studied with ambient pressure X-ray photo- electron spectroscopy (AP-XPS) under CO/O2 reaction in the Torr pressure regime. Under the reaction conditions of 80 mTorr CO and 200 mTorr O2 at 200 C, the surface region of Au0.75Pd0.25 NP is Au-rich (*70% by Au). All AuxPd1-x (x = 0.25, 0.5, 0.75) NP catalysts have higher turnover rates for the model CO/O2 reaction than pure Pd and pure Au NPs. The Pd-rich Au0.25Pd0.75 NPs show the highest turnover rates and the Pd-rich Au0.5Pd0.5 NPs the lowest turnover rates at 200 C. Interestingly, the Au-rich Au0.75Pd0.25 NPs exhibit steady-state turnover rates which are intermediate to those of the Pd-rich bimetallic nanoparticles.
