Anion-Selective Membrane - Explore the Science & Experts | ideXlab

Scan Science and Technology

Contact Leading Edge Experts & Companies

Anion-Selective Membrane

The Experts below are selected from a list of 144 Experts worldwide ranked by ideXlab platform

Timothy L. Cover – 1st expert on this subject based on the ideXlab platform

  • Structural Characterization of the Helicobacter Pylori VacA Toxin by Single Particle Em and X-Ray Crystallography
    Biophysical Journal, 2013
    Co-Authors: Melissa G. Chambers, Tasia M. Pyburn, Christian González-rivera, Scott E. Collier, Yoshimasa Takizawa, D. Borden Lacy, Timothy L. Cover

    Abstract:

    Helicobacter pylori is a Gram-negative bacterium that infects the human stomach and contributes to the pathogenesis of peptic ulceration, gastric adenocarcinoma and gastric lymphoma. H. pylori secretes an exotoxin called vacuolating toxin (VacA), known for its ability to induce vacuolation in the cytoplasm of mammalian cells. VacA can cause depolarization of Membrane potential, alteration of mitochondrial Membrane permeability, apoptosis, activation of mitogen-activated protein kinases, inhibition of T cell activation and proliferation, and autophagy. The mechanisms by which these processes occur are not yet fully understood but many of these toxic effects depend on the capacity of VacA to form Anion-Selective Membrane channels. VacA is an 88 kDa protein that contains two distinct domains, p55 and p33. The 88 kDa monomers can assemble into large water-soluble oligomeric “flower”-shaped structures. Using single particle electron microscopy and the random conical tilt approach, we have determined three-dimensional (3D) structures of six distinct VacA oligomeric conformations at ∼15 A resolution. This analysis shows that VacA can organize into a number oligomeric conformations that include both single and double layer hexamers and heptamers. The structures, regardless of oligomeric type, contain two prominent features: extended straight “legs” with a slight kink at the distal end and a central “spoke-like” density that contains two distinct globular domains separated by a thin connecting density. We have also generated structures of three VacA mutant proteins that all form oligomers but differ in activity. Overall, these studies provide the most detailed analysis of p33 structure to date and also provide a more thorough understanding of how VacA forms oligomers.

  • Random Mutagenesis of Helicobacter pylori vacA To Identify Amino Acids Essential for Vacuolating Cytotoxic Activity
    Infection and Immunity, 2006
    Co-Authors: Mark S. Mcclain, Gabor Szabo, Zhifeng Shao, Daniel M. Czajkowsky, Victor J. Torres, Timothy L. Cover

    Abstract:

    VacA is a secreted toxin that plays a role in Helicobacter pylori colonization of the stomach and may contribute to the pathogenesis of peptic ulcer disease and gastric cancer. In this study, we analyzed a library of plasmids expressing randomly mutated forms of recombinant VacA and identified 10 mutant VacA proteins that lacked vacuolating cytotoxic activity when added to HeLa cells. The mutations included six single amino acid substitutions within an amino-terminal hydrophobic region and four substitutions outside the amino-terminal hydrophobic region. All 10 mutations mapped within the p33 domain of VacA. By introducing mutations into the H. pylori chromosomal vacA gene, we showed that secreted mutant toxins containing V21L, S25L, G121R, or S246L mutations bound to cells and were internalized but had defects in vacuolating activity. In planar lipid bilayer and Membrane depolarization assays, VacA proteins containing V21L and S25L mutations were defective in formation of Anion-Selective Membrane channels, whereas proteins containing G121R or S246L mutations retained channel-forming capacity. These are the first point mutations outside the amino-terminal hydrophobic region that are known to abrogate vacuolating toxin activity. In addition, these are the first examples of mutant VacA proteins that have defects in vacuolating activity despite exhibiting channel activities similar to those of wild-type VacA.

  • Functional Properties of the p33 and p55 Domains of the Helicobacter pylori Vacuolating Cytotoxin
    Journal of Biological Chemistry, 2005
    Co-Authors: Victor J. Torres, Mark S. Mcclain, Susan E. Ivie, Timothy L. Cover

    Abstract:

    Helicobacter pylori secretes an 88-kDa vacuolating cytotoxin (VacA) that may contribute to the pathogenesis of peptic ulcer disease and gastric cancer. VacA cytotoxic activity requires assembly of VacA monomers into oligomeric structures, formation of Anion-Selective Membrane channels, and entry of VacA into host cells. In this study, we analyzed the functional properties of recombinant VacA fragments corresponding to two putative VacA domains (designated p33 and p55). Immunoprecipitation experiments indicated that these two domains can interact with each other to form protein complexes. In comparison to the individual VacA domains, a mixture of the p33 and p55 proteins exhibited markedly enhanced binding to the plasma Membrane of mammalian cells. Furthermore, internalization of the VacA domains was detected when cells were incubated with the p33/p55 mixture but not when the p33 and p55 proteins were tested individually. Incubation of cells with the p33/p55 mixture resulted in cell vacuolation, whereas the individual domains lacked detectable cytotoxic activity. Interestingly, sequential addition of p55 followed by p33 resulted in VacA internalization and cell vacuolation, whereas sequential addition in the reverse order was ineffective. These results indicate that both the p33 and p55 domains contribute to the binding and internalization of VacA and that both domains are required for vacuolating cytotoxic activity. Reconstitution of toxin activity from two separate domains, as described here for VacA, has rarely been described for pore-forming bacterial toxins, which suggests that VacA is a pore-forming toxin with unique structural properties.

Stefan Matile – 2nd expert on this subject based on the ideXlab platform

  • Anion-macrodipole interactions: self-assembling oligourea/amide macrocycles as anion transporters that respond to Membrane polarization.
    Journal of the American Chemical Society, 2009
    Co-Authors: Andreas Hennig, Lucile Fischer, Gilles Guichard, Stefan Matile

    Abstract:

    Macrocyclic urea/amide hybrids are introduced as functional, Anion-Selective Membrane transporters in lipid bilayer Membranes. Six derivatives with varying side chains (aliphatic and aromatic) and conformations (parallel and antiparallel carbonyl dipoles) are investigated by fluorescence methods, among which the more active aromatic derivatives were selected for an in-depth study. Strong response of transport activity toward anion exchange and weak response toward cation exchange establish anion selectivity for all macrocycles. “Antiparallel” macrocycles that self-assemble into “antiparallel” nanotubes without macrodipole exhibit Hofmeister selectivity. Parallel macrocycles that self-assemble into parallel nanotubes with strong macrodipole are capable of overcoming the dehydration penalty of the Hofmeister bias. Both systems show additional chloride selectivity. The activity of antiparallel and parallel nanotubes in binary mixtures of bromide/perchlorate and chloride/thiocyanate is over- and underadditive…

  • Anion-Macrodipole Interactions: Self-Assembling Oligourea/Amide Macrocycles as Anion Transporters that Respond to Membrane Polarization.
    Journal of the American Chemical Society, 2009
    Co-Authors: Andreas Hennig, Lucile Fischer, Gilles Guichard, Stefan Matile

    Abstract:

    Macrocyclic urea/amide hybrids are introduced as functional, Anion-Selective Membrane transporters in lipid bilayer Membranes. Six derivatives with varying side chains (aliphatic and aromatic) and conformations (parallel and antiparallel carbonyl dipoles) are investigated by fluorescence methods, among which the more active aromatic derivatives were selected for an in-depth study. Strong response of transport activity toward anion exchange and weak response toward cation exchange establish anion selectivity for all macrocycles. “Antiparallel” macrocycles that self-assemble into “antiparallel” nanotubes without macrodipole exhibit Hofmeister selectivity. Parallel macrocycles that self-assemble into parallel nanotubes with strong macrodipole are capable of overcoming the dehydration penalty of the Hofmeister bias. Both systems show additional chloride selectivity. The activity of antiparallel and parallel nanotubes in binary mixtures of bromide/perchlorate and chloride/thiocyanate is over- and underadditive, respectively (positive and negative AMFE). The activity of antiparallel nanotubes decreases rapidly with increasing Membrane polarization, whereas parallel nanotubes are inactivated at high and activated by Membrane potentials at low concentration. Hill coefficients of parallel nanotubes decrease significantly with Membrane polarization, whereas those of antiparallel nanotubes increase slightly. The overall unusual characteristics of parallel nanotubes call for a new transport mechanism, where macrodipole-potential interactions account for voltage sensitivity and anion-macrodipole interactions account for anion selectivity.

Andreas Hennig – 3rd expert on this subject based on the ideXlab platform

  • Anion-macrodipole interactions: self-assembling oligourea/amide macrocycles as anion transporters that respond to Membrane polarization.
    Journal of the American Chemical Society, 2009
    Co-Authors: Andreas Hennig, Lucile Fischer, Gilles Guichard, Stefan Matile

    Abstract:

    Macrocyclic urea/amide hybrids are introduced as functional, Anion-Selective Membrane transporters in lipid bilayer Membranes. Six derivatives with varying side chains (aliphatic and aromatic) and conformations (parallel and antiparallel carbonyl dipoles) are investigated by fluorescence methods, among which the more active aromatic derivatives were selected for an in-depth study. Strong response of transport activity toward anion exchange and weak response toward cation exchange establish anion selectivity for all macrocycles. “Antiparallel” macrocycles that self-assemble into “antiparallel” nanotubes without macrodipole exhibit Hofmeister selectivity. Parallel macrocycles that self-assemble into parallel nanotubes with strong macrodipole are capable of overcoming the dehydration penalty of the Hofmeister bias. Both systems show additional chloride selectivity. The activity of antiparallel and parallel nanotubes in binary mixtures of bromide/perchlorate and chloride/thiocyanate is over- and underadditive…

  • Anion-Macrodipole Interactions: Self-Assembling Oligourea/Amide Macrocycles as Anion Transporters that Respond to Membrane Polarization.
    Journal of the American Chemical Society, 2009
    Co-Authors: Andreas Hennig, Lucile Fischer, Gilles Guichard, Stefan Matile

    Abstract:

    Macrocyclic urea/amide hybrids are introduced as functional, Anion-Selective Membrane transporters in lipid bilayer Membranes. Six derivatives with varying side chains (aliphatic and aromatic) and conformations (parallel and antiparallel carbonyl dipoles) are investigated by fluorescence methods, among which the more active aromatic derivatives were selected for an in-depth study. Strong response of transport activity toward anion exchange and weak response toward cation exchange establish anion selectivity for all macrocycles. “Antiparallel” macrocycles that self-assemble into “antiparallel” nanotubes without macrodipole exhibit Hofmeister selectivity. Parallel macrocycles that self-assemble into parallel nanotubes with strong macrodipole are capable of overcoming the dehydration penalty of the Hofmeister bias. Both systems show additional chloride selectivity. The activity of antiparallel and parallel nanotubes in binary mixtures of bromide/perchlorate and chloride/thiocyanate is over- and underadditive, respectively (positive and negative AMFE). The activity of antiparallel nanotubes decreases rapidly with increasing Membrane polarization, whereas parallel nanotubes are inactivated at high and activated by Membrane potentials at low concentration. Hill coefficients of parallel nanotubes decrease significantly with Membrane polarization, whereas those of antiparallel nanotubes increase slightly. The overall unusual characteristics of parallel nanotubes call for a new transport mechanism, where macrodipole-potential interactions account for voltage sensitivity and anion-macrodipole interactions account for anion selectivity.