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Bilayer Membrane

The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform

Benoit Roux – 1st expert on this subject based on the ideXlab platform

  • molecular dynamics of the kcsa k channel in a Bilayer Membrane
    Biophysical Journal, 2000
    Co-Authors: Simon Berneche, Benoit Roux

    Abstract:

    Abstract Molecular dynamics (MD) simulations of an atomic model of the KcsA K + channel embedded in an explicit dipalmitoylphosphatidylcholine (DPPC) phospholipid Bilayer solvated by a 150mM KCl aqueous salt solution are performed and analyzed. The model includes the KcsA K + channel, based on the recent crystallographic structure of Doyle et al. (1998, Science. 280:69–77), 112 DPPC, K + and Cl − ions, as well as over 6500 water molecules for a total of more than 40,000 atoms. Three K + ions are explicitly included in the pore. Two are positioned in the selectivity filter on the extracellular side and one in the large water-filled cavity. Different starting configurations of the ions and water molecules in the selectivity filter are considered, and MD trajectories are generated for more than 4ns. The conformation of KcsA is very stable in all of the trajectories, with a global backbone root mean square (RMS) deviation of less than 1.9A with respect to the crystallographic structure. The RMS atomic fluctuations of the residues surrounding the selectivity filter on the extracellular side of the channel are significantly lower than those on the intracellular side. The motion of the residues with aromatic side chains surrounding the selectivity filter (Trp 67 , Trp 68 , Tyr 78 , and Tyr 82 ) is anisotropic with the smallest RMS fluctuations in the direction parallel to the Membrane plane. A concerted dynamic transition of the three K + ions in the pore is observed, during which the K + ion located initially in the cavity moves into the narrow part of the selectivity filter, while the other two K + ions move toward the extracellular side. A single water molecule is stabilized between each pair of ions during the transition, suggesting that each K + cation translocating through the narrow pore is accompanied by exactly one water molecule, in accord with streaming potential measurements (Alcayaga et al., 1989, Biophys. J. 55:367–371). The displacement of the ions is coupled with the structural fluctuations of Val 76 and Gly 77 , in the selectivity filter, as well as the side chains of Glu 71 , Asp 80 , and Arg 89 , near the extracellular side. Thus the mechanical response of the channel structure at distances as large as 10–20A from the ions in the selectivity filter appears to play an important role in the concerted transition.

  • molecular dynamics simulation of melittin in a dimyristoylphosphatidylcholine Bilayer Membrane
    Biophysical Journal, 1998
    Co-Authors: Simon Berneche, M Nina, Benoit Roux

    Abstract:

    Molecular dynamics trajectories of melittin in an explicit dimyristoyl phosphatidylcholine (DMPC) Bilayer are generated to study the details of lipid-protein interactions at the microscopic level. Melittin, a small amphipathic peptide found in bee venom, is known to have a pronounced effect on the lysis of Membranes. The peptide is initially set parallel to the Membrane-solution interfacial region in an alpha-helical conformation with unprotonated N-terminus. Solid-state nuclear magnetic resonance (NMR) and polarized attenuated total internal reflectance Fourier transform infrared (PATIR-FTIR) properties of melittin are calculated from the trajectory to characterize the orientation of the peptide relative to the Bilayer. The residue Lys7 located in the hydrophobic moiety of the helix and residues Lys23, Arg24, Gln25, and Gln26 at the C-terminus hydrophilic form hydrogen bonds with water molecules and with the ester carbonyl groups of the lipids, suggesting their important contribution to the stability of the helix in the Bilayer. Lipid acyl chains are closely packed around melittin, contributing to the stable association with the Membrane. Calculated density profiles and order parameters of the lipid acyl chains averaged over the molecular dynamics trajectory indicate that melittin has effects on both layers of the Membrane. The presence of melittin in the upper layer causes a local thinning of the Bilayer that favors the penetration of water through the lower layer. The energetic factors involved in the association of melittin at the Membrane surface are characterized using an implicit mean-field model in which the Membrane and the surrounding solvent are represented as structureless continuum dielectric material. The results obtained by solving the Poisson-Bolztmann equation numerically are in qualitative agreement with the detailed dynamics. The influence of the protonation state of the N-terminus of melittin is examined. After 600 ps, the N-terminus of melittin is protonated and the trajectory is continued for 400 ps, which leads to an important penetration of water molecules into the Bilayer. These observations provide insights into how melittin interacts with Membranes and the mechanism by which it enhances their lysis.

Lech Wieczorek – 2nd expert on this subject based on the ideXlab platform

  • Tethered Lipid Bilayer Membranes: Formation and Ionic Reservoir Characterization
    Langmuir, 1998
    Co-Authors: Burkhard Raguse, V. Braach-maksvytis, L G King, P. D J Osman, Bruce Cornell, And Ron J. Pace, Lech Wieczorek

    Abstract:

    Using novel synthetic lipids, a tethered Bilayer Membrane (tBLM) was formed onto a gold electrode such that a well-defined ionic reservoir exists between the gold surface and the Bilayer Membrane. Self-assembled monolayers of reservoir-forming lipids were first adsorbed onto the gold surface using gold−sulfur interactions, followed by the formation of the tBLM using the self-assembly properties of phosphatidylcholine-based lipids in aqueous solution. The properties of the tBLM were investigated by impedance spectroscopy. The capacitance of the tBLM indicated the formation of Bilayer Membranes of comparable thickness to solvent-free black (or Bilayer) lipid Membranes (BLM). The ionic sealing ability was comparable to those of classical BLMs. The function of the ionic reservoir was investigated using the potassium-specific ionophore valinomycin. Increasing the size of the reservoir by increasing the length of the hydrophilic region of the reservoir lipid or laterally spacing the reservoir lipid results in a…

  • Tethered lipid Bilayer Membranes: formation and ionic reservoir characterization
    Langmuir, 1998
    Co-Authors: Burkhard Raguse, V. Braach-maksvytis, B. A. Cornell, L G King, P. D J Osman, Ron J Pace, Lech Wieczorek

    Abstract:

    Abstract: Using novel synthetic lipids, a tethered Bilayer Membrane (tBLM) was formed onto a gold electrode such that a well-defined ionic reservoir exists between the gold surface and the Bilayer Membrane. Self-assembled monolayers of reservoir-forming lipids were first adsorbed onto the gold surface using gold-sulfur interactions, followed by the formation of the tBLM using the self-assembly properties of phosphatidylcholine-based lipids in aqueous solution. The properties of the tBLM were investigated by impedance spectroscopy. The capacitance of the tBLM indicated the formation of Bilayer Membranes of comparable thickness to solvent-free black (or Bilayer) lipid Membranes (BLM). The ionic sealing ability was comparable to those of classical BLMs. The function of the ionic reservoir was investigated using the potassium-specific ionophore valinomycin. Increasing the size of the reservoir by increasing the length of the hydrophilic region of the reservoir lipid or laterally spacing the reservoir lipid results in an improved ionic reservoir. Imposition of a dc bias voltage during the measurement of the impedance spectrum affected the conductivity of the tBLM. The conductivity and specificity of the valinomycin were comparable to those seen in a classical BLM.

Ali Hosseini – 3rd expert on this subject based on the ideXlab platform

  • proton switch for modulating oxygen reduction by a copper electrocatalyst embedded in a hybrid Bilayer Membrane
    Nature Materials, 2014
    Co-Authors: Christopher J Barile, Andrew A Gewirth, Ying Li, Thomas B Sobyra, Steven C Zimmerman, Ali Hosseini

    Abstract:

    Molecular switches regulate many fundamental processes in natural and artificial systems. An electrochemical platform in which a proton carrier switches the activity of a catalyst is now presented. A hybrid Bilayer Membrane allows the regulation of proton transport to a Cu-based molecular oxygen reduction reaction catalyst.

  • hybrid Bilayer Membrane a platform to study the role of proton flux on the efficiency of oxygen reduction by a molecular electrocatalyst
    Journal of the American Chemical Society, 2011
    Co-Authors: Ali Hosseini, Christopher J Barile, Todd A Eberspacher, Anando Devadoss, Richard A Decreau, James P Collman

    Abstract:

    In this report, we present a novel platform to study proton-coupled electron transfer (PCET) by controlling the proton flux using an electrode-supported hybrid Bilayer Membrane (HBM). Oxygen reduction by an iron porphyrin was used as a model PCET reaction. The proton flux was controlled by incorporating an aliphatic proton carrier, decanoic acid, into the lipid layer of the HBM. Using this system, we observed a different catalytic behavior than obtained by simply changing the pH of the solution in the absence of an HBM.

  • ferrocene embedded in an electrode supported hybrid lipid Bilayer Membrane a model system for electrocatalysis in a biomimetic environment
    Langmuir, 2010
    Co-Authors: Ali Hosseini, Christopher J Barile, James P Collman, Anando Devadoss, Genevieve Y Williams, Todd A Eberspacher

    Abstract:

    An electrode-supported system in which ferrocene molecules are embedded in a hybrid Bilayer Membrane (HBM) has been prepared and characterized. The redox properties of the ferrocene molecules were studied by varying the lipid and alkanethiol building blocks of the HBM. The midpoint potential and electron transfer rate of the embedded ferrocene were found to be dependent on the hydrophobic nature of the electrolyte and the distance at which the ferrocene was positioned in the HBM relative to the electrode and the solution. Additionally, the ability of the lipid-embedded ferrocenium ions to oxidize solution phase ascorbic acid was evaluated and found to be dependent on the nature of the counterion.