Browsing by Author "Cornell, BA"

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    The impact of pH on packing in tethered lipid bilayers
    (Australian Institute of Nuclear Science and Engineering, 2016-11-29) Cranfield, CG; Berry, T; Holt, SA; Le Brun, AP; Valenzuela, SM; Coster, HGL; Cornell, BA
    We report that increasing the H3O+ concentration when lowering the pH reduces the intrinsic ionic conduction through phospholipid bilayers (Fig 1A), which is counter to what might be expected from increasing the H3O+ concentration. We attribute the conduction decrease to a reduction of the molecular area per lipid (ao)[1]. These effects are seen at H3O+ concentrations in the range nM to µM despite these being very low concentrations compared to that of a typical bathing electrolyte solution of 135mM ionic concentration. We present a model, in which the pH dependent reduction in ao favours an increase in lipid packing. To support this model, we provide evidence of the effects of the hydronium ion on lipid geometry using neutron reflectometry (Fig 1C). Further examples will be given of the impact of the H3O ion concentration on the hydrogen bonding within the polar groups of lipid.
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    Regulation of the membrane insertion and conductance activity of the metamorphic chloride intracellular channel protein CLIC1 by cholesterol
    (Public Library of Science, 2013-02-14) Valenzuela, SM; Alkhamici, H; Brown, LJ; Almond, OC; Goodchild, SC; Carne, S; Curmi, PMG; Holt, SA; Cornell, BA
    The Chloride Intracellular ion channel protein CLIC1 has the ability to spontaneously insert into lipid membranes from a soluble, globular state. The precise mechanism of how this occurs and what regulates this insertion is still largely unknown, although factors such as pH and redox environment are known contributors. In the current study, we demonstrate that the presence and concentration of cholesterol in the membrane regulates the spontaneous insertion of CLIC1 into the membrane as well as its ion channel activity. The study employed pressure versus area change measurements of Langmuir lipid monolayer films; and impedance spectroscopy measurements using tethered bilayer membranes to monitor membrane conductance during and following the addition of CLIC1 protein. The observed cholesterol dependent behaviour of CLIC1 is highly reminiscent of the cholesterol-dependent-cytolysin family of bacterial pore-forming proteins, suggesting common regulatory mechanisms for spontaneous protein insertion into the membrane bilayer. © 2013, Valenzuela et al.