The transmembrane protein bacterioopsin affects the polarity of the hydrophobic core of the host lipid bilayer

AbstractInfluence of the transmembrane protein bacterioopsin (the retinal-free form of bacteriorhodopsin) on the polarity of egg-phosphatidylcholine bilayers was studied by means of a steady-state and time-resolved fluorescence approach exploiting the solvatochromic properties of the 2-anthroyl fluorophore. Introduced in phosphatidylcholine molecules in the form of 8-(2-anthroyl)octanoic acid, this fluorophore probed the hydrocarbon core of the lipid bilayer. As previously shown (E. Pérochon et al., Biochemistry 31 (1992) 7672–7682), water molecules were detected in this region of the terminal part of the lipid acyl chains. Their number was considerably reduced upon addition of bacterioopsin to the lipids. This was assessed by a blue shift in the fluorescence emission spectra of the probe and a marked decrease in the fractional population of fluorophores interacting with water, to the benefit of those experiencing a hydrophobic environment. In agreement with current theories, this decrease in the hydration of the bilayer may be linked to an increase in the acyl chain order and a decrease in the lateral diffusion coefficient of lipids near the protein. The data obtained at high protein concentration accounts for a protein/lipid interface which is much less hydrated than the hydrophobic core of a protein-free lipid bilayer

Plasma membrane coating with cationic silica particles and osmotic shock alters the morphology of bovine aortic endothelial cells

International audienceWe have used a published method of membrane preparation based on the precoating of the apical membrane of aortic endothelial cells with cationic silica microbeads (with or without polyacrylic acid) in combination with an osmotic shock and mechanical shearing to isolate the apical from the basal plasma membranes of these cells, in vitro. After labeling of the plasma membrane of adherent endothelial cells with a fluorescent derivative of phosphatidylcholine and by using laser confocal fluorescence scanning microscopy, we found that this method of membrane isolation rapidly induced invaginations of the basal plasma membrane to an extent which makes this method unsuitable for further membrane lipid analysis. Morphological analysis of the cells and fluorescence recovery after photobleaching experiments on the plasma membranes were performed at each step of the purification procedure and showed that only hypotonic shock and mechanical shearing of the cells enabled the basal plasma membranes to be purified without significant morphological changes.

Evaluation of drug-lipid association constants from microelectrophoretic mobility measurements

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A comparative model membrane study on structural effects of membrane-active positively charged anti-tumor drugs.

The interaction of a number of positively charged anti-tumor drugs with cardiolipin-containing model membranes has been investigated using 31P nuclear magnetic resonance (31P-NMR), differential scanning calorimetry (DSC) and monolayer techniques. It appeared that the ellipticines used (i.e. celiptium and 2-N-methylellipticinium), and also ethidium bromide, completely blocked Ca2+-induced HII phase formation in pure cardiolipin liposomes at molar ratios of drug-to-lipid of approx. 1:1. For the anthracyclines adriamycin and 4'-epi-adriamycin, a similar effect was observed, but now a 2:1 ratio was required. 31P-NMR experiments on dioleoylphosphatidylethanolamine/cardiolipin mixed liposomes indicated that the two anthracyclines, but not the other three drugs, were capable of inducing macroscopic phase separation into domains enriched in drug-cardiolipin complexes and domains enriched in the zwitterionic phospholipid species. DSC experiments on dipalmitoylphosphatidylcholine/cardiolipin mixtures led, with the exception of 2-N-methylellipticinium, to the same conclusion. Measurements of surface pressure and surface potential of cardiolipin monolayers at the air/water interface as well as conformational analysis of the various drug-cardiolipin recombinants showed that the ellipticines are deeply embedded in the acyl chain region of the bilayer, while the anthracyclines and ethidium bromide are preferentially localized in the interface. All drugs share an important electrostatic interaction with the negatively charged phosphates of cardiolipin.Comparative StudyJournal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe