The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Linda J. Johnston - One of the best experts on this subject based on the ideXlab platform.
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the size of lipid rafts an atomic force microscopy study of ganglioside gm1 domains in sphingomyelin dopc cholesterol membranes
Biophysical Journal, 2002Co-Authors: Chunbo Yuan, Jennifer Furlong, Pierre Burgos, Linda J. JohnstonAbstract:Atomic force microscopy has been used to study the distribution of ganglioside GM1 in model membranes composed of ternary lipid mixtures that mimic the composition of lipid rafts. The results demonstrate that addition of 1% GM1 to 1:1:1 sphingomyelin/Dioleoylphosphatidylcholine/cholesterol monolayers leads to the formation of small ganglioside-rich microdomains (40-100 nm in size) that are localized preferentially in the more ordered sphingomyelin/cholesterol-rich phase. With 5% GM1 some GM1 microdomains are also detected in the Dioleoylphosphatidylcholine-rich phase. A similar preferential localization of GM1 in the ordered phase is observed for bilayers with the same ternary lipid mixture in the upper leaflet. The small GM1-rich domains observed in these experiments are similar to the sizes for lipid rafts in natural membranes but considerably smaller than the ordered bilayer domains that have been shown to be enriched in GM1 in recent fluorescence microscopy studies of lipid bilayers. The combined data from a number of studies of model membranes indicate that lateral organization occurs on a variety of length scales and mimics many of the properties of natural membranes.
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The Size of Lipid Rafts: An Atomic Force Microscopy Study of Ganglioside GM1 Domains in Sphingomyelin/DOPC/Cholesterol Membranes
Biophysical Journal, 2002Co-Authors: Chunbo Yuan, Jennifer Furlong, Pierre Burgos, Linda J. JohnstonAbstract:Atomic force microscopy has been used to study the distribution of ganglioside GM1 in model membranes composed of ternary lipid mixtures that mimic the composition of lipid rafts. The results demonstrate that addition of 1% GM1 to 1:1:1 sphingomyelin/Dioleoylphosphatidylcholine/cholesterol monolayers leads to the formation of small ganglioside-rich microdomains (40-100 nm in size) that are localized preferentially in the more ordered sphingomyelin/cholesterol-rich phase. With 5% GM1 some GM1 microdomains are also detected in the Dioleoylphosphatidylcholine-rich phase. A similar preferential localization of GM1 in the ordered phase is observed for bilayers with the same ternary lipid mixture in the upper leaflet. The small GM1-rich domains observed in these experiments are similar to the sizes for lipid rafts in natural membranes but considerably smaller than the ordered bilayer domains that have been shown to be enriched in GM1 in recent fluorescence microscopy studies of lipid bilayers. The combined data from a number of studies of model membranes indicate that lateral organization occurs on a variety of length scales and mimics many of the properties of natural membranes.
Stephanie Tristram-nagle - One of the best experts on this subject based on the ideXlab platform.
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Penetration of HIV-1 tat47–57into PC/PE bilayers assessed by MD simulation and X-ray scattering
Membranes, 2015Co-Authors: Chris Neale, Angel E. Garcia, Kun Huang, Stephanie Tristram-nagleAbstract:The interactions of the basic, cell-penetrating region (Y47GRKKRRQRRR57) of the HIV-1 Tat protein with Dioleoylphosphatidylcholine (DOPC) bilayers were previously assessed by comparing experimental X-ray diffuse scattering with atomistic molecular dynamics simulations. Here, we extend this investigation by evaluating the influence of phosphatidylethanolamine (PE) lipids. Using experimental bilayer form factors derivedfrom X-ray diffuse scattering data as a guide, our simulations indicate that Tat peptides localize close to the carbonyl-glycerol group in the headgroup region of bilayers composed of either DOPC or DOPC:DOPE (1:1) lipid. Our results also suggest that Tat peptides may more frequently insert into the hydrophobic core of bilayers composed of PC:PE (1:1) lipids than into bilayers composed entirely of PC lipids. PE lipids may facilitate peptide translocation across a lipid bilayer by stabilizing intermediate states in which hydrated peptides span the bilayer.
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Structure and interactions of fully hydrated Dioleoylphosphatidylcholine bilayers
Biophysical Journal, 1998Co-Authors: Stephanie Tristram-nagle, Horia I Petrache, John F. NagleAbstract:This study focuses on Dioleoylphosphatidylcholine (DOPC) bilayers near full hydration. Volumetric data and high-resolution synchrotron x-ray data are used in a method that compares DOPC with well determined gel phase dipalmitoylphosphatidylcholine (DPPC). The key structural quantity obtained is fully hydrated area/lipid A(O) = 72.2 ± 1.1 Å2 at 30°C, from which other quantities such as thickness of the bilayer are obtained. Data for samples over osmotic pressures from 0 to 56 atmospheres give an estimate for the area compressibility of K(A) = 188 dyn/cm. Obtaining the continuous scattering transform and electron density profiles requires correction for liquid crystal fluctuations. Quantitation of these fluctuations opens an experimental window on the fluctuation pressure, the primary repulsive interaction near full hydration. The fluctuation pressure decays exponentially with water spacing, in agreement with analytical results for soft confinement. However, the ratio of decay length λ(fl) = 5.8 Å to hydration pressure decay length λ = 2.2 Å is significantly larger than the value of 2 predicted by analytical theory and close to the ratio obtained in recent simulations. We also obtain the traditional osmotic pressure versus water spacing data. Our analysis of these data shows that estimates of the Hamaker parameter H and the bending modulus K(c) are strongly coupled.
Douglas G. Dalgleish - One of the best experts on this subject based on the ideXlab platform.
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Competitive Adsorption between Dioleoylphosphatidylcholine and Sodium Caseinate on Oil−Water Interfaces
Journal of Agricultural and Food Chemistry, 1996Co-Authors: Yuan Fang, Douglas G. DalgleishAbstract:Oil-in-water emulsions stabilized by sodium caseinate and Dioleoylphosphatidylcholine (DOPC) were studied by dynamic light scattering and electrophoresis. The initial mean droplet size of the emulsions depended strongly on the concentration of casein, but was virtually independent of DOPC. However, the emulsion stability was strongly affected by the presence of DOPC; with a DOPC:casein molar ratio of
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competitive adsorption between Dioleoylphosphatidylcholine and sodium caseinate on oil water interfaces
Journal of Agricultural and Food Chemistry, 1996Co-Authors: Yuan Fang, Douglas G. DalgleishAbstract:Oil-in-water emulsions stabilized by sodium caseinate and Dioleoylphosphatidylcholine (DOPC) were studied by dynamic light scattering and electrophoresis. The initial mean droplet size of the emulsions depended strongly on the concentration of casein, but was virtually independent of DOPC. However, the emulsion stability was strongly affected by the presence of DOPC; with a DOPC:casein molar ratio of <10, the emulsions were stable, but at higher ratios, the average size of emulsion droplets increased during storage. Competitive adsorption between DOPC and casein occurred during both the formation and storage of the emulsions. Of the constituents of whole casein, β-casein interacted most with DOPC. At casein concentrations of <0.7%, β-casein was completely removed from the oil−water interface when the emulsions were stored for 48 h, but αs1-casein remained on the surface even at the highest DOPC:casein molar ratio (49:1) used in this study. As well as changing the adsorption characteristics of the differen...
John F. Nagle - One of the best experts on this subject based on the ideXlab platform.
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temperature dependence of structure bending rigidity and bilayer interactions of Dioleoylphosphatidylcholine bilayers
Biophysical Journal, 2008Co-Authors: Stephanie Tristramnagle, Norbert Kucerka, John F. NagleAbstract:X-ray diffuse scattering was measured from oriented stacks and unilamellar vesicles of Dioleoylphosphatidylcholine lipid bilayers to obtain the temperature dependence of the structure and of the material properties. The area/molecule, A, was 75.5 A2 at 45°C, 72.4 A2 at 30°C, and 69.1 A2 at 15°C, which gives the area expansivity αA = 0.0029/deg at 30°C, and we show that this value is in excellent agreement with the polymer brush theory. The bilayer becomes thinner with increasing temperature; the contractivity of the hydrocarbon portion was αDc = 0.0019/deg; the difference between αA and αDc is consistent with the previously measured volume expansivity αVc = 0.0010/deg. The bending modulus KC decreased as exp(455/T) with increasing T (K). Our area compressibility modulus KA decreased with increasing temperature by 5%, the same as the surface tension of dodecane/water, in agreement again with the polymer brush theory. Regarding interactions between bilayers, the compression modulus B as a function of interbilayer water spacing D′W was found to be nearly independent of temperature. The repulsive fluctuation pressure calculated from B and KC increased with temperature, and the Hamaker parameter for the van der Waals interaction was nearly independent of temperature; this explains why the fully hydrated water spacing, D′W, that we obtain from our structural results increases with temperature.
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Structure and interactions of fully hydrated Dioleoylphosphatidylcholine bilayers
Biophysical Journal, 1998Co-Authors: Stephanie Tristram-nagle, Horia I Petrache, John F. NagleAbstract:This study focuses on Dioleoylphosphatidylcholine (DOPC) bilayers near full hydration. Volumetric data and high-resolution synchrotron x-ray data are used in a method that compares DOPC with well determined gel phase dipalmitoylphosphatidylcholine (DPPC). The key structural quantity obtained is fully hydrated area/lipid A(O) = 72.2 ± 1.1 Å2 at 30°C, from which other quantities such as thickness of the bilayer are obtained. Data for samples over osmotic pressures from 0 to 56 atmospheres give an estimate for the area compressibility of K(A) = 188 dyn/cm. Obtaining the continuous scattering transform and electron density profiles requires correction for liquid crystal fluctuations. Quantitation of these fluctuations opens an experimental window on the fluctuation pressure, the primary repulsive interaction near full hydration. The fluctuation pressure decays exponentially with water spacing, in agreement with analytical results for soft confinement. However, the ratio of decay length λ(fl) = 5.8 Å to hydration pressure decay length λ = 2.2 Å is significantly larger than the value of 2 predicted by analytical theory and close to the ratio obtained in recent simulations. We also obtain the traditional osmotic pressure versus water spacing data. Our analysis of these data shows that estimates of the Hamaker parameter H and the bending modulus K(c) are strongly coupled.
Richard H. Templer - One of the best experts on this subject based on the ideXlab platform.
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buffer induced swelling and vesicle budding in binary lipid mixtures of Dioleoylphosphatidylcholine dioleoylphosphatidylethanolamine and Dioleoylphosphatidylcholine lysophosphatidylcholine using small angle x ray scattering and 31p static nmr
Langmuir, 2015Co-Authors: Hanna M G Barriga, Richard Bazin, Richard H. TemplerAbstract:A large variety of data exists on lipid phase behavior; however, it is mostly in nonbuffered systems over nonbiological temperature ranges. We present biophysical data on lipid mixtures of Dioleoylphosphatidylcholine (DOPC), dioleoylphosphatidylethanolamine (DOPE), and lysophosphatidylcholine (LysoPC) examining their behaviors in excess water and buffer systems over the temperature range 4–34 °C. These mixtures are commonly used to investigate the effects of spontaneous curvature on integral membrane proteins. Using small-angle X-ray scattering (SAXS) and 31P NMR, we observed lamellar and vesicle phases, with the buffer causing an increase in the layer spacing. Increasing amounts of DOPE in a DOPC bilayer decreased the layer spacing of the mesophase, while the opposite trend was observed for increasing amounts of LysoPC. 31P static NMR was used to analyze the DOPC:LysoPC samples to investigate the vesicle sizes present, with evidence of vesicle budding observed at LysoPC concentrations above 30 mol %. NMR...
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Lipid membrane curvature induced by distearoyl phosphatidylinositol 4-phosphate
Soft Matter, 2012Co-Authors: Samuel Furse, Nicholas J. Brooks, Ruediger Woscholski, Richard H. Templer, Edward W Tate, Annela M Seddon, Piers R. J. GaffneyAbstract:In this paper we present evidence that phosphatidylinositol 4-phosphate induces curvature in biological membranes. The phase behaviour of mixtures of distearoylphosphatidylinositol 4-phosphate (DSPIP) and Dioleoylphosphatidylcholine (DOPC) as a function of pressure and temperature has been studied using small-angle X-ray scattering and in the presence of biologically relevant magnesium concentrations. Our results demonstrate that at physiologically relevant concentrations (2 mol%), DSPIP is capable of inducing the formation of the inverse hexagonal phase (HII) over a wide range of conditions. This result has implications for the structural role of phosphatidylinositol lipidsin vivo.