Results 1 - 10 of 74

Liquid-liquid domains in bilayers detected by wide angle x-ray scattering

by Thalia T. Mills, Y Stephanie Tristram-nagle, Y Frederick A. Heberle, Z Nelson F. Morales, Jiang Zhao, Jing Wu, Z Gilman E. S. Toombes, John F. Nagle, Gerald W. Feigenson Z , 2008
"... ABSTRACT Wide angle x-ray scattering (WAXS) from oriented lipid multilayers is used to examine liquid-ordered (Lo)/liquiddisordered (Ld) phase coexistence in the system 1,2-dioleoyl-sn-glycero-3-phosphocholine/1,2-dipalmitoyl-sn-glycero-3-phosphocholine/cholesterol (DOPC/DPPC/Chol), which is a model ..."
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ABSTRACT Wide angle x-ray scattering (WAXS) from oriented lipid multilayers is used to examine liquid-ordered (Lo)/liquiddisordered (Ld) phase coexistence in the system 1,2-dioleoyl-sn-glycero-3-phosphocholine/1,2-dipalmitoyl-sn-glycero-3-phosphocholine/cholesterol (DOPC/DPPC/Chol), which is a model for the outer leaflet of the animal cell plasma membrane. Using the method of analysis developed in the accompanying work, we find that two orientational distributions are necessary to fit the WAXS data at lower temperatures, whereas only one distribution is needed at temperatures higher than the miscibility transition temperature, Tmix 25–35°C (for 1:1 DOPC/DPPC with 15%, 20%, 25%, and 30 % Chol). We propose that the necessity for two distributions is a criterion for coexistence of Lo domains with a high Sx-ray order parameter and Ld domains with a lower order parameter. This criterion is capable of detecting coexistence of small domains or rafts that the conventional x-ray criterion of two lamellar D spacings may not. Our Tmix values tend to be slightly larger than published NMR results and microscopy results when the fluorescence probe artifact is considered. This is consistent with the sensitivity of WAXS to very short time and length scales, which makes it more capable of detecting small, short-lived domains that are likely close to Tmix.
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Greasing their way: Lipid modifications determine protein association with membrane rafts

by Ilya Levental, Michal Grzybek, Kai Simons - Biochemistry 2010
"... ABSTRACT: Increasing evidence suggests that biological membranes can be laterally subdivided into domains enriched in specific lipid and protein components and that these domains may be involved in the regulation of a number of vital cellular processes. An example is membrane rafts, which are lipid- ..."
Abstract - Cited by 15 (1 self) - Add to MetaCart
ABSTRACT: Increasing evidence suggests that biological membranes can be laterally subdivided into domains enriched in specific lipid and protein components and that these domains may be involved in the regulation of a number of vital cellular processes. An example is membrane rafts, which are lipid-mediated domains dependent on preferential association between sterols and sphingolipids and inclusive of a specific subset of membrane proteins. While the lipid and protein composition of rafts has been extensively characterized, the structural details determining protein partitioning to these domains remain unresolved. Here, we review evidence suggesting that post-translation modification by saturated lipids recruits both peripheral and transmembrane proteins to rafts, while short, unsaturated, and/or branched hydrocarbon chains prevent raft association. The most widely studied group of raft-associated proteins are glycophosphatidylinositol-anchored proteins (GPI-AP), and we review a variety of evidence supporting raft-association of these saturated lipid-anchored extracellular peripheral proteins. For transmembrane and intracellular peripheral proteins, S-acylation with saturated fatty acids mediates raft partitioning, and the dynamic nature of this modification presents an exciting possibility of enzymatically regulated raft association. The other common lipid modifications, that is, prenylation and myristoylation, are discussed in light of their likely role in targeting proteins to nonraft membrane regions. Finally, although the association between raft affinity and
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Actin polymerization serves as a membrane domain switch in model lipid bilayers

by Lipid Bilayers, Allen P. Liu, Daniel A. Fletcher Y - Biophys. J. 91:4064–4070 , 2006
"... ABSTRACT The ability of cells to mount localized responses to external or internal stimuli is critically dependent on organization of lipids and proteins in the plasma membrane. Involvement of the actin cytoskeleton in membrane organization has been documented, but an active role for actin networks ..."
Abstract - Cited by 13 (1 self) - Add to MetaCart
ABSTRACT The ability of cells to mount localized responses to external or internal stimuli is critically dependent on organization of lipids and proteins in the plasma membrane. Involvement of the actin cytoskeleton in membrane organization has been documented, but an active role for actin networks that directly links internal organization of the cytoskeleton with membrane organization has not yet been identified. Here we show that branched actin networks formed on model lipid membranes enriched with the lipid second messenger PIP 2 trigger both temporal and spatial rearrangement of membrane components. Using giant unilamellar vesicles able to separate into two coexisting liquid phases, we demonstrate that polymerization of dendritic actin networks on the membrane induces phase separation of initially homogenous vesicles. This switch-like behavior depends only on the PIP 2-N-WASP link between the membrane and actin network, and we find that the presence of a preexisting actin network spatially biases the location of phase separation. These results show that dynamic, membrane-bound actin networks alone can control when and where membrane domains form and may actively contribute to membrane organization during cell signaling.
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More than a monolayer: relating lung surfactant structure and mechanics to composition

by Coralie Alonso, Tim Alig, Joonsung Yoon, Frank Bringezu, Y Heidi Warriner, Joseph A. Zasadzinski - Biophys. J , 2004
"... ABSTRACT Survanta, a clinically used bovine lung surfactant extract, in contact with surfactant in the subphase, shows a coexistence of discrete monolayer islands of solid phase coexisting with continuous multilayer ‘‘reservoirs’ ’ of fluid phase adjacent to the air-water interface. Exchange between ..."
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ABSTRACT Survanta, a clinically used bovine lung surfactant extract, in contact with surfactant in the subphase, shows a coexistence of discrete monolayer islands of solid phase coexisting with continuous multilayer ‘‘reservoirs’ ’ of fluid phase adjacent to the air-water interface. Exchange between the monolayer, the multilayer reservoir, and the subphase determines surfactant mechanical properties such as the monolayer collapse pressure and surface viscosity by regulating solid-fluid coexistence. Grazing incidence x-ray diffraction shows that the solid phase domains consist of two-dimensional crystals similar to those formed by mixtures of dipalmitoylphosphatidylcholine and palmitic acid. The condensed domains grow as the surface pressure is increased until they coalesce, trapping protrusions of liquid matrix. At;40 mN/m, a plateau exists in the isotherm at which the solid phase fraction increases from;60 to 90%, at which the surface viscosity diverges. The viscosity is driven by the percolation of the solid phase domains, which depends on the solid phase area fraction of the monolayer. The high viscosity may lead to high monolayer collapse pressures, help prevent atelectasis, and minimize the flow of lung surfactant out of the alveoli due to surface tension gradients.
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Coherent anti-Stokes Raman scattering imaging of live spinal tissues

by Li Li, Haifeng Wang, Ji-xin Cheng - Biophys. J. 89:581 , 2005
"... ABSTRACT We demonstrate quantitative vibrational imaging of specific lipid molecules in single bilayers using laser-scanning coherent anti-StokesRaman scattering (CARS)microscopywith a lateral resolution of 0.25mm.A lipid is spectrally separated from othermolecules by using deuterated acyl chains th ..."
Abstract - Cited by 9 (4 self) - Add to MetaCart
ABSTRACT We demonstrate quantitative vibrational imaging of specific lipid molecules in single bilayers using laser-scanning coherent anti-StokesRaman scattering (CARS)microscopywith a lateral resolution of 0.25mm.A lipid is spectrally separated from othermolecules by using deuterated acyl chains that provide a largeCARS signal from the symmetric CD2 stretch vibration around 2100 cm1. Our temperature control experiments show that d62-DPPC has similar bilayer phase segregation property as DPPC whenmixingwithDOPC. By using epi-detection and optimizing excitation and detection conditions, we are able to generate a clear vibrational contrast from d62-DPPCof 10%molar fraction in a single bilayer of DPPC/d62-DPPCmixture.We have developed and experimentally verified an image analysis model that can derive the relativemolecular concentration from the difference of the two CARS intensities measured at the peak and dip frequencies of a CARS band. With the above strategies, we have measured the molar density of d62-DPPC in the coexisting domains inside the DOPC/d62-DPPC (1:1) supported bilayers incorporated with 0– 40 % cholesterol. The observed interesting changes of phospholipid organization upon addition of cholesterol to the bilayer are discussed.
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Line tensions, correlation lengths, and critical exponents in lipid membranes near critical points

by Aurelia R. Honerkamp-smith, Pietro Cicuta, Y Marcus D. Collins, Sarah L. Veatch, Z Marcel Den Nijs, M. Schick, Sarah L. Keller - Biophys. J
"... ABSTRACT Membranes containing a wide variety of ternary mixtures of high chain-melting temperature lipids, low chain-melting temperature lipids, and cholesterol undergo lateral phase separation into coexisting liquid phases at a miscibility transition. When membranes are prepared from a ternary lipi ..."
Abstract - Cited by 9 (3 self) - Add to MetaCart
ABSTRACT Membranes containing a wide variety of ternary mixtures of high chain-melting temperature lipids, low chain-melting temperature lipids, and cholesterol undergo lateral phase separation into coexisting liquid phases at a miscibility transition. When membranes are prepared from a ternary lipid mixture at a critical composition, they pass through a miscibility critical point at the transition temperature. Since the critical temperature is typically on the order of room temperature, membranes provide an unusual opportunity in which to perform a quantitative study of biophysical systems that exhibit critical phenomena in the two-dimensional Ising universality class. As a critical point is approached from either high or low temperature, the scale of fluctuations in lipid composition, set by the correlation length, diverges. In addition, as a critical point is approached from low temperature, the line tension between coexisting phases decreases to zero. Here we quantitatively evaluate the temperature dependence of line tension between liquid domains and of fluctuation correlation lengths in lipid membranes to extract a critical exponent, n. We obtain n 1.2 6 0.2, consistent with the Ising model prediction n 1. We also evaluate the probability distributions of pixel intensities in fluorescence images of membranes. From the temperature dependence of these distributions above the critical temperature, we
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2005. The effect of ergosterol on dipalmitoylphosphatidylcholine bilayers: A deuterium NMR and calorimetric study Biophys

by Ya-wei Hsueh, Kyle Gilbert, C. Tr, Z M. Zuckermann
"... ABSTRACT We have studied the effect of ergosterol, an important component of fungal plasma membranes, on the physical properties of dipalmitoylphosphatidylcholine (DPPC) multibilayers using deuterium nuclear magnetic resonance (2H NMR) and differential scanning calorimetry (DSC). For the 2H NMR expe ..."
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ABSTRACT We have studied the effect of ergosterol, an important component of fungal plasma membranes, on the physical properties of dipalmitoylphosphatidylcholine (DPPC) multibilayers using deuterium nuclear magnetic resonance (2H NMR) and differential scanning calorimetry (DSC). For the 2H NMR experiments the sn-1 chain of DPPC was perdeuterated and NMR spectra were taken as a function of temperature and ergosterol concentration. The phase diagram, constructed from the NMR

Aqueous phase separation as a possible route to compartmentalization of biological molecules

by Christine D. Keating, Cons P Ec Tu S - Acc. Chem. Res , 2012
"... H ow could the incredible complexity of modern cellsevolve from something simple enough to have appeared in a primordial soup? This enduring question has sparked the interest of researchers since Darwin first considered his theory of natural selection. Organic mole-cules, even potentially functional ..."
Abstract - Cited by 7 (1 self) - Add to MetaCart
H ow could the incredible complexity of modern cellsevolve from something simple enough to have appeared in a primordial soup? This enduring question has sparked the interest of researchers since Darwin first considered his theory of natural selection. Organic mole-cules, even potentially functional molecules including peptides and nucleotides, can be produced abiotically. Amphiphiles such as surfactants and lipids display re-markable self-assembly processes including the sponta-neous formation of vesicles resembling the membranes of living cells. Nonetheless, numerous questions remain. Given the presumably dilute concentrations of macromo-lecules in the prebiotic pools where the earliest cells are thought to have appeared, how could the necessary components become concentrated and encapsulated within a semipermeable membrane? What would drive the further structural complexity that is a hallmark of modern living systems? The interior of modern cells is subdivided into microcompartments such as the nucleoid of bacteria or the organelles of eukaryotic cells. Even within what at first appears to be a single compartment, for example, the

Investigation of Domain Formation in Sphingomyelin/Cholesterol/POPC Mixtures by Fluorescence Resonance Energy Transfer and Monte Carlo

by Monica L. Frazier, Jenny R. Wright, Antje Pokorny, Paulo F. F. Almeida , 2007
"... ABSTRACT We have recently proposed a phase diagram for mixtures of porcine brain sphingomyelin (BSM), cholesterol (Chol), and 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) on the basis of kinetics of carboxyfluorescein efflux induced by the amphipathic peptide d-lysin. Although that study indicate ..."
Abstract - Cited by 6 (1 self) - Add to MetaCart
ABSTRACT We have recently proposed a phase diagram for mixtures of porcine brain sphingomyelin (BSM), cholesterol (Chol), and 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) on the basis of kinetics of carboxyfluorescein efflux induced by the amphipathic peptide d-lysin. Although that study indicated the existence of domains, phase separations in the micrometer scale have not been observed by fluorescence microscopy in BSM/Chol/POPC mixtures, though they have for some other sphingomyelins (SM). Here we examine the same BSM/Chol/POPC system by a combination of fluorescence resonance energy transfer (FRET) and Monte Carlo simulations. The results clearly demonstrate that domains are formed in this system. Comparison of the FRET experimental data with the computer simulations allows the estimate of lipid-lipid interaction Gibbs energies between SM/Chol, SM/ POPC, and Chol/POPC. The latter two interactions are weakly repulsive, but the interaction between SM and Chol is favorable. Furthermore, those three unlike lipid interaction parameters between the three possible lipid pairs are sufficient for the existence of a closed loop in the ternary phase diagram, without the need to involve multibody interactions. The calculations also indicate that the largest POPC domains contain several thousand lipids, corresponding to linear sizes of the order of a few hundred nanometers.
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Cholesterol Depletion Induces Solid-like Regions in the Plasma Membrane

by Stefanie F. Nishimura, et al. , 2006
"... Glycosylphosphatidylinositol-linked and transmembrane major histocompatibility complex (MHC) class II I-Ek proteins, as well as N-(6-tetramethylrhodaminethiocarbamoyl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (Tritc-DHPE), are used as probes to determine the effect of cholesterol concent ..."
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Glycosylphosphatidylinositol-linked and transmembrane major histocompatibility complex (MHC) class II I-Ek proteins, as well as N-(6-tetramethylrhodaminethiocarbamoyl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (Tritc-DHPE), are used as probes to determine the effect of cholesterol concentration on the organization of the plasma membrane at temperatures in the range 22C–42C. Cholesterol depletion caused a decrease in the diffusion coefficients for the MHC II proteins and also for a slow fraction of the Tritc-DHPE population. At 37C, reduction of the total cell cholesterol concentration results in a smaller suppression of the translational diffusion for I-Ek proteins (twofold) than was observed in earlier work at 22C (five sevenfold) Vrljic, M., S. Y. Nishimura, W. E. Moerner, and H. M. McConnell. 2005. Biophys. J. 88:334–347. At 37C, the diffusion of both I-Ek proteins is Brownian (0.9, a-parameter, 1.1). More than 99 % of the protein population diffuses homogeneously when imaged at 65 frames per s. As the temperature is raised from 22C to 42C, a change in activation energy is seen at;35C in the Arrhenius plots. Cytoskeletal effects appear to be minimal. These results are consistent with a previously described model of solid-like domain formation in the plasma membrane.