The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Marcus Muller - One of the best experts on this subject based on the ideXlab platform.
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Line Tension controlled mechanism for influenza fusion
PLOS ONE, 2012Co-Authors: Herre Jelger Risselada, Giovanni Marelli, Marc Fuhrmans, Yuliya G Smirnova, Helmut Grubmuller, Siewert J Marrink, Marcus MullerAbstract:Our molecular simulations reveal that wild-type influenza fusion peptides are able to stabilize a highly fusogenic pre-fusion structure, i.e. a peptide bundle formed by four or more trans-membrane arranged fusion peptides. We rationalize that the lipid rim around such bundle has a non-vanishing rim energy (Line-Tension), which is essential to (i) stabilize the initial contact point between the fusing bilayers, i.e. the stalk, and (ii) drive its subsequent evolution. Such Line-Tension controlled fusion event does not proceed along the hypothesized standard stalk-hemifusion pathway. In modeled influenza fusion, single point mutations in the influenza fusion peptide either completely inhibit fusion (mutants G1V and W14A) or, intriguingly, specifically arrest fusion at a hemifusion state (mutant G1S). Our simulations demonstrate that, within a Line-Tension controlled fusion mechanism, these known point mutations either completely inhibit fusion by impairing the peptide’s ability to stabilize the required peptide bundle (G1V and W14A) or stabilize a persistent bundle that leads to a kinetically trapped hemifusion state (G1S). In addition, our results further suggest that the recently discovered leaky fusion mutant G13A, which is known to facilitate a pronounced leakage of the target membrane prior to lipid mixing, reduces the membrane integrity by forming a ‘super’ bundle. Our simulations offer a new interpretation for a number of experimentally observed features of the fusion reaction mediated by the prototypical fusion protein, influenza hemagglutinin, and might bring new insights into mechanisms of other viral fusion reactions.
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main phase transition in lipid bilayers phase coexistence and Line Tension in a soft solvent free coarse grained model
Journal of Chemical Physics, 2010Co-Authors: Martin Homberg, Marcus MullerAbstract:We devise a soft, solvent-free, coarse-grained model for lipid bilayer membranes. The nonbonded interactions take the form of a weighted-density functional, which allows us to describe the thermodynamics of self-assembly and packing effects of the coarse-grained beads in terms of a density expansion of the equation of state and weighting functions that regularize the microscopic bead densities, respectively. Identifying the length and energy scales via the bilayer thickness and the thermal energy scale, kBT, the model qualitatively reproduces key characteristics (e.g., bending rigidity, area per molecule, and compressibility) of lipid membranes. We employ this model to study the main phase transition between the fluid and the gel phase of the bilayer membrane. We accurately locate the phase coexistence using free energy calculations and also obtain estimates for the bare and the thermodynamic Line Tension.
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main phase transition in lipid bilayers phase coexistence and Line Tension in a soft solvent free coarse grained model
arXiv: Soft Condensed Matter, 2010Co-Authors: Martin Homberg, Marcus MullerAbstract:We devise a soft, solvent-free, coarse-grained model for lipid bilayer membranes. The non-bonded interactions take the form of a weighted-density functional which allows us to describe the thermodynamics of self-assembly and packing effects of the coarse-grained beads in terms of a density expansion of the equation of state and the weighting functions that regularize the microscopic bead densities, respectively. Identifying the length and energy scales via the bilayer thickness and the thermal energy scale, kT, the model qualitatively reproduces key characteristics (e.g., bending rigidity, area per lipid molecules, and compressibility) of lipid membranes. We employ this model to study the main phase transition between the liquid and the gel phase of the bilayer membrane. We accurately locate the phase coexistence using free energy calculations and also obtain estimates for the bare and the thermodynamic Line Tension.
Joseph A Zasadzinski - One of the best experts on this subject based on the ideXlab platform.
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comparison of Line Tension measurement methods for lipid monolayers at liquid liquid coexistence
Langmuir, 2019Co-Authors: Benjamin L Stottrup, Juan Tigrelazo, Vision B Bagonza, Joan C Kunz, Joseph A ZasadzinskiAbstract:Several methods of measuring the Line Tension between phase-separated liquid-ordered–liquid -disordered domains in phospholipid–cholesterol systems have been proposed. These experimental techniques...
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lipid protein interactions alter Line Tensions and domain size distributions in lung surfactant monolayers
Biophysical Journal, 2012Co-Authors: Prajnaparamita Dhar, Alan J Waring, Elizabeth Eck, Jacob N Israelachvili, Dong Woog Lee, Younjin Min, Arun Ramachandran, Joseph A ZasadzinskiAbstract:The size distribution of domains in phase-separated lung surfactant monolayers influences monolayer viscoelas- ticity and compressibility which, in turn, influence monolayer collapse and set the compression at which the minimum surface Tension is reached. The surfactant-specific protein SP-B decreases the mean domain size and polydispersity as shown by fluorescence microscopy. From the images, the Line Tension and dipole density difference are determined by comparing the measured size distributions with a theory derived by minimizing the free energy associated with the domain energy and mixing entropy. We find that SP-B increases the Line Tension, dipole density difference, and the compressibility modulus at surface pressures up to the squeeze-out pressure. The increase in Line Tension due to SP-B indicates the protein avoids domain bound- aries due to its solubility in the more fluid regions of the film.
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relating domain size distribution to Line Tension and molecular dipole density in model cytoplasmic myelin lipid monolayers
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Prajnaparamitra Dhar, Arun Ramachandran, Jacob N Israelachvili, Joseph A ZasadzinskiAbstract:We fit the size distribution of liquid-ordered (Lo) domains measured from fluorescence images of model cytoplasmic myelin monolayers with an equilibrium thermodynamic expression that includes the competing effects of Line Tension, λ, dipole density difference, Δm, and the mixing entropy. From these fits, we extract the Line Tension, λ, and dipole density difference, Δm, between the Lo and liquid-disordered (Ld) phases. Both λ and Δm decrease with increasing surface pressure, , although λ/Δm2 remains roughly constant as the monolayer approaches the miscibility surface pressure. As a result, the mean domain size changed little with surface pressure, although the polydispersity increased significantly. The most probable domain radius was significantly smaller than that predicted by the energy alone, showing that the mixing entropy promotes a greater number of smaller domains. Our results also explain why domain shapes are stable; at equilibrium, only a small fraction of the domains are large enough to undergo theoretically predicted shape fluctuations. Monolayers based on the composition of myelin from animals with experimental allergic encephalomyelitis had slightly lower values of λ and Δm, and a higher area fraction of domains, than control monolayers at all . While it is premature to generalize these results to myelin bilayers, our results show that the domain distribution in myelin may be an equilibrium effect and that subtle changes in surface pressure and composition can alter the distribution of material in the monolayer, which will likely also alter the interactions between monolayers important to the adhesion of the myelin sheath.
Martin Homberg - One of the best experts on this subject based on the ideXlab platform.
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main phase transition in lipid bilayers phase coexistence and Line Tension in a soft solvent free coarse grained model
Journal of Chemical Physics, 2010Co-Authors: Martin Homberg, Marcus MullerAbstract:We devise a soft, solvent-free, coarse-grained model for lipid bilayer membranes. The nonbonded interactions take the form of a weighted-density functional, which allows us to describe the thermodynamics of self-assembly and packing effects of the coarse-grained beads in terms of a density expansion of the equation of state and weighting functions that regularize the microscopic bead densities, respectively. Identifying the length and energy scales via the bilayer thickness and the thermal energy scale, kBT, the model qualitatively reproduces key characteristics (e.g., bending rigidity, area per molecule, and compressibility) of lipid membranes. We employ this model to study the main phase transition between the fluid and the gel phase of the bilayer membrane. We accurately locate the phase coexistence using free energy calculations and also obtain estimates for the bare and the thermodynamic Line Tension.
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main phase transition in lipid bilayers phase coexistence and Line Tension in a soft solvent free coarse grained model
arXiv: Soft Condensed Matter, 2010Co-Authors: Martin Homberg, Marcus MullerAbstract:We devise a soft, solvent-free, coarse-grained model for lipid bilayer membranes. The non-bonded interactions take the form of a weighted-density functional which allows us to describe the thermodynamics of self-assembly and packing effects of the coarse-grained beads in terms of a density expansion of the equation of state and the weighting functions that regularize the microscopic bead densities, respectively. Identifying the length and energy scales via the bilayer thickness and the thermal energy scale, kT, the model qualitatively reproduces key characteristics (e.g., bending rigidity, area per lipid molecules, and compressibility) of lipid membranes. We employ this model to study the main phase transition between the liquid and the gel phase of the bilayer membrane. We accurately locate the phase coexistence using free energy calculations and also obtain estimates for the bare and the thermodynamic Line Tension.
Gerald W. Feigenson - One of the best experts on this subject based on the ideXlab platform.
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investigation of the domain Line Tension in asymmetric vesicles prepared via hemifusion
Biochimica et Biophysica Acta, 2021Co-Authors: Frederick A Heberle, Thais A Enoki, Gerald W. FeigensonAbstract:Abstract The plasma membrane (PM) is asymmetric in lipid composition. The distinct and characteristic lipid compositions of the exoplasmic and cytoplasmic leaflets lead to different lipid-lipid interactions and physical-chemical properties in each leaflet. The exoplasmic leaflet possesses an intrinsic ability to form coexisting ordered and disordered fluid domains, whereas the cytoplasmic leaflet seems to form a single fluid phase. To better understand the interleaflet interactions that influence domains, we compared asymmetric model membranes that capture salient properties of the PM with simpler symmetric membranes. Using asymmetric giant unilamellar vesicles (aGUVs) prepared by hemifusion with a supported lipid bilayer, we investigate the domain Line Tension that characterizes the behavior of coexisting ordered + disordered domains. The Line Tension can be related to the contact perimeter of the different phases. Compared to macroscopic phase separation, the appearance of modulated phases was found to be a robust indicator of a decrease in domain Line Tension. Symmetric GUVs of 1,2-distearoyl-sn-glycero-3-phosphochoLine (DSPC)/1,2-dioleoyl-sn-glycero-3-phosphochoLine (DOPC)/1-palmitoyl-2-oleoyl-glycero-3-phosphochoLine (POPC)/cholesterol (chol) were formed into aGUVs by replacing the GUV outer leaflet with DOPC/chol = 0.8/0.2 in order to create a cytoplasmic leaflet model. These aGUVs revealed lower Line Tension for the ordered + disordered domains of the exoplasmic model leaflet.
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calculation of liquid disordered liquid ordered Line Tension from pairwise lipid interactions
Journal of Physical Chemistry B, 2020Co-Authors: Juyang Huang, Shinya Hiraki, Gerald W. FeigensonAbstract:The energy penalty for bilayer phase domain interfaces, Line Tension, is an important quantity for describing the phase domain size transition from the nanometer scale to the micrometer scale and l...
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lowering Line Tension with high cholesterol content induces a transition from macroscopic to nanoscopic phase domains in model biomembranes
Biochimica et Biophysica Acta, 2019Co-Authors: Wenchyan Tsai, Gerald W. FeigensonAbstract:Abstract Chemically simplified lipid mixtures are used here as models of the cell plasma membrane exoplasmic leaflet. In such models, phase separation and morphology transitions controlled by Line Tension in the liquid-disordered (Ld) + liquid-ordered (Lo) coexistence regime have been described [1]. Here, we study two four-component lipid mixtures at different cholesterol fractions: brain sphingomyelin (BSM) or 1,2-distearoyl-sn-glycero-3-phosphochoLine (DSPC)/1,2-dioleoyl-sn-glycero-3-phosphochoLine (DOPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphochoLine (POPC)/cholesterol (Chol). On giant unilamellar vesicles (GUVs) display a nanoscopic-to-macroscopic transition of Ld + Lo phase domains as POPC is replaced by DOPC, and this transition also depends on the cholesterol fraction. Line Tension decreases with increasing cholesterol mole fractions in both lipid mixtures. For the ternary BSM/DOPC/Chol mixture, the published phase diagram [19] requires a modification to show that when cholesterol mole fraction is >~0.33, coexisting phase domains become nanoscopic.
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competition between Line Tension and curvature stabilizes modulated phase patterns on the surface of giant unilamellar vesicles a simulation study
Biophysical Journal, 2013Co-Authors: Jonathan J Amazon, Shih Lin Goh, Gerald W. FeigensonAbstract:When prepared in the liquid-liquid coexistence region, the four-component lipid system distearoyl-phospha-tidylchoLine--dioleoyl-phosphatidylchoLine--palmitoyl,oleoyl-phosphatidylchoLine--cholesterol (DSPC-DOPC-POPC-Cholesterol), with certain ratios of DOPC and POPC, shows striking modulated phase patterns on the surface of giant unilamellar vesicles (GUVs). In this simulation study, we show that the morphology of these patterns can be explained by the competition of Line Tension (which tends to favor large round domains) and curvature, as specified by the Helfrich energy functional. In this study we use a Monte-Carlo simulation on the surface of a GUV to determine the equilibrium shape and phase morphology. We find that the patterns arising from these competing interactions very closely approximate those observed, that the patterned morphologies represent thermodynamically stable configurations, and that the geometric nature of these patterns is closely tied to the relative and absolute values of the model parameters.
Fivel Marc - One of the best experts on this subject based on the ideXlab platform.
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The effect of stress on the cross-slip energy in face-centered cubic metals: A study using dislocation dynamics simulations and Line Tension models
Journal of the Mechanics and Physics of Solids, 2021Co-Authors: Margarita Longsworth, Fivel MarcAbstract:Dislocation dynamics simulations were used to calculate the energy barrier of cross-slip via Friedel–Escaig mechanism in face centered-cubic copper. The energy barrier in the unstressed case was found to be 1.9 eV, as reported by Ramírez et al. (2012). The energy barrier was reduced by applying an external stress. The most effective way of reducing it, was by applying a compressive stress on the glide plane. Furthermore, it was confirmed using dislocation dynamics simulations, that both the Schmid and Escaig stress have a comparable effect in reducing the energy barrier, in qualitative agreement with the atomistic simulations performed by Kang et al. (2014) in face-centered cubic nickel. Most of the energy barrier values for stressed cross-slip fell within the experimental error of 1.15 ± 0.37 eV measured by Bonneville et al. (1988). Moreover, the activation enthalpy obtained from the Line Tension model of Kang et al. (2014) and the general expression for the activation enthalpy proposed by Malka-Markovitz and Mordehai (2019) were in good quantitative agreement with the simulation results. Hence, both could be used to calculate the activation enthalpy of screw segments in dislocation dynamics simulations.