Macroscopic phase separation, modulated phases, and microemulsions: a unified picture of rafts.

We simulate a simple phenomenological model describing phase behavior in a multicomponent membrane, a model capable of producing macroscopic phase separation, modulated phases, and microemulsions, all of which have been discussed in terms of raft phenomena. We show that one effect of thermal fluctuations on the mean-field phase diagram is that it permits a direct transition between either one of the coexisting liquid phases to a microemulsion. This implies that one system exhibiting phase separation can be related to a similar system exhibiting the heterogeneities characteristic of a microemulsion. The two systems could differ in their average membrane composition or in the relative compositions of their exoplasmic and cytoplasmic leaves. The model provides a unified description of these raft-associated phenomena.

[1]  W. Prinz,et al.  Direct imaging reveals stable, micrometer-scale lipid domains that segregate proteins in live cells , 2013, The Journal of cell biology.

[2]  S. Safran,et al.  Hybrid lipids increase the probability of fluctuating nanodomains in mixed membranes. , 2013, Langmuir : the ACS journal of surfaces and colloids.

[3]  S. Shtrikman,et al.  Critical Behavior at the Onset of k --> -Space Instability on the lamda Line , 1975 .

[4]  G. Feigenson,et al.  Competition between line tension and curvature stabilizes modulated phase patterns on the surface of giant unilamellar vesicles: a simulation study. , 2013, Physical review. E, Statistical, nonlinear, and soft matter physics.

[5]  Schick,et al.  Lattice model of microemulsions: The effect of fluctuations in one and two dimensions. , 1990, Physical review. A, Atomic, molecular, and optical physics.

[6]  M. Schick,et al.  Phase behavior of a model bilayer membrane with coupled leaves. , 2008, Biophysical journal.

[7]  P B Sunil Kumar,et al.  Modulated phases in multicomponent fluid membranes. , 1999, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[8]  Frederick A. Heberle,et al.  Comparison of three ternary lipid bilayer mixtures: FRET and ESR reveal nanodomains. , 2010, Biophysical journal.

[9]  D. Andelman,et al.  Concentration fluctuations and phase transitions in coupled modulated bilayers. , 2012, Physical review. E, Statistical, nonlinear, and soft matter physics.

[10]  G. Pabst,et al.  Monolayer spontaneous curvature of raft-forming membrane lipids , 2013, Soft matter.

[11]  R. Brewster,et al.  Hybrid lipids as a biological surface-active component. , 2009, Biophysical journal.

[12]  Marcus D. Collins,et al.  Tuning lipid mixtures to induce or suppress domain formation across leaflets of unsupported asymmetric bilayers , 2008, Proceedings of the National Academy of Sciences.

[13]  Christer S. Ejsing,et al.  Charting molecular composition of phosphatidylcholines by fatty acid scanning and ion trap MS3 fragmentation Published, JLR Papers in Press, August 16, 2003. DOI 10.1194/jlr.D300020-JLR200 , 2003, Journal of Lipid Research.

[14]  J. Swift,et al.  Hydrodynamic fluctuations at the convective instability , 1977 .

[15]  Alexander J. Wagner,et al.  Influence of Monolayer-Monolayer Coupling on the Phase Behavior of a Fluid Lipid Bilayer , 2007, Biophysical journal.

[16]  Kim Ekroos,et al.  Analysis of Lipid Experiments (ALEX): A Software Framework for Analysis of High-Resolution Shotgun Lipidomics Data , 2013, PloS one.

[17]  L. Tamm,et al.  Transbilayer effects of raft-like lipid domains in asymmetric planar bilayers measured by single molecule tracking. , 2006, Biophysical journal.

[18]  N. Mueller,et al.  Patchwork organization of the yeast plasma membrane into numerous coexisting domains , 2012, Nature Cell Biology.

[19]  G. Feigenson,et al.  Toward a better raft model: modulated phases in the four-component bilayer, DSPC/DOPC/POPC/CHOL. , 2013, Biophysical journal.

[20]  M. Seul,et al.  Domain Shapes and Patterns: The Phenomenology of Modulated Phases , 1995, Science.

[21]  Frederick A Heberle,et al.  Control of a nanoscopic-to-macroscopic transition: modulated phases in four-component DSPC/DOPC/POPC/Chol giant unilamellar vesicles. , 2011, Biophysical journal.

[22]  Samuel A. Safran,et al.  Chain ordering of hybrid lipids can stabilize domains in saturated/hybrid/cholesterol lipid membranes , 2010 .

[23]  Dawson,et al.  Renormalization of a Landau-Ginzburg-Wilson theory of microemulsion. , 1992, Physical review. A, Atomic, molecular, and optical physics.

[24]  David R. Nelson,et al.  Smectic, cholesteric, and Rayleigh-Benard order in two dimensions , 1981 .

[25]  Gerhard Gompper,et al.  Self-assembling amphiphilic systems , 1995 .

[26]  G. Feigenson,et al.  Hybrid and nonhybrid lipids exert common effects on membrane raft size and morphology. , 2013, Journal of the American Chemical Society.

[27]  Roie Shlomovitz,et al.  Model of a raft in both leaves of an asymmetric lipid bilayer. , 2013, Biophysical journal.

[28]  Jing Zhao,et al.  Phase studies of model biomembranes: Macroscopic coexistence of Lα + Lβ, with light-induced coexistence of Lα + Lo Phases , 2007 .

[29]  S. Leibler,et al.  Curvature instability in membranes , 1986 .

[30]  F. Schmid,et al.  Monolayer curvature stabilizes nanoscale raft domains in mixed lipid bilayers , 2013, Proceedings of the National Academy of Sciences.

[31]  Kai Simons,et al.  Lipid Rafts As a Membrane-Organizing Principle , 2010, Science.

[32]  S. Leibler,et al.  Ordered and curved meso-structures in membranes and amphiphilic films , 1987 .

[33]  E. London,et al.  Interactions between saturated acyl chains confer detergent resistance on lipids and glycosylphosphatidylinositol (GPI)-anchored proteins: GPI-anchored proteins in liposomes and cells show similar behavior. , 1994, Proceedings of the National Academy of Sciences of the United States of America.