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Doktorova M, Heberle FA, Kingston RL, Khelashvili G, Cuendet MA, Wen Y, Katsaras J, Feigenson GW, Vogt VM, Dick RA. Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties. Biophys J 2017. [PMID: 29117524 DOI: 10.1016/j.bpj.2017.08.055.] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein's matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here, using a broad set of in vitro and in silico techniques we addressed molecular mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins.
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27
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Usery RD, Enoki TA, Wickramasinghe SP, Weiner MD, Tsai WC, Kim MB, Wang S, Torng TL, Ackerman DG, Heberle FA, Katsaras J, Feigenson GW. Line Tension Controls Liquid-Disordered + Liquid-Ordered Domain Size Transition in Lipid Bilayers. Biophys J 2017; 112:1431-1443. [PMID: 28402885 DOI: 10.1016/j.bpj.2017.02.033] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 01/27/2017] [Accepted: 02/16/2017] [Indexed: 12/28/2022] Open
Abstract
To better understand animal cell plasma membranes, we studied simplified models, namely four-component lipid bilayer mixtures. Here we describe the domain size transition in the region of coexisting liquid-disordered (Ld) + liquid-ordered (Lo) phases. This transition occurs abruptly in composition space with domains increasing in size by two orders of magnitude, from tens of nanometers to microns. We measured the line tension between coexisting Ld and Lo domains close to the domain size transition for a variety of lipid mixtures, finding that in every case the transition occurs at a line tension of ∼0.3 pN. A computational model incorporating line tension and dipole repulsion indicated that even small changes in line tension can result in domains growing in size by several orders of magnitude, consistent with experimental observations. We find that other properties of the coexisting Ld and Lo phases do not change significantly in the vicinity of the abrupt domain size transition.
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Enoki TA, Heberle FA, Feigenson GW. Probe Partition between Liquid-Disordered (LD) and Liquid-Ordered (Lo) Phases and Investigation of Nanodomain Sizes. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.2040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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29
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Weiner MD, Feigenson GW. Molecular Dynamics Simulations Reveal the Impact of Compositional Asymmetry in Lipid Membranes on Phase Behavior and Leaflet Interactions. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.2049] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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30
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Feigenson GW. Pictures of the Substructure of Liquid-Ordered Domains. Biophys J 2016; 109:854-5. [PMID: 26331243 DOI: 10.1016/j.bpj.2015.07.037] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Accepted: 07/28/2015] [Indexed: 11/13/2022] Open
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31
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Heberle FA, Marquardt D, Doktorova M, Geier B, Standaert RF, Heftberger P, Kollmitzer B, Nickels JD, Dick R, Feigenson GW, Katsaras J, London E, Pabst G. Subnanometer Structure of an Asymmetric Model Membrane: Interleaflet Coupling Influences Domain Properties. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:5195-200. [PMID: 27128636 PMCID: PMC4910133 DOI: 10.1021/acs.langmuir.5b04562] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Cell membranes possess a complex three-dimensional architecture, including nonrandom lipid lateral organization within the plane of a bilayer leaflet, and compositional asymmetry between the two leaflets. As a result, delineating the membrane structure-function relationship has been a highly challenging task. Even in simplified model systems, the interactions between bilayer leaflets are poorly understood, due in part to the difficulty of preparing asymmetric model membranes that are free from the effects of residual organic solvent or osmotic stress. To address these problems, we have modified a technique for preparing asymmetric large unilamellar vesicles (aLUVs) via cyclodextrin-mediated lipid exchange in order to produce tensionless, solvent-free aLUVs suitable for a range of biophysical studies. Leaflet composition and structure were characterized using isotopic labeling strategies, which allowed us to avoid the use of bulky labels. NMR and gas chromatography provided precise quantification of the extent of lipid exchange and bilayer asymmetry, while small-angle neutron scattering (SANS) was used to resolve bilayer structural features with subnanometer resolution. Isotopically asymmetric POPC vesicles were found to have the same bilayer thickness and area per lipid as symmetric POPC vesicles, demonstrating that the modified exchange protocol preserves native bilayer structure. Partial exchange of DPPC into the outer leaflet of POPC vesicles produced chemically asymmetric vesicles with a gel/fluid phase-separated outer leaflet and a uniform, POPC-rich inner leaflet. SANS was able to separately resolve the thicknesses and areas per lipid of coexisting domains, revealing reduced lipid packing density of the outer leaflet DPPC-rich phase compared to typical gel phases. Our finding that a disordered inner leaflet can partially fluidize ordered outer leaflet domains indicates some degree of interleaflet coupling, and invites speculation on a role for bilayer asymmetry in modulating membrane lateral organization.
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Ackerman DG, Feigenson GW. Effects of Transmembrane α-Helix Length and Concentration on Phase Behavior in Four-Component Lipid Mixtures: A Molecular Dynamics Study. J Phys Chem B 2016; 120:4064-77. [PMID: 27081858 DOI: 10.1021/acs.jpcb.6b00611] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
We used coarse-grained molecular dynamics simulations to examine the effects of transmembrane α-helical WALP peptides on the behavior of four-component lipid mixtures. These mixtures contain a high-melting temperature (high-Tm) lipid, a nanodomain-inducing low-Tm lipid, a macrodomain-inducing low-Tm lipid and cholesterol to model the outer leaflet of cell plasma membranes. In a series of simulations, we incrementally replace the nanodomain-inducing low-Tm lipid by the macrodomain-inducing low-Tm lipid and measure how lipid and phase properties are altered by the addition of WALPs of different length. Regardless of the ratio of the two low-Tm lipids, shorter WALPs increase domain size and all WALPs increase domain alignment between the two leaflets. These effects are smallest for the longest WALP tested, and increase with increasing WALP concentration. Thus, our simulations explain the experimental observation that WALPs induce macroscopic domains in otherwise nanodomain-forming lipid-only mixtures (unpublished). Since the cell plasma membrane contains a large fraction of transmembrane proteins, these findings link the behavior of lipid-only model membranes in vitro to phase behavior in vivo.
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Mudgal S, Keresztes I, Feigenson GW, Rizvi S. Controlling the taste receptor accessible structure of rebaudioside A via binding to bovine serum albumin. Food Chem 2016; 197:84-91. [DOI: 10.1016/j.foodchem.2015.10.064] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 09/20/2015] [Accepted: 10/14/2015] [Indexed: 11/30/2022]
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34
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Doktorova M, Dick R, Heberle FA, Feigenson GW, Vogt VM. Cholesterol Promotes the Peripheral Binding of Retroviral Proteins to Lipid Bilayers. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.1921] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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35
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Doktorova M, Feigenson GW, Weinstein H. The Interaction of Proteins with Asymmetric Lipid Bilayers. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.2265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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36
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Tsai WC, Feigenson GW. Line Tension and Phase Separation of a Four-Component Phospholipid Bilayer. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.462] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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37
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Enoki TA, Kim S, Heberle FA, Feigenson GW. Partition Coefficient of a Transmembrane Peptide, between Lo and Ld Phases: Does the Peptide Distinguish Macro from Nano Domains? Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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38
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Wen Y, Dick RA, Feigenson GW, Vogt VM. Principles Underlying Membrane Interaction of Retroviral Structural Protein Gag. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.3089] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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39
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Konyakhina TM, Feigenson GW. Phase diagram of a polyunsaturated lipid mixture: Brain sphingomyelin/1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine/cholesterol. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1858:153-61. [PMID: 26525664 DOI: 10.1016/j.bbamem.2015.10.016] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2015] [Revised: 09/28/2015] [Accepted: 10/21/2015] [Indexed: 12/17/2022]
Abstract
Phospholipids having a polyunsaturated acyl chain are abundant in biological membranes, but their behavior in lipid mixtures is difficult to study. Here we elucidate the nature of such mixtures with this report of the first ternary phase diagram containing the polyunsaturated lipid SDPC in mixtures of BSM/SDPC/Chol (brain sphingomyelin/1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine/cholesterol). These mixtures show coexisting macroscopic liquid-disordered (Ld) and liquid-ordered (Lo) phase separation, with phase boundaries determined by FRET and by fluorescence microscopy imaging of giant unilamellar vesicles (GUVs). Surprisingly, SDPC mixes with BSM/Chol similarly to how DOPC and POPC mix with BSM/Chol. Notably, intermediate states are produced within the Ld+Lo liquid-liquid immiscibility region upon addition of fourth component POPC. These mixtures of BSM/SDPC/POPC/Chol exhibit nanoscopic Ld+Lo domains over a very large volume of composition space, possibly because Ld/Lo line tension is not high.
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Ackerman DG, Feigenson GW. Multiscale modeling of four-component lipid mixtures: domain composition, size, alignment, and properties of the phase interface. J Phys Chem B 2015; 119:4240-50. [PMID: 25564922 DOI: 10.1021/jp511083z] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Simplified lipid mixtures are often used to model the complex behavior of the cell plasma membrane. Indeed, as few as four components-a high-melting lipid, a nandomain-inducing low-melting lipid, a macrodomain-inducing low-melting lipid, and cholesterol (chol)-can give rise to a wide range of domain sizes and patterns that are highly sensitive to lipid compositions. Although these systems are studied extensively with experiments, the molecular-level details governing their phase behavior are not yet known. We address this issue by using molecular dynamics simulations to analyze how phase separation evolves in a four-component system as it transitions from small domains to large domains. To do so, we fix concentrations of the high-melting lipid 16:0,16:0-phosphatidylcholine (DPPC) and chol, and incrementally replace the nanodomain-inducing low-melting lipid 16:0,18:2-PC (PUPC) by the macrodomain-inducing low-melting lipid 18:2,18:2-PC (DUPC). Coarse-grained simulations of this four-component system reveal that lipid demixing increases as the amount of DUPC increases. Additionally, we find that domain size and interleaflet alignment change sharply over a narrow range of replacement of PUPC by DUPC, indicating that intraleaflet and interleaflet behaviors are coupled. Corresponding united atom simulations show that only lipids within ∼2 nm of the phase interface are significantly perturbed regardless of domain composition or size. Thus, whereas the fraction of interface-perturbed lipids is negligible for large domains, it is significant for smaller ones. Together, these results reveal characteristic traits of bilayer thermodynamic behavior in four-component mixtures, and provide a baseline for investigation of the effects of proteins and other lipids on membrane phase properties.
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Wickramasinghe SP, Ackerman DG, Feigenson GW. Appearance of Modulated Bilayer Morphology for Coexisting LD and LO Phases is Correlated with Line Tension. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.1335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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42
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Weiner MD, Feigenson GW. Coarse Grained Molecular Dynamics Simulations to Study Asymmetric Membranes. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.1329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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43
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Ackerman DG, Feigenson GW. The Effects of Walp Peptides on Phase Behavior in Quaternary Lipid Mixtures: A Molecular Dynamics Study. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.1334] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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44
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Amazon JJ, Feigenson GW. Lattice simulations of phase morphology on lipid bilayers: renormalization, membrane shape, and electrostatic dipole interactions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:022702. [PMID: 25353504 PMCID: PMC4391078 DOI: 10.1103/physreve.89.022702] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Indexed: 06/03/2023]
Abstract
When liquid phases coexist at equilibrium but are not driven to minimize domain interfacial contact energy, the resulting patterns of phase domains can have important implications for living cells. In this study we explore some of the interactions and conditions that produce the stable patterned phases that are observed in model lipid mixtures. By use of Monte Carlo simulations we find that background curvature is important for the formation of patterned (modulated) phases. The interactions that stabilize nanoscopic phase separation are still not well understood. We show that inclusion of an electrostatic dipole repulsion with decay lengths as short as two to four lipid diameters can break up domains at the nanometer scale and that the location of the miscibility critical point is sensitive to this interaction. The use of a coarse-grained simulation raises questions about comparing parameters in simulations performed at different length scales. Using renormalization group techniques we show how to reconcile this problem, treating line tension as a running coupling constant.
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Doktorova M, Heberle FA, Goh SL, Standaert RF, Katsaras J, Feigenson GW. Hybrid and Nonhybrid Lipids Exert Common Effects on Membrane Raft Size and Morphology. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.2803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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46
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Ackerman DG, Feigenson GW. Multiscale Modeling of Four Component Lipid Mixtures: Coarse Grained and United Atom Simulations Reveal Trends in Phase Separation. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.1700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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47
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Heberle FA, Petruzielo RS, Pan J, Drazba P, Kucerka N, Standaert RF, Feigenson GW, Katsaras J. Bilayer Thickness Mismatch Controls Domain Size in Model Membranes. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.1686] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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48
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Heberle FA, Doktorova M, Goh SL, Standaert RF, Katsaras J, Feigenson GW. Hybrid and nonhybrid lipids exert common effects on membrane raft size and morphology. J Am Chem Soc 2013; 135:14932-5. [PMID: 24041024 DOI: 10.1021/ja407624c] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Nanometer-scale domains in cholesterol-rich model membranes emulate lipid rafts in cell plasma membranes (PMs). The physicochemical mechanisms that maintain a finite, small domain size are, however, not well understood. A special role has been postulated for chain-asymmetric or hybrid lipids having a saturated sn-1 chain and an unsaturated sn-2 chain. Hybrid lipids generate nanodomains in some model membranes and are also abundant in the PM. It was proposed that they align in a preferred orientation at the boundary of ordered and disordered phases, lowering the interfacial energy and thus reducing domain size. We used small-angle neutron scattering and fluorescence techniques to detect nanoscopic and modulated liquid phase domains in a mixture composed entirely of nonhybrid lipids and cholesterol. Our results are indistinguishable from those obtained previously for mixtures containing hybrid lipids, conclusively showing that hybrid lipids are not required for the formation of nanoscopic liquid domains and strongly implying a common mechanism for the overall control of raft size and morphology. We discuss implications of these findings for theoretical descriptions of nanodomains.
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49
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Konyakhina TM, Wu J, Mastroianni JD, Heberle FA, Feigenson GW. Phase diagram of a 4-component lipid mixture: DSPC/DOPC/POPC/chol. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2204-14. [PMID: 23747294 DOI: 10.1016/j.bbamem.2013.05.020] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Revised: 05/20/2013] [Accepted: 05/22/2013] [Indexed: 11/15/2022]
Abstract
We report the first 4-component phase diagram for the lipid bilayer mixture, DSPC/DOPC/POPC/chol (distearoylphosphatidylcholine/dioleoylphosphatidylcholine/1-palmitoyl, 2-oleoylphosphatidylcholine/cholesterol). This phase diagram, which has macroscopic Ld+Lo phase domains, clearly shows that all phase boundaries determined for the 3-component mixture containing DOPC transition smoothly into the boundaries for the 3-component mixture containing POPC, which has nanoscopic phase domains of Ld+Lo. Our studies start from two published ternary phase diagrams, and show how these can be combined into a quaternary phase diagram by study of a few hundred samples of intermediate compositions.
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Key Words
- 1,1′-didodecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate
- 1,1′-dieicosanyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate
- 1,2-Dilauroyl-sn-glycero-3-phosphocholine
- 1,2-Dioleoyl-sn-glycero-3-phosphocholine
- 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine
- 1,2-Distearoyl-sn-glycero-3-phosphocholine
- 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine
- 1-Stearoyl-2-oleoyl-sn-glycero-3-phosphocholine
- 2-(4,4-Difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine
- 3-Dye method
- 4-Component lipid phase diagram
- BoDIPY-PC
- C12:0-DiI
- C20:0-DiI
- Chol
- Cholesterol
- Competing interaction
- DHE
- DLPC
- DOPC
- DPPC
- DSPC
- Ergosta-5,7,9(11),22-tetraen-3β-ol
- FRET
- Förster resonance energy transfer
- GUV
- Giant unilamellar vesicle
- LHS
- Left hand side refers to left side of phase diagram, i.e. at lower χ(DSPC)
- Lipid raft
- Modulated phase
- PC
- POPC
- Phosphatidylcholine
- Quaternary phase diagram
- REE
- RHS
- RRE
- RSE
- Rapid solvent exchange
- Region of enhanced efficiency
- Region of reduced efficiency
- Right hand side, refers to right side of phase diagram, i.e.,, at higher χ(DSPC)
- SAE
- SM
- SOPC
- Sensitized acceptor emission
- Sphingomyelin
- T1–T6
- TLC
- TOE
- Thin-layer chromatography
- Trajectories 1–6. bSM, sphingomyelin derived from porcine brain
- Trp-Oleoyl Ester, N-oleoyl-dl-tryptophan ethyl ester
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Ackerman DG, Heberle FA, Feigenson GW. Limited perturbation of a DPPC bilayer by fluorescent lipid probes: a molecular dynamics study. J Phys Chem B 2013; 117:4844-52. [PMID: 23548205 DOI: 10.1021/jp400289d] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The properties of lipid bilayer nanometer-scale domains could be crucial for understanding cell membranes. Fluorescent probes are often used to study bilayers, yet their effects on host lipids are not well understood. We used molecular dynamics simulations to investigate perturbations in a fluid DPPC bilayer upon incorporation of three indocarbocyanine probes: DiI-C18:0, DiI-C18:2, or DiI-C12:0. We find a 10-12% decrease in chain order for DPPC in the solvation shell nearest the probe but smaller effects in subsequent shells, indicating that the probes significantly alter only their local environment. We also observe order perturbations of lipids directly across from the probe in the opposite leaflet. Additionally, the DPPC headgroup phosphorus-to-nitrogen vector of lipids nearest the probe exhibits preferential orientation pointing away from the DiI. We show that, while DiI probes perturb their local environment, they do not strongly influence the average properties of "nanoscopic" domains containing a few hundred lipids.
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