51
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Armstrong CL, Häussler W, Seydel T, Katsaras J, Rheinstädter MC. Nanosecond lipid dynamics in membranes containing cholesterol. SOFT MATTER 2014; 10:2600-2611. [PMID: 24647350 DOI: 10.1039/c3sm51757h] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Lipid dynamics in the cholesterol-rich (40 mol%) liquid-ordered (lo) phase of dimyristoylphosphatidylcholine membranes were studied using neutron spin-echo and neutron backscattering. Recent theoretical and experimental evidence supports the notion of the liquid-ordered phase in phospholipid membranes as a locally structured liquid, with small ordered 'domains' of a highly dynamic nature in equilibrium with a disordered matrix [S. Meinhardt, R. L. C. Vink and F. Schmid, Proc. Natl. Acad. Sci. U. S. A., 2013, 110(12), 4476-4481, C. L. Armstrong et al., PLoS One, 2013, 8(6), e66162]. This local structure was found to have a pronounced impact on the membranes' dynamical properties. We found that the long-wavelength dynamics in the liquid-ordered phase, associated with the elastic properties of the membranes, were faster by two orders of magnitude as compared to the liquid disordered phase. At the same time, collective nanoscale diffusion was significantly slower. The presence of a soft-mode (a slowing down) in the long-wavelength dispersion relationship suggests an upper size limit for the ordered lipid domain of ≈220 Å. Moreover, from the relaxation rate of the collective lipid diffusion of lipid-lipid distances, the lifetime of these domains was estimated to be about 100 nanoseconds.
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Affiliation(s)
- Clare L Armstrong
- Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada.
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52
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Boscia AL, Akabori K, Benamram Z, Michel JA, Jablin MS, Steckbeck JD, Montelaro RC, Nagle JF, Tristram-Nagle S. Membrane structure correlates to function of LLP2 on the cytoplasmic tail of HIV-1 gp41 protein. Biophys J 2014; 105:657-66. [PMID: 23931314 DOI: 10.1016/j.bpj.2013.06.042] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 06/18/2013] [Accepted: 06/24/2013] [Indexed: 11/30/2022] Open
Abstract
Mutation studies previously showed that the lentivirus lytic peptide (LLP2) sequence of the cytoplasmic C-terminal tail of the HIV-1 gp41 envelope protein inhibited viral-initiated T-cell death and T-cell syncytium formation, at which time in the HIV life cycle the gp41 protein is embedded in the T-cell membrane. In striking contrast, the mutants did not affect virion infectivity, during which time the gp41 protein is embedded in the HIV envelope membrane. To examine the role of LLP2/membrane interactions, we applied synchrotron x-radiation to determine structure of hydrated membranes. We focused on WT LLP2 peptide (+3 charge) and MX2 mutant (-1 charge) with membrane mimics for the T-cell and the HIV-1 membranes. To investigate the influence of electrostatics, cholesterol content, and peptide palmitoylation, we also studied three other LLP2 variants and HIV-1 mimics without negatively charged lipids or cholesterol as well as extracted HIV-1 lipids. All LLP2 peptides bound strongly to T-cell membrane mimics, as indicated by changes in membrane structure and bending. In contrast, none of the weakly bound LLP2 variants changed the HIV-1 membrane mimic structure or properties. This correlates well with, and provides a biophysical basis for, previously published results that reported lack of a mutant effect in HIV virion infectivity in contrast to an inhibitory effect in T-cell syncytium formation. It shows that interaction of LLP2 with the T-cell membrane modulates biological function.
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Affiliation(s)
- Alexander L Boscia
- Biological Physics Group, Physics Department, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA
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53
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Hakobyan D, Heuer A. Key molecular requirements for raft formation in lipid/cholesterol membranes. PLoS One 2014; 9:e87369. [PMID: 24498317 PMCID: PMC3911970 DOI: 10.1371/journal.pone.0087369] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Accepted: 12/20/2013] [Indexed: 11/25/2022] Open
Abstract
The lipid mixture of DPPC (saturated lipid)/DUPC (unsaturated lipid)/CHOL (cholesterol) is studied with respect to its ability to form liquid-ordered and liquid-disordered phases. We employ coarse-grained simulations with MARTINI force field. All three components are systematically modified in order to explore the relevant molecular properties, leading to phase separation. Specifically, we show that the DPPC/DUPC/CHOL system unmixes due to enthalpic DPPC-DPPC and DPPC-CHOL interactions. The phase separation remains unchanged, except for the formation of a gel phase at long times after decreasing the conformational degrees of freedom of the unsaturated DUPC. In contrast, the phase separation can be suppressed by softening the DPPC chains. In an attempt to mimic the ordering and unmixing effect of CHOL the latter is replaced by a stiff and shortened DPPC-like lipid. One still observes phase separation, suggesting that it is mainly the rigid and planar structure of CHOL which is important for raft formation. Addition of an extra bead to the head of CHOL has no notable impact on the phase separation of the system, supporting the irrelevance of the Umbrella model for the phase separation. Reduction of the conformational entropy of CHOL by stiffening its last bead results in a significant increase of the order of the DPPC/CHOL domain. This suggests that the conformational entropy of CHOL is important to prohibit the gelation process. The interleaflet interactions as mediated by the terminal molecular groups seem to have a strong impact on the possibility of a subsequent gelation process after phase separation.
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Affiliation(s)
- Davit Hakobyan
- Theory of Complex Systems, University of Muenster, Muenster, Germany
- * E-mail:
| | - Andreas Heuer
- Theory of Complex Systems, University of Muenster, Muenster, Germany
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54
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Boscia AL, Treece BW, Mohammadyani D, Klein-Seetharaman J, Braun AR, Wassenaar TA, Klösgen B, Tristram-Nagle S. X-ray structure, thermodynamics, elastic properties and MD simulations of cardiolipin/dimyristoylphosphatidylcholine mixed membranes. Chem Phys Lipids 2014; 178:1-10. [PMID: 24378240 PMCID: PMC4026202 DOI: 10.1016/j.chemphyslip.2013.12.010] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Revised: 12/18/2013] [Accepted: 12/20/2013] [Indexed: 12/13/2022]
Abstract
Cardiolipins (CLs) are important biologically for their unique role in biomembranes that couple phosphorylation and electron transport like bacterial plasma membranes, chromatophores, chloroplasts and mitochondria. CLs are often tightly coupled to proteins involved in oxidative phosphorylation. The first step in understanding the interaction of CL with proteins is to obtain the pure CL structure, and the structure of mixtures of CL with other lipids. In this work we use a variety of techniques to characterize the fluid phase structure, material properties and thermodynamics of mixtures of dimyristoylphosphatidylcholine (DMPC) with tetramyristoylcardiolipin (TMCL), both with 14-carbon chains, at several mole percentages. X-ray diffuse scattering was used to determine structure, including bilayer thickness and area/lipid, the bending modulus, KC, and SXray, a measure of chain orientational order. Our results reveal that TMCL thickens DMPC bilayers at all mole percentages, with a total increase of ∼6 Å in pure TMCL, and increases AL from 64 Å(2) (DMPC at 35 °C) to 109 Å(2) (TMCL at 50 °C). KC increases by ∼50%, indicating that TMCL stiffens DMPC membranes. TMCL also orders DMPC chains by a factor of ∼2 for pure TMCL. Coarse grain molecular dynamics simulations confirm the experimental thickening of 2 Å for 20mol% TMCL and locate the TMCL headgroups near the glycerol-carbonyl region of DMPC; i.e., they are sequestered below the DMPC phosphocholine headgroup. Our results suggest that TMCL plays a role similar to cholesterol in that it thickens and stiffens DMPC membranes, orders chains, and is positioned under the umbrella of the PC headgroup. CL may be necessary for hydrophobic matching to inner mitochondrial membrane proteins. Differential scanning calorimetry, SXray and CGMD simulations all suggest that TMCL does not form domains within the DMPC bilayers. We also determined the gel phase structure of TMCL, which surprisingly displays diffuse X-ray scattering, like a fluid phase lipid. AL=40.8 Å(2) for the ½TMCL gel phase, smaller than the DMPC gel phase with AL=47.2 Å(2), but similar to AL of DLPE=41 Å(2), consistent with untilted chains in gel phase TMCL.
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Affiliation(s)
- Alexander L Boscia
- Biological Physics Group, Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, United States
| | - Bradley W Treece
- Biological Physics Group, Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, United States
| | - Dariush Mohammadyani
- Bioengineering Department, University of Pittsburgh, Pittsburgh, PA 15260, United States
| | - Judith Klein-Seetharaman
- Metabolic & Vascular Health, Medical School, University of Warwick, Coventry, England CV4 7AL, United Kingdom
| | - Anthony R Braun
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, United States
| | - Tsjerk A Wassenaar
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Beate Klösgen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Stephanie Tristram-Nagle
- Biological Physics Group, Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, United States.
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55
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Sodt AJ, Sandar ML, Gawrisch K, Pastor RW, Lyman E. The molecular structure of the liquid-ordered phase of lipid bilayers. J Am Chem Soc 2014; 136:725-32. [PMID: 24345334 DOI: 10.1021/ja4105667] [Citation(s) in RCA: 173] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Molecular dynamics simulations reveal substructures within the liquid-ordered phase of lipid bilayers. These substructures, identified in a 10 μs all-atom trajectory of liquid-ordered/liquid-disordered coexistence (L(o)/L(d)) are composed of saturated hydrocarbon chains packed with local hexagonal order and separated by interstitial regions enriched in cholesterol and unsaturated chains. Lipid hydrocarbon chain order parameters calculated from the L(o) phase are in excellent agreement with (2)H NMR measurements; the local hexagonal packing is also consistent with (1)H-MAS NMR spectra of the L(o) phase, NMR diffusion experiments, and small-angle X-ray and neutron scattering. The balance of cholesterol-rich to local hexagonal order is proposed to control the partitioning of membrane components into the L(o) regions. The latter have been frequently associated with formation of so-called rafts, platforms in the plasma membranes of cells that facilitate interaction between components of signaling pathways.
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Affiliation(s)
- Alexander J Sodt
- National Heart, Lung, and Blood Institute and §National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health , Bethesda, Maryland 20892, United States
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56
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Ramirez DMC, Jakubek ZJ, Lu Z, Ogilvie WW, Johnston LJ. Changes in order parameters associated with ceramide-mediated membrane reorganization measured using pTIRFM. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:15907-15918. [PMID: 24308875 DOI: 10.1021/la403585v] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The enzymatic generation of ceramide has significant effects on the biophysical properties of lipid bilayers and can lead to the extensive reorganization of cell membranes. We have synthesized and characterized a headgroup-labeled fluorescent lipid probe (NBD-ceramide, NBD-Cer) and demonstrated that it can be used for polarized total internal reflection fluorescence microscopy experiments to probe changes in membrane order that result from ceramide incorporation. NBD-Cer measures significantly higher order parameters for the liquid-ordered (Lo) domains ([P2] = 0.40 ± 0.03) than for the liquid-disordered phase (Ld, fluid, [P2] = 0.22 ± 0.02) of phase-separated bilayers prepared from egg sphingomyelin, dioleolyphosphatidylcholine, and cholesterol mixtures. The probe also responds to changes in packing induced by the direct incorporation of ceramide or the variation in the ionic strength of the aqueous medium. Order parameter maps obtained after enzyme treatment of bilayers with coexisting Lo and Ld phases show two distinct types of behavior. In regions of high enzyme activity, the initial Lo/Ld domains are replaced by large, dark features that have high membrane order corroborating previous hypotheses that these are ceramide-enriched regions of the membrane. In areas of low enzyme activity, the size and shape of the Lo domains are conserved, but there is an increase in the order parameter for the initial Ld phase ([P2] = 0.30 ± 0.01). This is attributed to the incorporation of ceramide in the Lo domains with the concomitant expulsion of cholesterol into the surrounding fluid phase, increasing its order parameter.
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Affiliation(s)
- Daniel M Carter Ramirez
- Measurement Science and Standards, National Research Council of Canada , Ottawa, Ontario K1A 0R6, Canada
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57
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Weinrich M, Worcester DL. Xenon and other volatile anesthetics change domain structure in model lipid raft membranes. J Phys Chem B 2013; 117:16141-7. [PMID: 24299622 DOI: 10.1021/jp411261g] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Inhalation anesthetics have been in clinical use for over 160 years, but the molecular mechanisms of action continue to be investigated. Direct interactions with ion channels received much attention after it was found that anesthetics do not change the structure of homogeneous model membranes. However, it was recently found that halothane, a prototypical anesthetic, changes domain structure of a binary lipid membrane. The noble gas xenon is an excellent anesthetic and provides a pivotal test of the generality of this finding, extended to ternary lipid raft mixtures. We report that xenon and conventional anesthetics change the domain equilibrium in two canonical ternary lipid raft mixtures. These findings demonstrate a membrane-mediated mechanism whereby inhalation anesthetics can affect the lipid environment of transmembrane proteins.
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Affiliation(s)
- Michael Weinrich
- Eunice Kennedy Shriver National Institute of Child Health and Human Development , Bethesda, Maryland 20892, United States
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58
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Rheinstädter MC, Mouritsen OG. Small-scale structure in fluid cholesterol–lipid bilayers. Curr Opin Colloid Interface Sci 2013. [DOI: 10.1016/j.cocis.2013.07.001] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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59
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Abstract
The physiological properties of biological soft matter are the product of collective interactions, which span many time and length scales. Recent computational modeling efforts have helped illuminate experiments that characterize the ways in which proteins modulate membrane physics. Linking these models across time and length scales in a multiscale model explains how atomistic information propagates to larger scales. This paper reviews continuum modeling and coarse-grained molecular dynamics methods, which connect atomistic simulations and single-molecule experiments with the observed microscopic or mesoscale properties of soft-matter systems essential to our understanding of cells, particularly those involved in sculpting and remodeling cell membranes.
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Affiliation(s)
- Ryan Bradley
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Ravi Radhakrishnan
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA 19104, USA
- Author to whom correspondence should be addressed; ; Tel.: +1-215-898-0487; Fax: +1-215-573-2071
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60
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The Observation of Highly Ordered Domains in Membranes with Cholesterol. PLoS One 2013; 8:e66162. [PMID: 23823623 PMCID: PMC3688844 DOI: 10.1371/journal.pone.0066162] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Accepted: 05/02/2013] [Indexed: 12/22/2022] Open
Abstract
Rafts, or functional domains, are transient nano- or mesoscopic structures in the exoplasmic leaflet of the plasma membrane, and are thought to be essential for many cellular processes. Using neutron diffraction and computer modelling, we present evidence for the existence of highly ordered lipid domains in the cholesterol-rich (32.5 mol%) liquid-ordered ([Formula: see text]) phase of dipalmitoylphosphatidylcholine membranes. The liquid ordered phase in one-component lipid membranes has previously been thought to be a homogeneous phase. The presence of highly ordered lipid domains embedded in a disordered lipid matrix implies non-uniform distribution of cholesterol between the two phases. The experimental results are in excellent agreement with recent computer simulations of DPPC/cholesterol complexes [Meinhardt, Vink and Schmid (2013). Proc Natl Acad Sci USA 110(12): 4476-4481], which reported the existence of nanometer size [Formula: see text] domains in a liquid disordered lipid environment.
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61
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Hakobyan D, Heuer A. Phase Separation in a Lipid/Cholesterol System: Comparison of Coarse-Grained and United-Atom Simulations. J Phys Chem B 2013; 117:3841-51. [DOI: 10.1021/jp312245y] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Davit Hakobyan
- Institute of Physical Chemistry, Corrensstr. 28/30, Muenster D-48149,
Germany
| | - Andreas Heuer
- Institute of Physical Chemistry, Corrensstr. 28/30, Muenster D-48149,
Germany
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62
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Pan J, Heberle FA, Petruzielo RS, Katsaras J. Using small-angle neutron scattering to detect nanoscopic lipid domains. Chem Phys Lipids 2013; 170-171:19-32. [PMID: 23518250 DOI: 10.1016/j.chemphyslip.2013.02.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 02/27/2013] [Accepted: 02/28/2013] [Indexed: 11/25/2022]
Abstract
The cell plasma membrane is a complex system, which is thought to be capable of exhibiting non-random lateral organization. Studies of live cells and model membranes have yielded mechanisms responsible for the formation, growth, and maintenance of nanoscopic heterogeneities, although the existence and mechanisms that give rise to these heterogeneities remain controversial. Small-angle neutron scattering (SANS) is a tool ideally suited to interrogate lateral heterogeneity in model membranes, primarily due to its unique spatial resolution (i.e., ~5-100nm) and its ability to resolve structure with minimal perturbation to the membrane. In this review we examine several methods used to analyze the SANS signal arising from freely suspended unilamellar vesicles containing lateral heterogeneity. Specifically, we discuss an analytical model for a single, round domain on a spherical vesicle. We then discuss a numerical method that uses Monte Carlo simulation to describe systems with multiple domains and/or more complicated morphologies. Also discussed are several model-independent approaches that are sensitive to membrane heterogeneity. The review concludes with several recent applications of SANS to the study of membrane raft mixtures.
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Affiliation(s)
- Jianjun Pan
- Biology and Soft Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States.
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63
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Boulgaropoulos B, Rappolt M, Sartori B, Amenitsch H, Pabst G. Lipid sorting by ceramide and the consequences for membrane proteins. Biophys J 2012; 102:2031-8. [PMID: 22824266 DOI: 10.1016/j.bpj.2012.03.059] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Revised: 03/08/2012] [Accepted: 03/23/2012] [Indexed: 01/09/2023] Open
Abstract
We mimicked the effect of sphingomyelinase activity on lipid mixtures of palmitoyl-oleoyl-phosphatidylcholine, sphingomyelin, ceramide, and 10 mol % cholesterol. Using x-ray diffraction experiments in combination with osmotic stress we found, in agreement with previous studies, that ceramide induces a coexistence of L(α) and L(β) domains. A detailed structural analysis of the coexisting domains demonstrated an increase of lipid packing density and membrane thickness in the L(α) domains upon increasing overall ceramide levels. This provides evidence for a ceramide-driven accumulation of cholesterol in the L(α) domains, in support of previous reports. We further determined the bending rigidities of the coexisting domains and found that the accumulation of cholesterol in the L(α) domains stabilizes their bending rigidity, which experiences a dramatic drop in the absence of cholesterol. Deriving experimental estimates for the spontaneous curvature and Gaussian modulus of curvature, we show, using a simple geometric model for ion channels, that in this way changes in the conformational equilibrium of membrane proteins can be kept small.
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Affiliation(s)
- Beate Boulgaropoulos
- Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Graz, Austria
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64
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Prades J, Funari SS, Gomez-Florit M, Vögler O, Barceló F. Effect of a 2-hydroxylated fatty acid on Cholesterol-rich membrane domains. Mol Membr Biol 2012; 29:333-43. [DOI: 10.3109/09687688.2012.705023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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65
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Use of X-ray scattering to aid the design and delivery of membrane-active drugs. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2012; 41:915-29. [DOI: 10.1007/s00249-012-0821-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Revised: 04/30/2012] [Accepted: 05/05/2012] [Indexed: 10/28/2022]
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66
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Soloviov DV, Gorshkova YE, Ivankov OI, Zhigunov AN, Bulavin LA, Gordeliy VI, Kuklin AI. Ripple Phase Behavior in Mixtures of DPPC/POPC lipids: SAXS and SANS Studies. ACTA ACUST UNITED AC 2012. [DOI: 10.1088/1742-6596/351/1/012010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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67
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Weinrich M, Nanda H, Worcester DL, Majkrzak CF, Maranville BB, Bezrukov SM. Halothane changes the domain structure of a binary lipid membrane. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:4723-8. [PMID: 22352350 PMCID: PMC3302933 DOI: 10.1021/la204317k] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
X-ray and neutron diffraction studies of a binary lipid membrane demonstrate that halothane at physiological concentrations produces a pronounced redistribution of lipids between domains of different lipid types identified by different lamellar d-spacings and isotope composition. In contrast, dichlorohexafluorocyclobutane (F6), a halogenated nonanesthetic, does not produce such significant effects. These findings demonstrate a specific effect of inhalational anesthetics on mixing phase equilibria of a lipid mixture.
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Affiliation(s)
- Michael Weinrich
- National Center for Medical Rehabilitation Research, Eunice Kennedy Shriver Institute of Child Health and Human Development, Bethesda, Maryland, United States.
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68
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Smith EA, Wang W, Dea PK. Effects of cholesterol on phospholipid membranes: inhibition of the interdigitated gel phase of F-DPPC and F-DPPC/DPPC. Chem Phys Lipids 2011; 165:151-9. [PMID: 22200532 DOI: 10.1016/j.chemphyslip.2011.12.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2011] [Revised: 12/09/2011] [Accepted: 12/10/2011] [Indexed: 11/18/2022]
Abstract
Unlike the parent phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), the monofluorinated analog, 1-palmitoyl-2-(16-fluoropalmitoyl)sn-glycero-3-phosphocholine (F-DPPC), spontaneously forms an interdigitated gel phase (L(β)I) below the main transition temperature (T(m)). We have examined the effects of introducing cholesterol to F-DPPC and 1:1 F-DPPC/DPPC membranes using a combination of DSC, optical density, fluorescence intensity and polarization, (31)P NMR, and X-ray diffraction techniques. Cholesterol increases the fluidity of the gel phase, broadens the main transition, and decreases the main transition enthalpy. However, these results also reveal that there is an unusually large degree of phase coexistence between the L(β)I and non-interdigitated gel phases when cholesterol is added. Cholesterol encourages this phase segregation by partitioning into the thicker non-interdigitated domains. At higher cholesterol concentrations, the majority or all of the L(β)I phase of F-DPPC and 1:1 F-DPPC/DPPC is eliminated and is replaced by a non-interdigitated liquid-ordered (l(o)) phase with properties similar to DPPC/cholesterol. Consequently, cholesterol mitigates the influence the CF moiety has on the thermodynamic phase behavior of F-DPPC. Our findings demonstrate that there are multiple characteristics of cholesterol-rich membranes that disfavor interdigitation.
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Affiliation(s)
- Eric A Smith
- Department of Chemistry, Occidental College, Los Angeles, CA 90041, USA
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69
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Perlmutter JD, Sachs JN. Interleaflet Interaction and Asymmetry in Phase Separated Lipid Bilayers: Molecular Dynamics Simulations. J Am Chem Soc 2011; 133:6563-77. [DOI: 10.1021/ja106626r] [Citation(s) in RCA: 145] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jason D. Perlmutter
- Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Jonathan N. Sachs
- Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
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70
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Abstract
Sub-diffraction optical imaging with nanometer resolution of lipid phase-separated regions is reported. Merocyanine 540, a probe whose fluorescence is sensitive to the lipid phase, is combined with super-resolution imaging to distinguish the liquid- and gel-phase nanoscale domains of lipid bilayers supported on glass. The monomer-dimer equilibrium of MC540 in membranes is deemed responsible for the population difference of single-molecule fluorescence bursts in the different phase regions. The extension of this method to other binary or ternary lipid models or natural systems provides a promising new super-resolution strategy.
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Affiliation(s)
- Chinkuei Kuo
- Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, PA 19104-6323
| | - Robin M. Hochstrasser
- Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, PA 19104-6323
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71
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Ziblat R, Leiserowitz L, Addadi L. Kristalline Lipiddomänen: Charakterisierung durch Röntgenbeugung und ihre Rolle in der Biologie. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201004470] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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72
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Ziblat R, Leiserowitz L, Addadi L. Crystalline lipid domains: characterization by X-ray diffraction and their relation to biology. Angew Chem Int Ed Engl 2011; 50:3620-9. [PMID: 21472900 DOI: 10.1002/anie.201004470] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2010] [Indexed: 12/29/2022]
Abstract
Biological membranes comprise thousands of different lipids, differing in their alkyl chains, headgroups, and degree of saturation. It is estimated that 5% of the genes in the human genome are responsible for regulating the lipid composition of cell membranes. Conceivably, the functional explanation for this diversity is found, at least in part, in the propensity of lipids to segregate into distinct domains, which are important for cell function. X-ray diffraction has been used increasingly to characterize the packing and phase behavior of lipids in membranes. Crystalline domains have been studied in synthetic membranes using wide- and small-angle X-ray scattering, and grazing incidence X-ray diffraction. Herein we summarize recent results obtained using the various X-ray methods, discuss the correlation between crystalline domains and liquid ordered domains studied with other techniques, and the relevance of crystalline domains to functional lipid domains in biological membranes.
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Affiliation(s)
- Roy Ziblat
- Department of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel
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73
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Banc A, Bauduin P, Desbat B, Ly I, Diat O. Ion Extraction Mechanism Studied in a Lyotropic Lamellar Phase. J Phys Chem B 2011; 115:1376-84. [DOI: 10.1021/jp108585f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Amélie Banc
- Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA/CNRS/UM2/ENSCM), BP 17171, F-30206 Bagnols sur Cèze, France
| | - Pierre Bauduin
- Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA/CNRS/UM2/ENSCM), BP 17171, F-30206 Bagnols sur Cèze, France
| | - Bernard Desbat
- Laboratoire de Chimie et Biologie des Membranes et Nanoobjets, Université Bordeaux-1, UMR 5248-CNRS, ENITAB, 2 rue Robert Escarpit, F-33607 Pessac, France
| | - Isabelle Ly
- Centre de Recherche Paul-Pascal, Université Bordeaux-1 CNRS, UPR 8641, 115 avenue A. Schweitzer, F-33600 Pessac, France
| | - Olivier Diat
- Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA/CNRS/UM2/ENSCM), BP 17171, F-30206 Bagnols sur Cèze, France
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74
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Extracting Experimental Measurables from Molecular Dynamics Simulations of Membranes. ACTA ACUST UNITED AC 2011. [DOI: 10.1016/b978-0-444-53835-2.00006-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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75
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Uppamoochikkal P, Tristram-Nagle S, Nagle JF. Orientation of tie-lines in the phase diagram of DOPC/DPPC/cholesterol model biomembranes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:17363-8. [PMID: 20968281 PMCID: PMC2978278 DOI: 10.1021/la103024f] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
We report the direction of tie-lines of coexisting phases in a ternary diagram of DOPC/DPPC/cholesterol lipid bilayers, which has been a system of interest in the discussion of biological rafts. For coexisting Ld and Lo phases, we find that the orientation angle α of the tie-lines increases as the cholesterol concentration increases and it also increases as temperature increases from T = 15 °C to T = 30 °C. Results at lower cholesterol concentrations support the existence of a different two-phase coexistence region of Ld and So phases and the existence of a three-phase region separating the two two-phase regions. Our method uses the X-ray lamellar D-spacings observed in oriented bilayers as a function of varying hydration. Although this method does not obtain the ends of the tie-lines, it gives precise values (±1°) of their angles α in the ternary phase diagram.
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76
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77
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78
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Mannock DA, Lewis RN, McMullen TP, McElhaney RN. The effect of variations in phospholipid and sterol structure on the nature of lipid–sterol interactions in lipid bilayer model membranes. Chem Phys Lipids 2010; 163:403-48. [DOI: 10.1016/j.chemphyslip.2010.03.011] [Citation(s) in RCA: 119] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2009] [Revised: 03/13/2010] [Accepted: 03/27/2010] [Indexed: 01/30/2023]
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79
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Marsh D. Liquid-ordered phases induced by cholesterol: a compendium of binary phase diagrams. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:688-99. [PMID: 20060378 DOI: 10.1016/j.bbamem.2009.12.027] [Citation(s) in RCA: 171] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2009] [Revised: 12/08/2009] [Accepted: 12/29/2009] [Indexed: 12/21/2022]
Abstract
Mixtures of phospholipids with cholesterol are able to form liquid-ordered phases that are characterised by short-range orientational order and long-range translational disorder. These L(o)-phases are distinct from the liquid-disordered, fluid L(alpha)-phases and the solid-ordered, gel L(beta)-phases that are assumed by the phospholipids alone. The liquid-ordered phase can produce spatially separated in-plane fluid domains, which, in the form of lipid rafts, are thought to act as platforms for signalling and membrane sorting in cells. The areas of domain formation are defined by the regions of phase coexistence in the phase diagrams for the binary mixtures of lipid with cholesterol. In this paper, the available binary phase diagrams of lipid-cholesterol mixtures are all collected together. It is found that there is not complete agreement between different determinations of the phase diagrams for the same binary mixture. This can be attributed to the indirect methods largely used to establish the phase boundaries. Intercomparison of the various data sets allows critical assessment of which phase boundaries are rigorously established from direct evidence for phase coexistence.
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Affiliation(s)
- Derek Marsh
- Max-Planck-Institut für biophysikalische Chemie, Abteilung Spektroskopie und photochemische Kinetik, 37070 Göttingen, Germany.
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80
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X-ray and Neutron Scattering Studies of Lipid–Sterol Model Membranes. ACTA ACUST UNITED AC 2010. [DOI: 10.1016/s1554-4516(10)11008-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/23/2023]
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81
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Perlmutter JD, Sachs JN. Experimental verification of lipid bilayer structure through multi-scale modeling. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:2284-90. [DOI: 10.1016/j.bbamem.2009.07.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2009] [Revised: 07/06/2009] [Accepted: 07/08/2009] [Indexed: 11/24/2022]
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82
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Quinn PJ. Long N-acyl fatty acids on sphingolipids are responsible for miscibility with phospholipids to form liquid-ordered phase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:2267-76. [DOI: 10.1016/j.bbamem.2009.06.020] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2009] [Revised: 06/18/2009] [Accepted: 06/25/2009] [Indexed: 01/06/2023]
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83
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Aeffner S, Reusch T, Weinhausen B, Salditt T. Membrane fusion intermediates and the effect of cholesterol: an in-house X-ray scattering study. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2009; 30:205-214. [PMID: 19533189 DOI: 10.1140/epje/i2009-10466-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Revised: 04/05/2009] [Accepted: 04/23/2009] [Indexed: 05/27/2023]
Abstract
We have developed an X-ray scattering setup which allows to study membrane fusion intermediates or other nonlamellar lipid mesophases by laboratory-scale X-ray sources alone, thus taking advantage of unrestricted beamtime compared to synchrotron sources. We report results of a study of pure lipid bilayers and phospholipid/cholesterol binary mixtures. Stalks, putative intermediate structures occurring during the membrane fusion process, can clearly be identified from reconstructed electron density maps. Phase diagrams of the lyotropic phase behavior of DOPC/cholesterol and DPhPC/cholesterol samples are presented. If cholesterol is present in moderate concentrations, it can substantially promote the formation of stalks at higher degree of hydration. In addition, a possibly new phase in DOPC/cholesterol is found at high cholesterol content in the low humidity range.
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Affiliation(s)
- S Aeffner
- Institut für Röntgenphysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
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84
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Kastantin M, Ananthanarayanan B, Karmali P, Ruoslahti E, Tirrell M. Effect of the lipid chain melting transition on the stability of DSPE-PEG(2000) micelles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:7279-86. [PMID: 19358585 PMCID: PMC2756452 DOI: 10.1021/la900310k] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Micellar nanoparticles are showing promise as carriers of diagnostic and therapeutic biofunctionality, leading to increased interest in their properties and behavior, particularly their size, shape, and stability. This work investigates the physical chemistry of micelles formed from DSPE-PEG(2000) monomers as it pertains to these properties. A melting transition in the lipid core of spheroidal DSPE-PEG(2000) micelles is observed as an endothermic peak at 12.8 degrees C upon heating in differential scanning calorimetry thermograms. Bulky PEG(2000) head groups prevent regular crystalline packing of lipids in both the low-temperature glassy and high-temperature fluid phases, as evidenced by wide-angle X-ray scattering. Equilibrium micelle geometry is spheroidal above and below the transition temperature, indicating that the entropic penalty to force the PEG brush into flat geometry is greater than the enthalpic benefit to the glassy core to pack in an extended configuration. Increased micelle stability is seen in the glassy phase with monomer desorption rates significantly lower than in the fluid phase. Activation energies for monomer desorption are 156+/-6.7 and 79+/-5.0 kJ/mol for the glassy and fluid phases, respectively. The observation of a glass transition that increases micelle stability but does not perturb micelle geometry is useful for the design of more effective biofunctional micelles.
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Affiliation(s)
- Mark Kastantin
- Department of Chemical Engineering, University of California, Santa Barbara, CA, USA
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85
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Mills TT, Huang J, Feigenson GW, Nagle JF. Effects of cholesterol and unsaturated DOPC lipid on chain packing of saturated gel-phase DPPC bilayers. Gen Physiol Biophys 2009; 28:126-139. [PMID: 19592709 PMCID: PMC2731993 DOI: 10.4149/gpb_2009_02_126] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/02/2023]
Abstract
Wide angle x-ray scattering (WAXS) from oriented lipid multilayers was used to study the effect of adding cholesterol (Chol) or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) to gel-phase 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers. Small quantities (X < 0.10 mole fraction) of both molecules disrupt the tight packing of tilted chains of pure gel-phase DPPC, forming a more disordered, untilted phase. The addition of larger quantities of DOPC causes the sample to phase-separate into a gel-phase, characterized by a narrow WAXS peak, and liquid disordered phase, characterized by wide, diffuse WAXS scattering. In contrast, two WAXS peaks indicative of two coexisting phases were not observed in Chol/DPPC mixtures (X(Chol) = 0.07 to 0.40). Instead, Chol caused a gradual increase in the width of the WAXS peak, consistent with a gradual change from a more gel-like to a more liquid-like state rather than passing through a region of two phase coexistence. Our WAXS data include a huge amount of information. A new method of analysis suggests that WAXS data may provide definitive results relating to the disagreements between previously published phase diagrams for Chol/DPPC.
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Affiliation(s)
- Thalia T. Mills
- Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
| | - Juyang Huang
- Department of Physics, Texas Tech University, Lubbock, TX 79409
| | | | - John F. Nagle
- Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
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86
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Quinn PJ, Wolf C. Hydrocarbon chains dominate coupling and phase coexistence in bilayers of natural phosphatidylcholines and sphingomyelins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1126-37. [DOI: 10.1016/j.bbamem.2008.12.011] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2008] [Revised: 12/02/2008] [Accepted: 12/17/2008] [Indexed: 11/16/2022]
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87
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Yuan J, Kiss A, Pramudya YH, Nguyen LT, Hirst LS. Solution synchrotron x-ray diffraction reveals structural details of lipid domains in ternary mixtures. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:031924. [PMID: 19391988 DOI: 10.1103/physreve.79.031924] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2008] [Revised: 12/22/2008] [Indexed: 05/27/2023]
Abstract
The influence of cholesterol on lipid bilayer structure is significant and the effect of cholesterol on lipid sorting and phase separation in lipid-raft-forming model membrane systems has been well investigated by microscopy methods on giant vesicles. An important consideration however is the influence of fluorescence illumination on the phase state of these lipids and this effect must be carefully minimized. In this paper, we show that synchrotron x-ray scattering on solution lipid mixtures is an effective alternative technique for the identification and characterization of the l_{o} (liquid ordered) and l_{d} (liquid disordered) phases. The high intensity of synchrotron x rays allows the observation of up to 5 orders of diffraction from the l_{o} phase, whereas only two are clearly visible when the l_{d} phase alone is present. This data can be collected in approximately 1 min/sample , allowing rapid generation of phase data. In this paper, we measure the lamellar spacing in both the liquid-ordered and liquid-disordered phases simultaneously, as a function of cholesterol concentration in two different ternary mixtures. We also observe evidence of a third gel-phaselike population at 10-12 mol % cholesterol and determine the thickness of the bilayer for this phase. Importantly we are able to look at phase coexistence in the membrane independent of photoeffects.
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Affiliation(s)
- Jing Yuan
- Department of Physics and MARTECH, Florida State University, Tallahassee, Florida 32306, USA
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88
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Phase diagrams of lipid mixtures relevant to the study of membrane rafts. Biochim Biophys Acta Mol Cell Biol Lipids 2008; 1781:665-84. [PMID: 18952002 DOI: 10.1016/j.bbalip.2008.09.002] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2008] [Revised: 08/10/2008] [Accepted: 09/09/2008] [Indexed: 12/15/2022]
Abstract
The present paper reviews the phase properties of phosphatidylcholine-sphingomyelin-cholesterol mixtures, that are often used as models for membrane "raft" microdomains. The available data based on X-ray, microscopic and spectroscopic observations, surface pressure and calorimetric measurements, and detergent solubilization assays, are critically evaluated and rationalized in terms of triangular phase diagrams. The remaining uncertainties are discussed specifically and separately from the data on which a consensus appears to exist.
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89
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Goñi FM, Alonso A. Effects of ceramide and other simple sphingolipids on membrane lateral structure. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1788:169-77. [PMID: 18848519 DOI: 10.1016/j.bbamem.2008.09.002] [Citation(s) in RCA: 167] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Revised: 09/09/2008] [Accepted: 09/10/2008] [Indexed: 10/21/2022]
Abstract
The available data concerning the ability of ceramide and other simple sphingolipids to segregate laterally into rigid, gel-like domains in a fluid bilayer has been reviewed. Ceramides give rise to rigid ceramide-enriched domains when their N-acyl chain is longer than C12. The high melting temperature of hydrated ceramides, revealing a tight intermolecular interaction, is probably responsible for their lateral segregation. Ceramides compete with cholesterol for the formation of domains with lipids such as sphingomyelin or saturated phosphatidylcholines; under these conditions displacement of cholesterol by ceramide involves a transition from a liquid-ordered to a gel-like phase in the domains involved. When ceramide is generated in situ by a sphingomyelinase, instead of being premixed with the other lipids, gel-like domain formation occurs as well, although the topology of the domains may not be the same, the enzyme causing clustering of domains that is not detected with premixed ceramide. Ceramide-1-phosphate is not likely to form domains in fluid bilayers, and the same is true of sphingosine and of sphingosine-1-phosphate. However, sphingosine does rigidify pre-existing gel domains in mixed bilayers.
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Affiliation(s)
- Félix M Goñi
- Unidad de Biofísica (Centro Mixto CSIC-UPV/EHU), Departamento de Bioquímica, Universidad del País Vasco, Bilbao, Spain.
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90
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Pan J, Mills TT, Tristram-Nagle S, Nagle JF. Cholesterol perturbs lipid bilayers nonuniversally. PHYSICAL REVIEW LETTERS 2008; 100:198103. [PMID: 18518492 PMCID: PMC2695669 DOI: 10.1103/physrevlett.100.198103] [Citation(s) in RCA: 218] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2008] [Indexed: 05/07/2023]
Abstract
Cholesterol is well known to modulate the physical properties of biomembranes. Using modern x-ray scattering methods, we have studied the effects of cholesterol on the bending modulus K(C), the thickness D(HH), and the orientational order parameter S(xray) of lipid bilayers. We find that the effects are different for at least three classes of phospholipids characterized by different numbers of saturated hydrocarbon chains. Most strikingly, cholesterol strongly increases K(C) when both chains of the phospholipid are fully saturated but not at all when there are two monounsaturated chains.
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Affiliation(s)
- Jianjun Pan
- Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA
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91
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Order parameters and areas in fluid-phase oriented lipid membranes using wide angle X-ray scattering. Biophys J 2008; 95:669-81. [PMID: 18390624 DOI: 10.1529/biophysj.107.127845] [Citation(s) in RCA: 152] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We used wide angle x-ray scattering (WAXS) from stacks of oriented lipid bilayers to measure chain orientational order parameters and lipid areas in model membranes consisting of mixtures of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/cholesterol and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/cholesterol in fluid phases. The addition of 40% cholesterol to either DOPC or DPPC changes the WAXS pattern due to an increase in acyl chain orientational order, which is one of the main properties distinguishing the cholesterol-rich liquid-ordered (Lo) phase from the liquid-disordered (Ld) phase. In contrast, powder x-ray data from multilamellar vesicles does not yield information about orientational order, and the scattering from the Lo and Ld phases looks similar. An analytical model to describe the relationship between the chain orientational distribution and WAXS data was used to obtain an average orientational order parameter, S(x-ray). When 40% cholesterol is added to either DOPC or DPPC, S(x-ray) more than doubles, consistent with previous NMR order parameter measurements. By combining information about the average chain orientation with the chain-chain correlation spacing, we extended a commonly used method for calculating areas for gel-phase lipids to fluid-phase lipids and obtained agreement to within 5% of literature values.
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92
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CRAC motif peptide of the HIV-1 gp41 protein thins SOPC membranes and interacts with cholesterol. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1120-30. [PMID: 18262490 DOI: 10.1016/j.bbamem.2008.01.008] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Revised: 01/03/2008] [Accepted: 01/08/2008] [Indexed: 01/09/2023]
Abstract
This study uses low-angle (LAXS) and wide-angle (WAXS) X-ray synchrotron scattering, volume measurements and thin layer chromatography to determine the structure and interactions of SOPC, SOPC/cholesterol mixtures, SOPC/peptide and SOPC/cholesterol/peptide mixtures. N-acetyl-LWYIK-amide (LWYIK) represents the naturally-occurring CRAC motif segment in the pretransmembrane region of the gp41 protein of HIV-1, and N-acetyl-IWYIK-amide (IWYIK), an unnatural isomer, is used as a control. Both peptides thin the SOPC bilayer by approximately 3 A, and cause the area/unit cell (peptide+SOPC) to increase by approximately 9 A2 from the area/lipid of SOPC at 30 degrees C (67.0+/-0.9 A2). Model fitting suggests that LWYIK's average position is slightly closer to the bilayer center than IWYIK's, and both peptides are just inside of the phosphate headgroup. Both peptides increase the wide-angle spacing d of SOPC without cholesterol, whereas with 50% cholesterol LWYIK increases d but IWYIK decreases d. TLC shows that LWYIK is more hydrophobic than IWYIK; this difference persists in peptide/SOPC 1:9 mole ratio mixtures. Both peptides counteract the chain ordering effect of cholesterol to roughly the same degree, and both decrease KC, the bending modulus, thus increasing the SOPC membrane fluidity. Both peptides nucleate crystals of cholesterol, but the LWYIK-induced crystals are weaker and dissolve more easily.
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