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Toward a better raft model: modulated phases in the four-component bilayer, DSPC/DOPC/POPC/CHOL. Biophys J 2013; 104:853-62. [PMID: 23442964 DOI: 10.1016/j.bpj.2013.01.003] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Revised: 12/18/2012] [Accepted: 01/04/2013] [Indexed: 01/20/2023] Open
Abstract
The liquid-liquid (Ld + Lo) coexistence region within a distearoyl-phosphatidylcholine/dioleoyl-phosphatidylcholine/palmitoyl-oleoyl-phosphatidylcholine/cholesterol (DSPC/DOPC/POPC/CHOL) mixture displays a nanoscopic-to-macroscopic transition of phase domains as POPC is replaced by DOPC. Previously, we showed that the transition goes through a modulated phase regime during this replacement, in which patterned liquid phase morphologies are observed on giant unilamellar vesicles (GUVs). Here, we describe a more detailed investigation of the modulated phase regime along two different thermodynamic tielines within the Ld + Lo region of this four-component mixture. Using fluorescence microscopy of GUVs, we found that the modulated phase regime occurs at relatively narrow DOPC/(DOPC+POPC) ratios. This modulated phase window shifts to higher values of DOPC/(DOPC+POPC) when CHOL concentration is increased, and coexisting phases become closer in properties. Monte Carlo simulations reproduced the patterns observed on GUVs, using a competing interactions model of line tension and curvature energies. Sufficiently low line tension and high bending moduli are required to generate stable modulated phases. Altogether, our studies indicate that by tuning the lipid composition, both the domain size and morphology can be altered drastically within a narrow composition space. This lends insight into a possible mechanism whereby cells can reorganize plasma membrane compartmentalization simply by tuning the local membrane composition or line tension.
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Fritzsching KJ, Kim J, Holland GP. Probing lipid–cholesterol interactions in DOPC/eSM/Chol and DOPC/DPPC/Chol model lipid rafts with DSC and 13C solid-state NMR. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:1889-98. [DOI: 10.1016/j.bbamem.2013.03.028] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 03/25/2013] [Accepted: 03/28/2013] [Indexed: 10/27/2022]
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53
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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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54
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Klotzsch E, Schütz GJ. A critical survey of methods to detect plasma membrane rafts. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120033. [PMID: 23267184 PMCID: PMC3538433 DOI: 10.1098/rstb.2012.0033] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The plasma membrane is still one of the enigmatic cellular structures. Although the microscopic structure is getting clearer, not much is known about the organization at the nanometre level. Experimental difficulties have precluded unambiguous approaches, making the current picture rather fuzzy. In consequence, a variety of different membrane models has been proposed over the years, on the basis of different experimental strategies. Recent data obtained via high-resolution single-molecule microscopy shed new light on the existing hypotheses. We thus think it is a good time for reviewing the consistency of the existing models with the new data. In this paper, we summarize the available models in ten propositions, each of which is discussed critically with respect to the applied technologies and the strengths and weaknesses of the approaches. Our aim is to provide the reader with a sound basis for his own assessment. We close this chapter by exposing our picture of the membrane organization at the nanoscale.
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Affiliation(s)
| | - Gerhard J. Schütz
- Institute of Applied Physics, Vienna University of Technology, Wiedner Hauptstraße 8–10, Vienna 1040, Austria
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55
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Amazon JJ, Goh SL, Feigenson GW. Competition between line tension and curvature stabilizes modulated phase patterns on the surface of giant unilamellar vesicles: a simulation study. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 87:022708. [PMID: 23496549 DOI: 10.1103/physreve.87.022708] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2012] [Revised: 11/27/2012] [Indexed: 05/25/2023]
Abstract
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.
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Affiliation(s)
- Jonathan J Amazon
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, USA.
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56
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Mainali L, Hyde JS, Subczynski WK. Using spin-label W-band EPR to study membrane fluidity profiles in samples of small volume. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 226:35-44. [PMID: 23207176 PMCID: PMC3529815 DOI: 10.1016/j.jmr.2012.11.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 10/15/2012] [Accepted: 11/03/2012] [Indexed: 05/18/2023]
Abstract
Conventional and saturation-recovery (SR) EPR at W-band (94GHz) using phosphatidylcholine spin labels (labeled at the alkyl chain [n-PC] and headgroup [T-PC]) to obtain profiles of membrane fluidity has been demonstrated. Dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol have been studied, and the results have been compared with similar studies at X-band (9.4 GHz) (L. Mainali, J.B. Feix, J.S. Hyde, W.K. Subczynski, J. Magn. Reson. 212 (2011) 418-425). Profiles of the spin-lattice relaxation rate (T(1)(-1)) obtained from SR EPR measurements for n-PCs and T-PC were used as a convenient quantitative measure of membrane fluidity. Additionally, spectral analysis using Freed's MOMD (microscopic-order macroscopic-disorder) model (E. Meirovitch, J.H. Freed J. Phys. Chem. 88 (1984) 4995-5004) provided rotational diffusion coefficients (R(perpendicular) and R(||)) and order parameters (S(0)). Spectral analysis at X-band provided one rotational diffusion coefficient, R(perpendicular). T(1)(-1), R(perpendicular), and R(||) profiles reflect local membrane dynamics of the lipid alkyl chain, while the order parameter shows only the amplitude of the wobbling motion of the lipid alkyl chain. Using these dynamic parameters, namely T(1)(-1), R(perpendicular), and R(||), one can discriminate the different effects of cholesterol at different depths, showing that cholesterol has a rigidifying effect on alkyl chains to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. The nondynamic parameter, S(0), shows that cholesterol has an ordering effect on alkyl chains at all depths. Conventional and SR EPR measurements with T-PC indicate that cholesterol has a fluidizing effect on phospholipid headgroups. EPR at W-band provides more detailed information about the depth-dependent dynamic organization of the membrane compared with information obtained at X-band. EPR at W-band has the potential to be a powerful tool for studying membrane fluidity in samples of small volume, ~30 nL, compared with a representative sample volume of ~3 μL at X-band.
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Affiliation(s)
| | | | - Witold K. Subczynski
- Author to whom correspondence should be addressed: Witold Karol Subczynski, Ph.D., D.Sc., Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226-0509, Phone: (414) 456-4038, Fax: (414) 456-6512,
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57
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Smith AK, Freed JH. Dynamics and ordering of lipid spin-labels along the coexistence curve of two membrane phases: An ESR study. Chem Phys Lipids 2012; 165:348-61. [DOI: 10.1016/j.chemphyslip.2012.02.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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58
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Dzikovski B, Tipikin D, Freed J. Conformational distributions and hydrogen bonding in gel and frozen lipid bilayers: a high frequency spin-label ESR study. J Phys Chem B 2012; 116:6694-706. [PMID: 22324811 DOI: 10.1021/jp211879s] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The ESR parameters of PC spin labels in frozen membranes do not simply represent the membrane polarity or water penetration profile. Instead, they show a distribution between hydrogen-bonded (HB) and non-hydrogen-bonded (non-HB) states, which is affected by a number of factors in the membrane composition. Similar to the exclusion of solutes from crystallizing solvents, the pure bulk gel phase excludes nitroxides, forcing acyl chains to take bent conformations. In these conformations, the nitroxide is hydrogen-bonded. Furthermore, upon gradual cooling in the supercooled gel, PC labels undergo slow lateral aggregation, resulting in a broad background signal. However, if the sample is instantly frozen, this background is replaced by the HB component. In membranes with cholesterol, the observed HB/non-HB ratio can best be described by a partition-like equilibrium between nitroxides located in defects of lipid structure within the hydrophobic core and those close to the membrane surface.
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Affiliation(s)
- Boris Dzikovski
- National Biomedical Center for Advanced ESR Technology, Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA
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59
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Singh P, Tarafdar PK, Swamy MJ, Chattopadhyay A. Organization and Dynamics of Hippocampal Membranes in a Depth-Dependent Manner: An Electron Spin Resonance Study. J Phys Chem B 2012; 116:2999-3006. [DOI: 10.1021/jp211485a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Pushpendra Singh
- Centre for Cellular and Molecular
Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad 500 007, India
| | | | - Musti J. Swamy
- School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
| | - Amitabha Chattopadhyay
- Centre for Cellular and Molecular
Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad 500 007, India
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60
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Reeves VL, Thomas CM, Smart EJ. Lipid rafts, caveolae and GPI-linked proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 729:3-13. [PMID: 22411310 DOI: 10.1007/978-1-4614-1222-9_1] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Lipid rafts and caveolae are specialized membrane microdomains enriched in sphingolipids and cholesterol. They function in a variety of cellular processes including but not limited to endocytosis, transcytosis, signal transduction and receptor recycling. Here, we outline the similarities and differences between lipid rafts and caveolae as well as discuss important components and functions of each.
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61
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Mainali L, Raguz M, Subczynski WK. Phases and domains in sphingomyelin-cholesterol membranes: structure and properties using EPR spin-labeling methods. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2011; 41:147-59. [PMID: 22033879 DOI: 10.1007/s00249-011-0766-4] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Revised: 10/06/2011] [Accepted: 10/11/2011] [Indexed: 11/25/2022]
Abstract
EPR spin-labeling methods were used to investigate the order and fluidity of alkyl chains, the hydrophobicity of the membrane interior, and the order and motion of cholesterol molecules in coexisting phases and domains, or in a single phase of fluid-phase cholesterol/egg-sphingomyelin (Chol/ESM) membranes with a Chol/ESM mixing ratio from 0 to 3. A complete set of profiles for these properties was obtained for the liquid-disordered (l (d)) phase without cholesterol, for the liquid-ordered (l (o)) phase for the entire region of cholesterol solubility in this phase (from 33 to 66 mol%), and for the l (o)-phase domain that coexists with the cholesterol bilayer domain (CBD). Alkyl chains in the l (o) phase are more ordered than in the l (d) pure ESM membrane. However, fluidity in the membrane center is greater. Also, the profile of hydrophobicity changed from a bell to a rectangular shape. These differences are enhanced when the cholesterol content of the l (o) phase is increased from 33 to 66 mol%, with clear brake-points between the C9 and C10 positions (approximately where the steroid-ring structure of cholesterol reaches into the membrane). The organization and motion of cholesterol molecules in the CBD are similar to those in the l (o)-phase domain that coexists with the CBD.
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Affiliation(s)
- Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
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62
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Mainali L, Feix JB, Hyde JS, Subczynski WK. Membrane fluidity profiles as deduced by saturation-recovery EPR measurements of spin-lattice relaxation times of spin labels. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 212:418-25. [PMID: 21868272 PMCID: PMC3214655 DOI: 10.1016/j.jmr.2011.07.022] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2011] [Revised: 07/07/2011] [Accepted: 07/28/2011] [Indexed: 05/18/2023]
Abstract
There are no easily obtainable EPR spectral parameters for lipid spin labels that describe profiles of membrane fluidity. The order parameter, which is most often used as a measure of membrane fluidity, describes the amplitude of wobbling motion of alkyl chains relative to the membrane normal and does not contain explicitly time or velocity. Thus, this parameter can be considered as nondynamic. The spin-lattice relaxation rate (T(1)(-1)) obtained from saturation-recovery EPR measurements of lipid spin labels in deoxygenated samples depends primarily on the rotational correlation time of the nitroxide moiety within the lipid bilayer. Thus, T(1)(-1) can be used as a convenient quantitative measure of membrane fluidity that reflects local membrane dynamics. T(1)(-1) profiles obtained for 1-palmitoyl-2-(n-doxylstearoyl)phosphatidylcholine (n-PC) spin labels in dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol are presented in parallel with profiles of the rotational diffusion coefficient, R(⊥), obtained from simulation of EPR spectra using Freed's model. These profiles are compared with profiles of the order parameter obtained directly from EPR spectra and with profiles of the order parameter obtained from simulation of EPR spectra. It is shown that T(1)(-1) and R(⊥) profiles reveal changes in membrane fluidity that depend on the motional properties of the lipid alkyl chain. We find that cholesterol has a rigidifying effect only to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. These effects cannot be differentiated by profiles of the order parameter. All profiles in this study were obtained at X-band (9.5 GHz).
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Affiliation(s)
- Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
| | - Jimmy B. Feix
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
| | - James S. Hyde
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
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63
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Chiang YW, Costa-Filho AJ, Baird B, Freed JH. 2D-ELDOR study of heterogeneity and domain structure changes in plasma membrane vesicles upon cross-linking of receptors. J Phys Chem B 2011; 115:10462-9. [PMID: 21780815 DOI: 10.1021/jp2016243] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
2D electron-electron double resonance (2D-ELDOR) with the "full Sc-" method of analysis is applied to the study of plasma membrane vesicles. Membrane structural changes upon antigen cross-linking of IgE receptors (IgE-FcεRI) in plasma membrane vesicles (PMVs) isolated from RBL-2H3 mast cells are investigated, for the first time, by means of these 2D-ELDOR techniques. Spectra of 1-palmitoyl-2-(16-doxyl stearoyl) phosphatidylcholine (16-PC) from PMVs before and after this stimulation at several temperatures are reported. The results demonstrate a coexistence of liquid-ordered (L(o)) and liquid-disordered (L(d)) components. We find that upon cross-linking, the membrane environment is remodeled to become more disordered, as shown by a moderate increase in the population of the L(d) component. This change in the relative amount of the L(o) versus L(d) components upon cross-linking is consistent with a model wherein the IgE receptors, which when clustered by antigen to cause cell stimulation, lead to more disordered lipids, and their dynamic and structural properties are slightly altered. This study demonstrates that 2D-ELDOR, analyzed by the full Sc- method, is a powerful approach for capturing the molecular dynamics in biological membranes. This is a particular case showing how 2D-ELDOR can be applied to study physical processes in complex systems that yield subtle changes.
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Affiliation(s)
- Yun-Wei Chiang
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States
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64
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Raguz M, Mainali L, Widomska J, Subczynski WK. Using spin-label electron paramagnetic resonance (EPR) to discriminate and characterize the cholesterol bilayer domain. Chem Phys Lipids 2011; 164:819-29. [PMID: 21855534 DOI: 10.1016/j.chemphyslip.2011.08.001] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Revised: 06/14/2011] [Accepted: 08/02/2011] [Indexed: 11/19/2022]
Abstract
Electron paramagnetic resonance (EPR) spin-labeling methods make it possible not only to discriminate the cholesterol bilayer domain (CBD) but also to obtain information about the organization and dynamics of cholesterol molecules in the CBD. The abilities of spin-label EPR were demonstrated for Chol/POPC (cholesterol/1-palmitoyl-2-oleoylphosphatidylcholine) membranes, with a Chol/POPC mixing ratio that changed from 0 to 3. Using the saturation-recovery (SR) EPR approach with cholesterol analogue spin labels, ASL and CSL, and oxygen or NiEDDA relaxation agents, it was confirmed that the CBD was present in all membrane suspensions when the mixing ratio exceeded the cholesterol solubility threshold (CST). Conventional EPR spectra of ASL and CSL in the CBD were similar to those in the surrounding POPC bilayer (which is saturated with cholesterol), indicating that in both domains, cholesterol exists in the lipid-bilayer-like structures. The behavior of ASL and CSL (and, thus, the behavior of cholesterol molecules) in the CBD was compared with that in the surrounding POPC-cholesterol domain (PCD). In the CBD, ASL and CSL molecules are better ordered than in the surrounding PCD. This difference is small and can be compared to that induced in the surrounding domain by an ~10°C decrease in temperature. Thus, cholesterol molecules are unexpectedly dynamic in the CBD, which should enhance their interaction with the surrounding domain. The polarity of the water/membrane interface of the CBD is significantly greater than that of the surrounding PCD, which significantly enhances penetration of the water-soluble relaxation agent, NiEDDA, into that region. Hydrophobicity measured in the centers of both domains is similar. The oxygen transport parameter (oxygen diffusion-concentration product) measured in the center of the CBD is about ten times smaller than that measured in the center of the surrounding domain. Thus, the CBD can form a significant barrier to oxygen transport. The results presented here point out similarities between the organization and dynamics of cholesterol molecules in the CBD and in the surrounding PCD, as well as significant differences between CBDs and cholesterol crystals.
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Affiliation(s)
- Marija Raguz
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
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65
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Chiang YW, Freed JH. A new Lanczos-based algorithm for simulating high-frequency two-dimensional electron spin resonance spectra. J Chem Phys 2011; 134:034112. [PMID: 21261335 DOI: 10.1063/1.3523576] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The Lanczos algorithm (LA) is a useful iterative method for the reduction of a large matrix to tridiagonal form. It is a storage efficient procedure requiring only the preceding two Lanczos vectors to compute the next. The quasi-minimal residual (QMR) method is a powerful method for the solution of linear equation systems, Ax = b. In this report we provide another application of the QMR method: we incorporate QMR into the LA to monitor the convergence of the Lanczos projections in the reduction of large sparse matrices. We demonstrate that the combined approach of the LA and QMR can be utilized efficiently for the orthogonal transformation of large, but sparse, complex, symmetric matrices, such as are encountered in the simulation of slow-motional 1D- and 2D-electron spin resonance (ESR) spectra. Especially in the 2D-ESR simulations, it is essential that we store all of the Lanczos vectors obtained in the course of the LA recursions and maintain their orthogonality. In the LA-QMR application, the QMR weight matrix mitigates the problem that the Lanczos vectors lose orthogonality after many LA projections. This enables substantially more Lanczos projections, as required to achieve convergence for the more challenging ESR simulations. It, therefore, provides better accuracy for the eigenvectors and the eigenvalues of the large sparse matrices originating in 2D-ESR simulations than does the previously employed method, which is a combined approach of the LA and the conjugate-gradient (CG) methods, as evidenced by the quality and convergence of the 2D-ESR simulations. Our results show that very slow-motional 2D-ESR spectra at W-band (95 GHz) can be reliably simulated using the LA-QMR method, whereas the LA-CG consistently fails. The improvements due to the LA-QMR are of critical importance in enabling the simulation of high-frequency 2D-ESR spectra, which are characterized by their very high resolution to molecular orientation.
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Affiliation(s)
- Yun-Wei Chiang
- Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
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66
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Fluorescence and ESR spectroscopy studies on the interaction of isoflavone genistein with biological and model membranes. Chem Phys Lipids 2011; 164:283-91. [DOI: 10.1016/j.chemphyslip.2011.03.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2010] [Revised: 02/04/2011] [Accepted: 03/03/2011] [Indexed: 11/19/2022]
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67
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Impact of oxLDL on Cholesterol-Rich Membrane Rafts. J Lipids 2011; 2011:730209. [PMID: 21490811 PMCID: PMC3066652 DOI: 10.1155/2011/730209] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2010] [Accepted: 11/29/2010] [Indexed: 11/26/2022] Open
Abstract
Numerous studies have demonstrated that cholesterol-rich membrane rafts play critical roles in multiple cellular functions. However, the impact of the lipoproteins on the structure, integrity and cholesterol composition of these domains is not well understood. This paper focuses on oxidized low-density lipoproteins (oxLDLs) that are strongly implicated in the development of the cardiovascular disease and whose impact on membrane cholesterol and on membrane rafts has been highly controversial. More specifically, we discuss three major criteria for the impact of oxLDL on membrane rafts: distribution of different membrane raft markers, changes in membrane cholesterol composition, and changes in lipid packing of different membrane domains. We also propose a model to reconcile the controversy regarding the relationship between oxLDL, membrane cholesterol, and the integrity of cholesterol-rich membrane domains.
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68
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Laradji M, Sunil Kumar P. Coarse-Grained Computer Simulations of Multicomponent Lipid Membranes. ADVANCES IN PLANAR LIPID BILAYERS AND LIPOSOMES 2011. [DOI: 10.1016/b978-0-12-387720-8.00007-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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69
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Plochberger B, Stockner T, Chiantia S, Brameshuber M, Weghuber J, Hermetter A, Schwille P, Schütz GJ. Cholesterol slows down the lateral mobility of an oxidized phospholipid in a supported lipid bilayer. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:17322-9. [PMID: 20942393 PMCID: PMC2977985 DOI: 10.1021/la1026202] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2010] [Revised: 09/26/2010] [Indexed: 05/24/2023]
Abstract
We investigated the mobility and phase-partitioning of the fluorescent oxidized phospholipid analogue 1-palmitoyl-2-glutaroyl-sn-glycero-3-phospho-N-Alexa647-ethanolamine (PGPE-Alexa647) in supported lipid bilayers. Compared to the conventional phospholipid dihexadecanoylphosphoethanolamine (DHPE)-Bodipy we found consistently higher diffusion constants. The effect became dramatic when immobile obstacles were inserted into the bilayer, which essentially blocked the diffusion of DHPE-Bodipy but hardly influenced the movements of PGPE-Alexa647. In a supported lipid bilayer made of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the differences in probe mobility leveled off with increasing cholesterol content. Using coarse-grained molecular dynamics simulations, we could ascribe this effect to increased interactions between the oxidized phospholipid and the membrane matrix, concomitant with a translation in the headgroup position of the oxidized phospholipid: at zero cholesterol content, its headgroup is shifted to the outside of the DOPC headgroup region, whereas increasing cholesterol concentrations pulls the headgroup into the bilayer plane.
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Affiliation(s)
- Birgit Plochberger
- Biophysics Institute, Johannes Kepler University Linz, A-4040 Linz, Austria
| | - Thomas Stockner
- Bioresources, Austrian Institute of Technology, Seibersdorf, A-2444, Austria
- Department of Medical Chemistry, Medical University of Vienna, A-1090 Vienna, Austria
| | - Salvatore Chiantia
- Technical University of Dresden, Biotechnologisches Zentrum, Dresden, Germany
| | - Mario Brameshuber
- Biophysics Institute, Johannes Kepler University Linz, A-4040 Linz, Austria
| | - Julian Weghuber
- Biophysics Institute, Johannes Kepler University Linz, A-4040 Linz, Austria
| | - Albin Hermetter
- Institute of Biochemistry, Graz University of Technology, A-8010 Graz, Austria
| | - Petra Schwille
- Technical University of Dresden, Biotechnologisches Zentrum, Dresden, Germany
| | - Gerhard J. Schütz
- Biophysics Institute, Johannes Kepler University Linz, A-4040 Linz, Austria
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70
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Kucherak OA, Oncul S, Darwich Z, Yushchenko DA, Arntz Y, Didier P, Mély Y, Klymchenko AS. Switchable nile red-based probe for cholesterol and lipid order at the outer leaflet of biomembranes. J Am Chem Soc 2010; 132:4907-16. [PMID: 20225874 DOI: 10.1021/ja100351w] [Citation(s) in RCA: 290] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Cholesterol and sphingomyelin form together a highly ordered membrane phase, which is believed to play important biological functions in plasma membranes of mammalian cells. Since sphingomyelin is present mainly at the outer leaflet of cell membranes, monitoring its lipid order requires molecular probes capable to bind specifically at this leaflet and exhibit negligibly slow flip-flop. In the present work, such a probe was developed by modifying the solvatochromic fluorescent dye Nile Red with an amphiphilic anchor group. To evaluate the flip-flop of the obtained probe (NR12S), we developed a methodology of reversible redox switching of its fluorescence at one leaflet using sodium dithionite. This method shows that NR12S, in contrast to parent Nile Red, binds exclusively the outer membrane leaflet of model lipid vesicles and living cells with negligible flip-flop in the time scale of hours. Moreover, the emission maximum of NR12S in model vesicles exhibits a significant blue shift in liquid ordered phase (sphingomyelin-cholesterol) as compared to liquid disordered phase (unsaturated phospholipids). As a consequence, these two phases could be clearly distinguished in NR12S-stained giant vesicles by fluorescence microscopy imaging of intensity ratio between the blue and red parts of the probe emission spectrum. Being added to living cells, NR12S binds predominantly, if not exclusively, their plasma membranes and shows an emission spectrum intermediate between those in liquid ordered and disordered phases of model membranes. Importantly, the emission color of NR12S correlates well with the cholesterol content in cell membranes, which allows monitoring the cholesterol depletion process with methyl-beta-cyclodextrin by fluorescence spectroscopy and microscopy. The attractive photophysical and switching properties of NR12S, together with its selective outer leaflet staining and sensitivity to cholesterol and lipid order, make it a new powerful tool for studying model and cell membranes.
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Affiliation(s)
- Oleksandr A Kucherak
- Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de Pharmacie, 74, Route du Rhin, 67401 Illkirch Cedex, France
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71
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Elson EL, Fried E, Dolbow JE, Genin GM. Phase separation in biological membranes: integration of theory and experiment. Annu Rev Biophys 2010; 39:207-26. [PMID: 20192775 DOI: 10.1146/annurev.biophys.093008.131238] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Lipid bilayer model membranes that contain a single lipid species can undergo transitions between ordered and disordered phases, and membranes that contain a mixture of lipid species can undergo phase separations. Studies of these transformations are of interest for what they can tell us about the interaction energies of lipid molecules of different species and conformations. Nanoscopic phases (<200 nm) can provide a model for membrane rafts, specialized membrane domains enriched in cholesterol and sphingomyelin, which are believed to have essential biological functions in cell membranes. Crucial questions are whether lipid nanodomains can exist in stable equilibrium in membranes and what is the distribution of their sizes and lifetimes in membranes of different composition. Theoretical methods have supplied much information on these questions, but better experimental methods are needed to detect and characterize nanodomains under normal membrane conditions. This review summarizes linkages between theoretical and experimental studies of phase separation in lipid bilayer model membranes.
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Affiliation(s)
- Elliot L Elson
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, and Department of Physics, Washington University, St. Louis, Missouri 63110, USA.
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72
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Liquid ordered phase in cell membranes evidenced by a hydration-sensitive probe: Effects of cholesterol depletion and apoptosis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:1436-43. [DOI: 10.1016/j.bbamem.2010.01.013] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Revised: 12/14/2009] [Accepted: 01/14/2010] [Indexed: 02/07/2023]
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73
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Villumsen KR, Duelund L, Lambert IH. Acute cholesterol depletion leads to net loss of the organic osmolyte taurine in Ehrlich Lettré tumor cells. Amino Acids 2010; 39:1521-36. [DOI: 10.1007/s00726-010-0621-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2009] [Accepted: 05/05/2010] [Indexed: 11/30/2022]
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74
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Abstract
Cell membranes display a tremendous complexity of lipids and proteins designed to perform the functions cells require. To coordinate these functions, the membrane is able to laterally segregate its constituents. This capability is based on dynamic liquid-liquid immiscibility and underlies the raft concept of membrane subcompartmentalization. Lipid rafts are fluctuating nanoscale assemblies of sphingolipid, cholesterol, and proteins that can be stabilized to coalesce, forming platforms that function in membrane signaling and trafficking. Here we review the evidence for how this principle combines the potential for sphingolipid-cholesterol self-assembly with protein specificity to selectively focus membrane bioactivity.
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Affiliation(s)
- Daniel Lingwood
- Max Planck Institute for Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
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75
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Gupta G, Surolia A. Glycosphingolipids in microdomain formation and their spatial organization. FEBS Lett 2009; 584:1634-41. [PMID: 19941856 DOI: 10.1016/j.febslet.2009.11.070] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Revised: 11/17/2009] [Accepted: 11/19/2009] [Indexed: 10/20/2022]
Abstract
Plasma membranes regulate the influx and efflux of molecules across themselves and are also responsible for primary signal transduction between cells or within the same cell. Presence of lateral heterogeneity and the ability of reorganization are essential requirements for effective functioning of biomembranes. Lipid rafts are small, heterogeneous, dynamic domains enriched in glycosphingolipids, sphingomyelin and cholesterol, and profoundly influence membrane organization. Glycosphingolipids are inclined towards formation of liquid-ordered phases in membranes, both with and without cholesterol; they are therefore prime players in domain formation. Here, we discuss the role of glycosphingolipids in microdomain formation and their spatial organization within these rafts.
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Affiliation(s)
- Garima Gupta
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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76
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Cholesterol-dependent phase separation in cell-derived giant plasma-membrane vesicles. Biochem J 2009; 424:163-7. [PMID: 19811449 DOI: 10.1042/bj20091283] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Cell-derived GPMVs (giant plasma-membrane vesicles) enable investigation of lipid phase separation in a system with appropriate biological complexity under physiological conditions, and in the present study were used to investigate the cholesterol-dependence of domain formation and stability. The cholesterol level is directly related to the abundance of the liquid-ordered phase fraction, which is the majority phase in vesicles from untreated cells. Miscibility transition temperature depends on cholesterol and correlates strongly with the presence of detergent-insoluble membrane in cell lysates. Fluorescence correlation spectroscopy reveals two distinct diffusing populations in phase-separated cell membrane-derived vesicles whose diffusivities correspond well to diffusivities in both model systems and live cells. The results of the present study extend previous observations in purified lipid systems to the complex environment of the plasma membrane and provide insight into the effect of cholesterol on lipid phase separation and abundance.
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77
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Formation and regulation of lipid microdomains in cell membranes: theory, modeling, and speculation. FEBS Lett 2009; 584:1678-84. [PMID: 19854186 DOI: 10.1016/j.febslet.2009.10.051] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Revised: 10/16/2009] [Accepted: 10/19/2009] [Indexed: 11/20/2022]
Abstract
Compositional lipid microdomains ("lipid rafts") in plasma membranes are believed to be important components of many cellular processes. The biophysical mechanisms by which cells regulate the size, lifetime, and spatial localization of these domains are rather poorly understood at the moment. Over the years, experimental studies of raft formation have inspired several phenomenological theories and speculations incorporating a wide variety of thermodynamic assumptions regarding lipid-lipid and lipid-protein interactions, and the potential role of active cellular processes on membrane structure. Here we critically review and discuss these theories, models, and speculations, and present our view on future directions.
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78
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Piehowski PD, Davey AM, Kurczy ME, Sheets ED, Winograd N, Ewing AG, Heien ML. Time-of-flight secondary ion mass spectrometry imaging of subcellular lipid heterogeneity: Poisson counting and spatial resolution. Anal Chem 2009; 81:5593-602. [PMID: 19530687 DOI: 10.1021/ac901065s] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mass spectrometric imaging is a powerful tool to interrogate biological complexity. One such technique, time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging, has been successfully utilized for subcellular imaging of cell membrane components. In order for this technique to provide insight into biological processes, it is critical to characterize the figures of merit. Because a SIMS instrument counts individual events, the precision of the measurement is controlled by counting statistics. As the analysis area decreases, the number of molecules available for analysis diminishes. This becomes critical when imaging subcellular features; it limits the information obtainable, resulting in images with only a few counts of interest per pixel. Many features observed in low intensity images are artifacts of counting statistics, making validation of these features crucial to arriving at accurate conclusions. With TOF-SIMS imaging, the experimentally attainable spatial resolution is a function of the molecule of interest, sample matrix, concentration, primary ion, instrument transmission, and spot size of the primary ion beam. A model, based on Poisson statistics, has been developed to validate SIMS imaging data when signal is limited. This model can be used to estimate the effective spatial resolution and limits of detection prior to analysis, making it a powerful tool for tailoring future investigations. In addition, the model allows comparison of pixel-to-pixel intensity and can be used to validate the significance of observed image features. The implications and capabilities of the model are demonstrated by imaging the cell membrane of resting RBL-2H3 mast cells.
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Affiliation(s)
- Paul D Piehowski
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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79
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Ge M, Freed JH. Fusion peptide from influenza hemagglutinin increases membrane surface order: an electron-spin resonance study. Biophys J 2009; 96:4925-34. [PMID: 19527651 DOI: 10.1016/j.bpj.2009.04.015] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2009] [Revised: 02/27/2009] [Accepted: 04/06/2009] [Indexed: 11/29/2022] Open
Abstract
A spin-labeling study of interactions of a fusion peptide from the hemagglutinin of the influenza virus, wt20, and a fusion-inactive mutant DeltaG1 with dimyristoylphosphatidylcholine (DMPC) and 1-palmitoyl-2-oleoyl-phosphatdylcholine bilayers was performed. We found that upon binding of wt20, the ordering of headgroups and the ordering of acyl chains near the headgroup increased significantly, in a manner consistent with a cooperative phenomenon. However, changes in the order at the end of the acyl chains were negligible. The ordering effect of wt20 on the headgroup was much stronger at pH 5 than at pH 7. No effect of DeltaG1 binding on the order of bilayers was evident. We also found that 1-palmitoyl-2-hydroxyl phosphatidylcholine, a membrane-fusion inhibitor, decreased the ordering of DMPC headgroups, whereas arachidonic acid, a membrane-fusion promoter, increased the ordering of DMPC headgroups. These results suggest that increases in headgroup ordering may be important for membrane fusion. We propose that upon binding of wt20, which is known to affect only the outer leaflet of the bilayer, this outer leaflet becomes more ordered, and thus more solid-like. Then the coupling between the hardened outer leaflet and the softer inner leaflet generates bending stresses in the bilayer, which tend to increase the negative curvature of the bilayer. We suggest that the increased ordering in the headgroup region enhances dipolar interactions and lowers electrostatic energy, which may provide an energy source for membrane fusion. Possible roles of bending stresses in promoting membrane fusion are discussed.
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Affiliation(s)
- Mingtao Ge
- National Biomedical Center for Advanced ESR Technology, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 15853, USA
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80
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Oliveira TR, Lamy MT, De Paula UM, Guimarães LL, Toledo MS, Takahashi HK, Straus AH, Lindsey CJ, Paiva TB. Structural properties of lipid reconstructs and lipid composition of normotensive and hypertensive rat vascular smooth muscle cell membranes. ACTA ACUST UNITED AC 2009; 42:844-53. [PMID: 19649392 DOI: 10.1590/s0100-879x2009005000012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Accepted: 06/10/2009] [Indexed: 11/22/2022]
Abstract
Multiple cell membrane alterations have been reported to be the cause of various forms of hypertension. The present study focuses on the lipid portion of the membranes, characterizing the microviscosity of membranes reconstituted with lipids extracted from the aorta and mesenteric arteries of spontaneously hypertensive (SHR) and normotensive control rat strains (WKY and NWR). Membrane-incorporated phospholipid spin labels were used to monitor the bilayer structure at different depths. The packing of lipids extracted from both aorta and mesenteric arteries of normotensive and hypertensive rats was similar. Lipid extract analysis showed similar phospholipid composition for all membranes. However, cholesterol content was lower in SHR arteries than in normotensive animal arteries. These findings contrast with the fact that the SHR aorta is hyporeactive while the SHR mesenteric artery is hyperreactive to vasopressor agents when compared to the vessels of normotensive animal strains. Hence, factors other than microviscosity of bulk lipids contribute to the vascular smooth muscle reactivity and hypertension of SHR. The excess cholesterol in the arteries of normotensive animal strains apparently is not dissolved in bulk lipids and is not directly related to vascular reactivity since it is present in both the aorta and mesenteric arteries. The lower cholesterol concentrations in SHR arteries may in fact result from metabolic differences due to the hypertensive state or to genes that co-segregate with those that determine hypertension during the process of strain selection.
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Affiliation(s)
- T R Oliveira
- Departamento de Física Geral, Instituto de Física, Universidade de São Paulo, SP, Brasil
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81
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Han X, Smith NL, Sil D, Holowka DA, McLafferty FW, Baird BA. IgE receptor-mediated alteration of membrane-cytoskeleton interactions revealed by mass spectrometric analysis of detergent-resistant membranes. Biochemistry 2009; 48:6540-50. [PMID: 19496615 DOI: 10.1021/bi900181w] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We use electrospray ionization mass spectrometry to quantify >100 phospholipid (PL) components in detergent-resistant membrane (DRM) domains that are related to ordered membrane compartments commonly known as lipid rafts. We previously compared PL compositions of DRMs with plasma membrane vesicles and whole cell lipid extracts from RBL mast cells, and we made the initial observation that antigen stimulation of IgE receptors (FcepsilonRI) causes a significant change in the PL composition of DRMs [Fridriksson, E. K., et al. (1999) Biochemistry 38, 8056-8063]. We now characterize the signaling requirements and time course for this change, which is manifested as an increase in the recovery of polyunsaturated PL in DRM, particularly in phosphatidylinositol species. We find that this change is largely independent of tyrosine phosphorylation, stimulated by engagement of FcepsilonRI, and can be activated by Ca(2+) ionophore in a manner independent of antigen stimulation. Unexpectedly, we found that inhibitors of actin polymerization (cytochalasin D and latrunculin A) cause a similar, but more rapid, change in the PL composition of DRMs in the absence of FcepsilonRI activation, indicating that perturbations in the actin cytoskeleton affect the organization of plasma membrane domains. Consistent with this interpretation, a membrane-permeable stabilizer of F-actin, jasplakinolide, prevents antigen-stimulated changes in DRM PL composition. These results are confirmed by a detailed analysis of multiple experiments, showing that receptor and cytochalasin D-stimulated changes in DRM lipid composition follow first-order kinetics. Analysis in terms of the number of double bonds in the fatty acid chains is valid for total PL of the major headgroups and for headgroups individually. In this manner, we show that, on average, concentrations of saturated or monounsaturated PL decrease in the DRM, whereas concentrations of PL with two or more double bonds (polyunsaturated PL) increase due to cytoskeletal perturbation. We find that these changes are independent of fatty acid chain length. Our mass spectrometric analyses provide a detailed accounting of receptor-activated alterations in the plasma membrane that are regulated by the actin cytoskeleton.
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Affiliation(s)
- Xuemei Han
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, USA
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82
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Smith AK, Freed JH. Determination of tie-line fields for coexisting lipid phases: an ESR study. J Phys Chem B 2009; 113:3957-71. [PMID: 19673072 PMCID: PMC2772187 DOI: 10.1021/jp808412x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A novel method we refer to as the tie-line field (TLF) method has been developed to globally determine the tie lines of any three-component two-phase coexistence region by fitting electron-spin resonance (ESR) spectra obtained from compositions on the coexistence curve and within the coexistence region. The TLF method is illustrated by applying it to the liquid-ordered (Lo) and liquid-disordered (Ld) phase coexistence region of the lipid system brain-sphingomyelin/dioleoylphosphatidylcholine/cholesterol (SPM/DOPC/chol), for which an estimate of a tie-line was previously obtained by an earlier method also using ESR spectra. The essential aspect of the TLF method is the unique parametrization of the coexistence region called a "ruled surface". The use of the ruled surface enables one to guarantee that tie lines do not cross, as required by the phase rule, whereas previous methods lack this important constraint. It also makes simultaneous use of the full data set in determining the TLF and leads to a more efficient experimental design than previously used. The method is first tested out on synthetic data sets, then least-squares fitting of the ESR spectra with the parametrized model results in a tie-line field consistent with other known information on this lipid system. The best-fit tie-line field consists of the set of tie lines which are not exactly parallel; they exhibit a gradual change in slope with the largest slope within the coexistence region connecting the coexistence curve compositions with the highest and lowest cholesterol concentrations. The results are compared with those from more constrained methods of representing the tie-line fields as well as with the previous tie-line determination for the SPM/DOPC/chol system. An accurate determination of the tie-line field of phase coexistence regions in lipid systems is a necessary step in determining coexisting lipid compositions to serve as models of cell plasma membranes.
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Affiliation(s)
- Andrew K Smith
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA
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83
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Bunge A, Windeck AK, Pomorski T, Schiller J, Herrmann A, Huster D, Müller P. Biophysical characterization of a new phospholipid analogue with a spin-labeled unsaturated fatty acyl chain. Biophys J 2009; 96:1008-15. [PMID: 19186138 DOI: 10.1016/j.bpj.2008.10.037] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Accepted: 10/21/2008] [Indexed: 11/27/2022] Open
Abstract
Spin-labeled analogs of phospholipids have been used widely to characterize the biophysical properties of membranes. We describe synthesis and application of a new spin-labeled phospholipid analog, SL-POPC. The advantage of this molecule is that the EPR active doxyl group is linked to an unsaturated fatty acyl chain different to saturated phospholipid analogs used so far. The need for those analogs arises from the fact that biological membranes contain unsaturated phospholipids to a large extent. The biophysical properties of SL-POPC in membranes were characterized using EPR and NMR spectroscopy and compared with those of the saturated spin-labeled phospholipid, SL-PSPC. To this end, POPC membranes were labeled with either analog to assess whether the spin-labeled counterpart SL-POPC mimics the membrane properties better than the often used SL-PSPC. The results show that SL-POPC and SL-PSPC explore different molecular environments of the bilayer, and that the type and degree of perturbation of bilayer caused by the label moiety also differs between both analogs. We found that SL-POPC is more appropriate to assess the versatile dynamics of POPC membranes than SL-PSPC.
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Affiliation(s)
- Andreas Bunge
- Institute of Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany
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84
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Martini G, Ciani L. Electron spin resonance spectroscopy in drug delivery. Phys Chem Chem Phys 2009; 11:211-54. [DOI: 10.1039/b808263d] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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85
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Isolation at physiological temperature of detergent-resistant membranes with properties expected of lipid rafts: the influence of buffer composition. Biochem J 2008; 417:525-33. [DOI: 10.1042/bj20081385] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The failure of most non-ionic detergents to release patches of DRM (detergent-resistant membrane) at 37 °C undermines the claim that DRMs consist of lipid nanodomains that exist in an Lo (liquid ordered) phase on the living cell surface. In the present study, we have shown that inclusion of cations (Mg2+, K+) to mimic the intracellular environment stabilizes membranes during solubilization sufficiently to allow the isolation of DRMs at 37 °C, using either Triton X-100 or Brij 96. These DRMs are sensitive to chelation of cholesterol, maintain outside-out orientation of membrane glycoproteins, have prolonged (18 h) stability at 37 °C, and are vesicles or sheets up to 150–200 nm diameter. DRMs containing GPI (glycosylphosphatidylinositol)-anchored proteins PrP (prion protein) and Thy-1 can be separated by immunoaffinity isolation, in keeping with their separate organization and trafficking on the neuronal surface. Thy-1, but not PrP, DRMs are associated with actin. EM (electron microscopy) immunohistochemistry shows most PrP, and some Thy-1, to be clustered on DRMs, again maintaining their organization on the neuronal surface. For DRMs labelled for either protein, the bulk of the surface of the DRM is not labelled, indicating that the GPI-anchored protein is a minor component of its lipid domain. These 37 °C DRMs thus have properties expected of raft membrane, yet pose more questions about how proteins are organized within these nanodomains.
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86
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Koklic T, Zeisig R, Šentjurc M. Interaction of alkylphospholipid liposomes with MT-3 breast-cancer cells depends critically on cholesterol concentration. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:2682-9. [DOI: 10.1016/j.bbamem.2008.08.024] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2008] [Revised: 08/21/2008] [Accepted: 08/21/2008] [Indexed: 11/25/2022]
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87
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The temperature effect during pulse application on cell membrane fluidity and permeabilization. Bioelectrochemistry 2008; 74:52-7. [DOI: 10.1016/j.bioelechem.2008.04.012] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2007] [Revised: 03/21/2008] [Accepted: 04/08/2008] [Indexed: 11/18/2022]
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88
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Veatch SL, Cicuta P, Sengupta P, Honerkamp-Smith A, Holowka D, Baird B. Critical fluctuations in plasma membrane vesicles. ACS Chem Biol 2008; 3:287-93. [PMID: 18484709 DOI: 10.1021/cb800012x] [Citation(s) in RCA: 337] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
We demonstrate critical behavior in giant plasma membrane vesicles (GPMVs) that are isolated directly from living cells. GPMVs contain two liquid phases at low temperatures and one liquid phase at high temperatures and exhibit transition temperatures in the range of 15 to 25 degrees C. In the two-phase region, line tensions linearly approach zero as temperature is increased to the transition. In the one-phase region, micrometer-scale composition fluctuations occur and become increasingly large and long-lived as temperature is decreased to the transition. These results indicate proximity to a critical point and are quantitatively consistent with established theory. Our observations of robust critical fluctuations suggest that the compositions of mammalian plasma membranes are tuned to reside near a miscibility critical point and that heterogeneity corresponding to < 50 nm-sized compositional fluctuations are present in GPMV membranes at physiological temperatures. Our results provide new insights for plasma membrane heterogeneity that may be related to functional lipid raft domains in live cells.
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Affiliation(s)
- Sarah L. Veatch
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
| | - Pietro Cicuta
- Cavendish Laboratory University of Cambridge, Cambridge, UK CB30HE
| | - Prabuddha Sengupta
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
| | | | - David Holowka
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
| | - Barbara Baird
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
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89
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Davey AM, Krise KM, Sheets ED, Heikal AA. Molecular Perspective of Antigen-mediated Mast Cell Signaling. J Biol Chem 2008; 283:7117-27. [DOI: 10.1074/jbc.m708879200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
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90
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Ciani L, Ristori S, Bonechi C, Rossi C, Martini G. Effect of the preparation procedure on the structural properties of oligonucleotide/cationic liposome complexes (lipoplexes) studied by electron spin resonance and Zeta potential. Biophys Chem 2007; 131:80-7. [PMID: 17950520 DOI: 10.1016/j.bpc.2007.09.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Revised: 09/12/2007] [Accepted: 09/13/2007] [Indexed: 10/22/2022]
Abstract
Lipoplexes with different surface charge were prepared from a short oligonucleotide (20 mer, dsAT) inserted into liposomes of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and 1,2-dioleoyl-sn-glycero-3-phospho-ethanolamine (DOPE). The starting liposomes were prepared by two different procedures, i.e. progressive dsAT addition starting from plain liposomes (titration) and direct mixing of dsAT with pure liposomes (point to point preparation). Lipoplexes were characterized from a molecular point of view by Electron Spin Resonance (ESR) of a cationic spin probe and by Nuclear Magnetic Resonance. Structural and surface features were analysed by Zeta potential (zeta) measurements and Cryo-TEM micrographs. The complete set of results allowed to demonstrate that: i) the interactions between dsAT and cationic lipids were strong and occurred at the liposome surface; ii) the overall shape and physicochemical properties of liposomes did not change when short nucleic acid fragments were added before surface charge neutralization; iii) the bilayer structure of the lipids in lipoplexes was substantially preserved at all charge ratios; iv) the physical status of lipoplexes with electrical charge far from neutrality did not depend on the preparation method.
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Affiliation(s)
- Laura Ciani
- Department of Chemistry & CSGI, University of Florence, Via della Lastruccia 3, 50019 Sesto F no, Firenze, Italy
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91
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Veatch SL. From small fluctuations to large-scale phase separation: Lateral organization in model membranes containing cholesterol. Semin Cell Dev Biol 2007; 18:573-82. [DOI: 10.1016/j.semcdb.2007.08.016] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Revised: 08/23/2007] [Accepted: 08/29/2007] [Indexed: 01/09/2023]
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92
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Chiang YW, Costa-Filho A, Freed JH. 2D-ELDOR using full S(c-) fitting and absorption lineshapes. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 188:231-45. [PMID: 17681478 DOI: 10.1016/j.jmr.2007.06.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2007] [Revised: 05/30/2007] [Accepted: 06/06/2007] [Indexed: 05/16/2023]
Abstract
Recent progress in developing 2D-ELDOR (2D electron-electron double resonance) techniques to better capture molecular dynamics in complex fluids, particularly in model and biological membranes, is reported. The new "full S(c-) method", which corrects the spectral analysis for the phase distortion effects present in the experiments, is demonstrated to enhance the sensitivity of 2D-ELDOR in reporting on molecular dynamics in complex membrane environments. That is, instead of performing spectral fitting in the magnitude mode, our new method enables simultaneous fitting of both the real and imaginary components of the S(c-) signal. The full S(c-) fitting not only corrects the phase distortions in the experimental data but also more accurately determines instrumental dead times. The phase corrections applied to the S(c-) spectrum enable the extraction of the pure absorption-mode spectrum, which is characterized by much better resolution than the magnitude-mode spectrum. In the absorption mode, the variation of homogeneous broadening, which reports on the dynamics of the spin probe, can even be observed by visual inspection. This new method is illustrated with results from model membranes of dipalmitoyl-sn-glycero-phosphatidylcholine (DPPC)-cholesterol binary mixtures, as well as with results from plasma membrane vesicles of mast cells. In addition to the dynamic parameters, which provide quantitative descriptions for membranes at the molecular level, the high-resolution absorption spectra themselves may be used as a "fingerprint" to characterize membrane phases and distinguish coexisting components in biomembranes. Thus we find that 2D-ELDOR is greatly improved with the new "full S(c-) method" especially for exploring the complexity of model and biological membranes.
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Affiliation(s)
- Yun-Wei Chiang
- Baker Laboratory of Chemistry and Chemical Biology, National Biomedical ACERT Center for Advanced ESR Technology, Cornell University, Ithaca, NY 14853-1301, USA
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93
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Yang Z, Becker J, Saxena S. On Cu(II)-Cu(II) distance measurements using pulsed electron electron double resonance. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 188:337-43. [PMID: 17825593 DOI: 10.1016/j.jmr.2007.08.006] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2007] [Revised: 08/10/2007] [Accepted: 08/10/2007] [Indexed: 05/17/2023]
Abstract
The effects of orientational selectivity on the 4-pulse electron electron double resonance (PELDOR) ESR spectra of coupled Cu(II)-Cu(II) spins are presented. The data were collected at four magnetic fields on a poly-proline peptide containing two Cu(II) centers. The Cu(II)-PELDOR spectra of this peptide do not change appreciably with magnetic field at X-band. The data were analyzed by adapting the theory of Maryasov, Tsvetkov, and Raap [A.G. Maryasov, Y.D. Tsvetkov, J. Raap, Weakly coupled radical pairs in solids:ELDOR in ESE structure studies, Appl. Magn. Reson. 14 (1998) 101-113]. Simulations indicate that orientational effects are important for Cu(II)-PELDOR. Based on simulations, the field-independence of the PELDOR data for this peptide is likely due to two effects. First, for this peptide, the Cu(II) g-tensor(s) are in a very specific orientation with respect to the interspin vector. Second, the flexibility of the peptide washes out the orientation effects. These effects reduce the suitability of the poly-proline based peptide as a good model system to experimentally probe orientational effects in such experiments. An average Cu(II)-Cu(II) distance of 2.1-2.2 nm was determined, which is consistent with earlier double quantum coherence ESR results.
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Affiliation(s)
- Zhongyu Yang
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
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94
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Levitan I, Gooch KJ. Lipid rafts in membrane-cytoskeleton interactions and control of cellular biomechanics: actions of oxLDL. Antioxid Redox Signal 2007; 9:1519-34. [PMID: 17576163 DOI: 10.1089/ars.2007.1686] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Membrane-cytoskeleton coupling is known to play major roles in a plethora of cellular responses, such as cell growth, differentiation, polarization, motility, and others. In this review, the authors discuss the growing amount of evidence indicating that membrane-cytoskeleton interactions are regulated by the lipid composition of the plasma membrane, suggesting that cholesterol-rich membrane domains (lipid rafts), including caveolae, are essential for membrane-cytoskeleton coupling. Several models for raft-cytoskeleton interactions are discussed. Also described is the evidence suggesting that raft-cytoskeleton interactions play key roles in several cytoskeleton-dependent processes, particularly in the regulation of cellular biomechanical properties. To address further the physiological significance of raft-cytoskeleton coupling, the authors focus on the impact of oxidized low density lipoproteins, one of the major cholesterol carriers and proatherogenic factors, on the integrity of lipid rafts/caveolae, and on the organization of the cytoskeleton. Finally, the authors review the recent studies showing that oxLDL and cholesterol depletion have similar impacts on the biomechanical properties of vascular endothelial cells, which in turn affect endothelial angiogenic potential.
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Affiliation(s)
- Irena Levitan
- Department of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
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95
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Chiang YW, Costa-Filho AJ, Freed JH. Dynamic molecular structure and phase diagram of DPPC-cholesterol binary mixtures: a 2D-ELDOR study. J Phys Chem B 2007; 111:11260-70. [PMID: 17760438 DOI: 10.1021/jp0732110] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This paper is an application of 2D electron-electron double resonance (2D-ELDOR) with the "full Sc- method" to study model membranes. We obtain and confirm the phase diagram of 1,2-dipalmitoyl-sn-glycerophosphatidylcholine (DPPC)-cholesterol binary mixtures versus temperature and provide quantitative descriptions for its dynamic molecular structure using 2D-ELDOR at the Ku band. The spectra from the end-chain 16-PC spin label in multilamellar phospholipid vesicles are obtained for cholesterol molar concentrations ranging from 0 to 50% and from 25 to 60 degrees C. This phase diagram consists of liquid-ordered, liquid-disordered, and gel phases and phase coexistence regions. The phase diagram is carefully examined according to the spectroscopic evidence, and the rigorous interpretation for the line shape changes. We show that the 2D-ELDOR spectra differ markedly with variation in the composition. The extensive line shape changes in the 2D-plus-mixing-time representation provide useful information to define and characterize the membrane phases with respect to their dynamic molecular structures and to determine the phase boundaries. The homogeneous T2's are extracted from the pure absorption spectra and are used to further distinguish the membrane phases. These results show 2D-ELDOR to be naturally suitable for probing and reporting the dynamic structures of microdomains in model membrane systems and, moreover, providing a very detailed picture of their molecular dynamic structure, especially with the aid of the "full Sc- method".
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Affiliation(s)
- Yun-Wei Chiang
- Baker Laboratory of Chemistry and Chemical Biology, and National Biomedical ACERT Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853-1301, USA
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96
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Zhao J, Wu J, Heberle FA, Mills TT, Klawitter P, Huang G, Costanza G, Feigenson GW. Phase studies of model biomembranes: complex behavior of DSPC/DOPC/cholesterol. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:2764-76. [PMID: 17825247 PMCID: PMC2701629 DOI: 10.1016/j.bbamem.2007.07.008] [Citation(s) in RCA: 177] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 07/11/2007] [Accepted: 07/13/2007] [Indexed: 11/20/2022]
Abstract
We have undertaken a series of experiments to examine the behavior of individual components of cell membranes. Here we report an initial stage of these experiments, in which the properties of a chemically simple lipid mixture are carefully mapped onto a phase diagram. Four different experimental methods were used to establish the phase behavior of the 3-component mixture DSPC/DOPC/chol: (1) confocal fluorescence microscopy observation of giant unilamellar vesicles, GUVs; (2) FRET from perylene to C20:0-DiI; (3) fluorescence of dilute dyes C18:2-DiO and C20:0-DiI; and (4) wide angle X-ray diffraction. This particular 3-component mixture was chosen, in part, for a high level of immiscibility of the components in order to facilitate solving the phase behavior at all compositions. At 23 degrees C, a large fraction of the possible compositions for this mixture give rise to a solid phase. A region of 3-phase coexistence of {Lalpha+Lbeta+Lo} was detected and defined based on a combination of fluorescence microscopy of GUVs, FRET, and dilute C20:0-DiI fluorescence. At very low cholesterol concentrations, the solid phase is the tilted-chain phase Lbeta'. Most of the phase boundaries have been determined to be within a few percent of the composition. Measurements of the perturbations of the boundaries of this accurate phase diagram could serve as a means to understand the behaviors of a range of added lipids and proteins.
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Affiliation(s)
| | | | | | - Thalia T. Mills
- Department of Physics, Cornell University, Ithaca, NewYork 14853
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97
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Sengupta P, Baird B, Holowka D. Lipid rafts, fluid/fluid phase separation, and their relevance to plasma membrane structure and function. Semin Cell Dev Biol 2007; 18:583-90. [PMID: 17764993 PMCID: PMC2147712 DOI: 10.1016/j.semcdb.2007.07.010] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2007] [Accepted: 07/20/2007] [Indexed: 12/20/2022]
Abstract
Novel biophysical approaches combined with modeling and new biochemical data have helped to recharge the lipid raft field and have contributed to the generation of a refined model of plasma membrane organization. In this review, we summarize new information in the context of previous literature to provide new insights into the spatial organization and dynamics of lipids and proteins in the plasma membrane of live cells. Recent findings of large-scale separation of liquid-ordered and liquid-disordered phases in plasma membrane vesicles demonstrate this capacity within the complex milieu of plasma membrane proteins and lipids. Roles for membrane heterogeneity and reorganization in immune cell activation are discussed in light of this new information.
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Affiliation(s)
| | | | - David Holowka
- *To whom correspondence should be addressed: ; 607-255-6140 (phone); 607-255-4137 (fax)
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98
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Radhakrishnan A, McConnell H. Composition fluctuations, chemical exchange, and nuclear relaxation in membranes containing cholesterol. J Chem Phys 2007; 126:185101. [PMID: 17508832 DOI: 10.1063/1.2730805] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A thermodynamic model of cholesterol-phospholipid complexes is used as a starting point for calculating fluctuations in membranes containing cholesterol and phospholipids. The calculations describe fluctuations in the concentration of complexes formed between cholesterol and phospholipids with longer saturated fatty acid chains. The fluctuations in complex concentrations arise by two distinct mechanisms. In one, the chemical composition of the sample varies from point to point, and the concentration of the complexes varies according to local chemical equilibrium. In the second, the composition remains fixed, and the complexes form and dissociate according to chemical reaction kinetics. In both cases the nuclear resonance frequency of a deuterium labeled phospholipid undergoes fluctuations and line broadening as a consequence of the formation and dissociation of complexes. For a specific ternary lipid mixture at its critical composition, deuterium nuclear resonance line broadening of chain labeled phospholipids is calculated for temperatures up to 10 degrees -20 degrees above the miscibility critical temperature. This line broadening is associated with fluctuations in the degree of phospholipid chain ordering related to the formation and dissociation of complexes.
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Affiliation(s)
- Arun Radhakrishnan
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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99
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Zidovetzki R, Levitan I. Use of cyclodextrins to manipulate plasma membrane cholesterol content: evidence, misconceptions and control strategies. BIOCHIMICA ET BIOPHYSICA ACTA 2007; 1768:1311-24. [PMID: 17493580 PMCID: PMC1948080 DOI: 10.1016/j.bbamem.2007.03.026] [Citation(s) in RCA: 821] [Impact Index Per Article: 48.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2006] [Revised: 03/12/2007] [Accepted: 03/15/2007] [Indexed: 12/14/2022]
Abstract
The physiological importance of cholesterol in the cell plasma membrane has attracted increased attention in recent years. Consequently, the use of methods of controlled manipulation of membrane cholesterol content has also increased sharply, especially as a method of studying putative cholesterol-enriched cell membrane domains (rafts). The most common means of modifying the cholesterol content of cell membranes is the incubation of cells or model membranes with cyclodextrins, a family of compounds, which, due to the presence of relatively hydrophobic cavity, can be used to extract cholesterol from cell membranes. However, the mechanism of this activity of cyclodextrins is not completely established. Moreover, under conditions commonly used for cholesterol extraction, cyclodextrins may remove cholesterol from both raft and non-raft domains of the membrane as well as alter the distribution of cholesterol between plasma and intracellular membranes. In addition, other hydrophobic molecules such as phospholipids may also be extracted from the membranes by cyclodextrins. We review the evidence for the specific and non-specific effects of cyclodextrins and what is known about the mechanisms for cyclodextrin-induced cholesterol and phospholipid extraction. Finally, we discuss useful control strategies that may help to verify that the observed effects are due specifically to cyclodextrin-induced changes in cellular cholesterol.
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Affiliation(s)
- Raphael Zidovetzki
- Department of Cell Biology and Neuroscience, University of California, Riverside, CA 90291, USA
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100
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Ulrich K, Sanders M, Vasenkov S. Probing lateral diffusion in lipid membranes on nanoscale by PFG NMR with high gradient strength. Magn Reson Imaging 2007; 25:493-6. [PMID: 17466771 DOI: 10.1016/j.mri.2006.11.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2006] [Accepted: 11/30/2006] [Indexed: 02/02/2023]
Abstract
This work demonstrates the feasibility of noninvasive studies of diffusion on a submicrometer length scale in aligned model lipid membranes using pulsed field gradient nuclear magnetic resonance with ultrahigh (up to 35 T/m) gradient strength. Application of such gradients allows the use of sufficiently small diffusion times under conditions of narrow-pulse approximation. As a result, monitoring anomalous or restricted diffusion in lipid membranes on a length scale in the range of 100 nm becomes possible. The ability to study diffusion in lipid membranes on this length scale is very important because it is comparable with the size of biologically relevant domains (i.e., rafts), which are believed to exist in biomembranes.
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Affiliation(s)
- Konstantin Ulrich
- Fakultät für Physik und Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany
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