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Lee H, Choi SQ. Sphingomyelinase-Mediated Multitimescale Clustering of Ganglioside GM1 in Heterogeneous Lipid Membranes. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2021; 8:e2101766. [PMID: 34473415 PMCID: PMC8529493 DOI: 10.1002/advs.202101766] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Revised: 07/19/2021] [Indexed: 05/05/2023]
Abstract
Several signaling processes in the plasma membrane are intensified by ceramides that are formed by sphingomyelinase-mediated hydrolysis of sphingomyelin. These ceramides trigger clustering of signaling-related biomolecules, but how they concentrate such biomolecules remains unclear. Here, the spatiotemporal localization of ganglioside GM1, a glycolipid receptor involved in signaling, during sphingomyelinase-mediated hydrolysis is described. Real-time visualization of the dynamic remodeling of the heterogeneous lipid membrane that occurs due to sphingomyelinase action is used to examine GM1 clustering, and unexpectedly, it is found that it is more complex than previously thought. Specifically, lipid membranes generate two distinct types of condensed GM1: 1) rapidly formed but short-lived GM1 clusters that are formed in ceramide-rich domains nucleated from the liquid-disordered phase; and 2) late-onset yet long-lasting, high-density GM1 clusters that are formed in the liquid-ordered phase. These findings suggest that multiple pathways exist in a plasma membrane to synergistically facilitate the rapid amplification and persistence of signals.
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Affiliation(s)
- Hyun‐Ro Lee
- Department of Chemical and Biomolecular EngineeringKorea Advanced Institute of Science and Technology (KAIST)Daejeon34141Republic of Korea
| | - Siyoung Q. Choi
- Department of Chemical and Biomolecular EngineeringKorea Advanced Institute of Science and Technology (KAIST)Daejeon34141Republic of Korea
- KAIST Institute for the NanoCenturyKorea Advanced Institute of Science and Technology (KAIST)Daejeon34141Republic of Korea
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Sugár IP, Bonanno AP, Chong PLG. Gramicidin Lateral Distribution in Phospholipid Membranes: Fluorescence Phasor Plots and Statistical Mechanical Model. Int J Mol Sci 2018; 19:E3690. [PMID: 30469389 PMCID: PMC6274966 DOI: 10.3390/ijms19113690] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Revised: 11/14/2018] [Accepted: 11/15/2018] [Indexed: 11/16/2022] Open
Abstract
When using small mole fraction increments to study gramicidins in phospholipid membranes, we found that the phasor dots of intrinsic fluorescence of gramicidin D and gramicidin A in dimyristoyl-sn-glycero-3-phosphocholine (DMPC) unilamellar and multilamellar vesicles exhibit a biphasic change with peptide content at 0.143 gramicidin mole fraction. To understand this phenomenon, we developed a statistical mechanical model of gramicidin/DMPC mixtures. Our model assumes a sludge-like mixture of fluid phase and aggregates of rigid clusters. In the fluid phase, gramicidin monomers are randomly distributed. A rigid cluster is formed by a gramicidin dimer and DMPC molecules that are condensed to the dimer, following particular stoichiometries (critical gramicidin mole fractions, Xcr including 0.143). Rigid clusters form aggregates in which gramicidin dimers are regularly distributed, in some cases, even to superlattices. At Xcr, the size of cluster aggregates and regular distributions reach a local maximum. Before a similar model was developed for cholesterol/DMPC mixtures (Sugar and Chong (2012) J. Am. Chem. Soc. 134, 1164⁻1171) and here the similarities and differences are discussed between these two models.
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Affiliation(s)
- István P Sugár
- Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.
| | - Alexander P Bonanno
- Department of Medical Genetics and Molecular Biochemistry, The Lewis Katz School of Medicine at Temple University, Philadelphia, PA 19140, USA.
| | - Parkson Lee-Gau Chong
- Department of Medical Genetics and Molecular Biochemistry, The Lewis Katz School of Medicine at Temple University, Philadelphia, PA 19140, USA.
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3
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Javanainen M, Martinez-Seara H, Vattulainen I. Nanoscale Membrane Domain Formation Driven by Cholesterol. Sci Rep 2017; 7:1143. [PMID: 28442766 PMCID: PMC5430823 DOI: 10.1038/s41598-017-01247-9] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Accepted: 03/27/2017] [Indexed: 11/09/2022] Open
Abstract
Biological membranes generate specific functions through compartmentalized regions such as cholesterol-enriched membrane nanodomains that host selected proteins. Despite the biological significance of nanodomains, details on their structure remain elusive. They cannot be observed via microscopic experimental techniques due to their small size, yet there is also a lack of atomistic simulation models able to describe spontaneous nanodomain formation in sufficiently simple but biologically relevant complex membranes. Here we use atomistic simulations to consider a binary mixture of saturated dipalmitoylphosphatidylcholine and cholesterol - the "minimal standard" for nanodomain formation. The simulations reveal how cholesterol drives the formation of fluid cholesterol-rich nanodomains hosting hexagonally packed cholesterol-poor lipid nanoclusters, both of which show registration between the membrane leaflets. The complex nanodomain substructure forms when cholesterol positions itself in the domain boundary region. Here cholesterol can also readily flip-flop across the membrane. Most importantly, replacing cholesterol with a sterol characterized by a less asymmetric ring region impairs the emergence of nanodomains. The model considered explains a plethora of controversial experimental results and provides an excellent basis for further computational studies on nanodomains. Furthermore, the results highlight the role of cholesterol as a key player in the modulation of nanodomains for membrane protein function.
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Affiliation(s)
- Matti Javanainen
- Laboratory of Physics, Tampere University of Technology, Tampere, Finland.,Department of Physics, University of Helsinki, Helsinki, Finland
| | - Hector Martinez-Seara
- Laboratory of Physics, Tampere University of Technology, Tampere, Finland. .,Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Prague, Czech Republic.
| | - Ilpo Vattulainen
- Laboratory of Physics, Tampere University of Technology, Tampere, Finland. .,Department of Physics, University of Helsinki, Helsinki, Finland. .,MEMPHYS - Centre for Biomembrane Physics, University of Southern Denmark, Odense, Denmark.
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4
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Litz JP, Thakkar N, Portet T, Keller SL. Depletion with Cyclodextrin Reveals Two Populations of Cholesterol in Model Lipid Membranes. Biophys J 2017; 110:635-645. [PMID: 26840728 DOI: 10.1016/j.bpj.2015.11.021] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Revised: 11/06/2015] [Accepted: 11/10/2015] [Indexed: 10/22/2022] Open
Abstract
Recent results provide evidence that cholesterol is highly accessible for removal from both cell and model membranes above a threshold concentration that varies with membrane composition. Here we measured the rate at which methyl-β-cyclodextrin depletes cholesterol from a supported lipid bilayer as a function of cholesterol mole fraction. We formed supported bilayers from two-component mixtures of cholesterol and a PC (phosphatidylcholine) lipid, and we directly visualized the rate of decrease in area of the bilayers with fluorescence microscopy. Our technique yields the accessibility of cholesterol over a wide range of concentrations (30-66 mol %) for many individual bilayers, enabling fast acquisition of replicate data. We found that the bilayers contain two populations of cholesterol, one with low surface accessibility and the other with high accessibility. A larger fraction of the total membrane cholesterol appears in the more accessible population when the acyl chains of the PC-lipid tails are more unsaturated. Our findings are most consistent with the predictions of the condensed-complex and cholesterol bilayer domain models of cholesterol-phospholipid interactions in lipid membranes.
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Affiliation(s)
- Jonathan P Litz
- Department of Chemistry, University of Washington, Seattle, Washington
| | - Niket Thakkar
- Department of Chemistry, University of Washington, Seattle, Washington; Department of Applied Mathematics, University of Washington, Seattle, Washington
| | - Thomas Portet
- Department of Chemistry, University of Washington, Seattle, Washington
| | - Sarah L Keller
- Department of Chemistry, University of Washington, Seattle, Washington; Department of Physics, University of Washington, Seattle, Washington.
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5
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Sodt AJ, Pastor RW, Lyman E. Hexagonal Substructure and Hydrogen Bonding in Liquid-Ordered Phases Containing Palmitoyl Sphingomyelin. Biophys J 2016; 109:948-55. [PMID: 26331252 DOI: 10.1016/j.bpj.2015.07.036] [Citation(s) in RCA: 100] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Revised: 07/11/2015] [Accepted: 07/14/2015] [Indexed: 10/23/2022] Open
Abstract
All-atom simulation data are presented for ternary mixtures of palmitoyl sphingomyelin (PSM), cholesterol, and either palmitoyl oleoyl phosphatidyl choline or dioleoyl phosphatidyl choline (DOPC). For comparison, data for a mixture of dipalmitoyl phosphatidyl choline (DPPC), cholesterol, and DOPC are also presented. Compositions corresponding to the liquid-ordered phase, the liquid-disordered phase, and coexistence of the two phases are simulated for each mixture. Within the liquid-ordered phase, cholesterol is preferentially solvated by DOPC if it is available, but if DOPC is replaced by POPC, cholesterol is preferentially solvated by PSM. In the DPPC mixtures, cholesterol interacts preferentially with the saturated chains via its smooth face, whereas in the PSM mixtures, cholesterol interacts preferentially with PSM via its rough face. Interactions between cholesterol and PSM have a very particular character: hydrogen bonding between cholesterol and the amide of PSM rotates the tilt of the amide plane, which primes it for more robust hydrogen bonding with other PSM. Cholesterol-PSM hydrogen bonding also locally modifies the hexagonal packing of hydrocarbon chains in the liquid-ordered phase of PSM mixtures.
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Affiliation(s)
- Alexander J Sodt
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Richard W Pastor
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Edward Lyman
- Department of Physics and Astronomy and Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware.
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6
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A DSC and FTIR spectroscopic study of the effects of the epimeric cholestan-3-ols and cholestan-3-one on the thermotropic phase behavior and organization of dipalmitoylphosphatidylcholine bilayer membranes: Comparison with their 5-cholesten analogs. Chem Phys Lipids 2015; 187:34-49. [DOI: 10.1016/j.chemphyslip.2015.02.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 02/06/2015] [Accepted: 02/07/2015] [Indexed: 11/23/2022]
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Beck Z, Matyas GR, Alving CR. Detection of liposomal cholesterol and monophosphoryl lipid A by QS-21 saponin and Limulus polyphemus amebocyte lysate. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:775-80. [DOI: 10.1016/j.bbamem.2014.12.005] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Revised: 11/26/2014] [Accepted: 12/05/2014] [Indexed: 11/16/2022]
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8
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Baoukina S, Tieleman DP. Computer simulations of phase separation in lipid bilayers and monolayers. Methods Mol Biol 2015; 1232:307-322. [PMID: 25331143 DOI: 10.1007/978-1-4939-1752-5_21] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Studying phase coexistence in lipid bilayers and monolayers is important for understanding lipid-lipid interactions underlying lateral organization in biological membranes. Computer simulations follow experimental approaches and use model lipid mixtures of simplified composition. Atomistic simulations give detailed information on the specificity of intermolecular interactions, while coarse-grained simulations achieve large time and length scales and provide a bridge towards state-of-the-art experimental techniques. Computer simulations allow characterizing the structure and composition of domains during phase transformations at Angstrom and picosecond resolution, and bring new insights into phase behavior of lipid membranes.
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Affiliation(s)
- Svetlana Baoukina
- Department of Biological Sciences, Centre for Molecular Simulation, University of Calgary, 2500 University Dr. NW, Calgary, AB, Canada, T2N 1N4,
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Robertson JD, Yealland G, Avila-Olias M, Chierico L, Bandmann O, Renshaw SA, Battaglia G. pH-sensitive tubular polymersomes: formation and applications in cellular delivery. ACS NANO 2014; 8:4650-61. [PMID: 24724711 DOI: 10.1021/nn5004088] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Optimizing the shape of a nanovector influences its interaction with a cell and determines the internalization kinetics. Block copolymer amphiphiles self-assemble into monodisperse structures in aqueous solutions and have been explored extensively as drug delivery vectors. However, the structure of self-assembled block copolymers has mainly been limited to spherical vesicles or spherical and worm-like micelles. Here we show the controlled formation and purification of tubular polymersomes, long cylindrical vesicles. Tubular polymersomes are purified from other structures, and their formation is manipulated by incorporating the biocompatible membrane components cholesterol and phospholipids. Finally we show that these tubular polymersomes have different cellular internalization kinetics compared with spherical polymersomes and can successfully encapsulate and deliver fluorescent bovine serum albumin protein intracellularly.
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Affiliation(s)
- James D Robertson
- Department of Chemistry, ‡The MRC/UCL Centre for Molecular and Medical Virology, University College London , London, United Kingdom
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10
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Sugár IP, Simon I, Chong PLG. Series of concentration-induced phase transitions in cholesterol/phosphatidylcholine mixtures. Biophys J 2014; 104:2448-55. [PMID: 23746517 DOI: 10.1016/j.bpj.2013.04.048] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 04/15/2013] [Accepted: 04/24/2013] [Indexed: 10/26/2022] Open
Abstract
In lipid membranes, temperature-induced transition from gel-to-fluid phase increases the lateral diffusion of the lipid molecules by three orders of magnitude. In cell membranes, a similar phase change may trigger the communication between the membrane components. Here concentration-induced phase transition properties of our recently developed statistical mechanical model of cholesterol/phospholipid mixtures are investigated. A slight (<1%) decrease in the model parameter values, controlling the lateral interaction energies, reveals the existence of a series of first- or second-order phase transitions. By weakening the lateral interactions first, the proportion of the ordered (i.e., superlattice) phase (Areg) is slightly and continuously decreasing at every cholesterol mole fraction. Then sudden decreases in Areg appear at the 0.18-0.26 range of cholesterol mole fractions. We point out that the sudden changes in Areg represent first- or second-order concentration-induced phase transitions from fluid to superlattice and from superlattice to fluid phase. Sudden changes like these were detected in our previous experiments at 0.2, 0.222, and 0.25 sterol mole fractions in ergosterol/DMPC mixtures. By further decreasing the lateral interactions, the fluid phase will dominate throughout the 0.18-0.26 interval, whereas outside this interval sudden increases in Areg may appear. Lipid composition-induced phase transitions as specified here should have far more important biological implications than temperature- or pressure-induced phase transitions. This is the case because temperature and pressure in cell membranes are largely invariant under physiological conditions.
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Affiliation(s)
- István P Sugár
- Department of Neurology and Center for Translational Systems Biology, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
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11
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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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12
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Rabinovich AL, Lyubartsev AP. Computer simulation of lipid membranes: Methodology and achievements. POLYMER SCIENCE SERIES C 2013. [DOI: 10.1134/s1811238213070060] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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13
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Baoukina S, Mendez-Villuendas E, Bennett WFD, Tieleman DP. Computer simulations of the phase separation in model membranes. Faraday Discuss 2013; 161:63-75; discussion 113-50. [DOI: 10.1039/c2fd20117h] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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14
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Venegas B, Zhu W, Haloupek NB, Lee J, Zellhart E, Sugár IP, Kiani MF, Chong PLG. Cholesterol superlattice modulates CA4P release from liposomes and CA4P cytotoxicity on mammary cancer cells. Biophys J 2012; 102:2086-94. [PMID: 22824272 DOI: 10.1016/j.bpj.2012.03.063] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Accepted: 03/22/2012] [Indexed: 01/08/2023] Open
Abstract
Liposomal drugs are a useful alternative to conventional drugs and hold great promise for targeted delivery in the treatment of many diseases. Most of the liposomal drugs on the market or under clinical trials include cholesterol as a membrane stabilizing agent. Here, we used liposomal CA4P, an antivascular drug, to demonstrate that cholesterol content can actually modulate the release and cytotoxicity of liposomal drugs in a delicate and predictable manner. We found that both the rate of the CA4P release from the interior aqueous compartment of the liposomes to the bulk aqueous phase and the extent of the drug's cytotoxicity undergo a biphasic variation, as large as 50%, with liposomal cholesterol content at the theoretically predicted C(r), e.g., 22.0, 22.2, 25.0, 33.3, 40.0, and 50.0 mol % cholesterol for maximal superlattice formation. It appears that at C(r), CA4P can be released from the liposomes more readily than at non-C(r), probably due to the increased domain boundaries between superlattice and nonsuperlattice regions, which consequently results in increased cytotoxicity. The idea that the increased domain boundaries at C(r) would facilitate the escape of molecules from membranes was further supported by the data of dehydroergosterol transfer from liposomes to MβCD. These results together show that the functional importance of sterol superlattice formation in liposomes can be propagated to distal targeted cells and reveal a new, to our knowledge, mechanism for how sterol content and membrane lateral organization can control the release of entrapped or embedded molecules in membranes.
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Affiliation(s)
- Berenice Venegas
- Department of Biochemistry, Temple University School of Medicine, Philadelphia, PA, USA
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15
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Cholesterol Organization in Phosphatidylcholine Liposomes: A Surface Plasmon Resonance Study. MATERIALS 2012. [PMCID: PMC5448994 DOI: 10.3390/ma5112306] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Models for the organization of sterols into regular arrays within phospholipid bilayers have been proposed previously. The existence of such arrays in real systems has been supported by the fact that concentration-dependent sterol properties show discontinuities at the cholesterol mole fractions corresponding to regular lattice arrangements. Experimental results presented here are based on a surface plasmon resonance assay that was used to analyze rates of cyclodextrin-mediated removal of cholesterol from adsorbed liposomes at cholesterol mole fractions up to χC = 0.55. Two kinetic pools of cholesterol were detected; there was a fast pool present at χC > 0.25, and a slow pool, with a removal rate that was dependent on the initial χC but that did not vary as χC decreased during the course of one experiment. The cholesterol activity therefore seems to be affected by sample history as well as local concentration, which could be explained in terms of the formation of superlattices that are stable for relatively long times. We also describe a variation on the traditional lattice models, with phosphatidylcholine (PC) being treated as an arrangement of hexagonal tiles; the cholesterol is then introduced at any vertex point, without increasing the total area occupied by all the lipid molecules. This model is consistent with Langmuir trough measurements of total lipid area and provides a simple explanation for the maximum solubility of cholesterol in the PC bilayer.
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Baoukina S, Mendez-Villuendas E, Tieleman DP. Molecular View of Phase Coexistence in Lipid Monolayers. J Am Chem Soc 2012; 134:17543-53. [DOI: 10.1021/ja304792p] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Svetlana Baoukina
- Department of Biological Sciences and Institute for Biocomplexity and Informatics, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada T2N 1N4
| | - Eduardo Mendez-Villuendas
- Department of Biological Sciences and Institute for Biocomplexity and Informatics, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada T2N 1N4
| | - D. Peter Tieleman
- Department of Biological Sciences and Institute for Biocomplexity and Informatics, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada T2N 1N4
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Large conductance, calcium- and voltage-gated potassium (BK) channels: regulation by cholesterol. Pharmacol Ther 2012; 135:133-50. [PMID: 22584144 DOI: 10.1016/j.pharmthera.2012.05.002] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Accepted: 04/09/2012] [Indexed: 11/21/2022]
Abstract
Cholesterol (CLR) is an essential component of eukaryotic plasma membranes. CLR regulates the membrane physical state, microdomain formation and the activity of membrane-spanning proteins, including ion channels. Large conductance, voltage- and Ca²⁺-gated K⁺ (BK) channels link membrane potential to cell Ca²⁺ homeostasis. Thus, they control many physiological processes and participate in pathophysiological mechanisms leading to human disease. Because plasmalemma BK channels cluster in CLR-rich membrane microdomains, a major driving force for studying BK channel-CLR interactions is determining how membrane CLR controls the BK current phenotype, including its pharmacology, channel sorting, distribution, and role in cell physiology. Since both BK channels and CLR tissue levels play a pathophysiological role in human disease, identifying functional and structural aspects of the CLR-BK channel interaction may open new avenues for therapeutic intervention. Here, we review the studies documenting membrane CLR-BK channel interactions, dissecting out the many factors that determine the final BK current response to changes in membrane CLR content. We also summarize work in reductionist systems where recombinant BK protein is studied in artificial lipid bilayers, which documents a direct inhibition of BK channel activity by CLR and builds a strong case for a direct interaction between CLR and the BK channel-forming protein. Bilayer lipid-mediated mechanisms in CLR action are also discussed. Finally, we review studies of BK channel function during hypercholesterolemia, and underscore the many consequences that the CLR-BK channel interaction brings to cell physiology and human disease.
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