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Melcrová A, Pokorna S, Vošahlíková M, Sýkora J, Svoboda P, Hof M, Cwiklik L, Jurkiewicz P. Concurrent Compression of Phospholipid Membranes by Calcium and Cholesterol. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:11358-11368. [PMID: 31393734 DOI: 10.1021/acs.langmuir.9b00477] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Regulation of cell metabolism, membrane fusion, association of proteins with cellular membranes, and cellular signaling altogether would not be possible without Ca2+ ions. The distribution of calcium within the cell is uneven with the negatively charged inner leaflet of the plasma membrane being one of the primary targets of its accumulation. Therefore, we decided to map the influence of Ca2+ on the properties of lipid bilayers closely resembling natural lipid membranes. We combined fluorescence spectroscopy (analysis of time-resolved emission spectra of Laurdan probe and derived parameters: integrated relaxation time related to local lipid mobility, and total emission shift reflecting membrane polarity and hydration) with molecular dynamics simulations to determine the effect of the increasing CaCl2 concentration on model lipid membranes containing POPC, POPS, and cholesterol. On top of that, the impact of calcium on the plasma membranes isolated from HEK293 cells was investigated using the steady-state fluorescence of Laurdan. We found that calcium increases rigidity of all the model lipid membranes used, elevates their thickness, increases lipid packing and ordering, and impedes the local lipid mobility. All these effects were to a great extent similar to those elicited by cholesterol. However, the changes of the membrane properties induced by calcium and cholesterol seem largely independent from each other. At sufficiently high concentrations of calcium or cholesterol, the steric effects hindered a further alteration of membrane organization, i.e., the compressibility limit of membrane structures was reached. We found no indication for mutual interaction between Ca2+ and cholesterol, nor competition of Ca2+ ions and hydroxyl groups of cholesterol for binding to phospholipids. Fluorescence measurements indicated that Ca2+ adsorption decreases mobility within the carbonyl region of model bilayers more efficiently than monovalent ions do (Ca2+ ≫ Li+ > Na+ > K+ > Cs+). The effects of calcium ions were to a great extent mitigated in the plasma membranes isolated from HEK293 cells when compared to the model lipid membranes. Noticeably, the plasma membranes showed remarkably higher resistance toward rigidification induced by calcium ions even when compared with the model membranes containing cholesterol.
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Affiliation(s)
- Adéla Melcrová
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , 182 23 Prague 8 , Czech Republic
| | - Sarka Pokorna
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , 182 23 Prague 8 , Czech Republic
| | - Miroslava Vošahlíková
- Institute of Physiology of the Czech Academy of Sciences , Vídeňská 1083 , 14220 Prague 4 , Czech Republic
| | - Jan Sýkora
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , 182 23 Prague 8 , Czech Republic
| | - Petr Svoboda
- Institute of Physiology of the Czech Academy of Sciences , Vídeňská 1083 , 14220 Prague 4 , Czech Republic
| | - Martin Hof
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , 182 23 Prague 8 , Czech Republic
| | - Lukasz Cwiklik
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , 182 23 Prague 8 , Czech Republic
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences , 166 10 Prague 6 , Czech Republic
| | - Piotr Jurkiewicz
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , 182 23 Prague 8 , Czech Republic
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Mendanha SA, dos Anjos JLV, Maione-Silva L, Silva HCB, Lima EM, Alonso A. An EPR spin probe study of the interactions between PC liposomes and stratum corneum membranes. Int J Pharm 2018; 545:93-100. [DOI: 10.1016/j.ijpharm.2018.04.057] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Revised: 04/23/2018] [Accepted: 04/25/2018] [Indexed: 10/17/2022]
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Kaur P, Li Y, Cai J, Song L. Selective Membrane Disruption Mechanism of an Antibacterial γ-AApeptide Defined by EPR Spectroscopy. Biophys J 2017; 110:1789-1799. [PMID: 27119639 DOI: 10.1016/j.bpj.2016.02.038] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 02/14/2016] [Accepted: 02/19/2016] [Indexed: 12/11/2022] Open
Abstract
γ-AApeptides are a new class of antibacterial peptidomimetics that are not prone to antibiotic resistance and are highly resistant to protease degradation. It is not clear how γ-AApeptides interact with bacterial membranes and alter lipid assembly, but such information is essential to understanding their antimicrobial activities and guiding future design of more potent and specific antimicrobial agents. Using electron paramagnetic resonance techniques, we characterized the membrane interaction and destabilizing mechanism of a lipo-cyclic-γ-AApeptide (AA1), which has broad-spectrum antibacterial activities. The analyses revealed that AA1 binding increases the membrane permeability of POPC/POPG liposomes, which mimic negatively charged bacterial membranes. AA1 binding also inhibits membrane fluidity and reduces solvent accessibility around the lipid headgroup region. Moreover, AA1 interacts strongly with POPC/POPG liposomes, inducing significant lipid lateral-ordering and membrane thinning. In contrast, minimal membrane property changes were observed upon AA1 binding for liposomes mimicking mammalian cell membranes, which consist of neutral lipids and cholesterol. Our findings suggest that AA1 interacts and disrupts bacterial membranes through a carpet-like mechanism. The results showed that the intrinsic features of γ-AApeptides are important for their ability to disrupt bacterial membranes selectively, the implications of which extend to developing new antibacterial biomaterials.
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Affiliation(s)
- Pavanjeet Kaur
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida
| | - Yaqiong Li
- Department of Chemistry, University of South Florida, Tampa, Florida
| | - Jianfeng Cai
- Department of Chemistry, University of South Florida, Tampa, Florida.
| | - Likai Song
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida.
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Wei M, Liu J, Xia Y, Feng F, Liu W, Zheng F. A polydiacetylene-based fluorescence assay for the measurement of lipid membrane affinity. RSC Adv 2015. [DOI: 10.1039/c5ra13445e] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Polydiacetylene (PDA) is a promising membrane-screening tool because lipid constituents can be incorporated into the PDA framework to form lipid/PDA vesicles used as lipid bilayers.
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Affiliation(s)
- Menglin Wei
- Department of Pharmaceutical Analysis
- China Pharmaceutical University
- Nanjing 210009
- China
| | - Jiajia Liu
- Department of Pharmaceutical Analysis
- China Pharmaceutical University
- Nanjing 210009
- China
| | - Yuanyuan Xia
- Department of Pharmaceutical Analysis
- China Pharmaceutical University
- Nanjing 210009
- China
| | - Feng Feng
- Key Laboratory of Biomedical Functional Materials
- China Pharmaceutical University
- Nanjing 211198
- China
| | - Wenyuan Liu
- Department of Pharmaceutical Analysis
- China Pharmaceutical University
- Nanjing 210009
- China
- Key Laboratory of Drug Quality Control and Pharmacovigilance
| | - Feng Zheng
- Department of Pharmaceutical Analysis
- China Pharmaceutical University
- Nanjing 210009
- China
- Key Laboratory of Drug Quality Control and Pharmacovigilance
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Urbančič I, Ljubetič A, Štrancar J. Resolving Internal Motional Correlations to Complete the Conformational Entropy Meter. J Phys Chem Lett 2014; 5:3593-3600. [PMID: 26278615 DOI: 10.1021/jz5020828] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Conformational entropy (SΩ) has long been used to theoretically characterize the dynamics of proteins, DNA, and other polymers. Though recent advances enabled its calculation also from simulations and nuclear magnetic resonance (NMR) relaxation experiments, correlated molecular motion has hitherto greatly hindered both numerical and experimental determination, requiring demanding empirical and computational calibrations. Herein, we show that these motional correlations can be estimated directly from the temperature-dependent SΩ series that reveal effective persistence lengths of the polymers, which we demonstrate by measuring SΩ of amphiphilic molecules in model lipid systems by spin-labeling electron paramagnetic resonance (EPR) spectroscopy. We validate our correlation-corrected SΩ meter against the basic biophysical interactions underlying biomembrane formation and stability, against the changes in enthalpy and diffusion coefficients upon phase transitions, and against the energetics of fatty acid dissociation. As the method can be directly applied to conformational analysis of proteins and other polymers, as well as adapted to NMR or polarized fluorescence techniques, we believe that the approach can greatly enrich the scope of experimentally available statistical thermodynamics, offering new physical insights into the behavior of biomolecules.
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Affiliation(s)
- Iztok Urbančič
- Laboratory of Biophysics, Condensed Matter Physics Department, "Jožef Stefan" Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia
| | - Ajasja Ljubetič
- Laboratory of Biophysics, Condensed Matter Physics Department, "Jožef Stefan" Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia
| | - Janez Štrancar
- Laboratory of Biophysics, Condensed Matter Physics Department, "Jožef Stefan" Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia
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Dzuba SA. Structural studies of biological membranes using ESEEM spectroscopy of spin labels and deuterium substitution. J STRUCT CHEM+ 2013. [DOI: 10.1134/s0022476613070019] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Ben-Dov N, Korenstein R. Proton-induced endocytosis is dependent on cell membrane fluidity, lipid-phase order and the membrane resting potential. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2672-81. [PMID: 23911577 DOI: 10.1016/j.bbamem.2013.07.027] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 07/20/2013] [Accepted: 07/22/2013] [Indexed: 01/13/2023]
Abstract
Recently it has been shown that decreasing the extracellular pH of cells stimulates the formation of inward membrane invaginations and vesicles, accompanied by an enhanced uptake of macromolecules. This type of endocytosis was coined as proton-induced uptake (PIU). Though the initial induction of inward membrane curvature was rationalized in terms of proton-based increase of charge asymmetry across the membrane, the dependence of the phenomenon on plasma membrane characteristics is still unknown. The present study shows that depolarization of the membrane resting potential elevates PIU by 25%, while hyperpolarization attenuates it by 25%. Comparison of uptake in suspended and adherent cells implicates that the resting-potential affects PIU through remodeling the actin-cytoskeleton. The pH at the external interface of the cell membrane rather than the pH gradient across it determines the extent of PIU. PIU increases linearly upon temperature increase in the range of 4-36°C, in correlation with the membrane fluidity. The plasma membrane fluidity and the lipid phase order are modulated by enriching the cell's membrane with cholesterol, tergitol, dimethylsulfoxide, 6-ketocholestanol and phloretin and by cholesterol depletion. These treatments are shown to alter the extent of PIU and are better correlated with membrane fluidity than with the lipid phase order. We suggest that the lipid phase order and fluidity influence PIU by regulating the lipid order gradient across the perimeter of the lipid-condensed microdomains (rafts) and alter the characteristic tension line that separates the higher ordered lipid-domains from the lesser ordered ones.
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Affiliation(s)
- Nadav Ben-Dov
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, 69978 Tel-Aviv, Israel.
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Follain N, Marais MF, Montanari S, Vignon MR. Coupling onto surface carboxylated cellulose nanocrystals. POLYMER 2010. [DOI: 10.1016/j.polymer.2010.09.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Isaev NP, Syryamina VN, Dzuba SA. Small-Angle Orientational Motions of Spin-Labeled Lipids in Cholesterol-Containing Bilayers Studied at Low Temperatures by Electron Spin Echo Spectroscopy. J Phys Chem B 2010; 114:9510-5. [DOI: 10.1021/jp1043927] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Nikolay P. Isaev
- Institute of Chemical Kinetics and Combustion, Institutskaya-3, 630090 Novosibirsk, Russia, and, Novosibirsk State University, 630090, Pirogova-2, Novosibirsk, Russia
| | - Victoria N. Syryamina
- Institute of Chemical Kinetics and Combustion, Institutskaya-3, 630090 Novosibirsk, Russia, and, Novosibirsk State University, 630090, Pirogova-2, Novosibirsk, Russia
| | - Sergei A. Dzuba
- Institute of Chemical Kinetics and Combustion, Institutskaya-3, 630090 Novosibirsk, Russia, and, Novosibirsk State University, 630090, Pirogova-2, Novosibirsk, Russia
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Ghimire H, Inbaraj JJ, Lorigan GA. A comparative study of the effect of cholesterol on bicelle model membranes using X-band and Q-band EPR spectroscopy. Chem Phys Lipids 2009; 160:98-104. [PMID: 19501076 PMCID: PMC2719848 DOI: 10.1016/j.chemphyslip.2009.05.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Revised: 05/21/2009] [Accepted: 05/22/2009] [Indexed: 11/16/2022]
Abstract
X-band and Q-band electron paramagnetic resonance (EPR) spectroscopic techniques were used to investigate the structure and dynamics of cholesterol containing phospholipid bicelles based upon molecular order parameters (S(mol)), orientational dependent hyperfine splittings and line shape analysis of the corresponding EPR spectra. The nitroxide spin-label 3-beta-doxyl-5-alpha-cholestane (cholestane) was incorporated into DMPC/DHPC bicelles to report the alignment of bicelles in the static magnetic field. The influence of cholesterol on aligned phospholipid bicelles in terms of ordering, the ease of alignment, phase transition temperature have been studied comparatively at X-band and Q-band. At a magnetic field of 1.25 T (Q-band), bicelles with 20 mol% cholesterol aligned at a much lower temperature (313 K), when compared to 318 K at a 0.35 T field strength for X-band, showed better hyperfine splitting values (18.29 G at X-band vs. 18.55 G at Q-band for perpendicular alignment and 8.25 G at X-band vs. 7.83 G at Q-band for the parallel alignment at 318 K) and have greater molecular order parameters (0.76 at X-band vs. 0.86 at Q-band at 318 K). Increasing cholesterol content increased the bicelle ordering, the bicelle-alignment temperature and the gel to liquid crystalline phase transition temperature. We observed that Q-band is more effective than X-band for studying aligned bicelles, because it yielded a higher ordered bicelle system for EPR spectroscopic studies.
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Affiliation(s)
| | - Johnson J. Inbaraj
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH, 45056,
| | - Gary A. Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH, 45056,
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McCrae KC, Weltman B, Alyward S, Shaw RA, Sowa MG, Unruh HW, Rand TG, Thliveris JA, Scott JE. The effect of elevated dietary cholesterol on pulmonary surfactant function in adolescent mice. Pediatr Pulmonol 2008; 43:426-34. [PMID: 18366117 DOI: 10.1002/ppul.20772] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
It has been established that phospholipids and cholesterol interact in films of pulmonary surfactant (PS). Generally it is thought that phospholipids increase film stability whereas cholesterol increases film fluidity. To study this further, we modified dietary cholesterol in mice which received either standard rodent lacking cholesterol (sd), or high cholesterol (2%) diet (hc) for 1 month. Phospholipid stability was investigated by a capillary surfactometer (CS), which measures airflow resistance and patency. PS was collected by bronchiolar lavage and centrifuged to obtain the surface-active film (SAF). Results showed that the hc-SAF had significantly more cholesterol than sd-SAF. CS analyses at 37 degrees C showed no significance differences in airflow resistance between hc-SAF and sd-SAF. However, at 37 degrees C, sd-SAF showed greater ability to maintain patency compared to hc-SAF, whereas at 42 degrees C hc-SAF showed patency ability similar to sd-SAF. The results suggested that increased cholesterol in hc-SAF induced less stability in the SAF possibly due to cholesterol's fluidizing effect on phospholipids at physiological temperatures.
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Affiliation(s)
- K C McCrae
- Department of Oral Biology, Faculties of Dentistry and Medicine, University of Manitoba, Winnipeg, Manitoba, Canada
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Leermakers FAM, Rabinovich AL. Interaction of cholesterol-like molecules in polyunsaturated phosphatidylcholine lipid bilayers as revealed by a self-consistent field theory. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 76:031904. [PMID: 17930268 DOI: 10.1103/physreve.76.031904] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2007] [Revised: 07/31/2007] [Indexed: 05/25/2023]
Abstract
Cholesterol is one of the most abundant components in biological membranes. In this paper we apply a detailed state-of-the-art self-consistent field (SCF) theory to predict the influence of cholesterol-look-alikes in the bilayer composed of 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphatidylcholine (18:022:6omega3cis PC) lipids with a polyunsaturated 22:6 and a fully saturated 18:0 tail. The cholesterol-like molecule is composed of a hydroxyl group, a rigid chain fragment with length n segments and a branched semiflexible moiety with methylene side groups. We vary both the length of the rigid fragment in the cholesterol-look-alikes and their mole fraction in the tensionless bilayers. We find that these additives significantly increase the order of the saturated tails, but influence the conformational properties of the unsaturated tail much less. With increasing loading the bilayer thickness and the area available per PC head group increase. The hydroxyl group anchors close to the membrane-water interface, but with increasing loading the distribution of this polar group widens. The orientational order of the rigid part is high and we conclude that the cholesterol has significant mobility in the normal direction in the hydrophobic region of the bilayer indicating that one singly hydroxyl group is giving only a weak anchoring to the water-interface. Cholesterol-look-alikes increase the fluctuation of the tail ends and decrease the interdigitation of the tails. Several of our predictions correspond to molecular dynamics (MD) simulation results, but there are also important differences. Most notably the cholesterol-look-alikes can visit the membrane symmetry-plane more easily in SCF than in MD. Possible reasons for this are discussed.
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Affiliation(s)
- F A M Leermakers
- Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, the Netherlands
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Thomae AV, Koch T, Panse C, Wunderli-Allenspach H, Krämer SD. Comparing the lipid membrane affinity and permeation of drug-like acids: the intriguing effects of cholesterol and charged lipids. Pharm Res 2007; 24:1457-72. [PMID: 17387599 DOI: 10.1007/s11095-007-9263-y] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2006] [Accepted: 02/06/2007] [Indexed: 10/23/2022]
Abstract
PURPOSE Lipid bilayers regulate the passage of solutes into and between cellular compartments. A general prerequisite for this passage is the partitioning of the solute into the bilayer. We investigated the relationship between bilayer partitioning and permeation of three drug-like acids in liposomal systems consisting of phosphatidylcholine alone or mixed with cholesterol or charged lipids. MATERIALS AND METHODS Bilayer partitioning was determined by equilibrium dialysis. Bilayer permeation was studied with a luminescence assay which is based on the energy transfer of the permeant to intraliposomal terbium(III). RESULTS The influence of the lipid composition on the pH-dependent membrane affinity was in accordance with the membrane rigidity and possible electrostatic interactions between the acids and the lipids. However, there was no direct relationship between membrane affinity and permeation. This seeming discrepancy was closer analyzed with numerical simulations of the permeation process based on the single rate constants for partitioning and translocation. The simulations were in line with our experimental findings. CONCLUSIONS Depending on the single rate constants and on the geometry of the system, lipid bilayer permeation may positively, negatively or not correlate with the bilayer affinity of the permeant.
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Affiliation(s)
- Anita V Thomae
- Institute of Pharmaceutical Sciences, Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland
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Subczynski WK, Wisniewska A, Hyde JS, Kusumi A. Three-dimensional dynamic structure of the liquid-ordered domain in lipid membranes as examined by pulse-EPR oxygen probing. Biophys J 2006; 92:1573-84. [PMID: 17142270 PMCID: PMC1796815 DOI: 10.1529/biophysj.106.097568] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Membranes made of dimyristoylphosphatidylcholine and cholesterol, one of the simplest paradigms for the study of liquid ordered-disordered phase separation, were investigated using a pulse-EPR spin-labeling method in which bimolecular collision of molecular oxygen with the nitroxide spin label is measured. This method allowed discrimination of liquid-ordered, liquid-disordered, and solid-ordered domains because the collision rates (OTP) differ in these domains. Furthermore, the oxygen transport parameter (OTP) profile across the bilayer provides unique information about the three-dimensional dynamic organization of the membrane domains. First, the OTP in the bilayer center in the liquid-ordered domain was comparable to that in the liquid-disordered domain without cholesterol, but the OTP near the membrane surface (up to carbon 9) was substantially smaller in the ordered domain, i.e., the cholesterol-based liquid-ordered domain is ordered only near the membrane surface, still retaining high levels of disorder in the bilayer center. This property may facilitate lateral mobility in ordered domains. Second, in the liquid-disordered domain, the domains with approximately 5 mol % cholesterol exhibited higher OTP than those without cholesterol, everywhere across the membrane. Third, the transmembrane OTP profile in the liquid-ordered domain that contained 50 mol % cholesterol dramatically differed from that which contained 27 mol % cholesterol.
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Affiliation(s)
- Witold K Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
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Livshits VA, Kurad D, Marsh D. Multifrequency simulations of the EPR spectra of lipid spin labels in membranes. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2006; 180:63-71. [PMID: 16448829 DOI: 10.1016/j.jmr.2006.01.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Revised: 01/10/2006] [Accepted: 01/11/2006] [Indexed: 05/06/2023]
Abstract
Simulations are performed of 34- and 9-GHz EPR spectra, together with 94-GHz EPR spectra, from phospholipid probes spin-labelled at the C4-C14 positions of the sn-2 chain, in liquid-ordered and gel-phase membranes of dimyristoyl phosphatidylcholine with high and low cholesterol contents. The multifrequency simulation strategy involves: (i) obtaining partially averaged spin-Hamiltonian tensors from fast-motional simulations of the 94-GHz spectra; (ii) performing slow-motional simulations of the 34- and 9-GHz spectra by using these pre-averaged tensors with the stochastic Liouville formalism; (iii) constructing, by simulation, slow-motional calibrations for the differences, DeltaA(zz)(qx) and Deltag(zz)(qx), in effective A(zz)-hyperfine splittings and g(zz)-values between 34- (or 94-GHz) and 9-GHz spectra; (iv) using such calibrations for DeltaA(zz)(qx) and Deltag(zz)(qx) and dynamic parameters from stage (ii) as a guide to adjust the extent of pre-averaging of the spin-Hamiltonian tensors; and (v) repeating the 34- and 9-GHz simulations of stage (ii). By using this scheme it is possible to obtain consistent values of the rotational diffusion coefficients, D(R perpendicular) and D(R//), and the long-axis order parameter, S(zz), that characterize the slow axial motion of the lipid chains, from spectra at both 34 and 9GHz. Inclusion of spectra at 34GHz greatly improves precision in determining the D(R//) element of the slow diffusion tensor in these systems.
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Affiliation(s)
- V A Livshits
- Max-Planck-Institut für biophysikalische Chemie, Abt. Spektroskopie, 37077 Göttingen, Germany
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Marsh D, Kurad D, Livshits VA. High-field spin-label EPR of lipid membranes. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2005; 43 Spec no.:S20-5. [PMID: 16235222 DOI: 10.1002/mrc.1680] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
High-field EPR of spin-labelled lipid chains has proved to be an extremely productive means for biophysical investigations of phospholipid bilayer membranes. Results on the following three topics are reviewed: 1. Non-axial ordering of lipid chains in cholesterol-containing membranes; 2. Transmembrane polarity profiles and water penetration in lipid membranes; 3. Role of HF-EPR in multi-frequency spectral simulations to investigate lipid-chain dynamics in membranes. These results are obtained from phosphatidylcholine spin probes with the nitroxide systematically stepped down the sn-2 chain, in fully hydrated bilayer membranes of dimyristoyl phosphatidylcholine (DMPC)-containing cholesterol.
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Affiliation(s)
- Derek Marsh
- Max-Planck Institut für biophysikalische Chemie, 37070 Göttingen, Germany.
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Subczynski WK, Felix CC, Klug CS, Hyde JS. Concentration by centrifugation for gas exchange EPR oximetry measurements with loop-gap resonators. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2005; 176:244-8. [PMID: 16040261 DOI: 10.1016/j.jmr.2005.06.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2005] [Revised: 05/31/2005] [Accepted: 06/13/2005] [Indexed: 05/03/2023]
Abstract
Measurement of the bimolecular collision rate between a spin label and oxygen is conveniently carried out using a gas permeable plastic sample tube of small diameter that fits a loop-gap resonator. It is often desirable to concentrate the sample by centrifugation in order to improve the signal-to-noise ratio (SNR), but the deformable nature of small plastic sample tubes presents technical problems. Solutions to these problems are described. Two geometries were considered: (i) a methylpentene polymer, TPX, from Mitsui Chemicals, at X-band and (ii) Teflon tubing with 0.075 mm wall thickness at Q-band. Sample holders were fabricated from Delrin that fit the Eppendorf microcentrifuge tubes and support the sample capillaries. For TPX, pressure of the sealant at the end of the sample tube against the Delrin sample holder provided an adequate seal. For Teflon, the holder permitted introduction of water around the tube in order to equalize pressures across the sealant during centrifugation. Typically, the SNR was improved by a factor of five to eight. Oxygen accessibility applications in site-directed spin labeling studies are discussed.
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Affiliation(s)
- Witold K Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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Dave PC, Nusair NA, Inbaraj JJ, Lorigan GA. Electron paramagnetic resonance studies of magnetically aligned phospholipid bilayers utilizing a phospholipid spin label: The effect of cholesterol. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1714:141-51. [PMID: 16061199 DOI: 10.1016/j.bbamem.2005.06.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2005] [Revised: 06/21/2005] [Accepted: 06/21/2005] [Indexed: 11/16/2022]
Abstract
X-band EPR spectroscopy has been employed to study the dynamic properties of magnetically aligned phospholipid bilayers (bicelles) utilizing a variety of phosphocholine spin labels (n-PCSL) as a function of cholesterol content. The utilization of both perpendicular and parallel aligned bicelles in EPR spectroscopy provides a more detailed structural and orientational picture of the phospholipid bilayers. The magnetically aligned EPR spectra of the bicelles and the hyperfine splitting values reveal that the addition of cholesterol increases the phase transition temperature and alignment temperature of the DMPC/DHPC bicelles. The corresponding molecular order parameter, Smol, of the DMPC/DHPC bicelles increased upon addition of cholesterol. Cholesterol also decreased the rotational motion and increased the degree of anisotropy in the interior region of the bicelles. This report reveals that the dynamic properties of DMPC/DHPC bicelles agree well with other model membrane systems and that the magnetically aligned bicelles are an excellent model membrane system.
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Affiliation(s)
- Paresh C Dave
- Department of Chemistry and Biochemistry, Miami University, Oxford OH 45056, USA
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Chachaty C, Rainteau D, Tessier C, Quinn PJ, Wolf C. Building up of the liquid-ordered phase formed by sphingomyelin and cholesterol. Biophys J 2005; 88:4032-44. [PMID: 15764672 PMCID: PMC1305634 DOI: 10.1529/biophysj.104.054155] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The long-range and molecular orders and dynamics in codispersions of egg sphingomyelin-cholesterol have been investigated by synchrotron x-ray diffraction and electron spin resonance using phosphatidylcholine spin-labeled at several positions on the sn-2 chain. Mixtures containing 0, 17, 33, 41, 50 mol% cholesterol exhibited a single phase by x-ray diffraction methods. The temperature dependence of the d-spacing between 20 and 50 degrees C is attenuated with increasing proportions of cholesterol, becoming invariant for cholesterol contents of 41 and 50 mol% on completion of the liquid-ordered phase. Electron spin resonance revealed two sites for 17 and 33 mol% cholesterol. One site is highly ordered and the other is less ordered than the fluid phase of pure sphingomyelin as shown by the molecular and the intramolecular order parameters reflecting the segmental motions of the probe. The two-sites exchange rate indicates a mean lifetime of the sites of approximately 0.1 micros during which the lipid displacement is approximately 1 nm. The short lifetime of the sites probed by ESR and the single phase detected by x-ray diffraction support in this binary mixture, the building up of the Lo phase by a progressive accumulation of randomly distributed sphingomyelin-cholesterol condensed complexes rather than by diffusional exchange between extended domains.
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Affiliation(s)
- C Chachaty
- Universite Paris 6, INSERM U538, Paris, France
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Nusair NA, Lorigan GA. Investigating the structural and dynamic properties of n-doxylstearic acid in magnetically-aligned phospholipid bilayers by X-band EPR spectroscopy. Chem Phys Lipids 2005; 133:151-64. [PMID: 15642584 DOI: 10.1016/j.chemphyslip.2004.09.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Revised: 09/28/2004] [Accepted: 09/28/2004] [Indexed: 11/20/2022]
Abstract
X-band electron paramagnetic resonance (EPR) spectroscopy has been employed to investigate the dynamic properties of magnetically-aligned phospholipid bilayers (bicelles) based on the molecular order parameters (S(mol)), the hyperfine splitting values and the line shapes of the EPR spectra. For the first time, a series of EPR spectra of n-doxylstearic acid spin-labels (n = 5, 7, 12, and 16) incorporated into Tm3+-doped parallel-aligned, Dy3+-doped perpendicular-aligned, and randomly dispersed 1,2-dimyristoyl-sn-glycero-3-phosphocholine/1,2-dihexanoyl-sn-glycero-3-phosphocholine (DMPC/DHPC) bicelles with respect to the direction of the static magnetic field have been investigated as a function of cholesterol content and temperature variation to characterize the orientational aspects along the hydrocarbon acyl chains. Important general observations are that under conditions for which the bicelle is poised in the liquid crystalline phase, the degree of ordering decreases as the nitroxide moiety is transferred toward the end of the stearic acid acyl chains. The addition of cholesterol increases the phase transition temperature and alignment temperature of the DMPC/DHPC phospholipid bilayers and increases the chain order. However, increasing the temperature of the bicelle system decreases the chain order. This report reveals that the dynamic properties of DMPC/DHPC bicelles agree well with other biological and model membrane systems. The results indicate that magnetically-aligned phospholipid bilayers are an excellent model membrane system.
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Affiliation(s)
- Nisreen A Nusair
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
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22
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Livshits VA, Kurad D, Marsh D. Simulation Studies on High-Field EPR Spectra of Lipid Spin Labels in Cholesterol-Containing Membranes. J Phys Chem B 2004. [DOI: 10.1021/jp035915p] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Vsevolod A. Livshits
- Max-Planck-Institut für biophysikalische Chemie, Abteilung Spektroskopie, 37077 Göttingen, Germany, and Centre of Photochemistry, Russian Academy of Sciences, 117427 Moscow, Russian Federation
| | - Dieter Kurad
- Max-Planck-Institut für biophysikalische Chemie, Abteilung Spektroskopie, 37077 Göttingen, Germany, and Centre of Photochemistry, Russian Academy of Sciences, 117427 Moscow, Russian Federation
| | - Derek Marsh
- Max-Planck-Institut für biophysikalische Chemie, Abteilung Spektroskopie, 37077 Göttingen, Germany, and Centre of Photochemistry, Russian Academy of Sciences, 117427 Moscow, Russian Federation
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