FRINK Linked Data Fragments server

Matches in SemOpenAlex for { <https://semopenalex.org/work/W1973918451> ?p ?o ?g. }

• W1973918451 endingPage "11184" @default.
• W1973918451 startingPage "11175" @default.
• W1973918451 abstract "Plasmon-waveguide resonance (PWR) spectroscopy has been used to examine solid-supported lipid bilayers consisting of dioleoylphosphatidylcholine (DOPC), palmitoyloleoylphosphatidylcholine (POPC), sphingomyelin (SM), and phosphatidylcholine/SM binary mixtures. Spectral simulation of the resonance curves demonstrated an increase in bilayer thickness, long-range order, and molecular packing density in going from DOPC to POPC to SM single component bilayers, as expected based on the decreasing level of unsaturation in the fatty acyl chains. DOPC/SM and POPC/SM binary mixtures yielded PWR spectra that can be ascribed to a superposition of two resonances corresponding to microdomains (rafts) consisting of phosphatidylcholine- and SM-rich phases coexisting within a single bilayer. These were formed spontaneously over time as a consequence of lateral phase separation. Each microdomain contained a small proportion (<20%) of the other lipid component, which increased their kinetic and thermodynamic stability. Incorporation of a glycosylphosphatidylinositol-linked protein (placental alkaline phosphatase) occurred within each of the single component bilayers, although the insertion was less efficient into the DOPC bilayer. Incorporation of placental alkaline phosphatase into a DOPC/SM binary bilayer occurred with preferential insertion into the SM-rich phase, although the protein incorporated into both phases at higher concentrations. These results demonstrate the utility of PWR spectroscopy to provide insights into raft formation and protein sorting in model lipid membranes. Plasmon-waveguide resonance (PWR) spectroscopy has been used to examine solid-supported lipid bilayers consisting of dioleoylphosphatidylcholine (DOPC), palmitoyloleoylphosphatidylcholine (POPC), sphingomyelin (SM), and phosphatidylcholine/SM binary mixtures. Spectral simulation of the resonance curves demonstrated an increase in bilayer thickness, long-range order, and molecular packing density in going from DOPC to POPC to SM single component bilayers, as expected based on the decreasing level of unsaturation in the fatty acyl chains. DOPC/SM and POPC/SM binary mixtures yielded PWR spectra that can be ascribed to a superposition of two resonances corresponding to microdomains (rafts) consisting of phosphatidylcholine- and SM-rich phases coexisting within a single bilayer. These were formed spontaneously over time as a consequence of lateral phase separation. Each microdomain contained a small proportion (<20%) of the other lipid component, which increased their kinetic and thermodynamic stability. Incorporation of a glycosylphosphatidylinositol-linked protein (placental alkaline phosphatase) occurred within each of the single component bilayers, although the insertion was less efficient into the DOPC bilayer. Incorporation of placental alkaline phosphatase into a DOPC/SM binary bilayer occurred with preferential insertion into the SM-rich phase, although the protein incorporated into both phases at higher concentrations. These results demonstrate the utility of PWR spectroscopy to provide insights into raft formation and protein sorting in model lipid membranes. The classical textbook model of biomembrane structure, usually referred to as the fluid-mosaic model, envisions a two-dimensional solution of integral membrane proteins in a homogeneous lipid solvent, albeit one composed of many molecular lipid species and possessing inside-outside asymmetry with respect to both protein and lipid components. However, in recent years, there has been a growing recognition that lateral segregation of lipids and proteins occurs within regions of biomembranes called rafts (cf. Refs. 1Simons K. Ikonen E. Nature. 1997; 387: 569-572Crossref PubMed Scopus (8015) Google Scholar and 2Simons K. Vaz W.L.C. Annu. Rev. Biophys. Biomol. Struct. 2004; 33 (W. L. C.): 269-295Crossref PubMed Scopus (1341) Google Scholar). Along with caveolae, which are invaginations of raft regions stabilized by interactions with oligomers of the protein caveolin, these microdomains have been suggested to play important roles in cell polarity, protein sorting, signal transduction, and membrane trafficking (cf. Refs. 3Chini B. Parenti M. J. Mol. Endrocrinol. 2004; 32: 325-338Crossref PubMed Scopus (305) Google Scholar and 4Ostrom R.S. Insel P.A. Br. J. Pharmacol. 2004; 145: 235-245Crossref Scopus (322) Google Scholar).One of the key properties of rafts is their high content of sphingomyelin (SM) 1The abbreviations used are: SM, sphingomyelin; PC, phosphatidylcholine; GPI, glycosylphosphatidylinositol; DOPC, dioleoylphosphatidylcholine; POPC, palmitoyloleoylphosphatidylcholine; PWR, plasmon-waveguide resonance; PLAP, placental alkaline phosphatase; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid.1The abbreviations used are: SM, sphingomyelin; PC, phosphatidylcholine; GPI, glycosylphosphatidylinositol; DOPC, dioleoylphosphatidylcholine; POPC, palmitoyloleoylphosphatidylcholine; PWR, plasmon-waveguide resonance; PLAP, placental alkaline phosphatase; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid. and cholesterol, which leads to their being organized into what are referred to as liquid-ordered domains. These are characterized by being more highly ordered and somewhat thicker than the surrounding liquid-disordered regions of the membrane. This is a consequence of the ordering influence of cholesterol and the presence in SM of a larger proportion of saturated fatty acyl chains. However, it should be noted that studies of model membranes have shown that microdomain formation also occurs in phosphatidylcholine (PC)/SM mixtures in the absence of cholesterol (2Simons K. Vaz W.L.C. Annu. Rev. Biophys. Biomol. Struct. 2004; 33 (W. L. C.): 269-295Crossref PubMed Scopus (1341) Google Scholar). These lipid phases can coexist within a single bilayer, giving rise to a heterogeneous pattern of islands of differing composition. Protein enrichment in raft/caveola microdomains (cf. Refs. 4Ostrom R.S. Insel P.A. Br. J. Pharmacol. 2004; 145: 235-245Crossref Scopus (322) Google Scholar and 5Pike L.J. Biochem. J. 2004; 378: 281-292Crossref PubMed Scopus (612) Google Scholar) is thought to be a consequence of selective interactions between the liquid-ordered microdomains and various types of membrane anchors, such as glycosylphosphatidylinositol (GPI) moieties bound to the C terminus or fatty acyl chains attached to serine residues, as well as interactions occurring between proteins and caveolin oligomers or via hydrophobic matching to the slightly thicker rafts in the case of transmembrane proteins. Such enrichment can have two consequences, i.e. co-localization of various signaling components (e.g. receptors and G-proteins) and microenvironmental effects on protein functional properties, both of which have important pharmacological implications (cf. Refs. 3Chini B. Parenti M. J. Mol. Endrocrinol. 2004; 32: 325-338Crossref PubMed Scopus (305) Google Scholar and 4Ostrom R.S. Insel P.A. Br. J. Pharmacol. 2004; 145: 235-245Crossref Scopus (322) Google Scholar). Examples of the former include the translocation of transducin to lipid rafts upon activation by rhodopsin (6Nair K.S. Balasubramanian N. Slepak V.Z. Curr. Biol. 2002; 12: 421-425Abstract Full Text Full Text PDF PubMed Scopus (100) Google Scholar) and the movement of the β2-adrenergic receptor out of rafts upon agonist binding (7Rybin V.O. Xu X. Lisanti M.P. Steinberg S.F. J. Biol. Chem. 2000; 275: 41447-41457Abstract Full Text Full Text PDF PubMed Scopus (463) Google Scholar, 8Xiang Y. Rybin V.O. Steinberg S.F. Kobilka B. J. Biol. Chem. 2002; 277: 34280-34286Abstract Full Text Full Text PDF PubMed Scopus (200) Google Scholar); examples of the latter include an increased affinity of agonist for the human oxytocin receptor (9Gimpl G. Burger K. Politowska E. Ciarkowski J. Farenholz F. Exp. Physiol. 2000; 85: 41S-49SCrossref PubMed Scopus (41) Google Scholar, 10Guzzi F. Zanchetta D. Cassoni P. Guzzi V. Francolini M. Parenti M. Chini B. Oncogene. 2002; 21: 1658-1667Crossref PubMed Scopus (86) Google Scholar) and for the Drosophila metabotropic glutamate receptor (11Eroglu C. Brugger B. Wieland F. Sinning I. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 10219-10224Crossref PubMed Scopus (87) Google Scholar) by raft localization.Model membrane studies have shown that lipid-lipid interactions are sufficient to induce the formation of raft-like domains (12Dietrich C. Bagatolli L.A. Volvyk Z.N. Thompson N.L. Levi M. Jacobson K. Gratton E. Biophys. J. 2001; 80: 1417-1428Abstract Full Text Full Text PDF PubMed Scopus (1186) Google Scholar, 13Saslowsky D.E. Lawrence J. Ren X. Brown D.A. Henderson R.M. Edwardson J.M. J. Biol. Chem. 2002; 277: 26966-26970Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar). It is well established that phase separation can occur in binary lipid mixtures consisting of lipids that have different phase transition temperatures. Typically, a gel phase, which is characterized by tightly packed lipids that have limited mobility, coexists with a fluid or liquid-disordered phase in which the lipids are loosely packed and have a high degree of lateral mobility. Addition of cholesterol has been reported to modify the gel phase component of such systems, resulting in the formation of a liquid-ordered phase in which the lipids are still tightly packed, but acquire a relatively high degree of lateral movement (14Sankaram M.B. Thompson T.E. Biochemistry. 1990; 29: 10670-10675Crossref PubMed Scopus (293) Google Scholar, 15Crane J.M. Tamm L.K. Biophys. J. 2004; 86: 2965-2979Abstract Full Text Full Text PDF PubMed Scopus (246) Google Scholar). Currently, however, the requirement for cholesterol in raft formation in biological membranes is unclear (13Saslowsky D.E. Lawrence J. Ren X. Brown D.A. Henderson R.M. Edwardson J.M. J. Biol. Chem. 2002; 277: 26966-26970Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 16Lawrence J.C. Saslowsky D.E. Edwardson J.M. Henderson R.M. Biophys. J. 2003; 84: 1827-1832Abstract Full Text Full Text PDF PubMed Scopus (200) Google Scholar, 17Milhiet P.-E. Giocondi M.-C. Baghdadi O. Ronzon F. Roux B. Le Grimelec C. EMBO Rep. 2002; 3: 485-490Crossref PubMed Scopus (130) Google Scholar).To investigate lipid raft characteristics in model membranes, SM is commonly combined with phospholipids having unsaturated and therefore kinked fatty acyl chains, such as dioleoylphosphatidylcholine (DOPC), with or without cholesterol. As noted above, SM lipids typically have long saturated acyl chains that facilitate close packing, an important feature of lipid raft organization (18Brown D.A. London E. J. Biol. Chem. 2000; 275: 17221-17224Abstract Full Text Full Text PDF PubMed Scopus (2043) Google Scholar). For this reason, SM-enriched domains in a bilayer are thicker than areas enriched in more fluid, unsaturated lipids, which have kinked chains that effectively shorten the molecular length. These structural differences between diverse types of membranes create significant modifications in their mechanical properties that in turn can lead to segregation of transmembrane proteins (19McIntosh T.J. Vidal A. Simon S.A. Biophys. J. 2003; 85: 1656-1666Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar, 20Simons K. Toomre D. Nat. Rev. Mol. Cell. Biol. 2000; 1: 31-39Crossref PubMed Scopus (5107) Google Scholar). Atomic force microscopy experiments (21Giocondi M.-C. Boichot S. Plenat T. Le Grimellec C. Ultramicroscopy. 2004; 100: 135-143Crossref PubMed Scopus (37) Google Scholar) have revealed the existence of a marked structural diversity of gel phase SM-enriched microdomains, which can adopt mesoscopic structures of varied sizes and shapes, for both single mixtures as well as different PC species (e.g. DOPC and palmitoyloleoylphosphatidylcholine (POPC)).A number of biochemical and biophysical methodologies have been used to investigate microdomain systems in both whole cells and model membranes, such as low temperature extraction with nonionic detergents; effects of cholesterol depletion; and various forms of visualization, including electron, atomic force, and fluorescence microscopies. All of these methods have potential problems (5Pike L.J. Biochem. J. 2004; 378: 281-292Crossref PubMed Scopus (612) Google Scholar); and thus, despite a great deal of effort in recent years, there is no consensus yet on the size, lifetime, composition, or even existence of rafts in the plasma membrane of living cells (cf. Refs. 2Simons K. Vaz W.L.C. Annu. Rev. Biophys. Biomol. Struct. 2004; 33 (W. L. C.): 269-295Crossref PubMed Scopus (1341) Google Scholar and 22Munro S. Cell. 2003; 115: 377-388Abstract Full Text Full Text PDF PubMed Scopus (1318) Google Scholar). As might be expected, the most definitive studies have been done with model membranes (cf. Ref. 2Simons K. Vaz W.L.C. Annu. Rev. Biophys. Biomol. Struct. 2004; 33 (W. L. C.): 269-295Crossref PubMed Scopus (1341) Google Scholar), with atomic force microscopy (13Saslowsky D.E. Lawrence J. Ren X. Brown D.A. Henderson R.M. Edwardson J.M. J. Biol. Chem. 2002; 277: 26966-26970Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 17Milhiet P.-E. Giocondi M.-C. Baghdadi O. Ronzon F. Roux B. Le Grimelec C. EMBO Rep. 2002; 3: 485-490Crossref PubMed Scopus (130) Google Scholar) and fluorescence correlation spectroscopy (23Bacia K. Scherfeld D. Kahya N. Schwille P. Biophys. J. 2004; 87: 1034-1043Abstract Full Text Full Text PDF PubMed Scopus (273) Google Scholar) being particularly effective in such systems. These methodologies have clearly shown the spontaneous formation of laterally segregated domains within lipid bilayers and selective protein incorporation into such domains.In this work, we will demonstrate that plasmon-waveguide resonance (PWR) spectroscopy, applied to self-assembled solid-supported lipid bilayers, provides a uniquely useful method for observing raft formation in real-time and for obtaining information on the molecular composition of microdomains. The uniqueness of this spectroscopic technique is that it allows the most important structural parameters of a lipid membrane, such as thickness, average surface area occupied by one lipid molecule (or molecular packing density), and degree of long-range molecular order, to be characterized for a single lipid bilayer in both steady-state and kinetic modes. Unlike other techniques for domain visualization, PWR can also provide insights into microenvironmental effects on protein functional properties (24Alves I.D. Ciano K.A. Boguslavski V. Varga E. Salamon Z. Yamamura H.I. Hruby V.J. Tollin G. J. Biol. Chem. 2004; 279: 44673-44682Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar). We have applied this methodology to solid-supported lipid bilayers composed of mixtures of SM with DOPC and with POPC. As will be seen below, these spontaneously generate segregated microdomains that can be directly observed and characterized by PWR spectroscopy. We have also incorporated a GPI-linked protein (placental alkaline phosphatase (PLAP)) into such bilayers and have shown that this protein preferentially associates with the SM-enriched microdomains.EXPERIMENTAL PROCEDURESPWR Spectroscopy—The principles of PWR spectroscopy have been thoroughly described in previous publications (25Salamon Z. Macleod H.A. Tollin G. Biophys. J. 1997; 73: 2791-2797Abstract Full Text PDF PubMed Scopus (221) Google Scholar, 26Salamon Z. Tollin G. Spectroscopy. 2001; 15: 161-175Crossref Scopus (37) Google Scholar). Here, we will briefly review those aspects that are especially relevant to this study. PWR spectra can be described by three parameters: spectral position, spectral width, and resonance depth. These experimental features depend on the optical properties of the bilayer membrane, which are determined by the surface mass density (i.e. the amount of mass per unit surface area), the spatial mass distribution (i.e. the internal structure of the membrane, including molecular anisotropy and the long-range molecular order of the bilayer), the membrane thickness, and the absorption or light scattering properties of the membrane at the plasmon excitation wavelength. These optical properties are described by three optical parameters, refractive index (n), extinction (or scattering) coefficient (k), and thickness (t) of the membrane, which can be evaluated by thin film electromagnetic theory based on Maxwell's equations (27Macleod H.A. Thin Film Optical Filters. ADAM Hilger, Bristol1986Crossref Google Scholar, 28Salamon Z. Brown M.F. Tollin G. Trends Biochem. Sci. 1999; 24: 213-219Abstract Full Text Full Text PDF PubMed Scopus (124) Google Scholar). Inasmuch as both excitation wavelengths (632.8 and 543.5 nm) in this work are far removed from the absorption bands of the lipids and proteins used, a k value different from zero reflects a decrease in reflected light intensity due only to scattering resulting from imperfections in the membrane film. It is important to recognize that for anisotropic thin films, such as the lipid bilayer membranes in this work, scattering will be different for different exciting light polarizations.The refractive index is a macroscopic quantity and is related to the properties of individual molecules through the molecular polarizability tensor as well as to the environment in which these molecules are located (e.g. packing density and internal organization) (29De Jeu W.H. Gray G. Liquid Crystal Monographs. 1. Gordon and Breach, Amsterdam1978: 31-48Google Scholar). Environmental properties are especially important when molecules are located in a matrix (such as a biomembrane) that has a nonrandom organization and thus possesses long-range spatial molecular order. Such molecular ordering creates an optically anisotropic system with a uniaxial optical axis having two (different) principal refractive indices, ne (also denoted as n∥ or np) and no (also referred to as n⊥ or ns) (29De Jeu W.H. Gray G. Liquid Crystal Monographs. 1. Gordon and Breach, Amsterdam1978: 31-48Google Scholar). The first of these indices is associated with a linearly polarized light wave in which the electric vector is polarized parallel to the optical axis. The second one is observed for light in which the electric vector is perpendicular to the optical axis. This is the fundamental basis upon which measurement of refractive indices with polarized light can lead to the evaluation of the structural parameters of anisotropic systems such as a lipid bilayer membrane. In the simplified case in which the molecular shape is rod-like (e.g. phospholipid molecules) and the molecules are ordered such that their long axes are parallel, one has an optically anisotropic system whose optical axis is perpendicular to the plane of the bilayer (30Salamon Z. Tollin G. Biophys. J. 2001; 80: 1557-1567Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar). The values of the refractive indices measured with two polarizations of light (i.e. parallel (np) and perpendicular (ns) to the optical axis) will describe this optical anisotropy (An) as follows (Equation 1), An=((np)2−(ns)2)/((nav)2+2)(Eq. 1) where nav is the average value of the refractive index. A uniaxial system in which the optical axis is parallel to the membrane normal is described by Equation 2. nav=1/3((np)2+2(ns)2)(Eq. 2) In summary, An reflects the spatial mass distribution created by both the anisotropy in the molecular polarizability and the degree of long-range order of molecules within the system (30Salamon Z. Tollin G. Biophys. J. 2001; 80: 1557-1567Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar).Furthermore, as can be seen from the Lorentz-Lorenz relation, nav is also directly related to the mass surface density (for details, see Refs. 31Born M. Wolf E. Principles of Optics. Pergamon Press, New York1965Google Scholar and 32Cuypers P.A. Corsel J.W. Janssen M.P. Kop J.M.M. Hermens W.T. Hemker H.C. J. Biol. Chem. 1983; 258: 2426-2431Abstract Full Text PDF PubMed Google Scholar) (Equation 3), m=0.1M/A(t((nav)2−1)/(nav)2+2)(Eq. 3) where M is molecular weight, A is molar refractivity, and t is the thickness of the membrane. For the lipid molecules used in this work, a reasonable approximation of M/A is 3.6 (32Cuypers P.A. Corsel J.W. Janssen M.P. Kop J.M.M. Hermens W.T. Hemker H.C. J. Biol. Chem. 1983; 258: 2426-2431Abstract Full Text PDF PubMed Google Scholar). Thus, from the thickness of the membrane (t) and nav, one can calculate the surface mass density (or molecular packing density), i.e. mass per unit surface area (or number of moles/unit surface area (30Salamon Z. Tollin G. Biophys. J. 2001; 80: 1557-1567Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar)), which reflects the surface area occupied by a single molecule.In these experiments, the plasmon-generating device was calibrated by measuring the PWR spectra of the resonator using two laser light wavelengths, green (λ = 543.5 nm) and red (λ = 632.8 nm), with both p- and s-polarized light and then simulating these spectra with theoretical curves. Both of these wavelengths produced essentially equivalent results in our experiments. The goal of such a calibration is to obtain the optical parameters of the sensor. This provides an input set of data that is used in analyzing the resonance spectra obtained with the lipid membrane system deposited on the resonator surface.Spectral Simulation—The purpose of simulating experimental spectra by theoretical resonance curves is to evaluate the optical parameters of the bilayer membrane (i.e. np, ns, t and k) and then to use these values (see Equations 1, 2, 3) to calculate the surface mass density (or packing density) and the refractive index anisotropy. This provides a detailed description of the membrane structure. Simulation is based on two facts. First, the PWR spectrum can be described by the classical electromagnetic theory of thin films (27Macleod H.A. Thin Film Optical Filters. ADAM Hilger, Bristol1986Crossref Google Scholar), and the equations describing such resonance curves can be used in the simulation to obtain the component curves. Second, the number of measured parameters (i.e. position, width, and depth of the curve) equals the number of unknown optical parameters. Hence, one can uniquely determine the latter from the simulated spectra. We used this approach in our previous study (33Salamon Z. Cowell S. Varga E. Yamamura H.I. Hruby V.J. Tollin G. Biophys. J. 2000; 79: 2463-2474Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar) by nonlinear least-squares fitting of a theoretical resonance curve to the experimental spectra. This is relatively easy to do when the spectrum corresponds to a single resonance. The current application of such an approach is made more complicated by the fact that the experimental spectrum is a complex one, i.e. it consists of more than one (usually two) single resonance curves. Therefore, the simulation has to be done in two steps. First, one must calculate single resonance curves for the components; and second, one must sum such single resonance curves using appropriate ratios to fit the complex spectrum.It is important to emphasize that the first step results in an evaluation of the optical parameters that describe the physical properties of those parts of the lipid membrane that contribute to this particular single resonance curve. As discussed in our previous studies (26Salamon Z. Tollin G. Spectroscopy. 2001; 15: 161-175Crossref Scopus (37) Google Scholar, 30Salamon Z. Tollin G. Biophys. J. 2001; 80: 1557-1567Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar, 33Salamon Z. Cowell S. Varga E. Yamamura H.I. Hruby V.J. Tollin G. Biophys. J. 2000; 79: 2463-2474Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar), the three optical parameters characterizing an immobilized lipid bilayer (n, k, and t) can be obtained with a high degree of accuracy because they are well separated in their effects on the plasmon resonance spectra. Theoretical analysis of the effect of each optical parameter on the resonance spectra allows the evaluation of error limits for each of these parameters (26Salamon Z. Tollin G. Spectroscopy. 2001; 15: 161-175Crossref Scopus (37) Google Scholar). The values of such errors have been included in the analysis of the experimental results presented below. The second step provides information about the ratio of the bilayer surfaces covered by the two different kinds of membrane that are exposed to the excitation laser beam. This is based on the fact that the area under a resonance curve is constant; and therefore, a single resonance will result in a narrow and deep resonance curve, whereas two resonances occurring simultaneously will broaden the spectrum and make it shallower. There is another important consequence of the simulation process in the case of PWR measurements with a single lipid membrane. Although repetition of the measurements in separate experiments with the same type of membrane will result in similar values of the optical properties of the components, the ratio of the surface areas covered by the different membrane components that are exposed to the excitation laser beam may vary from membrane to membrane; and therefore, the final complex spectrum may change its visual characteristics (see below). This implies that one can average the parameter values obtained from different measurements and use them to calculate physical quantities describing the properties of such types of bilayers. This has been done in this work.In the present case, because we were able to measure and simulate the spectra of membranes formed from a single component lipid (DOPC, POPC, and SM), we could use such curves as a starting point in simulation of spectra of lipid membranes consisting of mixtures of these components. Iteration of such simulation was performed by variation of the optical parameters of the appropriate single lipid component spectrum until appropriate agreement with the experimental spectra was obtained. As we will demonstrate below, the final deconvoluted component spectra obtained from the mixture that describe the separate phases were always different from those of the single component curves, indicating that each of the separate phases contained small amounts of the other lipid. This will be discussed further.Formation of Lipid Membranes and Incorporation of Protein—In this study, self-assembled solid-supported lipid membranes were used. The details of sample compartment design and the protocols for membrane formation and protein incorporation have been described previously (for example, see Refs. 25Salamon Z. Macleod H.A. Tollin G. Biophys. J. 1997; 73: 2791-2797Abstract Full Text PDF PubMed Scopus (221) Google Scholar, 26Salamon Z. Tollin G. Spectroscopy. 2001; 15: 161-175Crossref Scopus (37) Google Scholar, and 33Salamon Z. Cowell S. Varga E. Yamamura H.I. Hruby V.J. Tollin G. Biophys. J. 2000; 79: 2463-2474Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar). Here, we present a short summary of these descriptions. The method for membrane preparation involves spreading a small amount of lipid solution across an orifice in a Teflon block separating the silica surface of the PWR resonator from the aqueous phase. The hydrated silica surface attracts the polar groups of the lipid molecules to form a monolayer with the hydrocarbon chains oriented toward the excess lipid solution. Spontaneous bilayer formation is initiated when the sample compartment of the resonator is filled with an aqueous solution, resulting in a thinning process to form the second monolayer of the lipid and a plateau-Gibbs border consisting of lipid solution that anchors the bilayer to the Teflon block. This border allows excess lipid solution to flow in or out of the orifice in response to protein insertion and/or conformation changes.When the appropriate lipid compositions were used, the bilayers produced PWR spectra that displayed two resonances. As we will demonstrate below, these can be ascribed to the spontaneous formation of microdomains within the bilayer due to lateral segregation of lipid molecules. As has been shown by atomic force microscopy (13Saslowsky D.E. Lawrence J. Ren X. Brown D.A. Henderson R.M. Edwardson J.M. J. Biol. Chem. 2002; 277: 26966-26970Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 17Milhiet P.-E. Giocondi M.-C. Baghdadi O. Ronzon F. Roux B. Le Grimelec C. EMBO Rep. 2002; 3: 485-490Crossref PubMed Scopus (130) Google Scholar), SM-enriched microdomains are randomly distributed within the liquid-disordered regions of the bilayer. In the PWR device, the size of the laser probe (∼0.2-mm cross-section) is much larger than the individual microdomain sizes. Thus, in a typical PWR experiment, we are averaging across many such microdomains. Since the microdomain distribution, as well as the sampling of the population by the laser probe, can vary from one experiment to another, some variability is expected in the observed ratio between resonances associated with the liquid-ordered and liquid-disordered domains. As will be described below, this was indeed observed. However, the analysis of the resonance spectra in terms of the optical properties of the components will not be affected by this variability. It is important to point out that diffusion of these microdomains within the bilayer is relatively slow (on the order of minutes; see below for examples), so an individual PWR spectrum, which is obtained in a few seconds, is not influenced by such movement. Furthermore, we estimated that to be observable by PWR at the wavelengths we used, microdomain sizes must be larger than ∼100 nm.After lipid membrane equilibration, G" @default.
• W1973918451 created "2016-06-24" @default.
• W1973918451 creator A5012627839 @default.
• W1973918451 creator A5014002723 @default.
• W1973918451 creator A5038942774 @default.
• W1973918451 creator A5069607470 @default.
• W1973918451 date "2005-03-01" @default.
• W1973918451 modified "2023-10-17" @default.
• W1973918451 title "Plasmon-waveguide Resonance Studies of Lateral Segregation of Lipids and Proteins into Microdomains (Rafts) in Solid-supported Bilayers" @default.
• W1973918451 cites W1564861448 @default.
• W1973918451 cites W1949772429 @default.
• W1973918451 cites W1966995488 @default.
• W1973918451 cites W1974928798 @default.
• W1973918451 cites W1977085484 @default.
• W1973918451 cites W1980358526 @default.
• W1973918451 cites W1987506105 @default.
• W1973918451 cites W1988611050 @default.
• W1973918451 cites W1990912620 @default.
• W1973918451 cites W1998429632 @default.
• W1973918451 cites W1998697778 @default.
• W1973918451 cites W2009768558 @default.
• W1973918451 cites W2013073357 @default.
• W1973918451 cites W2018317182 @default.
• W1973918451 cites W2024156287 @default.
• W1973918451 cites W2024469024 @default.
• W1973918451 cites W2025529482 @default.
• W1973918451 cites W2037773086 @default.
• W1973918451 cites W2040281283 @default.
• W1973918451 cites W2048327066 @default.
• W1973918451 cites W2049007155 @default.
• W1973918451 cites W2053782828 @default.
• W1973918451 cites W2065886456 @default.
• W1973918451 cites W2070877441 @default.
• W1973918451 cites W2078383747 @default.
• W1973918451 cites W2081769662 @default.
• W1973918451 cites W2086652137 @default.
• W1973918451 cites W2092111186 @default.
• W1973918451 cites W2108598406 @default.
• W1973918451 cites W2114481572 @default.
• W1973918451 cites W2119882112 @default.
• W1973918451 cites W2121568234 @default.
• W1973918451 cites W2121936687 @default.
• W1973918451 cites W2133593241 @default.
• W1973918451 cites W2142083551 @default.
• W1973918451 cites W2146139787 @default.
• W1973918451 cites W2146439388 @default.
• W1973918451 cites W2156313755 @default.
• W1973918451 cites W2321461291 @default.
• W1973918451 cites W82875452 @default.
• W1973918451 doi "https://doi.org/10.1074/jbc.m411197200" @default.
• W1973918451 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/15668234" @default.
• W1973918451 hasPublicationYear "2005" @default.
• W1973918451 type Work @default.
• W1973918451 sameAs 1973918451 @default.
• W1973918451 citedByCount "42" @default.
• W1973918451 countsByYear W19739184512012 @default.
• W1973918451 countsByYear W19739184512013 @default.
• W1973918451 countsByYear W19739184512014 @default.
• W1973918451 countsByYear W19739184512015 @default.
• W1973918451 countsByYear W19739184512016 @default.
• W1973918451 countsByYear W19739184512018 @default.
• W1973918451 countsByYear W19739184512019 @default.
• W1973918451 countsByYear W19739184512020 @default.
• W1973918451 countsByYear W19739184512021 @default.
• W1973918451 crossrefType "journal-article" @default.
• W1973918451 hasAuthorship W1973918451A5012627839 @default.
• W1973918451 hasAuthorship W1973918451A5014002723 @default.
• W1973918451 hasAuthorship W1973918451A5038942774 @default.
• W1973918451 hasAuthorship W1973918451A5069607470 @default.
• W1973918451 hasBestOaLocation W19739184511 @default.
• W1973918451 hasConcept C106847996 @default.
• W1973918451 hasConcept C109214941 @default.
• W1973918451 hasConcept C110879396 @default.
• W1973918451 hasConcept C121332964 @default.
• W1973918451 hasConcept C12554922 @default.
• W1973918451 hasConcept C139210041 @default.
• W1973918451 hasConcept C155672457 @default.
• W1973918451 hasConcept C171250308 @default.
• W1973918451 hasConcept C185592680 @default.
• W1973918451 hasConcept C192562407 @default.
• W1973918451 hasConcept C41625074 @default.
• W1973918451 hasConcept C49040817 @default.
• W1973918451 hasConcept C55493867 @default.
• W1973918451 hasConcept C79266657 @default.
• W1973918451 hasConcept C86803240 @default.
• W1973918451 hasConceptScore W1973918451C106847996 @default.
• W1973918451 hasConceptScore W1973918451C109214941 @default.
• W1973918451 hasConceptScore W1973918451C110879396 @default.
• W1973918451 hasConceptScore W1973918451C121332964 @default.
• W1973918451 hasConceptScore W1973918451C12554922 @default.
• W1973918451 hasConceptScore W1973918451C139210041 @default.
• W1973918451 hasConceptScore W1973918451C155672457 @default.
• W1973918451 hasConceptScore W1973918451C171250308 @default.
• W1973918451 hasConceptScore W1973918451C185592680 @default.
• W1973918451 hasConceptScore W1973918451C192562407 @default.
• W1973918451 hasConceptScore W1973918451C41625074 @default.
• W1973918451 hasConceptScore W1973918451C49040817 @default.
• W1973918451 hasConceptScore W1973918451C55493867 @default.

• next