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1
Thompson, J. E., C. D. Froese, Y. Hong, K. A. Hudak, and M. D. Smith. "Membrane deterioration during senescence." Canadian Journal of Botany 75, no. 6 (June 1, 1997): 867–79. http://dx.doi.org/10.1139/b97-096.
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The lipid bilayers of plant membranes are normally liquid crystalline, reflecting the inherent rotational motion of membrane fatty acids at physiological temperature. With the onset of senescence, the chemical composition of membrane lipids changes resulting in lipid phase separations within the bilayer. These phase changes render the membranes leaky and lead to loss of essential ion gradients and impairment of cell function. The separation of lipid phases appears to be attributable to an accumulation of lipid metabolites in the bilayer that are formed during turnover and metabolism of membrane lipids. These metabolites are normally released from membranes as lipid–protein particles found in the cell cytosol and within organelles. The lipid–protein particles also contain catabolites of membrane proteins and appear to serve as a vehicle for removing lipid and protein metabolites that would otherwise destabilize the bilayer. They bear structural resemblance to oil bodies, which are abundant in oil seeds, and have been found in leaves, cotyledons, and petals as well as in insect and animal tissue. The accumulation of lipid metabolites in senescing membranes and ensuing separation of lipid phases appear to reflect impairment of lipid–protein particle release from membranes as tissues age and to be a seminal cause of membrane dysfunction with advancing senescence. Key words: lipid bilayer, lipid phase separation, lipid–protein particles, membrane, oil body, senescence.
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Maček Lebar, Alenka, Damijan Miklavčič, Malgorzata Kotulska, and Peter Kramar. "Water Pores in Planar Lipid Bilayers at Fast and Slow Rise of Transmembrane Voltage." Membranes 11, no. 4 (April 5, 2021): 263. http://dx.doi.org/10.3390/membranes11040263.
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Basic understanding of the barrier properties of biological membranes can be obtained by studying model systems, such as planar lipid bilayers. Here, we study water pores in planar lipid bilayers in the presence of transmembrane voltage. Planar lipid bilayers were exposed to fast and slow linearly increasing voltage and current signals. We measured the capacitance, breakdown voltage, and rupture time of planar lipid bilayers composed of 1-pamitoyl 2-oleoyl phosphatidylcholine (POPC), 1-pamitoyl 2-oleoyl phosphatidylserine (POPS), and a mixture of both lipids in a 1:1 ratio. Based on the measurements, we evaluated the change in the capacitance of the planar lipid bilayer corresponding to water pores, the radius of water pores at membrane rupture, and the fraction of the area of the planar lipid bilayer occupied by water pores.planar lipid bilayer capacitance, which corresponds to water pores, water pore radius at the membrane rupture, and a fraction of the planar lipid bilayer area occupied by water pores. The estimated pore radii determining the rupture of the planar lipid bilayer upon fast build-up of transmembrane voltage are 0.101 nm, 0.110 nm, and 0.106 nm for membranes composed of POPC, POPS, and POPC:POPS, respectively. The fraction of the surface occupied by water pores at the moment of rupture of the planar lipid bilayer The fraction of an area that is occupied by water pores at the moment of planar lipid bilayer rupture is in the range of 0.1–1.8%.
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Petelska, Aneta. "Interfacial tension of bilayer lipid membranes." Open Chemistry 10, no. 1 (February 1, 2012): 16–26. http://dx.doi.org/10.2478/s11532-011-0130-7.
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AbstractInterfacial tension is an important characteristic of a biological membrane because it determines its rigidity, thus affecting its stability. It is affected by factors such as medium pH and by the presence of certain substances, for example cholesterol, other lipids, fatty acids, amines, amino acids, or proteins, incorporated in the lipid bilayer. Here, the effects of various parameters to on interfacial tension values of bilayer lipid membranes are discussed.The mathematically derived and experimentally confirmed results presented in this paper are of importance to the interpretation of phenomena occurring in lipid bilayers. These results can lead to a better understanding of the physical properties of biological membranes. The simple interfacial tension method proposed herein may be successfully used to determine the interfacial tension values of 1:1 lipid-lipid, lipid-cholesterol, lipid-fatty acid, lipid-amine, and lipid-amino acid systems.
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Amador, Guillermo J., Dennis van Dijk, Roland Kieffer, Marie-Eve Aubin-Tam, and Daniel Tam. "Hydrodynamic shear dissipation and transmission in lipid bilayers." Proceedings of the National Academy of Sciences 118, no. 21 (May 21, 2021): e2100156118. http://dx.doi.org/10.1073/pnas.2100156118.
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Vital biological processes, such as trafficking, sensing, and motility, are facilitated by cellular lipid membranes, which interact mechanically with surrounding fluids. Such lipid membranes are only a few nanometers thick and composed of a liquid crystalline structure known as the lipid bilayer. Here, we introduce an active, noncontact, two-point microrheology technique combining multiple optical tweezers probes with planar freestanding lipid bilayers accessible on both sides. We use the method to quantify both fluid slip close to the bilayer surface and transmission of fluid flow across the structure, and we use numerical simulations to determine the monolayer viscosity and the intermonolayer friction. We find that these physical properties are highly dependent on the molecular structure of the lipids in the bilayer. We compare ordered-phase with liquid disordered-phase lipid bilayers, and we find the ordered-phase bilayers to be 10 to 100 times more viscous but with 100 times less intermonolayer friction. When a local shear is applied by the optical tweezers, the ultralow intermonolayer friction results in full slip of the two leaflets relative to each other and as a consequence, no shear transmission across the membrane. Our study sheds light on the physical principles governing the transfer of shear forces by and through lipid membranes, which underpin cell behavior and homeostasis.
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Macdonald, Peter M., Kevin J. Crowell, Carla M. Franzin, Peter Mitrakos, and Darlene J. Semchyschyn. "Polyelectrolyte-induced domains in lipid bilayer membranes: the deuterium NMR perspective." Biochemistry and Cell Biology 76, no. 2-3 (May 1, 1998): 452–64. http://dx.doi.org/10.1139/o98-044.
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Domain formation in lipid bilayer membranes can occur through electrostatic interactions between charged lipids and oppositely charged polyelectrolytes, such as proteins or polynucleic acids. This review describes a novel method for examining such domains in lipid bilayers, based on 2H NMR spectroscopy. The 2H NMR spectrum of choline-deuterated phosphatidylcholine is sensitive to, and reports on, lipid bilayer surface charge. When a charged lipid bilayer is exposed to an oppositely charged polyelectrolyte, the latter binds electrostatically to the bilayer surface and attracts charged lipids into its vicinity. The resulting inhomogeneous charge distribution produces overlapping 2H NMR subspectra arising from phosphatidylcholine within charge-enriched versus charge-depleted regions. Such spectral details as the quadrupolar splittings and the relative intensities of the subspectra permit a complete analysis of the domain composition, size, and, within limits, lifetime. Using 2H NMR, domain formation in lipid bilayer membranes can be observed with both cationic and anionic polyelectrolytes, whether of natural or synthetic origin. Domain size and composition prove to be sensitive to the detailed chemical structure of both the polyelectrolyte and the charged lipids. Within the domains there is always a stoichiometric anion/cation binding ratio, indicating that the polyelectrolyte lies flat on the membrane surface. The amount of phosphatidylcholine within the domain varies as a function of its statistical availability, in accordance with the predictions of a recent thermodynamic model of domain formation. When the molecular weight of the polyelectrolyte is varied, the domain size alters in accordance with the predictions of classical polymer physics. As expected for a predominantly electrostatic phenomenon, the observed domains dissipate at high ionic strength.Key words: electrostatic domains, polyelectrolytes, lipid bilayers, deuterium NMR.
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Ouberai, Myriam M., Juan Wang, Marcus J. Swann, Celine Galvagnion, Tim Guilliams, Christopher M. Dobson, and Mark E. Welland. "α-Synuclein Senses Lipid Packing Defects and Induces Lateral Expansion of Lipids Leading to Membrane Remodeling." Journal of Biological Chemistry 288, no. 29 (June 5, 2013): 20883–95. http://dx.doi.org/10.1074/jbc.m113.478297.
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There is increasing evidence for the involvement of lipid membranes in both the functional and pathological properties of α-synuclein (α-Syn). Despite many investigations to characterize the binding of α-Syn to membranes, there is still a lack of understanding of the binding mode linking the properties of lipid membranes to α-Syn insertion into these dynamic structures. Using a combination of an optical biosensing technique and in situ atomic force microscopy, we show that the binding strength of α-Syn is related to the specificity of the lipid environment (the lipid chemistry and steric properties within a bilayer structure) and to the ability of the membranes to accommodate and remodel upon the interaction of α-Syn with lipid membranes. We show that this interaction results in the insertion of α-Syn into the region of the headgroups, inducing a lateral expansion of lipid molecules that can progress to further bilayer remodeling, such as membrane thinning and expansion of lipids out of the membrane plane. We provide new insights into the affinity of α-Syn for lipid packing defects found in vesicles of high curvature and in planar membranes with cone-shaped lipids and suggest a comprehensive model of the interaction between α-Syn and lipid bilayers. The ability of α-Syn to sense lipid packing defects and to remodel membrane structure supports its proposed role in vesicle trafficking.
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Mouritsen, Ole G., and Luis A. Bagatolli. "Lipid domains in model membranes: a brief historical perspective." Essays in Biochemistry 57 (February 6, 2015): 1–19. http://dx.doi.org/10.1042/bse0570001.
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All biological membranes consist of a complex composite of macromolecules and macromolecular assemblies, of which the fluid lipid-bilayer component is a core element with regard to cell encapsulation and barrier properties. The fluid lipid bilayer also supports the functional machinery of receptors, channels and pumps that are associated with the membrane. This bilayer is stabilized by weak physical and colloidal forces, and its nature is that of a self-assembled system of amphiphiles in water. Being only approximately 5 nm in thickness and still encapsulating a cell that is three orders of magnitude larger in diameter, the lipid bilayer as a material has very unusual physical properties, both in terms of structure and dynamics. Although the lipid bilayer is a fluid, it has a distinct and structured trans-bilayer profile, and in the plane of the bilayer the various molecular components, viz different lipid species and membrane proteins, have the capacity to organize laterally in terms of differentiated domains on different length and time scales. These elements of small-scale structure and order are crucial for the functioning of the membrane. It has turned out to be difficult to quantitatively study the small-scale structure of biological membranes. A major part of the insight into membrane micro- and nano-domains and the concepts used to describe them have hence come from studies of simple lipid bilayers as models of membranes, by use of a wide range of theoretical, experimental and simulational approaches. Many questions remain to be answered as to which extent the result from model studies can carry over to real biological membranes.
8
Lee, Anthony G. "Integral membrane enzymes: What are the problems?" Biochemist 25, no. 4 (August 1, 2003): 17–19. http://dx.doi.org/10.1042/bio02504017.
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Integral membrane enzymes have to function in the environment provided by the lipid bilayer component of a membrane. This raises interesting problems of design; not only must these enzymes contain hydrophobic -helices or -barrels to span the lipid bilayer, they must also have a design compatible with the translocation machinery used to insert proteins into membranes. One solution is to separate functions in the enzyme as far as is possible, so that the enzymology is carried out in domains located outside the lipid bilayer. When active sites are located within the lipid bilayer, they are often located at protein-protein interfaces in dimeric structures. Because these enzymes are designed to operate in a lipid bilayer, they are best studied after reconstitution into lipid bilayers.
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Pasenkiewicz-Gierula, M., K. Murzyn, T. Róg, and C. Czaplewski. "Molecular dynamics simulation studies of lipid bilayer systems." Acta Biochimica Polonica 47, no. 3 (September 30, 2000): 601–11. http://dx.doi.org/10.18388/abp.2000_3982.
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The main structural element of biological membranes is a liquid-crystalline lipid bilayer. Other constituents, i.e. proteins, sterols and peptides, either intercalate into or loosely attach to the bilayer. We applied a molecular dynamics simulation method to study membrane systems at various levels of compositional complexity. The studies were started from simple lipid bilayers containing a single type phosphatidylcholine (PC) and water molecules (PC bilayers). As a next step, cholesterol (Chol) molecules were introduced to the PC bilayers (PC-Chol bilayers). These studies provided detailed information about the structure and dynamics of the membrane/water interface and the hydrocarbon chain region in bilayers built of various types of PCs and Chol. This enabled studies of membrane systems of higher complexity. They included the investigation of an integral membrane protein in its natural environment of a PC bilayer, and the antibacterial activity of magainin-2. The latter study required the construction of a model bacterial membrane which consisted of two types of phospholipids and counter ions. Whenever published experimental data were available, the results of the simulations were compared with them.
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Booth, Paula J., A. Rachael Curran, Richard H. Templer, Hui Lu, and Wim Meijberg. "Manipulating the folding of membrane proteins: using the bilayer to our advantage." Biochemical Society Symposia 68 (August 1, 2001): 27–33. http://dx.doi.org/10.1042/bss0680027.
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The folding mechanisms of integral membrane proteins have largely eluded detailed study. This is owing to the inherent difficulties in folding these hydrophobic proteins in vitro, which, in turn, reflects the often apparently insurmountable problem of mimicking the natural membrane bilayer with lipid or detergent mixtures. There is, however, a large body of information on lipid properties and, in particular, on phosphatidylcholine and phosphatidylethanolamine lipids, which are common to many biological membranes. We have exploited this knowledge to develop efficient in vitro lipid-bilayer folding systems for the membrane protein, bacteriorhodopsin. Furthermore, we have shown that a rate-limiting apoprotein folding step and the overall folding efficiency appear to be controlled by particular properties of the lipid bilayer. The properties of interest are the stored curvature elastic energy within the bilayer, and the lateral pressure that the lipid chains exert on the their neighbouring folding proteins. These are generic properties of the bilayer that can be achieved with simple mixtures of biological lipids, and are not specific to the lipids studied here. These bilayer properties also seem to be important in modulating the function of several membrane proteins, as well as the function of membranes in vivo. Thus, it seems likely that careful manipulations of lipid properties will shed light on the forces that drive membrane protein folding, and will aid the development of bilayer folding systems for other membrane proteins.
11
Ti Tien, H., Z. Salamon, D. L. Guo, and A. Ottova-Leitmannova. "The New Bilayer Lipid Membrane System: Self-Assembling Bilayer Lipid Membranes." Journal of Intelligent Material Systems and Structures 3, no. 3 (July 1992): 547–53. http://dx.doi.org/10.1177/1045389x9200300310.
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Wang, Meina, Adriana M. Mihut, Ellen Rieloff, Aleksandra P. Dabkowska, Linda K. Månsson, Jasper N. Immink, Emma Sparr, and Jérôme J. Crassous. "Assembling responsive microgels at responsive lipid membranes." Proceedings of the National Academy of Sciences 116, no. 12 (March 1, 2019): 5442–50. http://dx.doi.org/10.1073/pnas.1807790116.
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Directed colloidal self-assembly at fluid interfaces can have a large impact in the fields of nanotechnology, materials, and biomedical sciences. The ability to control interfacial self-assembly relies on the fine interplay between bulk and surface interactions. Here, we investigate the interfacial assembly of thermoresponsive microgels and lipogels at the surface of giant unilamellar vesicles (GUVs) consisting of phospholipids bilayers with different compositions. By altering the properties of the lipid membrane and the microgel particles, it is possible to control the adsorption/desorption processes as well as the organization and dynamics of the colloids at the vesicle surface. No translocation of the microgels and lipogels through the membrane was observed for any of the membrane compositions and temperatures investigated. The lipid membranes with fluid chains provide highly dynamic interfaces that can host and mediate long-range ordering into 2D hexagonal crystals. This is in clear contrast to the conditions when the membranes are composed of lipids with solid chains, where there is no crystalline arrangement, and most of the particles desorb from the membrane. Likewise, we show that in segregated membranes, the soft microgel colloids form closely packed 2D crystals on the fluid bilayer domains, while hardly any particles adhere to the more solid bilayer domains. These findings thus present an approach for selective and controlled colloidal assembly at lipid membranes, opening routes toward the development of tunable soft materials.
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Branton, Daniel. "Fracture faces of frozen membranes: 50th anniversary." Molecular Biology of the Cell 27, no. 3 (February 2016): 421–23. http://dx.doi.org/10.1091/mbc.e15-05-0287.
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In 1961, the development of an improved freeze-etching (FE) procedure to prepare rapidly frozen biological cells or tissues for electron microscopy raised two important questions. How does a frozen cell membrane fracture? What do the extensive face views of the cell’s membranes exposed by the fracture process of FE tell us about the overall structure of biological membranes? I discovered that all frozen membranes tend to split along weakly bonded lipid bilayers. Consequently, the fracture process exposes internal membrane faces rather than either of the membrane’s two external surfaces. During etching, when ice is allowed to sublime after fracturing, limited regions of the actual membrane surfaces are revealed. Examination of the fractured faces and etched surfaces provided strong evidence that biological membranes are organized as lipid bilayers with some proteins on the surface and other proteins extending through the bilayer. Membrane splitting made it possible for electron microscopy to show the relative proportion of a membrane’s area that exists in either of these two organizational modes.
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Prashar, Jognandan, Phillip Sharp, Mathew Scarffe, and Bruce Cornell. "Making lipid membranes even tougher." Journal of Materials Research 22, no. 8 (August 2007): 2189–94. http://dx.doi.org/10.1557/jmr.2007.0288.
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Biosensors based on lipid membranes promise an inexpensive and versatile platform for application in many fields of molecular sensing. An extensive review of the applications for tethered membranes was reported in the July 2006 MRS Bulletin [A.N. Parikh and J.T. Groves, Materials science of supported lipid membranes. MRS Bull.31(8), 507 (2006)]. The commercial use to which tethered lipid membranes have been applied has been limited by their stability under long-term storage. This report describes a novel membrane construct that is stable at room temperature for months, eliminates the mobile lipid phase present in lipid bilayers, and is robust against detergents under conditions that would destroy a lipid bilayer.
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Mathai, John C., Stephanie Tristram-Nagle, John F. Nagle, and Mark L. Zeidel. "Structural Determinants of Water Permeability through the Lipid Membrane." Journal of General Physiology 131, no. 1 (December 31, 2007): 69–76. http://dx.doi.org/10.1085/jgp.200709848.
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Despite intense study over many years, the mechanisms by which water and small nonelectrolytes cross lipid bilayers remain unclear. While prior studies of permeability through membranes have focused on solute characteristics, such as size, polarity, and partition coefficient in hydrophobic solvent, we focus here on water permeability in seven single component bilayers composed of different lipids, five with phosphatidylcholine headgroups and different chain lengths and unsaturation, one with a phosphatidylserine headgroup, and one with a phosphatidylethanolamine headgroup. We find that water permeability correlates most strongly with the area/lipid and is poorly correlated with bilayer thickness and other previously determined structural and mechanical properties of these single component bilayers. These results suggest a new model for permeability that is developed in the accompanying theoretical paper in which the area occupied by the lipid is the major determinant and the hydrocarbon thickness is a secondary determinant. Cholesterol was also incorporated into DOPC bilayers and X-ray diffuse scattering was used to determine quantitative structure with the result that the area occupied by DOPC in the membrane decreases while bilayer thickness increases in a correlated way because lipid volume does not change. The water permeability decreases with added cholesterol and it correlates in a different way from pure lipids with area per lipid, bilayer thickness, and also with area compressibility.
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Chattopadhyay, Madhurima, Hanna Orlikowska, Emilia Krok, and Lukasz Piatkowski. "Sensing Hydration of Biomimetic Cell Membranes." Biosensors 11, no. 7 (July 16, 2021): 241. http://dx.doi.org/10.3390/bios11070241.
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Biological membranes play a vital role in cell functioning, providing structural integrity, controlling signal transduction, and controlling the transport of various chemical species. Owing to the complex nature of biomembranes, the self-assembly of lipids in aqueous media has been utilized to develop model systems mimicking the lipid bilayer structure, paving the way to elucidate the mechanisms underlying various biological processes, as well as to develop a number of biomedical and technical applications. The hydration properties of lipid bilayers are crucial for their activity in various cellular processes. Of particular interest is the local membrane dehydration, which occurs in membrane fusion events, including neurotransmission, fertilization, and viral entry. The lack of universal technique to evaluate the local hydration state of the membrane components hampers understanding of the molecular-level mechanisms of these processes. Here, we present a new approach to quantify the hydration state of lipid bilayers. It takes advantage of the change in the lateral diffusion of lipids that depends on the number of water molecules hydrating them. Using fluorescence recovery after photobleaching technique, we applied this approach to planar single and multicomponent supported lipid bilayers. The method enables the determination of the hydration level of a biomimetic membrane down to a few water molecules per lipid.
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Krylov, Andrey V., Peter Pohl, Mark L. Zeidel, and Warren G. Hill. "Water Permeability of Asymmetric Planar Lipid Bilayers." Journal of General Physiology 118, no. 4 (September 18, 2001): 333–40. http://dx.doi.org/10.1085/jgp.118.4.333.
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To understand how plasma membranes may limit water flux, we have modeled the apical membrane of MDCK type 1 cells. Previous experiments demonstrated that liposomes designed to mimic the inner and outer leaflet of this membrane exhibited 18-fold lower water permeation for outer leaflet lipids than inner leaflet lipids (Hill, W.G., and M.L. Zeidel. 2000. J. Biol. Chem. 275:30176–30185), confirming that the outer leaflet is the primary barrier to permeation. If leaflets in a bilayer resist permeation independently, the following equation estimates single leaflet permeabilities: 1/PAB = 1/PA + 1/PB (Eq. l), where PAB is the permeability of a bilayer composed of leaflets A and B, PA is the permeability of leaflet A, and PB is the permeability of leaflet B. Using for the MDCK leaflet–specific liposomes gives an estimated value for the osmotic water permeability (Pf) of 4.6 × 10−4 cm/s (at 25°C) that correlated well with experimentally measured values in intact cells. We have now constructed both symmetric and asymmetric planar lipid bilayers that model the MDCK apical membrane. Water permeability across these bilayers was monitored in the immediate membrane vicinity using a Na+-sensitive scanning microelectrode and an osmotic gradient induced by addition of urea. The near-membrane concentration distribution of solute was used to calculate the velocity of water flow (Pohl, P., S.M. Saparov, and Y.N. Antonenko. 1997. Biophys. J. 72:1711–1718). At 36°C, Pf was 3.44 ± 0.35 × 10−3 cm/s for symmetrical inner leaflet membranes and 3.40 ± 0.34 × 10−4 cm/s for symmetrical exofacial membranes. From , the estimated permeability of an asymmetric membrane is 6.2 × 10−4 cm/s. Water permeability measured for the asymmetric planar bilayer was 6.7 ± 0.7 × 10−4 cm/s, which is within 10% of the calculated value. Direct experimental measurement of Pf for an asymmetric planar membrane confirms that leaflets in a bilayer offer independent and additive resistances to water permeation and validates the use of .
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Luchini, Alessandra, and Giuseppe Vitiello. "Mimicking the Mammalian Plasma Membrane: An Overview of Lipid Membrane Models for Biophysical Studies." Biomimetics 6, no. 1 (December 31, 2020): 3. http://dx.doi.org/10.3390/biomimetics6010003.
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Cell membranes are very complex biological systems including a large variety of lipids and proteins. Therefore, they are difficult to extract and directly investigate with biophysical methods. For many decades, the characterization of simpler biomimetic lipid membranes, which contain only a few lipid species, provided important physico-chemical information on the most abundant lipid species in cell membranes. These studies described physical and chemical properties that are most likely similar to those of real cell membranes. Indeed, biomimetic lipid membranes can be easily prepared in the lab and are compatible with multiple biophysical techniques. Lipid phase transitions, the bilayer structure, the impact of cholesterol on the structure and dynamics of lipid bilayers, and the selective recognition of target lipids by proteins, peptides, and drugs are all examples of the detailed information about cell membranes obtained by the investigation of biomimetic lipid membranes. This review focuses specifically on the advances that were achieved during the last decade in the field of biomimetic lipid membranes mimicking the mammalian plasma membrane. In particular, we provide a description of the most common types of lipid membrane models used for biophysical characterization, i.e., lipid membranes in solution and on surfaces, as well as recent examples of their applications for the investigation of protein-lipid and drug-lipid interactions. Altogether, promising directions for future developments of biomimetic lipid membranes are the further implementation of natural lipid mixtures for the development of more biologically relevant lipid membranes, as well as the development of sample preparation protocols that enable the incorporation of membrane proteins in the biomimetic lipid membranes.
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Zheng, Hui, Sungsoo Lee, Marc C. Llaguno, and Qiu-Xing Jiang. "bSUM: A bead-supported unilamellar membrane system facilitating unidirectional insertion of membrane proteins into giant vesicles." Journal of General Physiology 147, no. 1 (December 28, 2015): 77–93. http://dx.doi.org/10.1085/jgp.201511448.
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Fused or giant vesicles, planar lipid bilayers, a droplet membrane system, and planar-supported membranes have been developed to incorporate membrane proteins for the electrical and biophysical analysis of such proteins or the bilayer properties. However, it remains difficult to incorporate membrane proteins, including ion channels, into reconstituted membrane systems that allow easy control of operational dimensions, incorporation orientation of the membrane proteins, and lipid composition of membranes. Here, using a newly developed chemical engineering procedure, we report on a bead-supported unilamellar membrane (bSUM) system that allows good control over membrane dimension, protein orientation, and lipid composition. Our new system uses specific ligands to facilitate the unidirectional incorporation of membrane proteins into lipid bilayers. Cryo–electron microscopic imaging demonstrates the unilamellar nature of the bSUMs. Electrical recordings from voltage-gated ion channels in bSUMs of varying diameters demonstrate the versatility of the new system. Using KvAP as a model system, we show that compared with other in vitro membrane systems, the bSUMs have the following advantages: (a) a major fraction of channels are orientated in a controlled way; (b) the channels mediate the formation of the lipid bilayer; (c) there is one and only one bilayer membrane on each bead; (d) the lipid composition can be controlled and the bSUM size is also under experimental control over a range of 0.2–20 µm; (e) the channel activity can be recorded by patch clamp using a planar electrode; and (f) the voltage-clamp speed (0.2–0.5 ms) of the bSUM on a planar electrode is fast, making it suitable to study ion channels with fast gating kinetics. Our observations suggest that the chemically engineered bSUMs afford a novel platform for studying lipid–protein interactions in membranes of varying lipid composition and may be useful for other applications, such as targeted delivery and single-molecule imaging.
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Torres, Manuel, Catalina Ana Rosselló, Paula Fernández-García, Victoria Lladó, Or Kakhlon, and Pablo Vicente Escribá. "The Implications for Cells of the Lipid Switches Driven by Protein–Membrane Interactions and the Development of Membrane Lipid Therapy." International Journal of Molecular Sciences 21, no. 7 (March 27, 2020): 2322. http://dx.doi.org/10.3390/ijms21072322.
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The cell membrane contains a variety of receptors that interact with signaling molecules. However, agonist–receptor interactions not always activate a signaling cascade. Amphitropic membrane proteins are required for signal propagation upon ligand-induced receptor activation. These proteins localize to the plasma membrane or internal compartments; however, they are only activated by ligand-receptor complexes when both come into physical contact in membranes. These interactions enable signal propagation. Thus, signals may not propagate into the cell if peripheral proteins do not co-localize with receptors even in the presence of messengers. As the translocation of an amphitropic protein greatly depends on the membrane’s lipid composition, regulation of the lipid bilayer emerges as a novel therapeutic strategy. Some of the signals controlled by proteins non-permanently bound to membranes produce dramatic changes in the cell’s physiology. Indeed, changes in membrane lipids induce translocation of dozens of peripheral signaling proteins from or to the plasma membrane, which controls how cells behave. We called these changes “lipid switches”, as they alter the cell’s status (e.g., proliferation, differentiation, death, etc.) in response to the modulation of membrane lipids. Indeed, this discovery enables therapeutic interventions that modify the bilayer’s lipids, an approach known as membrane-lipid therapy (MLT) or melitherapy.
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Sokolov, Yuri, J. Ashot Kozak, Rakez Kayed, Alexandr Chanturiya, Charles Glabe, and James E. Hall. "Soluble Amyloid Oligomers Increase Bilayer Conductance by Altering Dielectric Structure." Journal of General Physiology 128, no. 6 (November 13, 2006): 637–47. http://dx.doi.org/10.1085/jgp.200609533.
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The amyloid hypothesis of Alzheimer's toxicity has undergone a resurgence with increasing evidence that it is not amyloid fibrils but a smaller oligomeric species that produces the deleterious results. In this paper we address the mechanism of this toxicity. Only oligomers increase the conductance of lipid bilayers and patch-clamped mammalian cells, producing almost identical current–voltage curves in both preparations. Oligomers increase the conductance of the bare bilayer, the cation conductance induced by nonactin, and the anion conductance induced by tetraphenyl borate. Negative charge reduces the sensitivity of the membrane to amyloid, but cholesterol has little effect. In contrast, the area compressibility of the lipid has a very large effect. Membranes with a large area compressibility modulus are almost insensitive to amyloid oligomers, but membranes formed from soft, highly compressible lipids are highly susceptible to amyloid oligomer-induced conductance changes. Furthermore, membranes formed using the solvent decane (instead of squalane) are completely insensitive to the presence of oligomers. One simple explanation for these effects on bilayer conductance is that amyloid oligomers increase the area per molecule of the membrane-forming lipids, thus thinning the membrane, lowering the dielectric barrier, and increasing the conductance of any mechanism sensitive to the dielectric barrier.
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Martins do Canto, A. M. T., A. J. Palace Carvalho, J. P. Prates Ramalho, and Luís M. S. Loura. "Molecular Dynamics Simulation of HIV Fusion Inhibitor T-1249: Insights on Peptide-Lipid Interaction." Computational and Mathematical Methods in Medicine 2012 (2012): 1–14. http://dx.doi.org/10.1155/2012/151854.
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T-1249 is a peptide that inhibits the fusion of HIV envelope with the target cell membrane. Recent results indicate that T-1249, as in the case of related inhibitor peptide T-20 (enfuvirtide), interacts with membranes, more extensively in the bilayer liquid disordered phase than in the liquid ordered state, which could be linked to its effectiveness. Extensive molecular dynamics simulations (100 ns) were carried out to investigate the interaction between T-1249 and bilayers of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and POPC/cholesterol (1 : 1). It was observed that T-1249 interacts to different extents with both membrane systems and that peptide interaction with the bilayer surface has a local effect on membrane structure. Formation of hydrogen bonding between certain peptide residues and several acceptor and donor groups in the bilayer molecules was observed. T-1249 showed higher extent of interaction with bilayers when compared to T-20. This is most notable in POPC/Chol membranes, owing to more peptide residues acting as H bond donors and acceptors between the peptide and the bilayer lipids, including H-bonds formed with cholesterol. This behavior is at variance with that of T-20, which forms no H bonds with cholesterol. This higher ability to interact with membranes is probably correlated with its higher inhibitory efficiency.
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Qiu, Weihua, Ziao Fu, Guoyan G. Xu, Robert A. Grassucci, Yan Zhang, Joachim Frank, Wayne A. Hendrickson, and Youzhong Guo. "Structure and activity of lipid bilayer within a membrane-protein transporter." Proceedings of the National Academy of Sciences 115, no. 51 (December 3, 2018): 12985–90. http://dx.doi.org/10.1073/pnas.1812526115.
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Membrane proteins function in native cell membranes, but extraction into isolated particles is needed for many biochemical and structural analyses. Commonly used detergent-extraction methods destroy naturally associated lipid bilayers. Here, we devised a detergent-free method for preparing cell-membrane nanoparticles to study the multidrug exporter AcrB, by cryo-EM at 3.2-Å resolution. We discovered a remarkably well-organized lipid-bilayer structure associated with transmembrane domains of the AcrB trimer. This bilayer patch comprises 24 lipid molecules; inner leaflet chains are packed in a hexagonal array, whereas the outer leaflet has highly irregular but ordered packing. Protein side chains interact with both leaflets and participate in the hexagonal pattern. We suggest that the lipid bilayer supports and harmonizes peristaltic motions through AcrB trimers. In AcrB D407A, a putative proton-relay mutant, lipid bilayer buttresses protein interactions lost in crystal structures after detergent-solubilization. Our detergent-free system preserves lipid–protein interactions for visualization and should be broadly applicable.
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Hickey, Katie D., and Mary M. Buhr. "Lipid Bilayer Composition Affects Transmembrane Protein Orientation and Function." Journal of Lipids 2011 (2011): 1–9. http://dx.doi.org/10.1155/2011/208457.
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Sperm membranes change in structure and composition upon ejaculation to undergo capacitation, a molecular transformation which enables spermatozoa to undergo the acrosome reaction and be capable of fertilization. Changes to the membrane environment including lipid composition, specifically lipid microdomains, may be responsible for enabling capacitation. To study the effect of lipid environment on proteins, liposomes were created using lipids extracted from bull sperm membranes, with or without a protein (Na+K+-ATPase or -amylase). Protein incorporation, function, and orientation were determined. Fluorescence resonance energy transfer (FRET) confirmed protein inclusion in the lipid bilayer, and protein function was confirmed using a colourometric assay of phosphate production from ATP cleavage. In the native lipid liposomes, ATPase was oriented with the subunit facing the outer leaflet, while changing the lipid composition to 50% native lipids and 50% exogenous lipids significantly altered this orientation of Na+K+-ATPase within the membranes.
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Tietz, Stefanie, Michelle Leuenberger, Ricarda Höhner, Alice H. Olson, Graham R. Fleming, and Helmut Kirchhoff. "A proteoliposome-based system reveals how lipids control photosynthetic light harvesting." Journal of Biological Chemistry 295, no. 7 (January 12, 2020): 1857–66. http://dx.doi.org/10.1074/jbc.ra119.011707.
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Integral membrane proteins are exposed to a complex and dynamic lipid environment modulated by nonbilayer lipids that can influence protein functions by lipid-protein interactions. The nonbilayer lipid monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in plant photosynthetic thylakoid membranes, but its impact on the functionality of energy-converting membrane protein complexes is unknown. Here, we optimized a detergent-based reconstitution protocol to develop a proteoliposome technique that incorporates the major light-harvesting complex II (LHCII) into compositionally well-defined large unilamellar lipid bilayer vesicles to study the impact of MGDG on light harvesting by LHCII. Using steady-state fluorescence spectroscopy, CD spectroscopy, and time-correlated single-photon counting, we found that both chlorophyll fluorescence quantum yields and fluorescence lifetimes clearly indicate that the presence of MGDG in lipid bilayers switches LHCII from a light-harvesting to a more energy-quenching mode that dissipates harvested light into heat. It is hypothesized that in the in vitro system developed here, MGDG controls light harvesting of LHCII by modulating the hydrostatic lateral membrane pressure profile in the lipid bilayer sensed by LHCII-bound peripheral pigments.
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Sanders, M. R., H. E. Findlay, and P. J. Booth. "Lipid bilayer composition modulates the unfolding free energy of a knotted α-helical membrane protein." Proceedings of the National Academy of Sciences 115, no. 8 (February 5, 2018): E1799—E1808. http://dx.doi.org/10.1073/pnas.1714668115.
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α-Helical membrane proteins have eluded investigation of their thermodynamic stability in lipid bilayers. Reversible denaturation curves have enabled some headway in determining unfolding free energies. However, these parameters have been limited to detergent micelles or lipid bicelles, which do not possess the same mechanical properties as lipid bilayers that comprise the basis of natural membranes. We establish reversible unfolding of the membrane transporter LeuT in lipid bilayers, enabling the comparison of apparent unfolding free energies in different lipid compositions. LeuT is a bacterial ortholog of neurotransmitter transporters and contains a knot within its 12-transmembrane helical structure. Urea is used as a denaturant for LeuT in proteoliposomes, resulting in the loss of up to 30% helical structure depending upon the lipid bilayer composition. Urea unfolding of LeuT in liposomes is reversible, with refolding in the bilayer recovering the original helical structure and transport activity. A linear dependence of the unfolding free energy on urea concentration enables the free energy to be extrapolated to zero denaturant. Increasing lipid headgroup charge or chain lateral pressure increases the thermodynamic stability of LeuT. The mechanical and charge properties of the bilayer also affect the ability of urea to denature the protein. Thus, we not only gain insight to the long–sought-after thermodynamic stability of an α-helical protein in a lipid bilayer but also provide a basis for studies of the folding of knotted proteins in a membrane environment.
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Der Loughian, Christelle, Pauline Muleki Seya, Christophe Pirat, Claude Inserra, Jean-Christophe Béra, and Jean-Paul Rieu. "Jumping acoustic bubbles on lipid bilayers." Soft Matter 11, no. 17 (2015): 3460–69. http://dx.doi.org/10.1039/c5sm00427f.
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Corey, Robin A., Phillip J. Stansfeld, and Mark S. P. Sansom. "The energetics of protein–lipid interactions as viewed by molecular simulations." Biochemical Society Transactions 48, no. 1 (December 24, 2019): 25–37. http://dx.doi.org/10.1042/bst20190149.
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Membranes are formed from a bilayer containing diverse lipid species with which membrane proteins interact. Integral, membrane proteins are embedded in this bilayer, where they interact with lipids from their surroundings, whilst peripheral membrane proteins bind to lipids at the surface of membranes. Lipid interactions can influence the function of membrane proteins, either directly or allosterically. Both experimental (structural) and computational approaches can reveal lipid binding sites on membrane proteins. It is, therefore, important to understand the free energies of these interactions. This affords a more complete view of the engagement of a particular protein with the biological membrane surrounding it. Here, we describe many computational approaches currently in use for this purpose, including recent advances using both free energy and unbiased simulation methods. In particular, we focus on interactions of integral membrane proteins with cholesterol, and with anionic lipids such as phosphatidylinositol 4,5-bis-phosphate and cardiolipin. Peripheral membrane proteins are exemplified via interactions of PH domains with phosphoinositide-containing membranes. We summarise the current state of the field and provide an outlook on likely future directions of investigation.
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Braunagel, Julia, Ann Junghans, and Ingo Köper. "Membrane-Based Sensing Approaches." Australian Journal of Chemistry 64, no. 1 (2011): 54. http://dx.doi.org/10.1071/ch10347.
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Tethered bilayer lipid membranes can be used as model platforms to host membrane proteins or membrane-active peptides, which can act as transducers in sensing applications. Here we present the synthesis and characterization of a valinomycin derivative, a depsipeptide that has been functionalized to serve as a redox probe in a lipid bilayer. In addition, we discuss the influence of the molecular structure of the lipid bilayer on its ability to host proteins. By using electrical impedance techniques as well as neutron scattering experiments, a clear correlation between the packing density of the lipids forming the membrane and its ability to host membrane proteins could be shown.
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Canepa, Ester, Sebastian Salassi, Anna Lucia de Marco, Chiara Lambruschini, Davide Odino, Davide Bochicchio, Fabio Canepa, et al. "Amphiphilic gold nanoparticles perturb phase separation in multidomain lipid membranes." Nanoscale 12, no. 38 (2020): 19746–59. http://dx.doi.org/10.1039/d0nr05366j.
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Foreman-Ortiz, Isabel U., Dongyue Liang, Elizabeth D. Laudadio, Jorge D. Calderin, Meng Wu, Puspam Keshri, Xianzhi Zhang, et al. "Anionic nanoparticle-induced perturbation to phospholipid membranes affects ion channel function." Proceedings of the National Academy of Sciences 117, no. 45 (October 26, 2020): 27854–61. http://dx.doi.org/10.1073/pnas.2004736117.
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Understanding the mechanisms of nanoparticle interaction with cell membranes is essential for designing materials for applications such as bioimaging and drug delivery, as well as for assessing engineered nanomaterial safety. Much attention has focused on nanoparticles that bind strongly to biological membranes or induce membrane damage, leading to adverse impacts on cells. More subtle effects on membrane function mediated via changes in biophysical properties of the phospholipid bilayer have received little study. Here, we combine electrophysiology measurements, infrared spectroscopy, and molecular dynamics simulations to obtain insight into a mode of nanoparticle-mediated modulation of membrane protein function that was previously only hinted at in prior work. Electrophysiology measurements on gramicidin A (gA) ion channels embedded in planar suspended lipid bilayers demonstrate that anionic gold nanoparticles (AuNPs) reduce channel activity and extend channel lifetimes without disrupting membrane integrity, in a manner consistent with changes in membrane mechanical properties. Vibrational spectroscopy indicates that AuNP interaction with the bilayer does not perturb the conformation of membrane-embedded gA. Molecular dynamics simulations reinforce the experimental findings, showing that anionic AuNPs do not directly interact with embedded gA channels but perturb the local properties of lipid bilayers. Our results are most consistent with a mechanism in which anionic AuNPs disrupt ion channel function in an indirect manner by altering the mechanical properties of the surrounding bilayer. Alteration of membrane mechanical properties represents a potentially important mechanism by which nanoparticles induce biological effects, as the function of many embedded membrane proteins depends on phospholipid bilayer biophysical properties.
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Whitaker, Michael. "How calcium may cause exocytosis in sea urchin eggs." Bioscience Reports 7, no. 5 (May 1, 1987): 383–97. http://dx.doi.org/10.1007/bf01362502.
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The process of secretory granule-plasma membrane fusion can be studied in sea urchin eggs. Micromolar calcium concentrations are all that is required to bring about exocytosis in vitro. I discuss recent experiments with sea urchin eggs that concentrate on the biophysical aspects of granule-membrane fusion. The backbone of biological membranes is the lipid bilayer. Sea urchin egg membrane lipids have negatively charged head groups that give rise to an electrical potential at the bilayer-water interface. We have found that this surface potential can affect the calcium required for exocytosis. Effects on the surface potential may also explain why drugs like trifluoperazine and tetracaine inhibit exocytosis: they absorb to the bilayer and reduce the surface potential. The membrane lipids may also be crucial to the formation of the exocytotic pore through which the secretory granule contents are released. We have measured calcium-induced production of the lipid, diacylglycerol. This lipid can induce a phase transition that will promote fusion of apposed lipid bilayers. The process of exocytosis involves the secretory granule core as well as the lipids of the membrane. The osmotic properties of the granule contents lead to swelling of the granule during exocytosis. Swelling promotes the dispersal of the contents as they are extruded through the exocytotic pore. The movements of water and ions during exocytosis may also stabilize the transient fusion intermediate and consolidate the exocytotic pore as fusion occurs.
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Janas, T., K. Nowotarski, W. I. Gruszecki, and T. Janas. "The effect of hexadecaprenol on molecular organisation and transport properties of model membranes." Acta Biochimica Polonica 47, no. 3 (September 30, 2000): 661–73. http://dx.doi.org/10.18388/abp.2000_3987.
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The Langmuir monolayer technique and voltammetric analysis were used to investigate the properties of model lipid membranes prepared from dioleoylphosphatidylcholine (DOPC), hexadecaprenol (C80), and their mixtures. Surface pressure-molecular area isotherms, current-voltage characteristics, and membrane conductance-temperature were measured. Molecular area isobars, specific molecular areas, excess free energy of mixing, collapse pressure and collapse area were determined for lipid monolayers. Membrane conductance, activation energy of ion migration across the membrane, and membrane permeability coefficient for chloride ions were determined for lipid bilayers. Hexadecaprenol decreases the activation energy and increases membrane conductance and membrane permeability coefficient. The results of monolayer and bilayer investigations show that some electrical, transport and packing properties of lipid membranes change under the influence of hexadecaprenol. The results indicate that hexadecaprenol modulates the molecular organisation of the membrane and that the specific molecular area of polyprenol molecules depends on the relative concentration of polyprenols in membranes. We suggest that hexadecaprenol modifies lipid membranes by the formation of fluid microdomains. The results also indicate that electrical transmembrane potential can accelerate the formation of pores in lipid bilayers modified by long chain polyprenols.
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Dlouhý, Ondřej, Uroš Javornik, Ottó Zsiros, Primož Šket, Václav Karlický, Vladimír Špunda, Janez Plavec, and Győző Garab. "Lipid Polymorphism of the Subchloroplast—Granum and Stroma Thylakoid Membrane—Particles. I. 31P-NMR Spectroscopy." Cells 10, no. 9 (September 8, 2021): 2354. http://dx.doi.org/10.3390/cells10092354.
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Build-up of the energized state of thylakoid membranes and the synthesis of ATP are warranted by organizing their bulk lipids into a bilayer. However, the major lipid species of these membranes, monogalactosyldiacylglycerol, is a non-bilayer lipid. It has also been documented that fully functional thylakoid membranes, in addition to the bilayer, contain an inverted hexagonal (HII) phase and two isotropic phases. To shed light on the origin of these non-lamellar phases, we performed 31P-NMR spectroscopy experiments on sub-chloroplast particles of spinach: stacked, granum and unstacked, stroma thylakoid membranes. These membranes exhibited similar lipid polymorphism as the whole thylakoids. Saturation transfer experiments, applying saturating pulses at characteristic frequencies at 5 °C, provided evidence for distinct lipid phases—with component spectra very similar to those derived from mathematical deconvolution of the 31P-NMR spectra. Wheat-germ lipase treatment of samples selectively eliminated the phases exhibiting sharp isotropic peaks, suggesting easier accessibility of these lipids compared to the bilayer and the HII phases. Gradually increasing lipid exchanges were observed between the bilayer and the two isotropic phases upon gradually elevating the temperature from 5 to 35 °C, suggesting close connections between these lipid phases. Data concerning the identity and structural and functional roles of different lipid phases will be presented in the accompanying paper.
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Ionov, Radoslav, and Angelina Angelova. "Swelling of bilayer lipid membranes." Thin Solid Films 284-285 (September 1996): 809–12. http://dx.doi.org/10.1016/s0040-6090(95)08452-5.
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Booth, P. J., R. H. Templer, A. R. Curran, and S. J. Allen. "Can we identify the forces that drive the folding of integral membrane proteins?" Biochemical Society Transactions 29, no. 4 (August 1, 2001): 408–13. http://dx.doi.org/10.1042/bst0290408.
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Protein folding has been at the forefront of molecular cell biology research for several years. However, integral membrane proteins have eluded detailed molecular level study until recently. One reason is the often apparently insurmountable problem of mimicking the natural membrane bilayer with lipid or detergent mixtures. There is nevertheless a large body of information on lipid properties and in particular on phosphatidylcholine and phosphatidylethanolamine lipids, which are common to many biological membranes. We have exploited this knowledge to design efficient in vitro, lipid-bilayer folding systems for membrane proteins. Bacteriorhodopsin has been used as a model system for our initial studies: we have shown that a rate-limiting apoprotein folding step and the overall folding efficiency seem to be controlled by particular properties of the lipid bilayer. The properties of interest are the stored curvature elastic energy within the bilayer and the lateral pressure that the lipid chains exert on their neighbouring folding protein. These are generic properties of the bilayer that can be achieved with simple mixtures of many types of biological lipid and seem to be important in vivo.
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Kremkow, Jan, Meike Luck, Daniel Huster, Peter Müller, and Holger A. Scheidt. "Membrane Interaction of Ibuprofen with Cholesterol-Containing Lipid Membranes." Biomolecules 10, no. 10 (September 28, 2020): 1384. http://dx.doi.org/10.3390/biom10101384.
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Deciphering the membrane interaction of drug molecules is important for improving drug delivery, cellular uptake, and the understanding of side effects of a given drug molecule. For the anti-inflammatory drug ibuprofen, several studies reported contradictory results regarding the impact of ibuprofen on cholesterol-containing lipid membranes. Here, we investigated membrane localization and orientation as well as the influence of ibuprofen on membrane properties in POPC/cholesterol bilayers using solid-state NMR spectroscopy and other biophysical assays. The presence of ibuprofen disturbs the molecular order of phospholipids as shown by alterations of the 2H and 31P-NMR spectra of the lipids, but does not lead to an increased membrane permeability or changes of the phase state of the bilayer. 1H MAS NOESY NMR results demonstrate that ibuprofen adopts a mean position in the upper chain/glycerol region of the POPC membrane, oriented with its polar carbonyl group towards the aqueous phase. This membrane position is only marginally altered in the presence of cholesterol. A previously reported result that ibuprofen is expelled from the membrane interface in cholesterol-containing DMPC bilayers could not be confirmed.
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Hill, Reghan J., and Chih-Ying Wang. "Diffusion in phospholipid bilayer membranes: dual-leaflet dynamics and the roles of tracer–leaflet and inter-leaflet coupling." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2167 (July 8, 2014): 20130843. http://dx.doi.org/10.1098/rspa.2013.0843.
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A variety of observations—sometimes controversial—have been made in recent decades when attempting to elucidate the roles of interfacial slip on tracer diffusion in phospholipid membranes. Evans–Sackmann theory (1988) has furnished membrane viscosities and lubrication-film thicknesses for supported membranes from experimentally measured lateral diffusion coefficients. Similar to the Saffman and Delbrück model, which is the well-known counterpart for freely supported membranes, the bilayer is modelled as a single two-dimensional fluid. However, the Evans–Sackman model cannot interpret the mobilities of monotopic tracers, such as individual lipids or rigidly bound lipid assemblies; neither does it account for tracer–leaflet and inter-leaflet slip. To address these limitations, we solve the model of Wang and Hill, in which two leaflets of a bilayer membrane, a circular tracer and supports are coupled by interfacial friction, using phenomenological friction/slip coefficients. This furnishes an exact solution that can be readily adopted to interpret the mobilities of a variety of mosaic elements—including lipids, integral monotopic and polytopic proteins, and lipid rafts—in supported bilayer membranes.
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Dawidowicz, E. A. "Membrane lipid biogenesis and transport." Proceedings, annual meeting, Electron Microscopy Society of America 44 (August 1986): 70–71. http://dx.doi.org/10.1017/s0424820100142050.
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Membrane biogenesis is an essential feature of cellular development and growth. The initial assembly of membrane lipids and proteins occurs primarily in the endoplasmic reticulum (ER). It has been demonstrated that the enzymes involved in the de novo biosynthesis of phospholipids are exclusively located on the cytoplasmic surface of the ER. A rapid transbilayer movement of phospholipids has also been reported in isolated liver microsomes, which is compatible with the movement of newly synthesized lipids to the lumenal surface of the ER. Comparison with the transbilayer movement of phospholipids across protein-free lipid bilayers, has lead to the proposal that a protein which would catalyze the translocation of phospholipids across the ER membrane (“flipase”), might be involved in the assembly of the lipid bilayer of the ER. Since the various membranes in a eukaryotic cell differ markedly in their lipid composition, it is clear that specific sorting and transport of these membrane components must occur.
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Hoogerheide, David P., Sergei Yu Noskov, Adam J. Kuszak, Susan K. Buchanan, Tatiana K. Rostovtseva, and Hirsh Nanda. "Structure of voltage-dependent anion channel-tethered bilayer lipid membranes determined using neutron reflectivity." Acta Crystallographica Section D Structural Biology 74, no. 12 (November 30, 2018): 1219–32. http://dx.doi.org/10.1107/s2059798318011749.
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Neutron reflectivity (NR) has emerged as a powerful technique to study the structure and behavior of membrane proteins at planar lipid interfaces. Integral membrane proteins (IMPs) remain a significant challenge for NR owing to the difficulty of forming complete bilayers with sufficient protein density for scattering techniques. One strategy to achieve high protein density on a solid substrate is the capture of detergent-stabilized, affinity-tagged IMPs on a nitrilotriacetic acid (NTA)-functionalized self-assembled monolayer (SAM), followed by reconstitution into the lipids of interest. Such protein-tethered bilayer lipid membranes (ptBLMs) have the notable advantage of a uniform IMP orientation on the substrate. Here, NR is used to provide a structural characterization of the ptBLM process from formation of the SAM to capture of the detergent-stabilized IMP and lipid reconstitution. The mitochondrial outer-membrane voltage-dependent anion channel (VDAC), which controls the exchange of bioenergetic metabolites between mitochondria and the cytosol, was used as a model β-barrel IMP. Molecular dynamics simulations were used for comparison with the experimental results and to inform the parameters of the physical models describing the NR data. The detailed structure of the SAM is shown to depend on the density of the NTA chelating groups. The relative content of detergent and protein in surface-immobilized, detergent-stabilized VDAC is measured, while the reconstituted lipid bilayer is shown to be complete to within a few percent, using the known atomic structure of VDAC. Finally, excess lipid above the reconstituted bilayer, which is of consequence for more indirect structural and functional studies, is shown to be present.
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Wanderlingh, U., G. D'Angelo, V. Conti Nibali, C. Crupi, S. Rifici, C. Corsaro, and G. Sabatino. "Interaction of alcohol with phospholipid membrane: NMR and XRD investigations on DPPC–hexanol system." Spectroscopy 24, no. 3-4 (2010): 375–80. http://dx.doi.org/10.1155/2010/730327.
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The investigations of the interaction between phospholipid bilayer and short-chain alcohols are relevant for the potential of lipid bilayer membranes to serve as model systems for studies of various biological processes including permeability of the plasma membrane and molecular mechanisms of anesthesia. Because the hydrophobic portion of an alcohol favorably interacts with lipid hydrocarbon chains, the polar hydroxyl group remains free to form hydrogen bonds with polar lipid atoms that are located near the water/lipid interface. Experiments on phospholipid membranes have shown that alcohols can induce an interdigitated phase and at high concentration even promote the assembly of some lipids into non-bilayer structures within the membrane interior. In this paper we have investigated the DPPC:hexanol system at high alcohol concentration (two molecules per phospholipid) by means of calorimetric, Nuclear Magnetic Resonance, X-ray diffraction and density measurements. We have found that the presence of a high alcohol concentration shifts the membrane transition temperature to lower values, and has a disordering effect on the phospholipid acyl chains in the gel phase. The bilayer spacing and the area of polar head have been also derived for the liquid phase.
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Coorssen, Jens R., and R. P. Rand. "Effects of cholesterol on the structural transitions induced by diacylglycerol in phosphatidylcholine and phosphatidylethanolamine bilayer systems." Biochemistry and Cell Biology 68, no. 1 (January 1, 1990): 65–69. http://dx.doi.org/10.1139/o90-008.
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The transient membrane lipid diacylglycerol (DG) is known to modify and destabilize phospholipid bilayers and can lead to the formation of nonbilayer structures. Since cholesterol forms a major fraction of many plasma membranes, we have investigated how it modifies the structural effects of DG on bilayers of egg phosphatidylcholine (PC) and egg phosphatidylethanolamine (PE). We view these systems as modelling the behaviour of local, DG-containing sites in membranes. Using X-ray diffraction, we have characterized the lamellar (Lα) and inverse hexagonal (HII) structures that these ternary lipid mixtures form in excess aqueous solution. As the DG level increases, the lipid progresses from a single Lα structure to a mixture of Lα and HII, and then to a pure HII structure. This allows determination of the DG levels at which the HII transition begins, which we interpret as those levels that destabilize bilayers. In both PC and PE bilayers, the presence of 30 mol% cholesterol reduces the amounts of DG required to destabilize the bilayer structure. The destabilization can be translated into the number of neighbouring lipid molecules that a DG molecule perturbs, and of bilayer areas that it affects. The data show that the presence of cholesterol greatly enhances the perturbing effects of DG. We examine the possible role of DG in enzyme activation and membrane fusion.Key words: diacylglycerol, cholesterol, bilayers, phosphatidylcholine, phosphatidylethanolamine.
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Kent, Ben, Taavi Hunt, Tamim A. Darwish, Thomas Hauß, Christopher J. Garvey, and Gary Bryant. "Localization of trehalose in partially hydrated DOPC bilayers: insights into cryoprotective mechanisms." Journal of The Royal Society Interface 11, no. 95 (June 6, 2014): 20140069. http://dx.doi.org/10.1098/rsif.2014.0069.
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Trehalose, a natural disaccharide with bioprotective properties, is widely recognized for its ability to preserve biological membranes during freezing and dehydration events. Despite debate over the molecular mechanisms by which this is achieved, and that different mechanisms imply quite different distributions of trehalose molecules with respect to the bilayer, there are no direct experimental data describing the location of trehalose within lipid bilayer membrane systems during dehydration. Here, we use neutron membrane diffraction to conclusively show that the trehalose distribution in a dioleoylphosphatidylcholine (DOPC) system follows a Gaussian profile centred in the water layer between bilayers. The absence of any preference for localizing near the lipid headgroups of the bilayers indicates that the bioprotective effects of trehalose at physiologically relevant concentrations are the result of non-specific mechanisms that do not rely on direct interactions with the lipid headgroups.
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Banerjee, Sourabh, and Crina M. Nimigean. "Non-vesicular transfer of membrane proteins from nanoparticles to lipid bilayers." Journal of General Physiology 137, no. 2 (January 31, 2011): 217–23. http://dx.doi.org/10.1085/jgp.201010558.
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Discoidal lipoproteins are a novel class of nanoparticles for studying membrane proteins (MPs) in a soluble, native lipid environment, using assays that have not been traditionally applied to transmembrane proteins. Here, we report the successful delivery of an ion channel from these particles, called nanoscale apolipoprotein-bound bilayers (NABBs), to a distinct, continuous lipid bilayer that will allow both ensemble assays, made possible by the soluble NABB platform, and single-molecule assays, to be performed from the same biochemical preparation. We optimized the incorporation and verified the homogeneity of NABBs containing a prototypical potassium channel, KcsA. We also evaluated the transfer of KcsA from the NABBs to lipid bilayers using single-channel electrophysiology and found that the functional properties of the channel remained intact. NABBs containing KcsA were stable, homogeneous, and able to spontaneously deliver the channel to black lipid membranes without measurably affecting the electrical properties of the bilayer. Our results are the first to demonstrate the transfer of a MP from NABBs to a different lipid bilayer without involving vesicle fusion.
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Neupane, Shova, George Cordoyiannis, Frank Uwe Renner, and Patricia Losada-Pérez. "Real-Time Monitoring of Interactions between Solid-Supported Lipid Vesicle Layers and Short- and Medium-Chain Length Alcohols: Ethanol and 1-Pentanol." Biomimetics 4, no. 1 (January 22, 2019): 8. http://dx.doi.org/10.3390/biomimetics4010008.
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Lipid bilayers represent the interface between the cell and its environment, serving as model systems for the study of various biological processes. For instance, the addition of small molecules such as alcohols is a well-known process that modulates lipid bilayer properties, being considered as a reference for general anesthetic molecules. A plethora of experimental and simulation studies have focused on alcohol’s effect on lipid bilayers. Nevertheless, most studies have focused on lipid membranes formed in the presence of alcohols, while the effect of n-alcohols on preformed lipid membranes has received much less research interest. Here, we monitor the real-time interaction of short-chain alcohols with solid-supported vesicles of dipalmitoylphosphatidylcholine (DPPC) using quartz crystal microbalance with dissipation monitoring (QCM-D) as a label-free method. Results indicate that the addition of ethanol at different concentrations induces changes in the bilayer organization but preserves the stability of the supported vesicle layer. In turn, the addition of 1-pentanol induces not only changes in the bilayer organization, but also promotes vesicle rupture and inhomogeneous lipid layers at very high concentrations.
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Weatherill, E. E., H. L. E. Coker, M. R. Cheetham, and M. I. Wallace. "Urea-mediated anomalous diffusion in supported lipid bilayers." Interface Focus 8, no. 5 (August 17, 2018): 20180028. http://dx.doi.org/10.1098/rsfs.2018.0028.
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Diffusion in biological membranes is seldom simply Brownian motion; instead, the rate of diffusion is dependent on the time scale of observation and so is often described as anomalous. In order to help better understand this phenomenon, model systems are needed where the anomalous diffusion of the lipid bilayer can be tuned and quantified. We recently demonstrated one such model by controlling the excluded area fraction in supported lipid bilayers (SLBs) through the incorporation of lipids derivatized with polyethylene glycol. Here, we extend this work, using urea to induce anomalous diffusion in SLBs. By tuning incubation time and urea concentration, we produce bilayers that exhibit anomalous behaviour on the same scale as that observed in biological membranes.
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Janas, T., T. Chojnacki, E. Swiezewska, and T. Janas. "The effect of undecaprenol on bilayer lipid membranes." Acta Biochimica Polonica 41, no. 3 (September 30, 1994): 351–58. http://dx.doi.org/10.18388/abp.1994_4725.
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The influence of undecaprenol on phosphatidylcholine macrovesicular bilayer lipid membranes has been studied by electrophysiological techniques. The current-voltage characteristics, ionic transference numbers, the membrane conductance-temperature relationships and the membrane breakdown voltage were measured. The permeability coefficients for Na+ and Cl- ions, the activation energy of ion migration across the membrane, the membrane hydrophobic thickness and the membrane Young's modulus were determined. Undecaprenol increases membrane conductance, membrane capacitance, membrane ionic permeability and membrane elastic deformability, decreases the activation energy, membrane hydrophobic thickness and membrane electromechanical stability, and does not change membrane selectivity. The formation by undecaprenyl molecules of fluid microdomains modulating membrane hydrophobic thickness is postulated. The data suggest that the behaviour of undecaprenol in membranes is regulated by transmembrane electrical potential.
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Clifton, Luke A., Maximilian W. A. Skoda, Emma L. Daulton, Arwel V. Hughes, Anton P. Le Brun, Jeremy H. Lakey, and Stephen A. Holt. "Asymmetric phospholipid: lipopolysaccharide bilayers; a Gram-negative bacterial outer membrane mimic." Journal of The Royal Society Interface 10, no. 89 (December 6, 2013): 20130810. http://dx.doi.org/10.1098/rsif.2013.0810.
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The Gram-negative bacterial outer membrane (OM) is a complex and highly asymmetric biological barrier but the small size of bacteria has hindered advances in in vivo examination of membrane dynamics. Thus, model OMs, amenable to physical study, are important sources of data. Here, we present data from asymmetric bilayers which emulate the OM and are formed by a simple two-step approach. The bilayers were deposited on an SiO 2 surface by Langmuir–Blodgett deposition of phosphatidylcholine as the inner leaflet and, via Langmuir–Schaefer deposition, an outer leaflet of either Lipid A or Escherichia coli rough lipopolysaccharides (LPS). The membranes were examined using neutron reflectometry (NR) to examine the coverage and mixing of lipids between the bilayer leaflets. NR data showed that in all cases, the initial deposition asymmetry was mostly maintained for more than 16 h. This stability enabled the sizes of the headgroups and bilayer roughness of 1,2-dipalmitoyl- sn -glycero-3-phosphocholine and Lipid A, Rc-LPS and Ra-LPS to be clearly resolved. The results show that rough LPS can be manipulated like phospholipids and used to fabricate advanced asymmetric bacterial membrane models using well-known bilayer deposition techniques. Such models will enable OM dynamics and interactions to be studied under in vivo -like conditions.
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Gabrielska, Janina, Teresa Kral, Marek Langner, and Stanislaw Przestalski. "Different Effects of Di- and Triphenyltin Compounds on Lipid Bilayer Dithionite Permeabilization." Zeitschrift für Naturforschung C 55, no. 9-10 (October 1, 2000): 758–63. http://dx.doi.org/10.1515/znc-2000-9-1014.
Full textAbstract:
Abstract Phenyltins are chemicals widely used in industry, hence their occurrence in the human environment is frequent and widespread. Such compounds include hydrophobic phenyl rings bonded to positively charged tin. This molecular structure makes them capable of adsorbing onto and penetrating through biological membranes, hence they are potentially hazardous. Two such compounds, diphenyltin and triphenyltin, show different steric constraints when interacting with the lipid bilayer. It has been demonstrated that these compounds are positioned at different locations within model lipid bilayers, causing dissimilarity in their ability to affect membrane properties. In this paper we present a study regarding the ability of these two phenyltins to facilitate the transport of S2O4-2 ions across the lipid bilayer, evaluated by a fluorescence quenching assay. In concentration range of up-to 60 μm those compounds do not affect lipid bilayer topology, when evaluated by vesicle size distribution. Both phenyltins facilitate the transfer of S2O4-2 across the model lipid bilayer, but the dependence of dithionite transport on phenyltin concentration is different for both. In principle, above 20 μm triphenyltin is more efficient in transfering ions across the lipid bilayer than diphenyltin.
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LEMMICH, JESPER, JOHN HJORT IPSEN, THOMAS HØNGER, KENT JØRGENSEN, OLE G. MOURITSEN, KELL MORTENSEN, and ROGERT BAUER. "SOFT AND REPULSIVE: RELATIONSHIP BETWEEN LIPID MEMBRANE IN-PLANE FLUCTUATIONS, BENDING RIGIDITY, AND REPULSIVE UNDULATION FORCES." Modern Physics Letters B 08, no. 29 (December 20, 1994): 1803–14. http://dx.doi.org/10.1142/s0217984994001710.
Full textAbstract:
Lipid membranes are soft and flexible bilayer surfaces that exhibit a substantial degree of in-plane fluctuations which become very strong near lipid phase transitions and in phase separation regions. The fluctuations couple to the out-of-plane motions as well as the large-scale mechanical modulii of the membrane leading to a thermal renormalization of, e.g., the bending rigidity. For multilamellar arrays of membranes, changes in the bending rigidity in turn lead to changes in the entropic repulsive undulation forces that act between the lamellae and which determine their swelling behavior. We briefly review recent results obtained from theoretical and experimental studies of phospholipid bilayers that clarify the relationship between lipid bilayer in-plane fluctuations (in density and composition), bending rigidity, and repulsive undulation forces. The results discussed derive from computer simulation calculations, field theory, as well as small angle neutron scattering.