Journal articles: 'Black lipid bilayers'

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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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Alghalayini, Amani, Alvaro Garcia, Thomas Berry, and Charles Cranfield. "The Use of Tethered Bilayer Lipid Membranes to Identify the Mechanisms of Antimicrobial Peptide Interactions with Lipid Bilayers." Antibiotics 8, no. 1 (January 30, 2019): 12. http://dx.doi.org/10.3390/antibiotics8010012.

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This review identifies the ways in which tethered bilayer lipid membranes (tBLMs) can be used for the identification of the actions of antimicrobials against lipid bilayers. Much of the new research in this area has originated, or included researchers from, the southern hemisphere, Australia and New Zealand in particular. More and more, tBLMs are replacing liposome release assays, black lipid membranes and patch-clamp electrophysiological techniques because they use fewer reagents, are able to obtain results far more quickly and can provide a uniformity of responses with fewer artefacts. In this work, we describe how tBLM technology can and has been used to identify the actions of numerous antimicrobial agents.

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Pazur, Alexander. "The Effect of Weak Permanent Magnetic Fields on the Electric Properties of Lipid-Bilayers." Zeitschrift für Naturforschung C 50, no. 11-12 (December 1, 1995): 833–39. http://dx.doi.org/10.1515/znc-1995-11-1215.

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Abstract Black lipid membranes were prepared on a Teflon septum separating electrically the two chambers of a Teflon cuvette, using the technique of Mueller et al., (Nature 194. 979 (1962)). An external, static magnetic field was applied, whose intensity varied from 0 G to 100 G at the membrane location. Field applications higher than 10 G are effecting higher leakage currents, increased capacity and faster breakdown of the bilayer state, as compared to the absence of a magnetic field. If bilayers were doped with chlorophyll a, these effects were increased. Quantum mechanical and thermodynamical phenomena on membranes will be discussed as possible origins of these effects.

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Geng, Shengyong, Lie Wu, Haodong Cui, Wenyong Tan, Tianfeng Chen, Paul K. Chu, and Xue-Feng Yu. "Synthesis of lipid–black phosphorus quantum dot bilayer vesicles for near-infrared-controlled drug release." Chemical Communications 54, no. 47 (2018): 6060–63. http://dx.doi.org/10.1039/c8cc03423k.

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Black phosphorus quantum dots are incorporated into liposomal bilayers to produce a drug delivery system with excellent near-infrared (NIR) photothermal properties and drug release capability controlled by light.

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Ovalle-García, Erasmo, and Iván Ortega-Blake. "Joining patch-clamp and atomic force microscopy techniques for studying black lipid bilayers." Applied Physics Letters 91, no. 9 (August 27, 2007): 093901. http://dx.doi.org/10.1063/1.2776356.

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Bednarczyk, Piotr, Adam Szewczyk, and Krzysztof Dołowy. "Transmembrane segment M2 of glycine receptor as a model system for the pore-forming structure of ion channels." Acta Biochimica Polonica 49, no. 4 (December 31, 2002): 869–75. http://dx.doi.org/10.18388/abp.2002_3746.

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The glycine receptor belongs to the ligand-gated ion channel superfamily. It is a chloride conducting channel composed of four transmembrane domains. It was previously shown that the second transmembrane domain (M2) of the glycine receptor forms an ion conduction pathway throughout lipid bilayers. The amino-acid sequence of the transmembrane segment M2 of the glycine receptor has a high homology to all receptors of the ligand-gated ion channel superfamily. In our report, we have used a synthetic M2 peptide. It was incorporated into a planar membrane of known lipid composition and currents induced by M2 were measured by the Black Lipid Membrane technique. When the planar lipid bilayer was composed of 75% phosphatidylethanolamine and 25% phosphatidylserine, the reversal potential measured in a 150/600 mM KCl (cis/trans) gradient was -19 mV suggesting that the examined >pore was preferential to anions, P(K)/P(Cl) = 0.25. In contrast, when 75% phosphatidylserine and 25% phosphatidylethanolamine was used, the reversal potential was +20 mV and the >pore was preferential to cations, P(K)/P(Cl) = 4.36. Single-channel currents were recorded with two predominant amplitudes corresponding to the main-conductance and sub-conductance states. Both conductance states (about 12 pS and 30 pS) were measured in a symmetric solution of 50 mM KCl. The observed single-channel properties suggest that the selectivity and conductance of the pore formed by the M2 peptide of the glycine receptor depend on the lipid composition of the planar bilayer.

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Takei, Tomohiko, Tatsuya Yaguchi, Takuya Fujii, Tomonori Nomoto, Taro Toyota, and Masanori Fujinami. "Measurement of membrane tension of free standing lipid bilayers via laser-induced surface deformation spectroscopy." Soft Matter 11, no. 44 (2015): 8641–47. http://dx.doi.org/10.1039/c5sm01264c.

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Non-invasive measurement of the membrane tension of free-standing black lipid membranes (BLMs), with sensitivity on the order of μN m⁻¹, was achieved using laser-induced surface deformation (LISD) spectroscopy.

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Jing, Peng, Hallel Paraiso, and Benjamin Burris. "Highly efficient integration of the viral portal proteins from different types of phages into planar bilayers for the black lipid membrane analysis." Molecular BioSystems 12, no. 2 (2016): 480–89. http://dx.doi.org/10.1039/c5mb00573f.

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Corvalán, Natalia A., and María A. Perillo. "Probing Thermotropic Phase Behavior of Dipalmitoylphosphatidylcholine Bilayers from Electrical and Topographic Data in a Horizontal Black Lipid Membrane Model." Langmuir 36, no. 5 (January 15, 2020): 1083–93. http://dx.doi.org/10.1021/acs.langmuir.9b02854.

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10

Kharchenko, L. P., and I. A. Lykova. "Littoral invertebrates in waders’ nutrition at migratory stopover sites in the Azov and Black Sea region." Ecology and Noospherology 25, no. 1-2 (January 14, 2014): 69–82. http://dx.doi.org/10.15421/031407.

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Seasonal migration for birds – distant migrants are the most energy intensive. Fat reserves accumulated in the bird’s body before migration and during migratory stopovers determine success of the long-distance flight. Lipids play a vital role both as a source of energy and as structural components of cell membranes. For most migrants to the speed and quality processes fat accumulation affects the feed ration in the field of migration stops. Fodder saturation with essential polyunsaturated fatty acids (PUFAs) is of great importance. Being paramount for physiological processes, these acids cannot be synthesized in the bird’s body. The proposed article is dedicated to the study of waders’ trophic relationships with their prey items, and the use of PUFAs as biochemical markers. This approach is based on the specificity of the fatty acids contained in the lipids of invertebrate to be used as food bird species studied. Significant amount NPZHK waders obtained from forage that can be considered PUFAs as biochemical markers to determine the range and diversity of food producing birds PUFAs ways, and also to study the food chain in ecosystems. A fatty acid spectrum (FAS) of the lipids common for nine littoral invertebrate species (Gammarus aequicauda, Idotea balthica, Artemia salina, Nerеis sp., Nerеis zonata, Theodoxces astrachanicus, Hydrobia acuta, Chironomus salinarius, Chironomus plumosus), which constitute the main component of waders’ diet at the migratory stopover sites in the Azov and Black Sea region, has been studied. Found that the largest amount of total lipids contained in Nereis zonata (4,6 %) and Artemia salina (4,4 %), the lowest amount of total lipids was observed in Chironomus (1,5–1,8 %), which implies that polychaete worms and Artemia salina, as a source of fat, are the most productive for waders. Our research has found that mollusks, polychaete worms, and Artemia salina are the most effective waders’ fodder in the PUFAs content. Mollusks contain the largest amount of PUFAs, their spectrum is ω3 and ω6 PUFAs, especially arаchidonic acid C20:4. Polychate worms are also characterized by a high PUFAs level; they serve for birds as a source of linolenic and linoleic acid groups. Artemia salina contains a large amount of eicosapentaenoic С20:5ω3 and docosahexaenoic С22:6ω3 acids, which getting to an organism of birds, participating in the formation of cell membranes, act as thermal stabilizer lipid bilayers, enhance stamina during long-distance flight. A high abundance of Artemia salina in the feeding areas permit tundra waders to use them as a prey item, which can fulfill the bird’s body with a required amount of fatty acids in a short time. We have established an influence of some environmental factors, as water temperature and salinity, on the lipids FAS of littoral invertebrates. Spectrum analysis of polyene fatty acids in the lipids closely related species of invertebrates living in different salinity water showed that the content of PUFAs in the lipid depend on their food spectrum, and the environmental conditions. Therefore, anthropogenic pressure and changes of water hydrological regime may affect PUFAs content in the lipids of littoral invertebrates. In its turn, this factor may change alimentary behavior and migratory strategy of the birds, which use migratory stopover sites in the region in question. Shallow waters of the Azov-Black Sea region are characterized by different climatic characteristics and a large reserve of phytoplankton. This explains the mass character species studied of invertebrates to feeding areas and their use as basic prey items, many species of waders.

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11

Park, Jin Bong, Hee Jeong Kim, Pan Dong Ryu, and Edward Moczydlowski. "Effect of Phosphatidylserine on Unitary Conductance and Ba2+ Block of the BK Ca2+–activated K+ Channel." Journal of General Physiology 121, no. 5 (April 14, 2003): 375–98. http://dx.doi.org/10.1085/jgp.200208746.

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Incorporation of BK Ca2+–activated K+ channels into planar bilayers composed of negatively charged phospholipids such as phosphatidylserine (PS) or phosphatidylinositol (PI) results in a large enhancement of unitary conductance (gch) in comparison to BK channels in bilayers formed from the neutral zwitterionic lipid, phospatidylethanolamine (PE). Enhancement of gch by PS or PI is inversely dependent on KCl concentration, decreasing from 70% at 10 mM KCl to 8% at 1,000 mM KCl. This effect was explained previously by a surface charge hypothesis (Moczydlowski, E., O. Alvarez, C. Vergara, and R. Latorre. 1985. J. Membr. Biol. 83:273–282), which attributed the conductance enhancement to an increase in local K+ concentration near the entryways of the channel. To test this hypothesis, we measured the kinetics of block by external and internal Ba2+, a divalent cation that is expected to respond strongly to changes in surface electrostatics. We observed little or no effect of PS on discrete blocking kinetics by external and internal Ba2+ at 100 mM KCl and only a small enhancement of discrete and fast block by external Ba2+ in PS-containing membranes at 20 mM KCl. Model calculations of effective surface potential sensed by the K+ conduction and Ba2+-blocking reactions using the Gouy-Chapman-Stern theory of lipid surface charge do not lend support to a simple electrostatic mechanism that predicts valence-dependent increase of local cation concentration. The results imply that the conduction pore of the BK channel is electrostatically insulated from the lipid surface, presumably by a lateral distance of separation (>20 Å) from the lipid head groups. The lack of effect of PS on apparent association and dissociation rates of Ba2+ suggest that lipid modulation of K+ conductance is preferentially coupled through conformational changes of the selectivity filter region that determine the high K+ flux rate of this channel relative to other cations. We discuss possible mechanisms for the effect of anionic lipids in the context of specific molecular interactions of phospholipids documented for the KcsA bacterial potassium channel and general membrane physical properties proposed to regulate membrane protein conformation via energetics of bilayer stress.

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12

Tan, Luoxi, James G. Elkins, Brian H. Davison, Elizabeth G. Kelley, and Jonathan Nickels. "Implementation of a self-consistent slab model of bilayer structure in the SasView suite." Journal of Applied Crystallography 54, no. 1 (February 1, 2021): 363–70. http://dx.doi.org/10.1107/s1600576720015526.

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Slab models are simple and useful structural descriptions which have long been used to describe lyotropic lamellar phases, such as lipid bilayers. Typically, slab models assume a midline symmetry and break a bilayer structure into three pieces, a central solvent-free core and two symmetric outer layers composed of the soluble portion of the amphiphile and associated solvent. This breakdown matches reasonably well to the distribution of neutron scattering length density and therefore is a convenient and common approach for the treatment of small-angle scattering data. Here, an implementation of this model within the SasView software suite is reported. The implementation is intended to provide physical consistency through the area per amphiphile molecule and number of solvent molecules included within the solvent-exposed outer layer. The proper use of this model requires knowledge of (or good estimates for) the amphiphile and solvent molecule volume and atomic composition, ultimately providing a self-consistent data treatment with only two free parameters: the lateral area per amphiphile molecule and the number of solvent molecules included in the outer region per amphiphile molecule. The use of this code is demonstrated in the fitting of standard lipid bilayer data sets, obtaining structural parameters consistent with prior literature and illustrating the typical and ideal cases of fitting for neutron scattering data obtained using single or multiple contrast conditions. While demonstrated here for lipid bilayers, this model is intended for general application to block copolymers, surfactants, and other lyotropic lamellar phase structures for which a slab model is able to reasonably estimate the neutron scattering length density/electron-density profile of inner and outer layers of the lamellae.

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Willes, Keith L., Jasmyn R. Genchev, and Walter F. Paxton. "Hybrid Lipid-Polymer Bilayers: pH-Mediated Interactions between Hybrid Vesicles and Glass." Polymers 12, no. 4 (March 28, 2020): 745. http://dx.doi.org/10.3390/polym12040745.

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One practical approach towards robust and stable biomimetic platforms is to generate hybrid bilayers that incorporate both lipids and block co-polymer amphiphiles. The currently limited number of reports on the interaction of glass surfaces with hybrid lipid and polymer vesicles—DOPC mixed with amphiphilic poly(ethylene oxide-b-butadiene) (PEO-PBd)—describe substantially different conclusions under very similar conditions (i.e., same pH). In this study, we varied vesicle composition and solution pH in order to generate a broader picture of spontaneous hybrid lipid/polymer vesicle interactions with rigid supports. Using quartz crystal microbalance with dissipation (QCM-D), we followed the interaction of hybrid lipid-polymer vesicles with borosilicate glass as a function of pH. We found pH-dependent adsorption/fusion of hybrid vesicles that accounts for some of the contradictory results observed in previous studies. Our results show that the formation of hybrid lipid-polymer bilayers is highly pH dependent and indicate that the interaction between glass surfaces and hybrid DOPC/PEO-PBd can be tuned with pH.

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Fischer, Torsten, Ivan I. Senin, Pavel P. Philippov, and Karl-Wilhelm Koch. "Application of Different Lipid Surfaces to Monitor Protein–Membrane Interactions by Surface Plasmon Resonance Spectroscopy." Spectroscopy 16, no. 3-4 (2002): 271–79. http://dx.doi.org/10.1155/2002/630549.

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Planar lipid bilayers on sensor chip surfaces have become useful tools to study membrane bound processes by surface plasmon resonance spectroscopy. We immobilized phospholipids on sensor chips by different approaches. First, a self-assembled monolayer of octadecylmercaptan was formed on a blank gold surface and subsequent addition of phospholipids led to formation of a heterobilayer. Second, a self-assembled monolayer of mercaptoundecanoic acid was formed on a gold surface, the carboxy groups of mercaptoundecanoic acid were activated and covalently linked to phosphatidylethanolamine. Addition of phospholipids then led to a bilayer with phosphatidylethanolamine as the lower leaflet. Third, a hydrophobic sensor chip (L1, BIAcore) was used as a binding matrix for phospholipids. These lipid surfaces were tested, whether they are suitable to study proteinamembrane interactions. As biological test system we used the Ca2+-myristoyl-switch of the neuronal Ca2+-binding protein recoverin. All three surfaces were sufficiently stable to monitor the Ca2+-dependent binding of recoverin to membranes.

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Exerowa, Dotchi, Roumen Todorov, and Ljubomir Nikolov. "Amphiphile bilayer films from DPPC: bilayer lipid membranes and Newton black films." Colloids and Surfaces A: Physicochemical and Engineering Aspects 250, no. 1-3 (December 2004): 195–201. http://dx.doi.org/10.1016/j.colsurfa.2004.04.089.

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Freisleben, Hans-Joachim. "The Main (Glyco) Phospholipid (MPL) of Thermoplasma acidophilum." International Journal of Molecular Sciences 20, no. 20 (October 21, 2019): 5217. http://dx.doi.org/10.3390/ijms20205217.

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The main phospholipid (MPL) of Thermoplasma acidophilum DSM 1728 was isolated, purified and physico-chemically characterized by differential scanning calorimetry (DSC)/differential thermal analysis (DTA) for its thermotropic behavior, alone and in mixtures with other lipids, cholesterol, hydrophobic peptides and pore-forming ionophores. Model membranes from MPL were investigated; black lipid membrane, Langmuir-Blodgett monolayer, and liposomes. Laboratory results were compared to computer simulation. MPL forms stable and resistant liposomes with highly proton-impermeable membrane and mixes at certain degree with common bilayer-forming lipids. Monomeric bacteriorhodopsin and ATP synthase from Micrococcus luteus were co-reconstituted and light-driven ATP synthesis measured. This review reports about almost four decades of research on Thermoplasma membrane and its MPL as well as transfer of this research to Thermoplasma species recently isolated from Indonesian volcanoes.

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Abu-Farha, Mohamed, Thangavel Alphonse Thanaraj, Mohammad G. Qaddoumi, Anwar Hashem, Jehad Abubaker, and Fahd Al-Mulla. "The Role of Lipid Metabolism in COVID-19 Virus Infection and as a Drug Target." International Journal of Molecular Sciences 21, no. 10 (May 17, 2020): 3544. http://dx.doi.org/10.3390/ijms21103544.

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The current Coronavirus disease 2019 or COVID-19 pandemic has infected over two million people and resulted in the death of over one hundred thousand people at the time of writing this review. The disease is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Even though multiple vaccines and treatments are under development so far, the disease is only slowing down under extreme social distancing measures that are difficult to maintain. SARS-COV-2 is an enveloped virus that is surrounded by a lipid bilayer. Lipids are fundamental cell components that play various biological roles ranging from being a structural building block to a signaling molecule as well as a central energy store. The role lipids play in viral infection involves the fusion of the viral membrane to the host cell, viral replication, and viral endocytosis and exocytosis. Since lipids play a crucial function in the viral life cycle, we asked whether drugs targeting lipid metabolism, such as statins, can be utilized against SARS-CoV-2 and other viruses. In this review, we discuss the role of lipid metabolism in viral infection as well as the possibility of targeting lipid metabolism to interfere with the viral life cycle.

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Hemsley, G., and D. Busath. "Small iminium ions block gramicidin channels in lipid bilayers." Biophysical Journal 59, no. 4 (April 1991): 901–7. http://dx.doi.org/10.1016/s0006-3495(91)82303-7.

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19

Kapicka, C. L., A. Carl, M. L. Hall, A. L. Percival, B. W. Frey, and J. L. Kenyon. "Comparison of large-conductance Ca(2+)-activated K+ channels in artificial bilayer and patch-clamp experiments." American Journal of Physiology-Cell Physiology 266, no. 3 (March 1, 1994): C601—C610. http://dx.doi.org/10.1152/ajpcell.1994.266.3.c601.

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We compared the gating, ion conduction, and pharmacology of large-conductance Ca(2+)-activated K+ channels (BK channels) from canine colon in artificial lipid bilayers and in excised patches. Both protocols identified 270-pS K(+)-selective channels activated by depolarization and Ca2+ (approximately 130-mV shift of half-activation voltage per 10-fold change in Ca2+) that were inhibited by extracellular tetraethylammonium (TEA) and charybdotoxin. These similarities suggest that the same BK channels are studied in the two techniques. However, we found three quantitative differences between channels in artificial bilayers and patches. 1) Channels in artificial bilayers required fivefold higher free Ca2+ or 80-mV stronger depolarization for activation. 2) The voltage dependence of TEA block was smaller for channels in artificial bilayers. The apparent distance across the membrane field for the TEA binding site was 0.031 for channels in artificial bilayers and 0.23 for channels in patches. 3) ATP (2 mM) decreased open probability (Po) of channels in artificial bilayers, whereas channels in patches were unaffected. Neither GTP nor UTP reduced Po of channels in artificial bilayers. It is possible that these differences may be due to a lack of molecular identity between the channels studied in the two protocols. Alternatively, they may be attributed to alterations in channel properties during reconstitution or to influences of the artificial lipid environment.

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Botosoa, Eliot P., Mike Maillasson, Marie Mougin-Degraef, Patricia Remaud-Le Saëc, Jean-François Gestin, Yannick Jacques, Jacques Barbet, and Alain Faivre-Chauvet. "Antibody-Hapten Recognition at the Surface of Functionalized Liposomes Studied by SPR: Steric Hindrance of Pegylated Phospholipids in Stealth Liposomes Prepared for Targeted Radionuclide Delivery." Journal of Drug Delivery 2011 (January 17, 2011): 1–9. http://dx.doi.org/10.1155/2011/368535.

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Targeted PEGylated liposomes could increase the amount of drugs or radionuclides delivered to tumor cells. They show favorable stability and pharmacokinetics, but steric hindrance of the PEG chains can block the binding of the targeting moiety. Here, specific interactions between an antihapten antibody (clone 734, specific for the DTPA-indium complex) and DTPA-indium-tagged liposomes were characterized by surface plasmon resonance (SPR). Non-PEGylated liposomes fused on CM5 chips whereas PEGylated liposomes did not. By contrast, both PEGylated and non-PEGylated liposomes attached to L1 chips without fusion. SPR binding kinetics showed that, in the absence of PEG, the antibody binds the hapten at the surface of lipid bilayers with the affinity of the soluble hapten. The incorporation of PEGylated lipids hinders antibody binding to extents depending on PEGylated lipid fraction and PEG molecular weight. SPR on immobilized liposomes thus appears as a useful technique to optimize formulations of liposomes for targeted therapy.

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Motsa, Balindile B., and Robert V. Stahelin. "Lipid–protein interactions in virus assembly and budding from the host cell plasma membrane." Biochemical Society Transactions 49, no. 4 (August 25, 2021): 1633–41. http://dx.doi.org/10.1042/bst20200854.

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Lipid enveloped viruses contain a lipid bilayer coat that protects their genome to help facilitate entry into the new host cell. This lipid bilayer comes from the host cell which they infect. After viral replication, the mature virion hijacks the host cell plasma membrane where it is then released to infect new cells. This process is facilitated by the interaction between phospholipids that make up the plasma membrane and specialized viral matrix proteins. This step in the viral lifecycle may represent a viable therapeutic strategy for small molecules that aim to block enveloped virus spread. In this review, we summarize the current knowledge on the role of plasma membrane lipid–protein interactions on viral assembly and budding.

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Frey, C. M., H. Barth, C. Kranz, and B. Mizaikoff. "Horizontal black lipid bilayer membranes for studying pore-forming toxins." Analytical Methods 10, no. 26 (2018): 3153–61. http://dx.doi.org/10.1039/c8ay01122b.

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The investigation of pore-forming proteins such as the toxin component C2IIa from the binary Clostridium botulinum type C2 toxin is of particular interest for pharmaceutical applications, e.g., such as drug delivery into cells.

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Tsai, Hsiang-Chi, Yan-Ling Yang, Yu-Jane Sheng, and Heng-Kwong Tsao. "Formation of Asymmetric and Symmetric Hybrid Membranes of Lipids and Triblock Copolymers." Polymers 12, no. 3 (March 11, 2020): 639. http://dx.doi.org/10.3390/polym12030639.

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Hybrid membranes formed by co-assembly of AxByAx (hydrophilic-hydrophobic-hydrophilic) triblock copolymers into lipid bilayers are investigated by dissipative particle dynamics. Homogeneous hybrid membranes are developed as lipids and polymers are fully compatible. The polymer conformations can be simply classified into bridge- and loop-structures in the membranes. It is interesting to find that the long-time fraction of loop-conformation ( f L ) of copolymers in the membrane depends significantly on the hydrophilic block length (x). As x is small, an equilibrium f L * always results irrespective of the initial conformation distribution and its value depends on the hydrophobic block length (y). For large x, f L tends to be time-invariant because polymers are kinetically trapped in their initial structures. Our findings reveal that only symmetric hybrid membranes are formed for small x, while membranes with stable asymmetric leaflets can be constructed with large x. The effects of block lengths on the polymer conformations, such as transverse and lateral spans ( d ⊥ and d ‖ ) of bridge- and loop-conformations, are discussed as well.

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Worley, J. F., R. J. French, and B. K. Krueger. "Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium." Journal of General Physiology 87, no. 2 (February 1, 1986): 327–49. http://dx.doi.org/10.1085/jgp.87.2.327.

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Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel.

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Green, W. N., L. B. Weiss, and O. S. Andersen. "Batrachotoxin-modified sodium channels in planar lipid bilayers. Ion permeation and block." Journal of General Physiology 89, no. 6 (June 1, 1987): 841–72. http://dx.doi.org/10.1085/jgp.89.6.841.

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Batrachotoxin-modified, voltage-dependent sodium channels from canine forebrain were incorporated into planar lipid bilayers. Single-channel conductances were studied for [Na+] ranging between 0.02 and 3.5 M. Typically, the single-channel currents exhibited a simple two-state behavior, with transitions between closed and fully open states. Two other conductance states were observed: a subconductance state, usually seen at [NaCl] greater than or equal to 0.5 M, and a flickery state, usually seen at [NaCl] less than or equal to 0.5 M. The flickery state became more frequent as [NaCl] was decreased below 0.5 M. The K+/Na+ permeability ratio was approximately 0.16 in 0.5 and 2.5 M salt, independent of the Na+ mole fraction, which indicates that there are no interactions among permeant ions in the channels. Impermeant and permeant blocking ions (tetraethylammonium, Ca++, Zn++, and K+) have different effects when added to the extracellular and intracellular solutions, which indicates that the channel is asymmetrical and has at least two cation-binding sites. The conductance vs. [Na+] relation saturated at high concentrations, but could not be described by a Langmuir isotherm, as the conductance at low [NaCl] is higher than predicted from the data at [NaCl] greater than or equal to 1.0 M. At low [NaCl] (less than or equal to 0.1 M), increasing the ionic strength by additions of impermeant monovalent and divalent cations reduced the conductance, as if the magnitude of negative electrostatic potentials at the channel entrances were reduced. The conductances were comparable for channels in bilayers that carry a net negative charge and bilayers that carry no net charge. Together, these results lead to the conclusion that negative charges on the channel protein near the channel entrances increase the conductance, while lipid surface charges are less important.

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Khan, Amit Kumar, James C. S. Ho, Susmita Roy, Bo Liedberg, and Madhavan Nallani. "Facile Mixing of Phospholipids Promotes Self-Assembly of Low-Molecular-Weight Biodegradable Block Co-Polymers into Functional Vesicular Architectures." Polymers 12, no. 4 (April 22, 2020): 979. http://dx.doi.org/10.3390/polym12040979.

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In this work, we have used low-molecular-weight (PEG12-b-PCL6, PEG12-b-PCL9 or PEG16-b-PLA38; MW, 1.25–3.45 kDa) biodegradable block co-polymers to construct nano- and micron-scaled hybrid (polymer/lipid) vesicles, by solvent dispersion and electroformation methods, respectively. The hybrid vesicles exhibit physical properties (size, bilayer thickness and small molecule encapsulation) of a vesicular boundary, confirmed by cryogenic transmission electron microscopy, calcein leakage assay and dynamic light scattering. Importantly, we find that these low MW polymers, on their own, do not self-assemble into polymersomes at nano and micron scales. Using giant unilamellar vesicles (GUVs) model, their surface topographies are homogeneous, independent of cholesterol, suggesting more energetically favorable mixing of lipid and polymer. Despite this mixed topography with a bilayer thickness similar to that of a lipid bilayer, variation in surface topology is demonstrated using the interfacial sensitive phospholipase A2 (sPLA2). The biodegradable hybrid vesicles are less sensitive to the phospholipase digestion, reminiscent of PEGylated vesicles, and the degree of sensitivity is polymer-dependent, implying that the nano-scale surface topology can further be tuned by its chemical composition. Our results reveal and emphasize the role of phospholipids in promoting low MW polymers for spontaneous vesicular self-assembly, generating a functional hybrid lipid-polymer interface.

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Kovacs, R. J., and M. T. Nelson. "ATP-sensitive K+ channels from aortic smooth muscle incorporated into planar lipid bilayers." American Journal of Physiology-Heart and Circulatory Physiology 261, no. 2 (August 1, 1991): H604—H609. http://dx.doi.org/10.1152/ajpheart.1991.261.2.h604.

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Glibenclamide binding sites were identified in a membrane preparation from canine aortic smooth muscle. The dissociation constant for [3H]glibenclamide binding was 10 +/- 2 nM, with a density of 420 +/- 108 fmol/mg protein. The properties of ATP-sensitive potassium (KATP) channels from the same membrane preparation incorporated into planar lipid bilayers were investigated. ATP was a potent inhibitor of the channels with half-maximal inhibition of channel activity by 41 microM ATP. Glibenclamide inhibited channel activity, and cromakalim activated the channel in the presence of ATP. Blockers of Ca(2+)-activated K+ (KCa) channels (charybdotoxin and tetraethylammonium ions) did not affect KATP channels in concentrations that caused significant block of KCa channels in bilayers. This membrane preparation should allow further biochemical and functional characterization of KATP channels and glibenclamide receptors in arterial smooth muscle.

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Recio-Pinto, E., D. S. Duch, S. R. Levinson, and B. W. Urban. "Purified and unpurified sodium channels from eel electroplax in planar lipid bilayers." Journal of General Physiology 90, no. 3 (September 1, 1987): 375–95. http://dx.doi.org/10.1085/jgp.90.3.375.

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Highly purified sodium channel protein from the electric eel, Electrophorus electricus, was reconstituted into liposomes and incorporated into planar bilayers made from neutral phospholipids dissolved in decane. The purest sodium channel preparations consisted of only the large, 260-kD tetrodotoxin (TTX)-binding polypeptide. For all preparations, batrachotoxin (BTX) induced long-lived single-channel currents (25 pS at 500 mM NaCl) that showed voltage-dependent activation and were blocked by TTX. This block was also voltage dependent, with negative potentials increasing block. The permeability ratios were 4.7 for Na+:K+ and 1.6 for Na+:Li+. The midpoint for steady state activation occurred around -70 mV and did not shift significantly when the NaCl concentration was increased from 50 to 1,000 mM. Veratridine-induced single-channel currents were about half the size of those activated by BTX. Unpurified, nonsolubilized sodium channels from E. electricus membrane fragments were also incorporated into planar bilayers. There were no detectable differences in the characteristics of unpurified and purified sodium channels, although membrane stability was considerably higher when purified material was used. Thus, in the eel, the large, 260-kD polypeptide alone is sufficient to demonstrate single-channel activity like that observed for mammalian sodium channel preparations in which smaller subunits have been found.

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Gao, Yiyi, Dangxin Mao, Jun Wu, Xiaogang Wang, Zhikun Wang, Guoquan Zhou, Liang Chen, Junlang Chen, and Songwei Zeng. "Carbon Nanotubes Translocation through a Lipid Membrane and Transporting Small Hydrophobic and Hydrophilic Molecules." Applied Sciences 9, no. 20 (October 12, 2019): 4271. http://dx.doi.org/10.3390/app9204271.

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Carbon nanotubes (CNTs) are extensively adopted in the applications of biotechnology and biomedicine. Their interactions with cell membranes are of great importance for understanding the toxicity of CNTs and the application of drug delivery. In this paper, we use atomic molecular dynamics simulations to study the permeation and orientation of pristine and functionalized CNTs in a lipid bilayer. Pristine CNT (PCNT) can readily permeate into the membrane and reside in the hydrophobic region without specific orientation. The insertion of PCNTs into the lipid bilayer is robust and independent on the lengths of PCNTs. Due to the presence of hydroxyl groups on both ends of the functionalized CNT (FCNT), FCNT prefers to stand upright in the lipid bilayer center. Compared with PCNT, FCNT is more suitable to be a bridge connecting the inner and outer lipid membrane. The inserted CNTs have no distinct effects on membrane structure. However, they may block the ion channels. In addition, preliminary explorations on the transport properties of CNTs show that the small hydrophobic molecule carbon dioxide can enter both PCNT and FCNT hollow channels. However, hydrophilic molecule urea is prone to penetrate the PCNT but finds it difficult to enter the FCNT. These results may provide new insights into the internalization of CNT in the lipid membrane and the transport properties of CNTs when embedded therein.

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Ishchenko, L. M., V. D. Ishchenko, and V. G. Spyrydonov. "ВМІСТ ЛІПІДІВ У СИРОВАТЦІ КРОВІ КОРІВ ЗА СПОНТАННОГО ІНФІКУВАННЯ ВІРУСОМ ЛЕЙКОЗУ ВЕЛИКОЇ РОГАТОЇ ХУДОБИ." Scientific Messenger of LNU of Veterinary Medicine and Biotechnology 18, no. 3(70) (September 9, 2016): 119–23. http://dx.doi.org/10.15421/nvlvet7028.

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Lipids take part in the biological cycle of retroviruses and regulation of their expression. In particular, in the processes associated with the interaction with the lipid bilayer of the host cell (virus penetration into the cell), and budding of newly synthesized viral particles. To study the effect bovine leukemia virus on lipid metabolism in the host organism is very important for veterinary medicine, because of its effect on animal blood system. At the same time, changes in the blood system of lactating cows have a significant impact on the biochemical indicators of quantitative composition of the milk and therefore its quality, nutritional value and safety for consumers. Investigated the lipid composition of blood serum of cattle spontaneous infected with the virus leukemia. For study was formed by two groups of cows black–and–white breed in 3 years of age on 3 – 4 months of lactation, body weight were 400 – 450 kg, 6 animals in each. In the first (control) group was clinically healthy animals, free from bovine leukemia virus (according to the RID, ELISA and PCR studies), the second (experimental) was animals which infected by virus bovine leukemia. Established that in the infected animals significantly increases the content of total phospholipid by 6.0%, total and esterified cholesterol by 4.3 and 4.2%, respectively. Thus, the correlation of total cholesterol to total phospholipids was unchanged in both groups of animals. Also, in the blood serum of cows research groups noted increase of free fatty acids content by 83.3%. Thus, at the spontaneous infection the bovine leukemia virus in animals is a disturbance qualitative and quantitative composition of blood serum lipids owing to disturbance of synthetic processes in liver, caused by the necessity in the plastic material for build lipid layer of shell pathogen.

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Berdiev, Bakhrom K., Ramon Latorre, Dale J. Benos, and Iskander I. Ismailov. "Actin Modifies Ca2+ Block of Epithelial Na+ Channels in Planar Lipid Bilayers." Biophysical Journal 80, no. 5 (May 2001): 2176–86. http://dx.doi.org/10.1016/s0006-3495(01)76190-5.

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Zhang, Wenjia, Karen J. Haman, Joseph M. Metzger, Benjamin J. Hackel, Frank S. Bates, and Timothy P. Lodge. "Quantifying Binding of Ethylene Oxide–Propylene Oxide Block Copolymers with Lipid Bilayers." Langmuir 33, no. 44 (October 25, 2017): 12624–34. http://dx.doi.org/10.1021/acs.langmuir.7b02279.

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Papagiannopoulos, Aristeidis, Natassa Pippa, Costas Demetzos, Stergios Pispas, and Aurel Radulescu. "Formation of Uni-Lamellar Vesicles in Mixtures of DPPC with PEO-b-PCL Amphiphilic Diblock Copolymers." Polymers 13, no. 1 (December 22, 2020): 4. http://dx.doi.org/10.3390/polym13010004.

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The ability of mixtures of 1.2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and the amphiphilic diblock copolymers poly (ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) to stabilize uni-lamellar nano-vesicles is reported. Small angle neutron scattering (SANS) is used to define their size distribution and bilayer structure and resolve the copresence of aggregates and clusters in solution. The vesicles have a broad size distribution which is compatible with bilayer membranes of relatively low bending stiffness. Their mean diameter increases moderately with temperature and their number density and mass is higher in the case of the diblock copolymer with the larger hydrophobic block. Bayesian analysis is performed in order to justify the use of the particular SANS fitting model and confirm the reliability of the extracted parameters. This study shows that amphiphilic block copolymers can be effectively used to prepare mixed lipid-block copolymer vesicles with controlled lamellarity and a significant potential as nanocarriers for drug delivery.

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Zimniak, L., C. J. Winters, W. B. Reeves, and T. E. Andreoli. "Cl- channels in basolateral renal medullary vesicles XI. rbClC-Ka cDNA encodes basolateral MTAL Cl- channels." American Journal of Physiology-Renal Physiology 270, no. 6 (June 1, 1996): F1066—F1072. http://dx.doi.org/10.1152/ajprenal.1996.270.6.f1066.

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The present experiments examined whether rbClC-Ka, a CIC family Cl-channel cDNA from rabbit outer medulla, encodes a basolateral membrane Cl- channel mediating net medullary thick ascending limb (MTAL) Cl- absorption. MTAL cells contain a Cl- channel having certain properties that make it a plausible candidate for the basolateral Cl- channel in that segment. Especially pertinent among properties is the fact that cytosolic Cl- increases in the range 2-25 mM activated these Cl- channels. Cultured mouse MTAL cells were grown in the presence of an antisense oligonucleotide specific for rbCIC-Ka or a random oligonucleotide with no complementarity to rbCIC-Ka. The abundance of Cl- channels was assessed by the frequency of incorporation of Cl- channels from membrane vesicles prepared from these cells into lipid bilayers and by Western blot analysis using an antiserum to the COOH terminus of the rbClC-ka protein. With the use of vesicles from untreated cells or cells treated with the random oligonucleotide, Cl- channels were incorporated into bilayers in 17% and 16% of trials, respectively. However, when vesicles were prepared from cells pretreated with antisense oligonucleotide, there was a virtual abolition of Cl- channel incorporation into bilayers but no effect on the frequency of K+ channel incorporation. In parallel with the reduction in Cl- channel incorporation, the abundance of rbClC-Ka protein was reduced approximately 50% on Western blots. Finally, exposure of Cl- channels in lipid bilayers to the rbClC-Ka antiserum resulted in a block in channel activity. These results support the contention that the basolateral Cl- channel mediating net Cl- absorption in the MTAL is encoded by rbClC-Ka.

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KRUEGER, BRUCE K., JENNINGS F. WORLEY, and ROBERT J. FRENCH. "Block of Sodium Channels in Planar Lipid Bilayers by Guanidinium Toxins and Calcium." Annals of the New York Academy of Sciences 479, no. 1 Tetrodotoxin, (December 1986): 257–68. http://dx.doi.org/10.1111/j.1749-6632.1986.tb15574.x.

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36

Heginbotham, Lise, Meredith LeMasurier, Ludmilla Kolmakova-Partensky, and Christopher Miller. "Single Streptomyces lividans K+ Channels." Journal of General Physiology 114, no. 4 (September 27, 1999): 551–60. http://dx.doi.org/10.1085/jgp.114.4.551.

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Basic electrophysiological properties of the KcsA K+ channel were examined in planar lipid bilayer membranes. The channel displays open-state rectification and weakly voltage-dependent gating. Tetraethylammonium blocking affinity depends on the side of the bilayer to which the blocker is added. Addition of Na+ to the trans chamber causes block of open-channel current, while addition to the cis side has no effect. Most striking is the activation of KcsA by protons; channel activity is observed only when the trans bilayer chamber is at low pH. To ascertain which side of the channel faces which chamber, residues with structurally known locations were mapped to defined sides of the bilayer. Mutation of Y82, an external residue, results in changes in tetraethylammonium affinity exclusively from the cis side. Channels with cysteine residues substituted at externally exposed Y82 or internally exposed Q119 are functionally modified by methanethiosulfonate reagents from the cis or trans chambers, respectively. Block by charybdotoxin, known to bind to the channel's external mouth, is observed only when the toxin is added to the cis side of channels mutated to be toxin sensitive. These results demonstrate unambiguously that the protonation sites linked to gating are on the intracellular portion of the KcsA protein.

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Tzan, C. J., J. R. Berg, and S. A. Lewis. "Mammalian urinary bladder permeability is altered by cationic proteins: modulation by divalent cations." American Journal of Physiology-Cell Physiology 267, no. 4 (October 1, 1994): C1013—C1026. http://dx.doi.org/10.1152/ajpcell.1994.267.4.c1013.

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It was previously demonstrated that protamine sulfate (PS, a cationic polypeptide) as well as synthetic cationic polypeptides (CpP, e.g., polylysine and polyarginine) caused an increase in the apical membrane conductance of the mammalian urinary bladder epithelium that was voltage dependent. The membrane conductance induced by these CpP was mediated by a saturable binding site and was partially blocked by CpP (self-inhibition). The PS-induced membrane conductance can be modified by polyvalent cations at three sites. The first site was to competitively inhibit the interaction of PS with an apical membrane binding site. The second site was to reversibly block the conductance induced by PS. The relative binding affinity (block of PS-induced conductance) sequence was as follows: UO2(2+) > La3+ > Mn2+ > Ba2+ > or = Ca2+ > Sr2+. Although La3+, Mn2+, Ba2+, Ca2+, and Sr2+ inhibited > or = 81% of the PS-induced conductance, UO2(2+) inhibited only 51% and Mg2+ was without effect. The third site was to increase the rate of loss of the PS-induced conductance from the apical membrane. Although neither carbodiimides (carboxyl group reactive reagents) nor neuraminidase (cleaves sialic acid residues) altered the effect of PS on the urinary bladder conductance, PS increased the conductance of lipid bilayers composed of negatively charged phospholipids. A candidate for the binding site might be the negatively charged phosphate groups of membrane lipids.

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Ismailov, I. I., B. K. Berdiev, V. G. Shlyonsky, and D. J. Benos. "Mechanosensitivity of an epithelial Na+ channel in planar lipid bilayers: release from Ca2+ block." Biophysical Journal 72, no. 3 (March 1997): 1182–92. http://dx.doi.org/10.1016/s0006-3495(97)78766-6.

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39

Kim, Mihee, Frank Heinrich, Greg Haugstad, Guichuan Yu, Guangcui Yuan, Sushil K. Satija, Wenjia Zhang, et al. "Spatial Distribution of PEO–PPO–PEO Block Copolymer and PEO Homopolymer in Lipid Bilayers." Langmuir 36, no. 13 (March 27, 2020): 3393–403. http://dx.doi.org/10.1021/acs.langmuir.9b03208.

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40

Bridges, R. J., R. T. Worrell, R. A. Frizzell, and D. J. Benos. "Stilbene disulfonate blockade of colonic secretory Cl- channels in planar lipid bilayers." American Journal of Physiology-Cell Physiology 256, no. 4 (April 1, 1989): C902—C912. http://dx.doi.org/10.1152/ajpcell.1989.256.4.c902.

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We studied blockade by 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS) of a secretory Cl- channel from colonic enterocyte plasma membrane vesicles incorporated into planar lipid bilayer membranes. Except for intermittent long-lived closed periods (100 ms to several min), the control channel open probability (Po) was greater than 90%. DNDS, added to the cis or vesicle-containing side, which corresponds to the outer membrane side of the channel, caused a dramatic increase in the number of current transitions from the open-to-closed state. DNDS caused a concentration-dependent decrease in Po with a maximum inhibition of 95 +/- 2.0% and a half-maximal inhibitory concentration of 3.3 +/- 1.4 microM. DNDS added to the trans side of the channel had no effect on either the single-channel conductance or kinetic behavior of the channel. Kinetic analysis revealed that DNDS blockade from the cis side could be explained by a linear, closed-open-blocked, kinetic scheme. The estimated DNDS block rate constants were kon = 3.2 X 10(7) M-1.s-1 and koff = 52 s-1, yielding an equilibrium dissociation constant (KD) of 2.1 +/- 0.38 microM, similar to the Ki for inhibition of Po. The effects of DNDS were fully reversible after perfusion of the cis compartment with DNDS-free solution. In contrast, the covalently reactive 4,4'-diisothiocyano-substituted stilbene disulfonate caused an irreversible blockade of the Cl- channel.

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41

Vasquez-Montes, Victor, Alexander Kyrychenko, Mauricio Vargas-Uribe, Mykola V. Rodnin, and Alexey S. Ladokhin. "Conformational Switching in Bcl-xL: Enabling Non-Canonic Inhibition of Apoptosis Involves Multiple Intermediates and Lipid Interactions." Cells 9, no. 3 (February 26, 2020): 539. http://dx.doi.org/10.3390/cells9030539.

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The inhibition of mitochondrial permeabilization by the anti-apoptotic protein Bcl-xL is crucial for cell survival and homeostasis. Its inhibitory role requires the partitioning of Bcl-xL to the mitochondrial outer membrane from an inactive state in the cytosol, leading to its extensive refolding. The molecular mechanisms behind these events and the resulting conformations in the bilayer are unclear, and different models have been proposed to explain them. In the most recently proposed non-canonical model, the active form of Bcl-xL employs its N-terminal BH4 helix to bind and block its pro-apoptotic target. Here, we used a combination of various spectroscopic techniques to study the release of the BH4 helix (α1) during the membrane insertion of Bcl-xL. This refolding was characterized by a gradual increase in helicity due to the lipid-dependent partitioning-coupled folding and formation of new helix αX (presumably in the originally disordered loop between helices α1 and α2). Notably, a comparison of various fluorescence and circular dichroism measurements suggested the presence of multiple Bcl-xL conformations in the bilayer. This conclusion was explicitly confirmed by single-molecule measurements of Förster Resonance Energy Transfer from Alexa-Fluor-488-labeled Bcl-xL D189C to a mCherry fluorescent protein attached at the N-terminus. These measurements clearly indicated that the refolding of Bcl-xL in the bilayer is not a two-state transition and involves multiple membranous intermediates of variable compactness.

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Pippa, Natassa, Maria Chountoulesi, Aimilia Kyrili, Anastasia Meristoudi, Stergios Pispas, and Costas Demetzos. "Calorimetric study on pH-responsive block copolymer grafted lipid bilayers: rational design and development of liposomes." Journal of Liposome Research 26, no. 3 (August 27, 2015): 211–20. http://dx.doi.org/10.3109/08982104.2015.1076464.

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43

Baekmark, T. R., S. Pedersen, K. Jørgensen, and O. G. Mouritsen. "The effects of ethylene oxide containing lipopolymers and tri-block copolymers on lipid bilayers of dipalmitoylphosphatidylcholine." Biophysical Journal 73, no. 3 (September 1997): 1479–91. http://dx.doi.org/10.1016/s0006-3495(97)78180-3.

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44

Shannon, Jennifer L., and Rachel C. Fernandez. "The C-Terminal Domain of the Bordetella pertussisAutotransporter BrkA Forms a Pore in Lipid Bilayer Membranes." Journal of Bacteriology 181, no. 18 (September 15, 1999): 5838–42. http://dx.doi.org/10.1128/jb.181.18.5838-5842.1999.

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ABSTRACT BrkA is a 103-kDa outer membrane protein of Bordetella pertussis that mediates resistance to antibody-dependent killing by complement. It is proteolytically processed into a 73-kDa N-terminal domain and a 30-kDa C-terminal domain as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. BrkA is also a member of the autotransporter family of proteins. Translocation of the N-terminal domain of the protein across the outer membrane is hypothesized to occur through a pore formed by the C-terminal domain. To test this hypothesis, we performed black lipid bilayer experiments with purified recombinant protein. The BrkA C-terminal protein showed an average single-channel conductance of 3.0 nS in 1 M KCl. This result strongly suggests that the C-terminal autotransporter domain of BrkA is indeed capable of forming a pore.

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45

Ismailov, I. I., B. K. Berdiev, C. M. Fuller, A. L. Bradford, R. P. Lifton, D. G. Warnock, J. K. Bubien, and D. J. Benos. "Peptide block of constitutively activated Na+ channels in Liddle's disease." American Journal of Physiology-Cell Physiology 270, no. 1 (January 1, 1996): C214—C223. http://dx.doi.org/10.1152/ajpcell.1996.270.1.c214.

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Hypertension is a multifactorial disorder that results in an increased risk of cardiovascular and end-stage renal disease. Liddle's disease represents a specific hypertensive disease and expresses itself in the human population as an autosomal dominant trait. Recent experimental evidence indicates that patients with Liddle's disease have constitutively active amiloride-sensitive Na+ channels and that these channels are phenotypically expressed in lymphocytes obtained from normal and affected members of the original Liddle's kindred. Linkage analysis indicates that this disease results from a deletion of the carboxy-terminal region of the beta-subunit of a recently cloned epithelial Na+ channel (ENaC). We report the successful immunopurification and reconstitution of both normal and constitutively active lymphocyte Na+ channels into planar lipid bilayers. These channels display all of the characteristics typical of renal Na+ channels, including sensitivity to protein kinase A phosphorylation. We demonstrate that gating of normal Na+ channels is removed by cytoplasmic trypsin digestion and that the constitutively active Liddle's Na+ channels are blocked by a beta- or gamma-ENaC carboxy-terminal peptide in a GTP-dependent fashion.

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Reese, Christoph, and Andreas Mayer. "Transition from hemifusion to pore opening is rate limiting for vacuole membrane fusion." Journal of Cell Biology 171, no. 6 (December 19, 2005): 981–90. http://dx.doi.org/10.1083/jcb.200510018.

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Fusion pore opening and expansion are considered the most energy-demanding steps in viral fusion. Whether this also applies to soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor (SNARE)– and Rab-dependent fusion events has been unknown. We have addressed the problem by characterizing the effects of lysophosphatidylcholine (LPC) and other late-stage inhibitors on lipid mixing and pore opening during vacuole fusion. LPC inhibits fusion by inducing positive curvature in the bilayer and changing its biophysical properties. The LPC block reversibly prevented formation of the hemifusion intermediate that allows lipid, but not content, mixing. Transition from hemifusion to pore opening was sensitive to guanosine-5′-(γ-thio)triphosphate. It required the vacuolar adenosine triphosphatase V0 sector and coincided with its transformation. Pore opening was rate limiting for the reaction. As with viral fusion, opening the fusion pore may be the most energy-demanding step for intracellular, SNARE-dependent fusion reactions, suggesting that fundamental aspects of lipid mixing and pore opening are related for both systems.

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Wang, G. K., R. Simon, and S. Y. Wang. "Quaternary ammonium compounds as structural probes of single batrachotoxin-activated Na+ channels." Journal of General Physiology 98, no. 5 (November 1, 1991): 1005–24. http://dx.doi.org/10.1085/jgp.98.5.1005.

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Quaternary ammonium (QA) blockers are well-known structural probes for studying the permeation pathway of voltage-gated K+ channels. In this study we have examined the effects of a series of n-alkyl-trimethylammonium compounds (Cn-QA) on batrachotoxin (BTX)-activated Na+ channels from skeletal muscle incorporated into planar lipid bilayers. We found that these amphipathic QA compounds (Cn-QA where n = 10-18) block single Na+ channels preferentially from the internal side with equilibrium dissociation constants (KD) in the submicromolar to micromolar range. External application of amphipathic QA compounds is far less effective, by a factor of greater than 200. The block can be described by a QA molecule binding to a single site in the Na+ channel permeation pathway. QA binding affinity is dependent on transmembrane voltage with an effective valence (delta) of approximately 0.5. QA dwell times (given as mean closed times, tau c) increase as a function of n-alkyl chain length, ranging from approximately 13 ms for C10-QA to 500 ms for C18-QA at +50 mV. The results imply that there is a large hydrophobic region within the Na+ channel pore which accepts up to 18 methylene groups of the Cn-QA cation. This hydrophobic domain may be of clinical significance since it also interacts with local anesthetics such as cocaine and mepivacaine. Finally, like BTX-activated Na+ channels in bilayers, unmodified Na+ channels in GH3 cells are also susceptible to QA block. Amphipathic QA cations elicit both tonic and use-dependent inhibitions of normal Na+ currents in a manner similar to that of local anesthetic cocaine. We conclude that amphipathic QA compounds are valuable structural probes to study the permeation pathway of both normal and BTX-activated Na+ channels.

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Worley, J. F., R. J. French, B. A. Pailthorpe, and B. K. Krueger. "Lipid surface charge does not influence conductance or calcium block of single sodium channels in planar bilayers." Biophysical Journal 61, no. 5 (May 1992): 1353–63. http://dx.doi.org/10.1016/s0006-3495(92)81942-2.

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Xu, Li, Xuejie Xu, Ganjun Yuan, Yimin Wang, Yunqiu Qu, and Erxiao Liu. "Mechanism of Azalomycin F5a against Methicillin-Resistant Staphylococcus aureus." BioMed Research International 2018 (2018): 1–5. http://dx.doi.org/10.1155/2018/6942452.

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To investigate the mechanism of azalomycin F5a against methicillin-resistant Staphylococcus aureus (MRSA), the conductivity of MRSA suspension and the adenylate kinase activity of MRSA culture were determined with the intervention of azalomycin F5a, which were significantly increased compared to those of blank controls. This inferred that azalomycin F5a could lead to the leakage of cellular substances possibly by increasing permeability to kill MRSA. As phospholipid bilayer was mainly responsible for cell-membrane permeability, the interaction between azalomycin F5a and cell-membrane lipids was further researched by determining the anti-MRSA activities of azalomycin F5a combined with cell-membrane lipids extracted from test MRSA or with 1,2-dipalmitoyl-sn-glycero-3-phospho-glycerol (DPPG) for possible molecular targets lying in MRSA cell-membrane. The results indicated that the anti-MRSA activity of azalomycin F5a remarkably decreased when it combined with membrane lipids or DPPG. This indicated that cell-membrane lipids especially DPPG might be important targets of azalomycin F5a against MRSA.

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Hezaveh, Samira, Susruta Samanta, Antonio De Nicola, Giuseppe Milano, and Danilo Roccatano. "Understanding the Interaction of Block Copolymers with DMPC Lipid Bilayer Using Coarse-Grained Molecular Dynamics Simulations." Journal of Physical Chemistry B 116, no. 49 (November 30, 2012): 14333–45. http://dx.doi.org/10.1021/jp306565e.

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Journal articles on the topic 'Black lipid bilayers'

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