scholarly journals SNAPPING ELASTIC CURVES AS A ONE-DIMENSIONAL ANALOGUE OF TWO-COMPONENT LIPID BILAYERS

2011 ◽  
Vol 21 (05) ◽  
pp. 1027-1042 ◽  
Author(s):  
MICHAEL HELMERS
Keyword(s):  
Lipid Bilayers ◽  
Spontaneous Curvature ◽  
Lipid Bilayer Membranes ◽  
Bilayer Membranes ◽  
Smooth Curves ◽  
One Dimensional ◽  
Elastic Curves ◽  
Phase Fields ◽  
Two Component ◽  
Two Phases

In order to study a one-dimensional analogue of the spontaneous curvature model for two-component lipid bilayer membranes, we consider planar curves that are made of a material with two phases. Each phase induces a preferred curvature to the curve, and these curvatures as well as phase boundaries may lead to the development of kinks. We introduce a family of energies for smooth curves and phase fields, and we show that these energies Γ-converge to an energy for curves with a finite number of kinks. The theoretical result is illustrated by some numerical examples.

Self-Assembly Processes Were Essential for Life’s Origin

2019 ◽  
Author(s):  
David W. Deamer
Keyword(s):  
Lipid Bilayers ◽  
Self Assembly ◽  
Directed Assembly ◽  
Living Cells ◽  
Light Energy ◽  
Ion Concentration ◽  
Future Research ◽  
Lipid Bilayer Membranes ◽  
Bilayer Membranes ◽  
Transmembrane Channels

In the absence of self-assembly processes, life as we know it would be impossible. This chapter begins by introducing self-assembly then focuses on the primary functions of membranes in living cells, most of which depend on highly evolved proteins embedded in lipid bilayers. These serve to capture light energy in photosynthesis and produce ion concentration gradients from which osmotic energy can be transduced into chemical energy. Although lipid bilayer membranes provide a permeability barrier, they cannot be absolutely impermeable because intracellular metabolic functions depend on external sources of nutrients. Therefore, another set of embedded proteins evolved to form transmembrane channels that allow selective permeation of certain solutes. The earliest life did not have proteins available, so in their absence what was the primary function of membranous compartments in prebiotic conditions? There are three possibilities. First, the compartments would allow encapsulated polymers to remain together as random mixtures called protocells. Second, populations of protocells that vary in composition would be subject to selective processes and the first steps of evolution. Even though any given protocell would be only transiently stable, certain mixtures of polymers would tend to stabilize the surrounding membrane. Such an encapsulated mixture would persist longer than the majority that would be dispersed and recycled, and these more robust protocells would tend to emerge as a kind of species. Last and perhaps most important, there had to be a point in early evolution at which light energy began to be captured by membranous structures, just as it is today. Bilayer membranes are not necessarily composed solely of amphiphilic molecules. They can also contain other nonpolar compounds that happen to be pigments capable of capturing light energy. This possibility is almost entirely unexplored, but the experiments are obvious and would be a fruitful focus for future research. Questions to be addressed: What is meant by self-assembly? Why is self-assembly important for the origin of life? What compounds can undergo self-assembly processes? How can mixtures of monomers and lipids assemble into protocells? We tend to think of living cells in terms of directed assembly.

scholarly journals Effect of Peptide PV on the Ionic Permeability of Lipid Bilayer Membranes

1974 ◽  
Vol 63 (4) ◽  
pp. 492-508 ◽  
Author(s):  
H. P. Ting-Beall ◽  
M. T. Tosteson ◽  
B. F. Gisin ◽  
D. C. Tosteson
Keyword(s):  
Lipid Bilayers ◽  
Membrane Conductance ◽  
Equilibrium Potential ◽  
Lipid Bilayer Membranes ◽  
Bilayer Membranes ◽  
Membrane Surfaces ◽  
Zero Current ◽  
Wide Range ◽  
Current Flows ◽  
Calculated Equilibrium

This paper reports the effects of peptide PV (primary structure: cyclo-(D-val-L-pro-L-val-D-pro)δ) on the electrical properties of sheep red cell lipid bilayers. The membrane conductance (Gm) induced by PV in either Na+ or K+ medium is proportional to the concentration of PV in the aqueous phase. The PV concentration required to produce a comparable increase in Gm in K+ medium is about 104 times greater than for its analogue, valinomycin (val). Although the selectivity sequence for PV and val is similar, K+ ≳ Rb+ > Cs+ > NH4+ > TI+ > Na+ > Li+; the ratio of GGm in K+ to that in Na+ is about 10 for PV compared to > 103 for val. When equal concentrations of PV are added to both sides of a bilayer, the membrane current approaches a maximum value independent of voltage when the membrane potential exceeds 100 mV. When PV is added to only one side of a bilayer separating identical salt solutions of either Na+ or K+ salts, rectification occurs such that the positive current flows more easily away rather than toward the side containing the carrier. Under these conditions, a large, stable, zero-current potential (VVm) is also observed, with the side containing PV being negative. The magnitude of this VVm is about 90 mV and relatively independent of PV concentration when the latter is larger than 2 Times; 10–5 M. From a model which assumes that Vm equals the equilibrium potential for the PV-cation complexes (MS+) and that the reaction between PV and cations is at equilibrium on the two membrane surfaces, we compute the permeability of the membrane to free PV to be about 10–5 cm s–1, which is about 10–7 times the permeability of similar membranes to free val. This interpretation is supported by the fact that the observed values of Vm are in agreement with the calculated equilibrium potential for MS+ over a wide range of ratios of concentrations of total PV in the two bathing solutions, if the unstirred layers are taken into account in computing the MS+ concentrations at the membrane surfaces.

scholarly journals The Amino Terminus of Pseudomonas aeruginosaOuter Membrane Protein OprF Forms Channels in Lipid Bilayer Membranes: Correlation with a Three-Dimensional Model

2000 ◽  
Vol 182 (18) ◽  
pp. 5251-5255 ◽  
Author(s):  
Fiona S. L. Brinkman ◽  
Manjeet Bains ◽  
Robert E. W. Hancock
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Three Dimensional ◽  
Comparative Modeling ◽  
Three Dimensions ◽  
Amino Terminus ◽  
Lipid Bilayer Membranes ◽  
Three Dimensional Model ◽  
Sequence Comparisons ◽  
Bilayer Membranes

ABSTRACT Pseudomonas aeruginosa OprF forms 0.36-nS channels and, rarely, 2- to 5-nS channels in lipid bilayer membranes. We show that a protein comprising only the N-terminal 162-amino-acid domain of OprF formed the smaller, but not the larger, channels in lipid bilayers. Circular dichroism spectroscopy indicated that this protein folds into a β-sheet-rich structure, and three-dimensional comparative modeling revealed that it shares significant structural similarity with the amino terminus of the orthologous protein Escherichia coliOmpA, which has been shown to form a β-barrel. OprF and OmpA share only 15% identity in this domain, yet these results support the utility of modeling such widely divergent β-barrel domains in three dimensions in order to reveal similarities not readily apparent through primary sequence comparisons. The model is used to further hypothesize why porin activity differs for the N-terminal domains of OprF and OmpA.

scholarly journals Ion Transport Through Excitability-Inducing Material (EIM) Channels in Lipid Bilayer Membranes

1972 ◽  
Vol 60 (1) ◽  
pp. 72-85 ◽  
Author(s):  
Ramon Latorre ◽  
Gerald Ehrenstein ◽  
Harold Lecar
Keyword(s):  
Aqueous Solution ◽  
Ion Transport ◽  
Lipid Bilayers ◽  
Voltage Dependence ◽  
The Other ◽  
Lipid Bilayer Membranes ◽  
Relative Permeabilities ◽  
Bilayer Membranes ◽  
Voltage Dependent ◽  
Ionic Mobilities

Two different methods were used to determine the relative permeability and the voltage-dependent conductance of several different cations in excitability-inducing material (EIM)-doped lipid bilayers. In one method, the conductances of individual channels were measured for Li, Na, K, Cs, NH4, and Ca, and in the other method biionic potentials of a membrane with many channels were measured for Li, Na, K, Cs, and Rb. The experimental results for the two methods are in agreement. The relative permeabilities are proportional to the ionic mobilities in free aqueous solution. The voltage dependence of the conductance is the same for all cations measured.

Polyelectrolyte-induced domains in lipid bilayer membranes: the deuterium NMR perspective

1998 ◽  
Vol 76 (2-3) ◽  
pp. 452-464 ◽  
Author(s):  
Peter M Macdonald ◽  
Kevin J Crowell ◽  
Carla M Franzin ◽  
Peter Mitrakos ◽  
Darlene J Semchyschyn
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Domain Size ◽  
Complete Analysis ◽  
Deuterium Nmr ◽  
Domain Formation ◽  
Lipid Bilayer Membranes ◽  
Bilayer Membranes ◽  
H Nmr ◽  
Oppositely Charged

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.

scholarly journals Interactions of Carbon Nanotube with Lipid Bilayer Membranes

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
Vamshi K. Gangupomu ◽  
Franco M. Capaldi
Keyword(s):  
Carbon Nanotube ◽  
Lipid Bilayers ◽  
Cholesterol Content ◽  
Biological Macromolecules ◽  
Rupture Force ◽  
Lipid Bilayer Membranes ◽  
Free Energies ◽  
Bilayer Membranes ◽  
Dynamics Simulations ◽  
Membrane Poration

Understanding the interaction between a carbon nanotube and biological macromolecules such as lipid bilayers is important for the design and development of nanovectors for gene and drug delivery. The forces of penetration and the free energies of rupture of lipid bilayers during nanotube penetration were studied using nonequilibrium, all-atom molecular dynamics simulations for pure POPC and POPC/cholesterol bilayers. The presence of cholesterol did not alter the magnitude of the rupture force and minimally increased the estimated free energy of rupture. However, the ability of the nanotube to disrupt the membrane leading to membrane poration increased with increasing cholesterol content.

Selective photoinduced Ca2+ diffusion in rhodopsin–lipid bilayers: an internal transmitter hypothesis

1985 ◽  
Vol 63 (7) ◽  
pp. 2026-2031 ◽  
Author(s):  
N'Suavi Kossi N'Soukpoé ◽  
Roger M. Leblanc
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
White Light ◽  
Monochromatic Light ◽  
Lipid Bilayer Membranes ◽  
Ion Diffusion ◽  
Bilayer Membranes ◽  
Excellent Candidate ◽  
Triton X ◽  
Selective Increase

Triton X-100 purified rhodopsin has been incorporated into lipid bilayer membranes prepared by the combined lifting-and-touching method. The illumination of the membranes with white light and monochromatic light of λ = 498 nm resulted in a high selective increase of Ca2+ diffusion through the lipid bilayers compared to Na+ and K+. The stoichiometric ratios of photoinduced ion diffusion were found to be more than 888 Ca2+ Rh*−1 s−1 and 166 Na+ Rh*−1 s−1 at 290 K using the white light, and 1 277 Ca2+ Rh*−1 s−1, 96 K+ Rh*−1 s−1, and 50 Na+ Rh*−1 s−1 at 276 K using the monochromatic light. It was inferred that Ca2+ is an excellent candidate as internal transmitter in the visual photo-transduction.

Some Unique Properties of a Bilayer and Liposome Forming System

1987 ◽  
Vol 110 ◽  
Author(s):  
Roderick D. Macgregor ◽  
Noel Taylor ◽  
C. Anthony Hunt
Keyword(s):  
Lipid Bilayer ◽  
Protein Denaturation ◽  
Submicron Particles ◽  
Lipid Bilayer Membranes ◽  
Slow Increase ◽  
Bilayer Membranes ◽  
Starting Solution ◽  
Common Structure ◽  
Section Electron ◽  
Two Phases

AbstractThe unique procedure developed for forming artificial red cells (Science 230, 1165, 1985) allows encapsulation of proteins to concentrations in excess of 20g%. The procedure requires a hypotonic starting solution, whereas the final suspension is equilibrated at 300 mOsm. Hemoglobin (Hb) was one of several proteins encapsulated. The procedure is based on emulsion formation and subsequent evaporation of the nonaqueous phase, a common liposome-formation procedure, but has unique features. The densities of the phases are matched by adding a Freon. The emulsion is formed using conditions that eliminate protein denaturation. This research was designed to evaluate the fine structure at each critical stage using thin section electron microscopy. The results revealed remarkable, previously unseen detail that raises questions about the variety of properties that can be engineered into lipid bilayer structures. The initial emulsion was nonclassical. Submicron particles in large relative numbers suggested a minimal surface tension difference between the two phases. After nearly complete evaporation of the nonaqueous phase, “microcapsule” particles were present but their architecture showed little in common with classical liposomes; there was no evidence of bilayer membranes. Following extrusion, a slow increase in the osmolality to 300 mOsm dramatically altered the architecture of the microcapsules: The encapsulated protein concentration increased, and lipid bilayer membranes were formed. The resulting “liposomes” were often chambered rather than having concentric bilayer structures. Two closely opposed bilayers surrounding a volume of protein solution was a common structure.

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