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1424 KiB

Open AccessArticle

Polymer-Induced Swelling of Solid-Supported Lipid Membranes

by Martin Kreuzer, Marcus Trapp, Reiner Dahint and Roland Steitz

Membranes 2016, 6(1), 2; https://doi.org/10.3390/membranes6010002 - 23 Dec 2015

Cited by 4 | Viewed by 5713

In this paper, we study the interaction of charged polymers with solid-supported 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes by in-situ neutron reflectivity. We observe an enormous swelling of the oligolamellar lipid bilayer stacks after incubation in solutions of poly(allylamine hydrochloride) (PAH) in D₂O. The [...] Read more.

In this paper, we study the interaction of charged polymers with solid-supported 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes by in-situ neutron reflectivity. We observe an enormous swelling of the oligolamellar lipid bilayer stacks after incubation in solutions of poly(allylamine hydrochloride) (PAH) in D₂O. The positively charged polyelectrolyte molecules interact with the lipid bilayers and induce a drastic increase in their d-spacing by a factor of ~4. Temperature, time, and pH influence the swollen interfacial lipid linings. From our study, we conclude that electrostatic interactions introduced by the adsorbed PAH are the main cause for the drastic swelling of the lipid coatings. The DMPC membrane stacks do not detach from their solid support at T > T_m. Steric interactions, also introduced by the PAH molecules, are held responsible for the stabilizing effect. We believe that this novel system offers great potential for fundamental studies of biomembrane properties, keeping the membrane’s natural fluidity and freedom, decoupled from a solid support at physiological conditions. Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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2784 KiB

Open AccessArticle

The Position of Aβ_22-40 and Aβ_1-42 in Anionic Lipid Membranes Containing Cholesterol

by Matthew A. Barrett, Richard J. Alsop, Thomas Hauß and Maikel C. Rheinstädter

Membranes 2015, 5(4), 824-843; https://doi.org/10.3390/membranes5040824 - 30 Nov 2015

Cited by 19 | Viewed by 6744

Abstract

Amyloid-β peptides interact with cell membranes in the human brain and are associated with neurodegenerative diseases, such as Alzheimer’s disease. An emerging explanation of the molecular mechanism, which results in neurodegeneration, places the cause of neurotoxicity of the amyloid- peptides on their potentially [...] Read more.

Amyloid-β peptides interact with cell membranes in the human brain and are associated with neurodegenerative diseases, such as Alzheimer’s disease. An emerging explanation of the molecular mechanism, which results in neurodegeneration, places the cause of neurotoxicity of the amyloid- peptides on their potentially negative interaction with neuronal membranes. It is known that amyloid-β peptides interact with the membrane, modifying the membrane’s structural and dynamic properties. We present a series of X-ray diffraction experiments on anionic model lipid membranes containing various amounts of cholesterol. These experiments provide experimental evidence for an interaction of both the full length amyloid-β_1-42 peptide, and the peptide fragment amyloid-β_22-40 with anionic bilayer containing cholesterol. The location of the amyloid-β peptides was determined from these experiments, with the full length peptide embedding into the membrane, and the peptide fragment occupying 2 positions—on the membrane surface and embedded into the membrane core. Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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3236 KiB

Open AccessArticle

Lipid Diffusion in Supported Lipid Bilayers: A Comparison between Line-Scanning Fluorescence Correlation Spectroscopy and Single-Particle Tracking

by Markus Rose, Nehad Hirmiz, Jose M. Moran-Mirabal and Cécile Fradin

Membranes 2015, 5(4), 702-721; https://doi.org/10.3390/membranes5040702 - 13 Nov 2015

Cited by 26 | Viewed by 7551

Abstract

Diffusion in lipid membranes is an essential component of many cellular process and fluorescence a method of choice to study membrane dynamics. The goal of this work was to directly compare two common fluorescence methods, line-scanning fluorescence correlation spectroscopy and single-particle tracking, to [...] Read more.

Diffusion in lipid membranes is an essential component of many cellular process and fluorescence a method of choice to study membrane dynamics. The goal of this work was to directly compare two common fluorescence methods, line-scanning fluorescence correlation spectroscopy and single-particle tracking, to observe the diffusion of a fluorescent lipophilic dye, DiD, in a complex five-component mitochondria-like solid-supported lipid bilayer. We measured diffusion coefficients of \(D_{\text{FCS}} \sim\) 3 \(μ\text{m}^2\cdot\text{s}^{-1}\) and \(D_{\text{SPT}} \sim\) 2 \( μ\text{m}^2\cdot\text{s}^{-1}\), respectively. These comparable, yet statistically different values are used to highlight the main message of the paper, namely that the two considered methods give access to distinctly different dynamic ranges: \(D \gtrsim\) 1 \(μ\text{m}^2\cdot\text{s}^{-1}\) for FCS and \(D \lesssim\) 5 \(μ\text{m}^2\cdot\text{s}^{-1}\) for SPT (with standard imaging conditions). In the context of membrane diffusion, this means that FCS allows studying lipid diffusion in fluid membranes, as well as the diffusion of loosely-bound proteins hovering above the membrane. SPT, on the other hand, is ideal to study the motions of membrane-inserted proteins, especially those presenting different conformations, but only allows studying lipid diffusion in relatively viscous membranes, such as supported lipid bilayers and cell membranes. Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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2590 KiB

Open AccessArticle

Effect of Cholesterol on the Structure of a Five-Component Mitochondria-Like Phospholipid Membrane

by Kelly Cathcart, Amit Patel, Hannah Dies, Maikel C. Rheinstädter and Cécile Fradin

Membranes 2015, 5(4), 664-684; https://doi.org/10.3390/membranes5040664 - 30 Oct 2015

Cited by 14 | Viewed by 8811

Abstract

Cellular membranes have a complex phospholipid composition that varies greatly depending on the organism, cell type and function. In spite of this complexity, most structural data available for phospholipid bilayers concern model systems containing only one or two different phospholipids. Here, we examine [...] Read more.

Cellular membranes have a complex phospholipid composition that varies greatly depending on the organism, cell type and function. In spite of this complexity, most structural data available for phospholipid bilayers concern model systems containing only one or two different phospholipids. Here, we examine the effect of cholesterol on the structure of a complex membrane reflecting the lipid composition of mitochondrial membranes, with five different types of headgroups (phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS) and cardiolipin (CL)) and a variety of hydrocarbon tails. This particular system was chosen because elevated cholesterol contents in mitochondrial membranes have been linked to a breaking down of Bax-mediated membrane permeabilization and resistance to cancer treatments. High resolution electron density profiles were determined by X-ray reflectivity, while the area per phospholipid chain, Apc, and the chain order parameter, SX-ray, were determined by wide-angle X-ray scattering (WAXS). We show that chain order increases upon the addition of cholesterol, resulting in both a thickening of the lipid bilayer and a reduction in the average surface area per phospholipid chain. This effect, well known as cholesterol’s condensation effect, is similar, but not as pronounced as for single-component phospholipid membranes. We conclude by discussing the relevance of these findings for the insertion of the pro-apoptotic protein Bax in mitochondrial membranes with elevated cholesterol content. Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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10985 KiB

Open AccessArticle

Strong Static Magnetic Fields Increase the Gel Signal in Partially Hydrated DPPC/DMPC Membranes

by Jennifer Tang, Richard J. Alsop, Karin Schmalzl, Richard M. Epand and Maikel C. Rheinstädter

Membranes 2015, 5(4), 532-552; https://doi.org/10.3390/membranes5040532 - 29 Sep 2015

Cited by 2 | Viewed by 6207

Abstract

It was recently reported that static magnetic fields increase lipid order in the hydrophobic membrane core of dehydrated native plant plasma membranes [Poinapen, Soft Matter 9:6804-6813, 2013]. As plasma membranes are multicomponent, highly complex structures, in order to elucidate the origin of this [...] Read more.

It was recently reported that static magnetic fields increase lipid order in the hydrophobic membrane core of dehydrated native plant plasma membranes [Poinapen, Soft Matter 9:6804-6813, 2013]. As plasma membranes are multicomponent, highly complex structures, in order to elucidate the origin of this effect, we prepared model membranes consisting of a lipid species with low and high melting temperature. By controlling the temperature, bilayers coexisting of small gel and fluid domains were prepared as a basic model for the plasma membrane core. We studied molecular order in mixed lipid membranes made of dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) using neutron diffraction in the presence of strong static magnetic fields up to 3.5 T. The contribution of the hydrophobic membrane core was highlighted through deuterium labeling the lipid acyl chains. There was no observable effect on lipid organization in fluid or gel domains at high hydration of the membranes. However, lipid order was found to be enhanced at a reduced relative humidity of 43%: a magnetic field of 3.5 T led to an increase of the gel signal in the diffraction patterns of 5%. While all biological materials have weak diamagnetic properties, the corresponding energy is too small to compete against thermal disorder or viscous effects in the case of lipid molecules. We tentatively propose that the interaction between the fatty acid chains’ electric moment and the external magnetic field is driving the lipid tails in the hydrophobic membrane core into a better ordered state. Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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1009 KiB

Open AccessArticle

The Effect of the Nonlinearity of the Response of Lipid Membranes to Voltage Perturbations on the Interpretation of Their Electrical Properties. A New Theoretical Description

by Lars D. Mosgaard, Karis A. Zecchi, Thomas Heimburg and Rima Budvytyte

Membranes 2015, 5(4), 495-512; https://doi.org/10.3390/membranes5040495 - 25 Sep 2015

Cited by 21 | Viewed by 7889

Abstract

Our understanding of the electrical properties of cell membranes is derived from experiments where the membrane is exposed to a perturbation (in the form of a time-dependent voltage or current change) and information is extracted from the measured output. The interpretation of such [...] Read more.

Our understanding of the electrical properties of cell membranes is derived from experiments where the membrane is exposed to a perturbation (in the form of a time-dependent voltage or current change) and information is extracted from the measured output. The interpretation of such electrical recordings consists in finding an electronic equivalent that would show the same or similar response as the biological system. In general, however, there is no unique circuit configuration, which can explain a single electrical recording and the choice of an electric model for a biological system is based on complementary information (most commonly structural information) of the system investigated. Most of the electrophysiological data on cell membranes address the functional role of protein channels while assuming that the lipid matrix is an insulator with constant capacitance. However, close to their melting transition the lipid bilayers are no inert insulators. Their conductivity and their capacitance are nonlinear functions of both voltage, area and volume density. This has to be considered when interpreting electrical data. Here we show how electric data commonly interpreted as gating currents of proteins and inductance can be explained by the nonlinear dynamics of the lipid matrix itself. Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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3843 KiB

Open AccessArticle

Penetration of HIV-1 Tat_47–57 into PC/PE Bilayers Assessed by MD Simulation and X-ray Scattering

by Chris Neale, Kun Huang, Angel E. García and Stephanie Tristram-Nagle

Membranes 2015, 5(3), 473-494; https://doi.org/10.3390/membranes5030473 - 22 Sep 2015

Cited by 11 | Viewed by 6499

Abstract

The interactions of the basic, cell-penetrating region (Y₄₇GRKKRRQRRR₅₇) of the HIV-1 Tat protein with dioleoylphosphatidylcholine (DOPC) bilayers were previously assessed by comparing experimental X-ray diffuse scattering with atomistic molecular dynamics simulations. Here, we extend this investigation by evaluating the [...] Read more.

The interactions of the basic, cell-penetrating region (Y₄₇GRKKRRQRRR₅₇) of the HIV-1 Tat protein with dioleoylphosphatidylcholine (DOPC) bilayers were previously assessed by comparing experimental X-ray diffuse scattering with atomistic molecular dynamics simulations. Here, we extend this investigation by evaluating the influence of phosphatidylethanolamine (PE) lipids. Using experimental bilayer form factors derivedfrom X-ray diffuse scattering data as a guide, our simulations indicate that Tat peptides localize close to the carbonyl-glycerol group in the headgroup region of bilayers composed of either DOPC or DOPC:DOPE (1:1) lipid. Our results also suggest that Tat peptides may more frequently insert into the hydrophobic core of bilayers composed of PC:PE (1:1) lipids than into bilayers composed entirely of PC lipids. PE lipids may facilitate peptide translocation across a lipid bilayer by stabilizing intermediate states in which hydrated peptides span the bilayer. Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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7339 KiB

Open AccessArticle

Multi-Stacked Supported Lipid Bilayer Micropatterning through Polymer Stencil Lift-Off

by Yujie Zhu, Ahmed Negmi and Jose Moran-Mirabal

Membranes 2015, 5(3), 385-398; https://doi.org/10.3390/membranes5030385 - 28 Aug 2015

Cited by 7 | Viewed by 7370

Abstract

Complex multi-lamellar structures play a critical role in biological systems, where they are present as lamellar bodies, and as part of biological assemblies that control energy transduction processes. Multi-lamellar lipid layers not only provide interesting systems for fundamental research on membrane structure and [...] Read more.

Complex multi-lamellar structures play a critical role in biological systems, where they are present as lamellar bodies, and as part of biological assemblies that control energy transduction processes. Multi-lamellar lipid layers not only provide interesting systems for fundamental research on membrane structure and bilayer-associated polypeptides, but can also serve as components in bioinspired materials or devices. Although the ability to pattern stacked lipid bilayers at the micron scale is of importance for these purposes, limited work has been done in developing such patterning techniques. Here, we present a simple and direct approach to pattern stacked supported lipid bilayers (SLBs) using polymer stencil lift-off and the electrostatic interactions between cationic and anionic lipids. Both homogeneous and phase-segregated stacked SLB patterns were produced, demonstrating that the stacked lipid bilayers retain lateral diffusivity. We demonstrate patterned SLB stacks of up to four bilayers, where fluorescence resonance energy transfer (FRET) and quenching was used to probe the interactions between lipid bilayers. Furthermore, the study of lipid phase behaviour showed that gel phase domains align between adjacent layers. The proposed stacked SLB pattern platform provides a robust model for studying lipid behaviour with a controlled number of bilayers, and an attractive means towards building functional bioinspired materials or devices. Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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Review

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496 KiB

Open AccessReview

Structural Significance of Lipid Diversity as Studied by Small Angle Neutron and X-ray Scattering

by Norbert Kučerka, Frederick A. Heberle, Jianjun Pan and John Katsaras

Membranes 2015, 5(3), 454-472; https://doi.org/10.3390/membranes5030454 - 21 Sep 2015

Cited by 69 | Viewed by 8399

Abstract

We review recent developments in the rapidly growing field of membrane biophysics, with a focus on the structural properties of single lipid bilayers determined by different scattering techniques, namely neutron and X-ray scattering. The need for accurate lipid structural properties is emphasized by [...] Read more.

We review recent developments in the rapidly growing field of membrane biophysics, with a focus on the structural properties of single lipid bilayers determined by different scattering techniques, namely neutron and X-ray scattering. The need for accurate lipid structural properties is emphasized by the sometimes conflicting results found in the literature, even in the case of the most studied lipid bilayers. Increasingly, accurate and detailed structural models require more experimental data, such as those from contrast varied neutron scattering and X-ray scattering experiments that are jointly refined with molecular dynamics simulations. This experimental and computational approach produces robust bilayer structural parameters that enable insights, for example, into the interplay between collective membrane properties and its components (e.g., hydrocarbon chain length and unsaturation, and lipid headgroup composition). From model studies such as these, one is better able to appreciate how a real biological membrane can be tuned by balancing the contributions from the lipid’s different moieties (e.g., acyl chains, headgroups, backbones, etc.). Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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1375 KiB

Open AccessReview

Asymmetric Lipid Membranes: Towards More Realistic Model Systems

by Drew Marquardt, Barbara Geier and Georg Pabst

Membranes 2015, 5(2), 180-196; https://doi.org/10.3390/membranes5020180 - 06 May 2015

Cited by 165 | Viewed by 19631

Abstract

Despite the ubiquity of transbilayer asymmetry in natural cell membranes, the vast majority of existing research has utilized chemically well-defined symmetric liposomes, where the inner and outer bilayer leaflets have the same composition. Here, we review various aspects of asymmetry in nature and [...] Read more.

Despite the ubiquity of transbilayer asymmetry in natural cell membranes, the vast majority of existing research has utilized chemically well-defined symmetric liposomes, where the inner and outer bilayer leaflets have the same composition. Here, we review various aspects of asymmetry in nature and in model systems in anticipation for the next phase of model membrane studies. Full article

(This article belongs to the Special Issue Membrane Structure and Dynamics)

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