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848 KiB

Open AccessArticle

Dynamic Morphological Changes Induced By GM1 and Protein Interactions on the Surface of Cell-Sized Liposomes

by Shruti Dhingra, Masamune Morita, Tsuyoshi Yoda, Mun'delanji C. Vestergaard, Tsutomu Hamada and Masahiro Takagi

Materials 2013, 6(6), 2522-2533; https://doi.org/10.3390/ma6062522 - 19 Jun 2013

Cited by 8 | Viewed by 7193

Abstract

It is important to understand the physicochemical mechanisms that are responsible for the morphological changes in the cell membrane in the presence of various stimuli such as osmotic pressure. Lipid rafts are believed to play a crucial role in various cellular processes. It [...] Read more.

It is important to understand the physicochemical mechanisms that are responsible for the morphological changes in the cell membrane in the presence of various stimuli such as osmotic pressure. Lipid rafts are believed to play a crucial role in various cellular processes. It is well established that Ctb (Cholera toxin B subunit) recognizes and binds to GM1 (monosialotetrahexosylganglioside) on the cell surface with high specificity and affinity. Taking advantage of Ctb-GM1 interaction, we examined how Ctb and GM1 molecules affect the dynamic movement of liposomes. GM1 a natural ligand for cholera toxin, was incorporated into liposome and the interaction between fluorescent Ctb and the liposome was analyzed. The interaction plays an important role in determining the various surface interaction phenomena. Incorporation of GM1 into membrane leads to an increase of the line tension leading to either rupture of liposome membrane or change in the morphology of the membrane. This change in morphology was found to be GM1 concentration specific. The interaction between Ctb-GM1 leads to fast and easy rupture or to morphological changes of the liposome. The interactions of Ctb and the glycosyl chain are believed to affect the surface and the curvature of the membrane. Thus, the results are highly beneficial in the study of signal transduction processes. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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1528 KiB

Open AccessArticle

Supported Membranes Meet Flat Fluidics: Monitoring Dynamic Cell Adhesion on Pump-Free Microfluidics Chips Functionalized with Supported Membranes Displaying Mannose Domains

by Jochen Oelke, Thomas Kaindl, Andreea Pasc, Zeno Guttenberg, Achim Wixforth and Motomu Tanaka

Materials 2013, 6(2), 669-681; https://doi.org/10.3390/ma6020669 - 22 Feb 2013

Cited by 2 | Viewed by 6591

Abstract

In this paper we demonstrate the combination of supported membranes and so-called flat microfluidics, which enables one to manipulate liquids on flat chip surfaces via “inverse piezoelectric effect”. Here, an alternating external electric field applied to the inter-digital transducers excites a surface acoustic [...] Read more.

In this paper we demonstrate the combination of supported membranes and so-called flat microfluidics, which enables one to manipulate liquids on flat chip surfaces via “inverse piezoelectric effect”. Here, an alternating external electric field applied to the inter-digital transducers excites a surface acoustic wave on a piezoelectric substrate. Employing lithographic patterning of self-assembled monolayers of alkoxysilanes, we successfully confine a free-standing, hemi-cylindrical channel with the volume of merely 7 µL . The experimentally determined maximum flow velocity scales linearly with the acoustic power, suggesting that our current setup can drive liquids at the speed of up to 7 cm/s (corresponding to a shear rate of 280 s⁻¹) without applying high pressures using a fluidic pump. After the establishment of the functionalization of fluidic chip surfaces with supported membranes, we deposited asymmetric supported membranes displaying well-defined mannose domains and monitored the dynamic adhesion of E. Coli HB101 expressing mannose-binding receptors. Despite of the further technical optimization required for the quantitative analysis, the obtained results demonstrate that the combination of supported membranes and flat fluidics opens a large potential to investigate dynamic adhesion of cells on biofunctional membrane surfaces with the minimum amount of samples, without any fluidic pump. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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2709 KiB

Open AccessArticle

Horizontal Bilayer for Electrical and Optical Recordings

by Philipp Bartsch, Claudius Walter, Philipp Selenschik, Alf Honigmann and Richard Wagner

Materials 2012, 5(12), 2705-2730; https://doi.org/10.3390/ma5122705 - 10 Dec 2012

Cited by 21 | Viewed by 8635

Abstract

Artificial bilayer containing reconstituted ion channels, transporters and pumps serve as a well-defined model system for electrophysiological investigations of membrane protein structure–function relationship. Appropriately constructed microchips containing horizontally oriented bilayers with easy solution access to both sides provide, in addition, the possibility to [...] Read more.

Artificial bilayer containing reconstituted ion channels, transporters and pumps serve as a well-defined model system for electrophysiological investigations of membrane protein structure–function relationship. Appropriately constructed microchips containing horizontally oriented bilayers with easy solution access to both sides provide, in addition, the possibility to investigate these model bilayer membranes and the membrane proteins therein with high resolution fluorescence techniques up to the single-molecule level. Here, we describe a bilayer microchip system in which long-term stable horizontal free-standing and hydrogel-supported bilayers can be formed and demonstrate its prospects particularly for single-molecule fluorescence spectroscopy and high resolution fluorescence microscopy in probing the physicochemical properties like phase behavior of the bilayer-forming lipids, as well as in functional studies of membrane proteins. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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1402 KiB

Open AccessArticle

Polydopamine-Supported Lipid Bilayers

by Souryvanh Nirasay, Antonella Badia, Grégoire Leclair, Jerome P. Claverie and Isabelle Marcotte

Materials 2012, 5(12), 2621-2636; https://doi.org/10.3390/ma5122621 - 4 Dec 2012

Cited by 24 | Viewed by 11865

Abstract

We report the formation of lipid membranes supported by a soft polymeric cushion of polydopamine. First, 20 nm thick polydopamine films were formed on mica substrates. Atomic force microscopy imaging indicated that these films were also soft with a surface roughness of 2 [...] Read more.

We report the formation of lipid membranes supported by a soft polymeric cushion of polydopamine. First, 20 nm thick polydopamine films were formed on mica substrates. Atomic force microscopy imaging indicated that these films were also soft with a surface roughness of 2 nm under hydrated conditions. A zwitterionic phospholipid bilayer was then deposited on the polydopamine cushion by fusion of dimyristoylphosphatidylcholine (DMPC) and dioleoylphosphatidylcholine (DOPC) vesicles. Polydopamine films preserved the lateral mobility of the phospholipids as shown by fluorescence microscopy recovery after photobleaching (FRAP) experiments. Diffusion coefficients of ~5.9 and 7.2 µm² s⁻¹ were respectively determined for DMPC and DOPC at room temperature, values which are characteristic of lipids in a free standing bilayer system. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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744 KiB

Open AccessArticle

Cholesterol Organization in Phosphatidylcholine Liposomes: A Surface Plasmon Resonance Study

by Kathryn A. Melzak, Shirley A. Melzak, Electra Gizeli and José L. Toca-Herrera

Materials 2012, 5(11), 2306-2325; https://doi.org/10.3390/ma5112306 - 13 Nov 2012

Cited by 22 | Viewed by 6951

Abstract

Models for the organization of sterols into regular arrays within phospholipid bilayers have been proposed previously. The existence of such arrays in real systems has been supported by the fact that concentration-dependent sterol properties show discontinuities at the cholesterol mole fractions corresponding to [...] Read more.

Models for the organization of sterols into regular arrays within phospholipid bilayers have been proposed previously. The existence of such arrays in real systems has been supported by the fact that concentration-dependent sterol properties show discontinuities at the cholesterol mole fractions corresponding to regular lattice arrangements. Experimental results presented here are based on a surface plasmon resonance assay that was used to analyze rates of cyclodextrin-mediated removal of cholesterol from adsorbed liposomes at cholesterol mole fractions up to χ_C = 0.55. Two kinetic pools of cholesterol were detected; there was a fast pool present at χ_C > 0.25, and a slow pool, with a removal rate that was dependent on the initial χ_C but that did not vary as χ_C decreased during the course of one experiment. The cholesterol activity therefore seems to be affected by sample history as well as local concentration, which could be explained in terms of the formation of superlattices that are stable for relatively long times. We also describe a variation on the traditional lattice models, with phosphatidylcholine (PC) being treated as an arrangement of hexagonal tiles; the cholesterol is then introduced at any vertex point, without increasing the total area occupied by all the lipid molecules. This model is consistent with Langmuir trough measurements of total lipid area and provides a simple explanation for the maximum solubility of cholesterol in the PC bilayer. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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5963 KiB

Open AccessArticle

Physisorbed Polymer-Tethered Lipid Bilayer with Lipopolymer Gradient

by Yu-Hung Lin, Daniel E. Minner, Vincent L. Herring and Christoph A. Naumann

Materials 2012, 5(11), 2243-2257; https://doi.org/10.3390/ma5112243 - 8 Nov 2012

Cited by 12 | Viewed by 6358

Abstract

Physisorbed polymer-tethered lipid bilayers consisting of phospholipids and lipopolymers represent an attractive planar model membrane platform, in which bilayer fluidity and membrane elastic properties can be regulated through lipopolymer molar concentration. Herein we report a method for the fabrication of such a planar [...] Read more.

Physisorbed polymer-tethered lipid bilayers consisting of phospholipids and lipopolymers represent an attractive planar model membrane platform, in which bilayer fluidity and membrane elastic properties can be regulated through lipopolymer molar concentration. Herein we report a method for the fabrication of such a planar model membrane system with a lateral gradient of lipopolymer density. In addition, a procedure is described, which leads to a sharp boundary between regions of low and high lipopolymer molar concentrations. Resulting gradients and sharp boundaries are visualized on the basis of membrane buckling structures at elevated lipopolymer concentrations using epifluorescence microscopy and atomic force microscopy. Furthermore, results from spot photobleaching experiments are presented, which provide insight into the lipid lateral fluidity in these model membrane architectures. The presented experimental data highlight a planar, solid-supported membrane characterized by fascinating length scale-dependent dynamics and elastic properties with remarkable parallels to those observed in cellular membranes. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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139 KiB

Open AccessArticle

Lateral Dynamics in Polymer-Supported Membranes

by Shigeyuki Komura, Sanoop Ramachandran and Kazuhiko Seki

Materials 2012, 5(10), 1923-1932; https://doi.org/10.3390/ma5101923 - 19 Oct 2012

Cited by 7 | Viewed by 5683

Abstract

We investigate the lateral dynamics in a purely viscous lipid membrane which is supported by a thin polymer sheet (polymer-supported membrane). The generalized frequency-dependent mobility tensor of the polymer-supported membrane is obtained by taking into account the viscoelasticity of the polymer sheet. Due [...] Read more.

We investigate the lateral dynamics in a purely viscous lipid membrane which is supported by a thin polymer sheet (polymer-supported membrane). The generalized frequency-dependent mobility tensor of the polymer-supported membrane is obtained by taking into account the viscoelasticity of the polymer sheet. Due to its viscoelasticity, the cross-correlation functions of two particles embedded in the membrane exhibit an anomalous diffusion. A useful relation for two-point microrheology connecting the cross-correlation function and the modulus of the polymer sheet is provided. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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Review

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1376 KiB

Open AccessReview

Substrate Effects on the Formation Process, Structure and Physicochemical Properties of Supported Lipid Bilayers

by Ryugo Tero

Materials 2012, 5(12), 2658-2680; https://doi.org/10.3390/ma5122658 - 7 Dec 2012

Cited by 127 | Viewed by 11274

Abstract

Supported lipid bilayers are artificial lipid bilayer membranes existing at the interface between solid substrates and aqueous solution. Surface structures and properties of the solid substrates affect the formation process, fluidity, two-dimensional structure and chemical activity of supported lipid bilayers, through the 1–2 [...] Read more.

Supported lipid bilayers are artificial lipid bilayer membranes existing at the interface between solid substrates and aqueous solution. Surface structures and properties of the solid substrates affect the formation process, fluidity, two-dimensional structure and chemical activity of supported lipid bilayers, through the 1–2 nm thick water layer between the substrate and bilayer membrane. Even on SiO₂/Si and mica surfaces, which are flat and biologically inert, and most widely used as the substrates for the supported lipid bilayers, cause differences in the structure and properties of the supported membranes. In this review, I summarize several examples of the effects of substrate structures and properties on an atomic and nanometer scales on the solid-supported lipid bilayers, including our recent reports. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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1413 KiB

Open AccessReview

Biotechnology Applications of Tethered Lipid Bilayer Membranes

by Joshua A. Jackman, Wolfgang Knoll and Nam-Joon Cho

Materials 2012, 5(12), 2637-2657; https://doi.org/10.3390/ma5122637 - 7 Dec 2012

Cited by 103 | Viewed by 14496

Abstract

The importance of cell membranes in biological systems has prompted the development of model membrane platforms that recapitulate fundamental aspects of membrane biology, especially the lipid bilayer environment. Tethered lipid bilayers represent one of the most promising classes of model membranes and are [...] Read more.

The importance of cell membranes in biological systems has prompted the development of model membrane platforms that recapitulate fundamental aspects of membrane biology, especially the lipid bilayer environment. Tethered lipid bilayers represent one of the most promising classes of model membranes and are based on the immobilization of a planar lipid bilayer on a solid support that enables characterization by a wide range of surface-sensitive analytical techniques. Moreover, as the result of molecular engineering inspired by biology, tethered bilayers are increasingly able to mimic fundamental properties of natural cell membranes, including fluidity, electrical sealing and hosting transmembrane proteins. At the same time, new methods have been employed to improve the durability of tethered bilayers, with shelf-lives now reaching the order of weeks and months. Taken together, the capabilities of tethered lipid bilayers have opened the door to biotechnology applications in healthcare, environmental monitoring and energy storage. In this review, several examples of such applications are presented. Beyond the particulars of each example, the focus of this review is on the emerging design and characterization strategies that made these applications possible. By drawing connections between these strategies and promising research results, future opportunities for tethered lipid bilayers within the biotechnology field are discussed. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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878 KiB

Open AccessReview

Cell-Sized Liposomes and Droplets: Real-World Modeling of Living Cells

by Tsutomu Hamada and Kenichi Yoshikawa

Materials 2012, 5(11), 2292-2305; https://doi.org/10.3390/ma5112292 - 13 Nov 2012

Cited by 46 | Viewed by 10235

Abstract

Recent developments in studies concerning cell-sized vesicles, such as liposomes with a lipid bilayer and water-in-oil droplets covered by a lipid monolayer, aim to realize the real-world modeling of living cells. Compartmentalization with a membrane boundary is essential for the organization of living [...] Read more.

Recent developments in studies concerning cell-sized vesicles, such as liposomes with a lipid bilayer and water-in-oil droplets covered by a lipid monolayer, aim to realize the real-world modeling of living cells. Compartmentalization with a membrane boundary is essential for the organization of living systems. Due to the relatively large surface/volume ratio in microconfinement, the membrane interface influences phenomena related to biological functions. In this article, we mainly focus on the following subjects: (i) conformational transition of biopolymers in a confined space; (ii) molecular association on the membrane surface; and (iii) remote control of cell-sized membrane morphology. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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1681 KiB

Open AccessReview

Challenges in the Development of Functional Assays of Membrane Proteins

by Louis Tiefenauer and Sophie Demarche

Materials 2012, 5(11), 2205-2242; https://doi.org/10.3390/ma5112205 - 7 Nov 2012

Cited by 41 | Viewed by 12955

Abstract

Lipid bilayers are natural barriers of biological cells and cellular compartments. Membrane proteins integrated in biological membranes enable vital cell functions such as signal transduction and the transport of ions or small molecules. In order to determine the activity of a protein of [...] Read more.

Lipid bilayers are natural barriers of biological cells and cellular compartments. Membrane proteins integrated in biological membranes enable vital cell functions such as signal transduction and the transport of ions or small molecules. In order to determine the activity of a protein of interest at defined conditions, the membrane protein has to be integrated into artificial lipid bilayers immobilized on a surface. For the fabrication of such biosensors expertise is required in material science, surface and analytical chemistry, molecular biology and biotechnology. Specifically, techniques are needed for structuring surfaces in the micro- and nanometer scale, chemical modification and analysis, lipid bilayer formation, protein expression, purification and solubilization, and most importantly, protein integration into engineered lipid bilayers. Electrochemical and optical methods are suitable to detect membrane activity-related signals. The importance of structural knowledge to understand membrane protein function is obvious. Presently only a few structures of membrane proteins are solved at atomic resolution. Functional assays together with known structures of individual membrane proteins will contribute to a better understanding of vital biological processes occurring at biological membranes. Such assays will be utilized in the discovery of drugs, since membrane proteins are major drug targets. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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