scholarly journals Assessing the use of ellipsoidal microparticles for determining lipid membrane viscosity

2021 ◽  
Author(s):  
Philip E. Jahl ◽  
Raghuveer Parthasarathy
Keyword(s):  
Lipid Membranes ◽  
Lipid Membrane ◽  
Translational Diffusion ◽  
Lipid Domains ◽  
Giant Vesicles ◽  
Membrane Viscosity ◽  
Cellular Processes ◽  
Wide Range ◽  
Chain Lengths ◽  
Good Agreement

The viscosity of lipid membranes sets the timescales of membrane-associated flows and therefore influences the dynamics of a wide range of cellular processes. Techniques to measure membrane viscosity remain sparse, however, and reported measurements to date, even of similar systems, give viscosity values that span orders of magnitude. To address this, we improve a method based on measuring both the rotational and translational diffusion of membrane-anchored microparticles and apply this approach and one based on tracking the motion of phase-separated lipid domains to the same system of phase-separated giant vesicles. We find good agreement between the two methods, with inferred viscosities within a factor of two of each other. Our technique uses ellipsoidal microparticles, and we show that the extraction of physically meaningful viscosity values from their motion requires consideration of their anisotropic shape. The validation of our method on phase-separated membranes makes possible its application to other systems, which we demonstrate by measuring the viscosity of bilayers composed of lipids with different chain lengths ranging from 14 to 20 carbon atoms, revealing a very weak dependence of two-dimensional viscosity on lipid size. The experimental and analysis methods described here should be generally applicable to a variety of membrane systems, both reconstituted and cellular.

scholarly journals Pressure effects on lipids and bio-membrane assemblies

IUCrJ ◽  
2014 ◽  
Vol 1 (6) ◽  
pp. 470-477 ◽  
Author(s):  
Nicholas J. Brooks
Keyword(s):  
High Pressure ◽  
Deep Sea ◽  
Lipid Membranes ◽  
Active Role ◽  
Pressure Effects ◽  
Protein Assemblies ◽  
Cellular Processes ◽  
Structure And Dynamics ◽  
Wide Range ◽  
Recent Developments

Membranes are amongst the most important biological structures; they maintain the fundamental integrity of cells, compartmentalize regions within them and play an active role in a wide range of cellular processes. Pressure can play a key role in probing the structure and dynamics of membrane assemblies, and is also critical to the biology and adaptation of deep-sea organisms. This article presents an overview of the effect of pressure on the mesostructure of lipid membranes, bilayer organization and lipid–protein assemblies. It also summarizes recent developments in high-pressure structural instrumentation suitable for experiments on membranes.

scholarly journals Nanotechnological advances of Lipid film-based biosensors for the rapid detection of biological compounds and toxicants

2019 ◽  
pp. 32-40
Author(s):  
Georgia-Paraskevi Nikoleli
Keyword(s):  
Lipid Membranes ◽  
Lipid Membrane ◽  
Cholesterol Oxidase ◽  
Environmental Pollutants ◽  
Clinical Analysis ◽  
Lipid Film ◽  
Biological Interest ◽  
Wide Range ◽  
Biological Compounds ◽  
Novel Devices

The exploration of lipid membranes for the construction of nanobiosensors has recently provided the opportunity to construct devices to monitor a wide range of compounds of biological interest. Nanobiosensor miniaturization using nanotechnological tools has given novel ways to attach a wide range of “receptors” in the lipid membrane. The lipids used to construct a lipid film-based device are dipalmiloylphosphatidylcholine {DPPC} and in some cases dipalmitoylphosphatidic acid (DPPA) which is an anionic lipid and is used to increase the sensitivity of detection. Most common “receptors” used in lipid film biosensors are enzymes such as urease, cholesterol oxidase, urecase, etc, antibodies such as D-dimer antibody and artificial or natural receptors such as saxitoxin, cholera toxin, calyx [4] arene phospjoryl receptor, etc. This chapter reviews and investigates the construction of nanobiosensors based on lipid membranes that are used to monitor various toxicants. It also exploits examples of applications with an emphasis on novel devices, new nanobiosensing techniques and nanotechnology-based transduction schemes. The compounds that can be detected are insecticides, toxins, hormones, dioxins, etc. Keywords: Lipid membrane based nanosensors; Nanoyechology; Graphene and ZnO electrodes; Food toxicants; Environmental pollutants; Clinical analysis

scholarly journals Nanotechnological advances of Lipid film based biosensors for the rapid detection of biological compounds and toxicants

2020 ◽  
pp. 27-35
Author(s):  
Georgia-Paraskevi Nikoleli ◽  
Keyword(s):  
Lipid Membranes ◽  
Rapid Detection ◽  
Lipid Membrane ◽  
Cholesterol Oxidase ◽  
Lipid Film ◽  
Biological Interest ◽  
Wide Range ◽  
Biological Compounds ◽  
Novel Devices ◽  
D Dimer

The exploration of lipid membranes for the construction of nanobiosensors has recently provided the opportunity to construct devices to monitor a wide range of compounds of biological interest. Nanobiosensor miniaturization using nanotechnological tools has given novel ways to attach a wide range of “receptors” in the lipid membrane. The lipids used to construct a lipid film based device are dipalmiloylphosphatidylcholine {DPPC} and in some cases dipalmitoylphosphatidic acid (DPPA) which is an anionic lipid and is used to increase the sensitivity of detection. Most common “receptors” used in lipid film biosensors are enzymes such as urease, cholesterol oxidase, urecase, etc, antibodies such as D-dimer antibody and artificial or natural receptors such as saxitoxin, cholera toxin, calyx[4]arene phospjoryl receptor, etc. This chapter reviews and investigates the construction of nanobiosensors based on lipid membranes that are used to monitor various toxicants. It also exploits examples of applications with an emphasis on novel devices, new nanobiosensing techniques and nanotechnology-based transduction schemes. The compounds that can be detected are insecticides, toxins, hormones, dioxins, etc.

scholarly journals Lifetime of actin-dependent protein nanoclusters

2022 ◽  
Author(s):  
Sumantra Sarkar ◽  
Debanjan Goswami
Keyword(s):  
Spatial Organization ◽  
Lipid Membrane ◽  
Simple Extension ◽  
Ligand Interaction ◽  
Cellular Processes ◽  
Wide Range ◽  
Dependent Protein ◽  
Protein Ligand Interaction ◽  
Kinetics Of

Protein nanoclusters (PNCs) are dynamic collections of a few proteins that spatially organize in nanometer length clusters. PNCs are one of the principal forms of spatial organization of membrane proteins and they have been shown or hypothesized to be important in various cellular processes, including cell signaling. PNCs show remarkable diversity in size, shape, and lifetime. In particular, the lifetime of PNCs can vary over a wide range of timescales. The diversity in size and shape can be explained by the interaction of the clustering proteins with the actin cytoskeleton or the lipid membrane, but very little is known about the processes that determine the lifetime of the nanoclusters. In this paper, using mathematical modelling of the cluster dynamics, we model the biophysical processes that determine the lifetime of actin-dependent PNCs. In particular, we investigated the role of actin aster fragmentation, which had been suggested to be a key determinant of the PNC lifetime, and found that it is important only for a small class of PNCs. A simple extension of our model allowed us to investigate the kinetics of protein-ligand interaction near PNCs. We found an anomalous increase in the lifetime of ligands near PNCs, which agrees remarkably well with experimental data on RAS-RAF kinetics. In particular, analysis of the RAS-RAF data through our model provides falsifiable predictions and novel hypotheses that will not only shed light on the role of RAS-RAF kinetics in various cancers, but also will be useful in studying membrane protein clustering in general.

scholarly journals Fluorescence Approaches for Characterizing Ion Channels in Synthetic Bilayers

Membranes ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 857
Author(s):  
Md. Sirajul Islam ◽  
James P. Gaston ◽  
Matthew A. B. Baker
Keyword(s):  
Ion Channels ◽  
Membrane Proteins ◽  
Lipid Bilayers ◽  
Lipid Membranes ◽  
Protein Composition ◽  
Cellular Processes ◽  
Model Lipid Membranes ◽  
Wide Range ◽  
Lipid Environment

Ion channels are membrane proteins that play important roles in a wide range of fundamental cellular processes. Studying membrane proteins at a molecular level becomes challenging in complex cellular environments. Instead, many studies focus on the isolation and reconstitution of the membrane proteins into model lipid membranes. Such simpler, in vitro, systems offer the advantage of control over the membrane and protein composition and the lipid environment. Rhodopsin and rhodopsin-like ion channels are widely studied due to their light-interacting properties and are a natural candidate for investigation with fluorescence methods. Here we review techniques for synthesizing liposomes and for reconstituting membrane proteins into lipid bilayers. We then summarize fluorescence assays which can be used to verify the functionality of reconstituted membrane proteins in synthetic liposomes.

scholarly journals New method for high-throughput measurements of viscosity in submicrometer-sized membrane systems

2019 ◽  
Author(s):  
Grzegorz Chwastek ◽  
Eugene P. Petrov ◽  
James Peter Sáenz
Keyword(s):  
High Throughput ◽  
Lipid Membranes ◽  
High Throughput Screening ◽  
Lipid Membrane ◽  
Fluorescence Emission ◽  
Lipid Phase ◽  
Bacterial Cells ◽  
Membrane Adaptation ◽  
Mycoplasma Mycoides ◽  
Good Agreement

AbstractIn order to unravel the underlying principles of membrane adaptation in small systems like bacterial cells, robust approaches to characterize membrane fluidity are needed. Currently available relevant methods require advanced instrumentation and are not suitable for high throughput settings needed to elucidate the biochemical pathways involved in adaptation. We developed a fast, robust, and financially accessible quantitative method to measure microviscosity of lipid membranes in bulk suspension using a commercially available plate reader. Our approach, which is suitable for high-throughput screening, is based on the simultaneous measurements of absorbance and fluorescence emission of a viscosity-sensitive fluorescent dye DCVJ incorporated into a lipid membrane. We validated our method using artificial membranes with various lipid compositions over a range of temperatures and observed values that were in good agreement with previously published results. Using our approach, we were able to detect a lipid phase transition in the ruminant pathogen Mycoplasma mycoides.

scholarly journals Electrochemical Properties of Lipid Membranes Self-Assembled from Bicelles

Membranes ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 11
Author(s):  
Damian Dziubak ◽  
Kamil Strzelak ◽  
Slawomir Sek
Keyword(s):  
Electrochemical Properties ◽  
Self Assembly ◽  
Lipid Membranes ◽  
Lipid Membrane ◽  
Membrane Resistance ◽  
Electrochemical Characteristics ◽  
Freeze Thaw ◽  
Lipid Films ◽  
Supported Lipid Membranes

Supported lipid membranes are widely used platforms which serve as simplified models of cell membranes. Among numerous methods used for preparation of planar lipid films, self-assembly of bicelles appears to be promising strategy. Therefore, in this paper we have examined the mechanism of formation and the electrochemical properties of lipid films deposited onto thioglucose-modified gold electrodes from bicellar mixtures. It was found that adsorption of the bicelles occurs by replacement of interfacial water and it leads to formation of a double bilayer structure on the electrode surface. The resulting lipid assembly contains numerous defects and pinholes which affect the permeability of the membrane for ions and water. Significant improvement in morphology and electrochemical characteristics is achieved upon freeze–thaw treatment of the deposited membrane. The lipid assembly is rearranged to single bilayer configuration with locally occurring patches of the second bilayer, and the number of pinholes is substantially decreased. Electrochemical characterization of the lipid membrane after freeze–thaw treatment demonstrated that its permeability for ions and water is significantly reduced, which was manifested by the relatively high value of the membrane resistance.

scholarly journals Separate Universe calibration of the dependence of halo bias on cosmic web anisotropy

2020 ◽  
Vol 499 (3) ◽  
pp. 4418-4431 ◽  
Author(s):  
Sujatha Ramakrishnan ◽  
Aseem Paranjape
Keyword(s):  
Dark Matter ◽  
High Precision ◽  
Gaussian Distribution ◽  
Initial Perturbation ◽  
Analytical Framework ◽  
Web Environment ◽  
Wide Range ◽  
Galaxy Assembly ◽  
Very High ◽  
Good Agreement

ABSTRACT We use the Separate Universe technique to calibrate the dependence of linear and quadratic halo bias b1 and b2 on the local cosmic web environment of dark matter haloes. We do this by measuring the response of halo abundances at fixed mass and cosmic web tidal anisotropy α to an infinite wavelength initial perturbation. We augment our measurements with an analytical framework developed in earlier work that exploits the near-lognormal shape of the distribution of α and results in very high precision calibrations. We present convenient fitting functions for the dependence of b1 and b2 on α over a wide range of halo mass for redshifts 0 ≤ z ≤ 1. Our calibration of b2(α) is the first demonstration to date of the dependence of non-linear bias on the local web environment. Motivated by previous results that showed that α is the primary indicator of halo assembly bias for a number of halo properties beyond halo mass, we then extend our analytical framework to accommodate the dependence of b1 and b2 on any such secondary property that has, or can be monotonically transformed to have, a Gaussian distribution. We demonstrate this technique for the specific case of halo concentration, finding good agreement with previous results. Our calibrations will be useful for a variety of halo model analyses focusing on galaxy assembly bias, as well as analytical forecasts of the potential for using α as a segregating variable in multitracer analyses.

scholarly journals Interactions of Linear Analogues of Battacin with Negatively Charged Lipid Membranes

Membranes ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 192
Author(s):  
Kinga Burdach ◽  
Dagmara Tymecka ◽  
Aneta Urban ◽  
Robert Lasek ◽  
Dariusz Bartosik ◽  
...  
Keyword(s):  
Lipid Membranes ◽  
Liquid Crystalline ◽  
Lipid Membrane ◽  
Attenuated Total Reflection ◽  
Gram Positive ◽  
Insertion Depth ◽  
Force Microscopy ◽  
Acyl Chains ◽  
Hydrophobic Portion ◽  
Membrane Fluidization

The increasing resistance of bacteria to available antibiotics has stimulated the search for new antimicrobial compounds with less specific mechanisms of action. These include the ability to disrupt the structure of the cell membrane, which in turn leads to its damage. In this context, amphiphilic lipopeptides belong to the class of the compounds which may fulfill this requirement. In this paper, we describe two linear analogues of battacin with modified acyl chains to tune the balance between the hydrophilic and hydrophobic portion of lipopeptides. We demonstrate that both compounds display antimicrobial activity with the lowest values of minimum inhibitory concentrations found for Gram-positive pathogens. Therefore, their mechanism of action was evaluated on a molecular level using model lipid films mimicking the membrane of Gram-positive bacteria. The surface pressure measurements revealed that both lipopeptides show ability to bind and incorporate into the lipid monolayers, resulting in decreased ordering of lipids and membrane fluidization. Atomic force microscopy (AFM) imaging demonstrated that the exposure of the model bilayers to lipopeptides leads to a transition from the ordered gel phase to disordered liquid crystalline phase. This observation was confirmed by attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) results, which revealed that lipopeptide action causes a substantial increase in the average tilt angle of lipid acyl chains with respect to the surface normal to compensate for lipopeptide insertion into the membrane. Moreover, the peptide moieties in both molecules do not adopt any well-defined secondary structure upon binding with the lipid membrane. It was also observed that a small difference in the structure of a lipophilic chain, altering the balance between hydrophobic and hydrophilic portion of the molecules, results in different insertion depth of the active compounds.

scholarly journals Intracellular Ionic Strength Sensing Using NanoLuc

2021 ◽  
Vol 22 (2) ◽  
pp. 677
Author(s):  
Tausif Altamash ◽  
Wesam Ahmed ◽  
Saad Rasool ◽  
Kabir H. Biswas
Keyword(s):  
Thermal Stability ◽  
Phase Separation ◽  
Drug Discovery ◽  
Ionic Strength ◽  
Cellular Signaling ◽  
Live Cells ◽  
Protein Activity ◽  
Cellular Survival ◽  
Cellular Processes ◽  
Wide Range

Intracellular ionic strength regulates myriad cellular processes that are fundamental to cellular survival and proliferation, including protein activity, aggregation, phase separation, and cell volume. It could be altered by changes in the activity of cellular signaling pathways, such as those that impact the activity of membrane-localized ion channels or by alterations in the microenvironmental osmolarity. Therefore, there is a demand for the development of sensitive tools for real-time monitoring of intracellular ionic strength. Here, we developed a bioluminescence-based intracellular ionic strength sensing strategy using the Nano Luciferase (NanoLuc) protein that has gained tremendous utility due to its high, long-lived bioluminescence output and thermal stability. Biochemical experiments using a recombinantly purified protein showed that NanoLuc bioluminescence is dependent on the ionic strength of the reaction buffer for a wide range of ionic strength conditions. Importantly, the decrease in the NanoLuc activity observed at higher ionic strengths could be reversed by decreasing the ionic strength of the reaction, thus making it suitable for sensing intracellular ionic strength alterations. Finally, we used an mNeonGreen–NanoLuc fusion protein to successfully monitor ionic strength alterations in a ratiometric manner through independent fluorescence and bioluminescence measurements in cell lysates and live cells. We envisage that the biosensing strategy developed here for detecting alterations in intracellular ionic strength will be applicable in a wide range of experiments, including high throughput cellular signaling, ion channel functional genomics, and drug discovery.

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