Incorporation of membrane proteins into interfacial films: model membranes for electrical and structural characterization (original) (raw)
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Electrochimica Acta, 2018
The interactions of cationic lipopeptide C 15 H 31 CO-Trp-Lys-D-Leu-Lys with model lipid bilayers supported on gold surface were investigated using electrochemical methods combined with atomic force microscopy imaging and quartz crystal microbalance measurements. It has been found that the mode of the lipopeptide action strongly depends on the net charge of the lipid membrane. In case of the negatively charged bilayers composed of L-a-phosphatidylethanolamines and L-a-phosphatidylglycerols extracted from E. coli bacteria, C 15 H 31 CO-Trp-Lys-D-Leu-Lys molecules initially aggregate on the top of the membrane as a result of the electrostatic attraction between cationic peptide moiety and anionic polar heads of phosphatidylglycerols. Further fusion of the aggregates leads to the swelling and partial disruption of the membrane, while its permeability is substantially increased. Interestingly, the changes in the molecular organization of negatively charged membrane were much more pronounced in the upper leaflet of the bilayer. The effect of C 15 H 31 CO-Trp-Lys-D-Leu-Lys on zwitterionic bilayer composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and cholesterol was definitely different. In this case, the disturbance of the membrane structure was rather subtle. It has been observed that a small fraction of lipopeptide molecules rapidly inserts into the bilayer and perturbation of the assembly is homogenous throughout the film. This was followed by a noticeable decrease in membrane permeability and stiffening of the lipid bilayer. Such sealing effect indicates that the insertion of lipopeptide did not result either in pore formation or membrane rupture.
Lipid-protein interactions in monolayers
Chemistry and Physics of Lipids, 1982
We restricted ourselves to a few examples of the different methodological aspects of the investigation of lipid-protein interactions in monotayer assemblies. Experiments with monolayers have the unique advantage that the arrangement and packing of the molecules can be easily measured and controlled.
Direct Visualization of Flow-Induced Anisotropy in a Fatty Acid Monolayer
Langmuir, 1996
Brewster angle microscopy is used to directly visualize the influence of an applied extensional flow on the domain structure and molecular orientation of a docosanoic acid monolayer at the air-water interface. At a surface pressure of 12 mN/m and a subphase temperature of 15 °C (L 2 phase), extensional flow causes domain elongation parallel to the extension axis. A frequency domain analysis of the Brewster angle images indicates that the domains undergo an affine deformation in response to flow. AT 20 mN/m (L 2 phase), the flow modifies not only the domain structure of the monolayer but also the azimuthal orientation of the fatty acid molecules. This flow-alignment process is strain-rate dependent. Thus, flow can couple to the monolayer order over a variety of length scales.
Formation of planar bilayer membranes from lipid monolayers. A critique
Biophysical Journal, 1976
The formation of planar bilayer membranes from lipid monolayers as described by Montal and Mueller (Proc. Natl. Acad. Sci. 1972. 69:3561) is analyzed. Bilayers absolutely free of alkane solvents or other nonpolar hydrocarbons can be formed on polytetrafluoroethylene (PTFE) (e.g. Teflon) septa only if certain boundary conditions are satisfied. Measurements have been made of the contact angles between monolayer-coated water and PTFE in the presence and absence of alkane solvents. The measurements suggest that the boundary conditions for formation of stable bilayers can be satisfied only when a nonpolar solvent is present. We conclude that the bilayer must be surrounded by a torus of alkane solvent, petroleum jelly, or silicone grease depending upon the details of technique used to form the bilayer. The nonpolar solvent used in the formation of the bilayer may or may not be present in the bilayer depending upon the water solubility and size of the solvent molecule relative to the size of the alkyl chain of the lipid. Detailed sketches describing the formation of bilayers from monolayers are presented.
Structure and dynamics of phospholipid bilayer films under electrochemical control
Faraday Discuss., 2010
Two fully hydrated pure-species phospholipids bilayers, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dioleoyl-sn-glycero-3-phosphorylcholine (DOPC), in the fluid phase and explicit solvent have been studied using molecular dynamics simulation. Atom interactions were modeled using recently developed force fields based on AMBER with full atomistic details. Several representative liquid phase properties for the structure and dynamics of lipids with different length of hydrocarbon chains and different level of saturation have been reproduced without artificially biasing the system in order to match experimental data. In particular, as the new GAFF (General Amber Force Field) has not been explicitly developed to reproduce lipid characteristics and is naturally compatible with standard AMBER nucleic acids and proteins parameters, it is here proven a promising tool to study mixed lipid-protein processes as protein activity dependence on membrane composition, permeation of solute across membranes, and other cellular processes.
Charge determination of membrane molecules in polymer-supported lipid layers
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1995
A method for two-dimensional micro-electrophoresis and charge determination of fluorescence-labeled membrane molecules in lipid layers is presented. Therefore, the labeled molecules are dissolved in a lipid monolayer which acts as a fluid matrix. The essential part of the sample preparation is an aqueous polymer film composed of agarose onto which the layer is transferred by Langmuir-Blodgett technique. The induced force of an applied electric field leads to a drift of the charged fluorescent molecules. The mobility is determined by an analysis of the steady-state bleach profile which is produced by continuous fluorescence micro-photolysis of a rectangular area of the monolayer. Testing a variety of amphiphilic molecules, measurements yielded values of zero, plus or minus one elementary net charge within a margin of error. The experimental setup described here can be used for lateral separation, enrichment and isoelectric focusing of membrane components.