Structural Studies on Nonequilibrium Microstructures of Dioctyl Sodium Dodecyl Sulfosuccinate (Aerosol-OT) in p-Toluenesulfonic Acid and Phosphatidylcholine (original) (raw)
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Interfacial films of whole myelin membrane adsorb at the air Á/water interface from myelin vesicles. The films show a liquid state and their equilibrium spreading pressure is equal to the collapse pressure (about 47 mN/m). The films appear microheterogeneous as seen by epifluorescence microscopy, consisting in two liquid phases over all the adsorption isotherm, starting with rounded liquid expanded domains (low surface pressure) immersed in a cholesterol enriched phase and reaching a fractal pattern at high surface pressure similar to those previously observed by compressing the film. Vesicles adsorb to the interfacial film mainly at the lateral interfaces. The high surface pressure at equilibrium (almost equal to the collapse pressure) indicates the formation of surface multilayers, also shown by fluorescence microscopy. #
Structure of Hydroxylated Galactocerebrosides from Myelin at the Air-Water Interface
Biophysical Journal, 2002
Hydroxy-galactocerebrosides (mixed chain length, constituent of myelin membranes) from bovine brain are investigated as monolayers at the air-water interface with isotherms, fluorescence microscopy, x-ray reflectivity and grazing incidence diffraction. With grazing incidence diffraction a monoclinic tilted chain lattice is found in the condensed phase.
Journal of Structural Biology, 2001
Myelin is one of the few biological membranes to contain the lipid galactocerebrosides, although their role in myelin is unclear. To explore its structural role, we used fluorescence and atomic force microscopy (AFM) to study nonhydroxy galactocerebrosides (NCer) at the air-water interface of a Langmuir-Blodgett trough. Fluorescence microscopy at the air-water interface indicated that NCer forms micrometer scale domains of varying radii with six fractal-like extensions. Atomic force microscopy using TappingMode in water on samples transferred to mica confirmed the fractal-like domain structure in the absence of dye and showed that the domains consisted of many aggregated nanotubes with a diameter of 30 nm. The Hausdorf fractal dimension was estimated to be 1.26 and 1.11 for two domains imaged with AFM. This evidence indicates that NCer forms a bulk phase of nanotubes at the air-water interface, unlike the liquidcondensed phase of a phospholipid monolayer. That NCer forms bilayer nanotubes that aggregate strongly suggests NCer helps maintain the stability of myelin by contributing to the curvature and adhesion of the membrane. We found that NCer appears to be decreased in myelin from multiple sclerosis normal appearing white matter, which could be an important event in the loss of myelin stability.
Myelin basic protein induces hexagonal phase formation in dispersions of diacylphosphatidic acid
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1985
3tp nuclear magnetic resonance and low-angle X-ray diffraction measurements have shown that the basic protein of myelin caused diacyiphosphatidic acid dispersions to change from a lamellar to a hexagonal lipid organisation. Several other basic proteins failed to effect a similar phase change, and had little influence on phospholipid headgroup structure and motion.
Biophysical Journal, 2000
The interaction of myelin basic protein (MBP) with dipalmitoylphosphatidylglycerol films has been investigated by means of a microgravimetric gauge sensitive to the changes in load and structural modifications of the layer deposited onto its surface. Fourier transform infrared spectroscopy, circular dichroism, and x-ray diffraction have confirmed protein uptake by the lipid phase along with a global disordering effect onto the lipid alkyl chains and have shown a temporal evolution of the structure of water penetrating the lipid phase together with the protein. These effects are clearly related to the temporal variation of the microgravimetric gauge signal. Finally, measurements carried out on pre-annealed samples point out the role of mesoscopic morphology in determining the pathways through which MBP penetrates the lipid multilayer. The results obtained in our model system could be useful in clarifying the mechanisms of the myelinating and demyelinating processes that take place in the natural membrane.
Biochimica Et Biophysica Acta-biomembranes, 2002
Monomolecular layers of whole myelin membrane can be formed at the air^water interface from vesicles or from solvent solution of myelin. The films appear microheterogeneous as seen by epifluorescence and Brewster angle microscopy. The pattern consists mainly of two coexisting liquid phases over the whole compression isotherm. The liquid nature of the phases is apparent from the fluorescent probe behavior, domain mobility, deformability and boundary relaxation due to the line tension of the surface domains. The monolayers were transferred to alkylated glass and fluorescently labeled against myelin components. The immunolabeling of two major proteins of myelin (myelin basic protein, proteolipid-DM20) and of 2P,3P-cyclic nucleotide 3P-phosphodiesterase shows colocalization with probes partitioning preferentially in liquidexpanded lipid domains also containing ganglioside G M1 . A different phase showing an enrichment in cholesterol, galactocerebroside and phosphatidylserine markers is also found. The distribution of components is qualitatively independent of the lateral surface pressure and is generally constituted by one phase enriched in charged components in an expanded state coexisting with another phase enriched in non-charged constituents of lower compressibility. The domain immiscibility provides a physical basis for the microheterogeneity found in this membrane model system. ß Brewster angle microscopy 0005-2736 / 02 / $^see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 5 -2 7 3 6 ( 0 2 ) 0 0 3 5 0 -4 * Corresponding
Myelin basic protein–lipid complex: an atomic force microscopy study
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2000
Myelin basic protein (MBP) efficiently bound Dilauroyl-La-phosphatidic acid (DLPA) monolayers at the air water interface. Langmuir -Blodgett (LB) films were prepared from these monolayers and the hydrophilic surface of the upper layer was inspected by atomic force microscopy (AFM) in a water solution. The topography images of nominally four-layer films of DLPA in the absence of MBP revealed regions of different thickness corresponding to different numbers of lipid bimolecular layers. This morphology is characteristic of those lipid films which reorganise spontaneously when kept under an aqueous solution. The DLPA films containing MBP did not reorganise; their thicknesses were uniform and surfaces were usually covered by disordered clusters of protein molecules. Quasi-ordered arrays of smaller particles were observed in films with small amounts of bound protein. The surface charge densities of DLPA and DLPA-MPA films were investigated performing force-distance measurements by using tips modified with surface carboxyl groups. The curves obtained on pure lipid films showed repulsive forces well described in terms of double layer forces. Repulsive forces were not observed in the presence of a uniform MBP overlayer indicating that MBP neutralised most of the lipid charge.
Myelin Structures Formed by Thermotropic Smectic Liquid Crystals
Langmuir, 2013
We report on transient structures, formed by thermotropic smectic-A liquid crystals, resembling the myelin figures of lyotropic lamellar liquid crystals. The thermotropic myelin structures form during the solubilization of a smectic-A droplet in an aqueous phase containing a cationic surfactant at concentrations above the critical micelle concentration. Similar to the lyotropic myelin figures, the thermotropic myelins appear in an optical microscope as flexible tubelike structures growing at the smectic/aqueous interface. Polarizing microscopy and confocal fluorescence microscopy show that the smectic layers are parallel to the tube surface and form a cylindrically bent arrangement around a central line defect in the tube. We study the growth behavior of this new type of myelins and discuss similarities to and differences from the classical lyotropic myelin figures.
European Biophysics Journal, 2005
We report an X-ray reflectivity study on the effects of adsorption of myelin basic protein (MBP) on Langmuir monolayers and on deposited Langmuir-Schaefer multilayers of the phospholipid dipalmitoyl phosphatidylglycerol (DPPG). We provide for the first time, direct microscopic evidence on the destructuring effects of MBP leading to plasticity of the DPPG layers supporting commonly accepted models of the stabilizing role of MBP in the myelin membrane. We also show how protein adsorption onto the layer is determined both by electrostatic and nonspecific hydrophobic interactions.
Membrane proteins as reverse micelles: myelin basic protein in a membrane-mimetic environment
Biochemistry, 1985
The solubility, reactivity, and conformational dynamics of myelin basic protein (MBP) from bovine brain were studied in reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (A0T)-isooctane and water. Such a membrane-mimetic system resembles the aqueous spaces of native myelin sheath in terms of physicochemical properties as reflected in the high affinity of MBP for interfacial bound water. This is marked by the unusual profile of the solubility curve of the protein in reverse micelles, which shows optimal solubility at a much lower molar ratio of water to surfactant ([H,O]/[AOT] = wo) than that reported for other water-soluble proteins. The role of counterions and/or charged polar head groups in the solubilization process is revealed by comparison of the solubility of MBP in nonionic surfactant micellar solutions. Whereas MBP is unfolded in aqueous solutions, insertion into reverse micelles generates a more folded structure, characterized by the presence of 20% a-helix. This conformation is unaffected by variations in the water content of the system (in the 2 . 0 -2 2 . 4~~ range). The reactivity of t-amino groups of lysine residues with aqueous solutions of o-phthalaldehyde demonstrates that segments of the peptide chain are accessible to water. Similar results were obtained with the sequence involved in heme binding. In contrast, the sole tryptophan residue, Trp-117, is shielded from the aqueous solvent, as indicated by lack of reaction with N-bromosuccinimide. The invariance of the wavelength maximum emission in the fluorescence spectra as a function of wo is consistent with this result. The internal dynamics of the protein in the vicinity of the tryptophan, as investigated by time-resolved fluorescence anisotropy techniques, indicates that the average distribution angle of the fluorophore absorption dipole remains constant with increasing wo, reflecting hindrance to its motion, whereas the rotational correlation time decreases, indicating a more relaxed local conformation around the chromophore, although the overall protein structure remains largely unaffected. The results reported here demonstrate that MBP, inserted in reverse micelles, displays distinctive properties that mirror its behavior as a water-soluble perimembrane protein in myelin, where it interacts with both interfacial water and charged membrane surfaces. ' Abbreviations: MBP, myelin basic protein; AOT, sodium bis(2ethylhexyl) sulfosuccinate; NATA, N-acetyltryptophanamide; ACTH, adrenocorticotropin hormone. A O T FIGURE 1 : Schematic representation of MBP in myelin and in a reverse micelle. (Upper part) The dotted circle underlines an inverted bilayer environment of MBP at the cytoplasmic apposition. (Lower part) Left-hand side shows the scheme of MBP in an AOT reverse micelle. Surfactant-charged head groups (designated as circles) are in contact with the water pool, while the hydrocarbon chains are directed toward the apolar solvent. Right-hand side shows the structure of the surfactant AOT.