This study examined the influence of nanomaterials (NMs) on the organization of membrane lipids and the resulting morphological changes. The cell plasma membrane is heterogeneous, featuring ...specialized lipid domains in the liquid-ordered (Lo) phase surrounded by regions in the liquid-disordered (Ld) phase. We utilized model membranes composed of various lipids and lipid mixtures in different phase states to investigate the interactions between the NMs and membrane lipids. Specifically, we explored the interactions of pure chitosan (CS) and CS-modified nanocomposites (NCs) with ZnO, CuO, and SiO2 with four lipid mixtures: egg-phosphatidylcholine (EggPC), egg-sphingomyelin/cholesterol (EggSM/Chol), EggPC/Chol, and EggPC/EggSM/Chol, which represent the coexistence of Ld, Lo, and Ld/Lo, respectively. The data show that CS NMs increase the membrane lipid order at glycerol level probed by Laurdan spectroscopy. Additionally, the interaction of CS-based NMs with membranes leads to an increase in bending elasticity modulus, zeta potential, and vesicle size. The lipid order changes are most significant in the highly fluid Ld phase, followed by the Lo/Ld coexistence phase, and are less pronounced in the tightly packed Lo phase. CS NMs induced egg PC vesicle adhesion, fusion, and shrinking. In heterogeneous Lo/Ld membranes, inward invaginations and vesicle shrinking via the Ld phase were observed. These findings highlight mechanisms involved in CS NM-lipid interactions in membranes that mimic plasma membrane heterogeneity.
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Caveolae, flask-shaped pits covered by caveolin-cavin coats, are abundant features of the plasma membrane of many cells. Besides appearing as single-membrane indentations, caveolae are organized as ...superstructures in the form of rosette-like clusters, whose mechanism of assembly and biological functions have been elusive. Here, we propose that clustering of caveolae in mature muscle cells is driven by forces originating from the elastic energy of membrane-bending deformations and membrane tension. We substantiate this mechanism by computational modeling, which recovers the unique shapes observed for the most ubiquitous caveolar clusters. We support the agreement between the calculated and observed configurations by electron tomography of caveolar clusters. The model predicts the experimentally assessable dependence of caveolar clustering on membrane tension and on the degree of the caveolar coat assembly. We reveal a difference in conformation and, possibly, in function and formation mechanism between caveolar clusters of muscle cells and of adipocytes.
•Caveolar superstructure formation can be driven by membrane curvature•Caveolar rosettes are stabilized by low and destabilized by high membrane tensions•Large rosettes can contribute to the mechano-protective function of caveolae•Configurations of caveolar rosettes of muscle cells differ from those of adipocytes
Golani, Ariotti et al. propose a mechanism of caveolar cluster formation based on the elastic energy of membrane bending deformations and membrane tension. Using computational modeling, they reproduce the shapes of caveolar clusters in muscle cells observed by electron microscopy and predict assessable dependencies of caveolar clustering on membrane tension.
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We examine the effect of hydrophobic gold nanoparticles in concentrations 0.5, 1, 5 w% on 1-Stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) model systems. To this aim, we used ...advanced experimental techniques, such as differential scanning calorimetry and infrared spectroscopy. An estimation of the bending elasticity modulus (kc) of vesicles with Au is achieved using the thermally induced shape fluctuation analysis. The obtained results support the hypothesis that Au nanoparticles penetrate into the region of hydrophobic tails of the phospholipid membrane. Furthermore, they strongly influence the phase behavior of the system, but within the error range, they do not affect the elastic properties of the lipid membrane. IR spectroscopy results indicate that the subsequent addition of Au nanoparticles to the lipid system results in gradual increase of the relative intensity of PO and CO stretching and CH2 scissoring bands, while the band positions are unaffected. We establish the existence of a threshold concentration of AuNPs above which SOPC/AuNPs membranes lose stability. The results of this study provide an in-depth picture of the effect of Au nanoparticles on the physicochemical properties of the lipid membrane. We expect them to contribute significantly to future nanomedical drug-delivery applications.
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Archaeal single-cell microorganisms are characterised by particularly strong resistance to harsh environments at extreme temperature ranges, pH values, high pressure and salinity. The ...recognition of molecules rendering the archaeal membranes stable in such conditions represents an important step towards understanding the molecular mechanisms, which underlie the cellular survival, in order to effectively exploit them in biomedicine and bionanotechnology. Here we report on the bending elasticity and phase behaviour of model lipid membranes containing tetraether archaeal lipids. The bending elasticity modulus of membranes composed of palmitoyl-oleoyl phosphatidylcholine and glycerol dialkyl glycerol tetraether extract from the archaeon Thermoplasma acidophilum’s plasma membrane is measured by analysis of the thermal shape fluctuations of nearly spherical giant unilamellar vesicles (tens of micrometers in size). The bending rigidity is reported to non-monotonically depend on the archaeal lipids’ concentration in the bilayer. At 50 wt% of tetraether lipids in the membrane we measure around 20% decrease of the bending modulus compared to the studied single-component phosphocholine bilayer. The membrane resistance to bending increases at archaeal lipids’ content higher than 70 wt%. These findings support the hypothesis about a probable looping conformation at very low amounts of bipolar lipids in the membrane and prevailing spanning tetraether molecules at higher concentrations. Fluorescence microscopy reveals structural phase coexistence at low temperatures (6 °C) for 75 wt% of bolalipids in the bilayer. Laurdan spectroscopy measurements of large unilamellar vesicles (hundreds of nanometers in size) provide evidences for increased lipid ordering at the glycerol level induced by the presence of up to 90 wt% of bolalipid in the bilayer. At this archaeal lipid content we measure increased bending rigidity of the membrane. The fatty acyl chain mobility probed by DPH fluorescence spectroscopy is significantly reduced in the presence of bolalipids. The lipid ordering decreases with increasing the temperature to an extent depending on the bolalipid content in the membrane. The presence of bipolar lipids in the bilayer affects the lipid packing more strongly at the glycerol level compared to the hydrophobic core of the membrane. By elucidating the effect of tetraether lipids on the structural and mechanical properties of the bilayer, the reported results are expected to help in advancing on liposome-based pharmaceuticals and biomedical applications as well as for developments in sensorics and nanotechnology.
The paper presents the results of tests of carbon plastic samples consisting of carbon fabric Grafill TR30S-S (Italy) and epoxy resin binder EPR 320 modified by WC tungsten carbide nanopowders in the ...form of agglomerates. The positive effect of additives on the tensile strength and on the modulus of elasticity at transverse bending of the concentration of additives 1-3% is shown.
The physics of microemulsions and in particular Dominique Langevin's contributions to the understanding of microemulsion structure and bending properties using scattering techniques are reviewed. ...Among the many methods used by her and her co-workers, we particularly emphasize optical techniques and small angle neutron scattering (SANS), but also neutron spin echo spectroscopy (NSE). The review is then extended to more recent studies of properties of microemulsions close to surfaces, using reflectometry and grazing-incidence small angle neutron scattering (GISANS).
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•Dominique Langevin's contribution to the understanding of the role of bending elasticity is shown.•Different values of the bending elastic constants are compared.•Microemulsions close to interfaces are discussed.
The phytoalexin resveratrol has received increasing attention for its potential to prevent oxidative damages in human organism. To shed further light on molecular mechanisms of its interaction with ...lipid membranes we study resveratrol influence on the organisation and mechanical properties of biomimetic lipid systems composed of synthetic phosphatidylcholines with mixed aliphatic chains and different degree of unsaturation at sn-2 position (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, and 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine, PDPC). High-sensitivity isothermal titration calorimetric measurements reveal stronger spontaneous resveratrol association to polyunsaturated phosphatidylcholine bilayers compared to the monounsaturated ones resulting from hydrophobic interactions, conformational changes of the interacting species and desolvation of molecular surfaces. The latter is supported by the results from Laurdan spectroscopy of large unilamellar vesicles providing data on hydration at the glycerol backbones of glycerophospholipides. Higher degree of lipid order is reported for POPC membranes compared to PDPC. While resveratrol mostly enhances the hydration of PDPC membranes, increasing POPC dehydration is reported upon treatment with the polyphenol. Dehydration of the polyunsaturated lipid bilayers is measured only at the highest phytoalexin content studied (resveratrol/lipid 0.5 mol/mol) and is less pronounced than the effect reported for POPC membranes. The polyphenol effect on membrane mechanics is probed by thermal shape fluctuation analysis of quasispherical giant unilamellar vesicles. Markedly different trend of the bending elasticity with increasing resveratrol concentration is reported for the two types of phospholipid bilayers studied. POPC membranes become more rigid in the presence of resveratrol, whereas PDPC-containing bilayers exhibit softening at lower concentrations of the polyphenol followed by a slight growth without bilayer stiffening even at the highest resveratrol content explored. The new data on the structural organization and membrane properties of resveratrol-treated phosphatidylcholine membranes may underpin the development of future liposomal applications of the polyphenol in medicinal chemistry.
•Stronger spontaneous resveratrol association to polyunsaturated phosphatidylcholine bilayers compared to monounsaturated ones.•Different degree of dehydration induced by resveratrol in mono- and polyunsaturated phosphatidylcholine matrices.•Resveratrol rigidifies monounsaturated bilayers as a “filler” increasing lipid packing.•Resveratrol softens polyunsaturated membranes as a “spacer” reducing lipid order.
In this study, we investigate the influence of the block copolymer architecture on the bending elasticity of polymer-rich lamellar phases. In detail, we study the polymer-rich system ...water/o-xylene/Pluronic triblock copolymer/C
TAB and change the polymer while keeping the mass ratios constant. We use neutron spin echo measurements (NSE) to determine κ. With the measurements we determine the relaxation rate
of the bilayer bending mode and subsequently calculate the bilayer bending modulus κ using the Zilman-Granek approach Zilman et al., Phys. Rev. Lett. 77, 4788-4791 (1996). Moreover, we have investigated the lamellar phases via small-angle X-ray scattering (SAXS) and have analysed the data with the modified Caillé theory to obtain the Caillé parameter η. Based on κ the bulk compression modulus
can be calculated. Increasing values of κ are found with increasing EO and PO block size in the range of 3.8 to 13.4
T. The computed values of
are in the range of 10
to 10
Pa.
Lipid bilayer is the main constitutive element of biological membrane, which confines intracellular space. The mechanical properties of biological membranes may be characterized by various parameters ...including membrane stiffness or membrane bending rigidity, which can be measured using flicker noise spectroscopy. The flicker noise spectroscopy exploits the spontaneous thermal undulations of the membrane. The method is based on the quantitative analysis of a series of microscopic images captured during thermal membrane fluctuations. Thus, measured bending rigidity coefficient depends on the image quality as well as the selection of computational tools for image processing and mathematical model used. In this work scanning and spinning disc confocal microscopies were used to visualize fluctuating membranes of giant unilamellar vesicles. The bending rigidity coefficient was calculated for different acquisition modes, using different fluorescent probes and different image processing methods. It was shown that both imaging approaches gave similar bending coefficient values regardless of acquisition time. Using the developed methodology the effect of fluorescent probe type and aqueous phase composition on the value of the membrane bending rigidity coefficient was measured. Specifically it was found that the bending rigidity coefficient of DOPC bilayer in water is smaller than that determined for POPC membrane. It has been found that the POPC and DOPC bending rigidities coefficient in sucrose solution was lower than that in water. Fluorescence imaging makes possible the quantitative analysis of membrane mechanical properties of inhomogeneous membrane.
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•Fluorescence based flicker noise spectroscopy•Methodology of image analysis and the bending rigidity coefficient determination•Effect of the fluorescence probe on the determined value of the bending rigidity coefficient•Effect of lipid and aqueous phase composition on the value of the bending rigidity coefficient
Background: Specifically designed peptide mimetics offer higher selectivity regarding their toxicity to mammalian cells. In addition to the α-helix conformation, the specific activity is related to ...the peptide’s ability to penetrate the cell membrane. The alterations in lipid membrane properties were addressed in the presence of the peptide KLAKLAK-NH2 and analogs containing β-alanine, strengthening the antibacterial activity and/or naphtalimide with proven anticancer properties. Methods: The molecular interactions of the peptide mimetics with POPC bilayers were studied using FTIR-ATR spectroscopy. The thermal shape fluctuation analysis of quasispherical unilamellar vesicles was applied to probe the membrane bending elasticity. The impedance characteristics of bilayer lipid membranes were measured using fast Fourier-transform electrochemical impedance spectroscopy. Results: A lateral peptide association with the membrane is reported for β-alanine-containing peptides. The most pronounced membrane softening is found for the NphtG-KLβAKLβAK-NH2 analog containing both active groups that corroborate with the indications for 1,8-naphthalimide penetration in the lipid hydrophobic area obtained from the FTIR-ATR spectra analysis. The β-alanine substitution induces strong membrane-rigidifying properties even at very low concentrations of both β-alanine-containing peptides. Conclusions: The reported results are expected to advance the progress in tailoring the pharmacokinetic properties of antimicrobial peptides with strengthened stability towards enzymatic degradation. The investigation of the nonspecific interactions of peptides with model lipid membranes is featured as a useful tool to assess the antitumor and antimicrobial potential of new peptide mimetics.
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