La3+ and Gd3+ induce shape change of giant unilamellar vesicles of phosphatidylcholine (original) (raw)
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Biophysical Journal, 2002
The structural phase behavior of phospholipid mixtures consisting of short-chain (dihexanoyl phosphatidylcholine) and long-chain lipids (dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol), with and without lanthanide ions was investigated by small-angle neutron scattering (SANS). SANS profiles were obtained from 10°C to 55°C using lipid concentrations ranging from 0.0025 g/ml to 0.25 g/ml. The results reveal a wealth of distinct morphologies, including lamellae, multi-lamellar vesicles, unilamellar vesicles, and bicellar disks.
Biochemistry, 1979
Proton magnetic resonance spectra of vesicles of various sizes composed of egg phosphatidylcholine (PC) with varying concentrations of cholesterol differed in the apparent line width of the signal of the methylene protons of PC (Avlj2). They also varied in the extent of lanthanide-induced shifts of the 31P and 'H N M R signals of the corresponding nuclei of the polar head groups located on the outer surface of the vesicles (As). The differences in the lanthanide-induced shifts of the 31P signals are fully accounted for by the ratio between the externally added lanthanide and the number of PC head S m a l l unilamellar phospholipid vesicles have been extensively used as models for biological membranes. Various techniques have been employed to study the mobility, viscosity, and local motions within the hydrophobic core of the bilayers and the dependence of these parameters on the composition of the liposomes . Efforts have also been devoted to the investigation of surface properties of the model membranes, mainly the binding of cations to the membrane components. Thus, the binding of lanthanides, Ca2+, and Mg2+ to phosphatidylcholine (PC)I vesicles has been investigated in terms of stoichiometry, apparent binding constants, and environmental conditions . The affinity of cations for other phospholipids also has been measured, and a pronounced effect of negatively charged phospholipids has been demonstrated . Moreover, the effects of cation binding on both the conformation of the PC polar group and the packing of the PC in the bilayer have been thoroughly studied .
Biophysical Journal, 2000
Ceramide has recently been established as a central messenger in the signaling cascades controlling cell behavior. Physicochemical studies have revealed a strong tendency of this lipid toward phase separation in mixtures with phosphatidylcholines. The thermal phase behavior and structure of fully hydrated binary membranes composed of dimyristoylphosphatidylcholine (DMPC) and N-palmitoyl-ceramide (C16:0-ceramide, up to a mole fraction X cer ϭ 0.35) were resolved in further detail by high-sensitivity differential scanning calorimetry (DSC) and x-ray diffraction. Both methods reveal very strong hysteresis in the thermal phase behavior of ceramide-containing membranes. A partial phase diagram was constructed based on results from a combination of these two methods. DSC heating scans show that with increased X cer the pretransition temperature T p first increases, whereafter at X cer Ͼ 0.06 it can no longer be resolved. The main transition enthalpy ⌬H remains practically unaltered while its width increases significantly, and the upper phase boundary temperature of the mixture shifts to ϳ63°C at X cer ϭ 0.30. Upon cooling, profound phase separation is evident, and for all of the studied compositions there is an endotherm in the region close to the T m for DMPC. At X cer Ն 0.03 a second endotherm is evident at higher temperatures, starting at 32.1°C and reaching 54.6°C at X cer ϭ 0.30. X-ray small-angle reflection heating scans reveal a lamellar phase within the temperature range of 15-60°C, regardless of composition. The pretransition is observed up to X cer Ͻ 0.18, together with an increase in T p . In the gel phase the lamellar repeat distance d increases from ϳ61 Å at X cer ϭ 0.03, to 67 Å at X cer ϭ 0.35. In the fluid phase increasing X cer from 0.06 to 0.35 augments d from 61 Å to 64 Å. An L Ј /L ␣ (ripple/fluid) phase coexistence region is observed at high temperatures (from 31 to 56.5°C) when X cer Ͼ 0.03. With cooling from temperatures above 50°C we observe a slow increase in d as the coexistence region is entered. A sudden solidification into a metastable, modulated gel phase with high d values is observed for all compositions at ϳ24°C. The anomalous swelling for up to X cer ϭ 0.30 in the transition region is interpreted as an indication of bilayer softening and thermally reduced bending rigidity.
Distribution of GD3 in DPPC Monolayers: A Thermodynamic and Atomic Force Microscopy Combined Study
Biophysical Journal, 2004
Gangliosides are the main component of lipid rafts. These microdomains, floating in the outer leaflet of cellular membrane, play a key role in fundamental cellular functions. Little is still known about ganglioside and phospholipid interaction. We studied mixtures of dipalmitoylphosphatidylcholine and GD3 (molar fraction of 0.2, 0.4, 0.6, 0.8) using complementary techniques: 1), thermodynamic properties of the Langmuir-Blodgett films were assessed at the air-water interface (surface tension, surface potential); and 2), three-dimensional morphology of deposited films on mica substrates were imaged by atomic force microscopy. Mixture thermodynamics were consistent with data in the literature. In particular, excess free energy was negative at each molar fraction, thus ruling out GD3 segregation. Atomic force microscopy showed that the height of liquidcondensed domains in deposited films varied with GD3 molar fraction, as compatible with a lipid aggregation model proposed by Maggio. No distinct GD3-rich domain was observed inside the films, suggesting that GD3 molecules gradually mix with dipalmitoylphosphatidylcholine molecules, confirming DG data. Morphological analysis revealed that the shape of liquidcondensed domains is strongly influenced by the amount of GD3, and an interesting stripe-formation phenomenon was observed. These data were combined with the thermodynamic results and interpreted in the light of McConnell's model.
Magnetic Field Alignable Domains in Phospholipid Vesicle Membranes Containing Lanthanides
The Journal of Physical Chemistry B, 2010
Magnetic fields were applied as a structuring force on phospholipid-based vesicular systems, using paramagnetic lanthanide ions as magnetic handles anchored to the vesicle membrane. Different vesicle formulations were investigated using small angle neutron scattering (SANS) in a magnetic field of up to 8 T, cryo-transmission electron microscopy (cryo-TEM), 31 P NMR spectroscopy, dynamic light scattering (DLS), and permeability measurements with a fluorescent water-soluble marker (calcein). The investigated vesicle formulations consisted usually of 80 mol % of the phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 20 mol % of a chelator lipid (DMPE-DTPA; 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-diethylenetriaminepentaacetate) with complexed lanthanide ions (Tm 3+ , Dy 3+ , or La 3+ ), and the total lipid concentration was 15 mM. Vesicles containing the paramagnetic lanthanide Tm 3+ or Dy 3+ exhibited a temperature-dependent response to magnetic fields, which can be explained by considering the formation of lipid domains, which upon reaching a critical size become alignable in a magnetic field. The features of this "magnetic field alignable domain model" are as follows: with decreasing temperature (from 30 to 2.5°C) solid domains, consisting mainly of the higher melting phospholipid (DMPE-DTPA · lanthanide), begin to form and grow in size. The domains assemble the large magnetic moments conferred by the lanthanides and orient in magnetic fields. The direction of alignment depends on the type of lanthanide used. The domains orient with their normal parallel to the magnetic field with thulium (Tm 3+ ) and perpendicular with dysprosium (Dy 3+ ). No magnetic field alignable domains were observed if DMPE-DTPA is replaced either by POPE-DTPA
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2003
This paper reports the EPR spectroscopic characterization of a model membrane system that magnetically aligns with a variety of different lanthanide ions in the applied magnetic field (< 1 T) of an X-band EPR spectrometer. The ability to align phospholipid bilayer systems is valuable because the anisotropic spectra provide a more detailed and complete description of the structural and motional properties of the membrane-associated spin label when compared to randomly dispersed EPR spectra. The nitroxide spin probe 3h-doxyl-5a-cholestane (cholestane or CLS) was inserted into the bilayer discs to demonstrate the effects of macroscopic bilayer alignment through the measurement of orientational dependent hyperfine splittings. The effects of different lanthanide ions with varying degrees of magnetic susceptibility anisotropy and relaxation properties were examined. For X-band EPR studies, the minimal amounts of the Tm 3 + , Yb 3 + , and Dy 3 + lanthanide ions needed to align the phospholipid bilayers were determined. Power saturation EPR experiments indicate that for the sample compositions described here, the spin-lattice relaxation rate of the CLS spin label was increased by varying amounts in the presence of different lanthanide (Gd 3 + , Dy 3 + , Er 3 + , Yb 3 + , and Tm 3 +) ions, and in the presence of molecular oxygen. The addition of Gd 3 + caused a significant increase in the spin-lattice relaxation rate of CLS when compared to the other lanthanide ions tested.