Anomalous swelling of lipid bilayer stacks is caused by softening of the bending modulus (original) (raw)
Related papers
The European Physical Journal E, 2008
Membrane fluctuations of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) were investigated by neutron spin echo spectroscopy. The intermediate structure factor was analyzed in terms of the model proposed by Zilman and Granek (Phys. Rev. Lett. 77, 4788 (1996)), and the bending modulus of lipid bilayers was derived. The hardening of a lipid bilayer upon approaching the main transition point in the anomalous swelling regime was observed, which naturally connects the bending modulus in the gel phase below the main transition temperature.
Experimentally determined tilt and bending moduli of single-component lipid bilayers
Chemistry and physics of lipids, 2017
Values of the bending modulus KC and the tilt modulus Kθ are reported for single component lipid bilayers. The lipids studied have the common names DOPC, DMPC, diC22:1PC, SOPC, POPC, diPhyPC, DLPC, DPPC, DHPC and DEPC, listed in the order of number of samples examined. The experimental method, thus far the only one that measures the tilt modulus of lipid bilayers, first obtains diffuse X-ray scattering data from oriented stacks of bilayers. The values of the moduli emerge from fitting the data to the accepted tilt-dependent continuum model for the free energy of a single bilayer, further enhanced by interactions between bilayers in the stack. The results indicate the broad trend that the tilt modulus for these PC lipids is smaller the closer the temperature is to the main transition temperature. Another trend is that inclusion of tilt raises the value of the bending modulus more for lipids with smaller values of the tilt modulus. Values of both moduli are compared to recent literatu...
Biophysical Journal, 2008
X-ray diffuse scattering was measured from oriented stacks and unilamellar vesicles of dioleoylphosphatidylcholine lipid bilayers to obtain the temperature dependence of the structure and of the material properties. The area/molecule, A, was 75.5 Å 2 at 45°C, 72.4 Å 2 at 30°C, and 69.1 Å 2 at 15°C, which gives the area expansivity a A ¼ 0.0029/deg at 30°C, and we show that this value is in excellent agreement with the polymer brush theory. The bilayer becomes thinner with increasing temperature; the contractivity of the hydrocarbon portion was a Dc ¼ 0.0019/deg; the difference between a A and a Dc is consistent with the previously measured volume expansivity a Vc ¼ 0.0010/deg. The bending modulus K C decreased as exp(455/T) with increasing T (K). Our area compressibility modulus K A decreased with increasing temperature by 5%, the same as the surface tension of dodecane/water, in agreement again with the polymer brush theory. Regarding interactions between bilayers, the compression modulus B as a function of interbilayer water spacing D9 W was found to be nearly independent of temperature. The repulsive fluctuation pressure calculated from B and K C increased with temperature, and the Hamaker parameter for the van der Waals interaction was nearly independent of temperature; this explains why the fully hydrated water spacing, D9 W , that we obtain from our structural results increases with temperature.
European Biophysics Journal, 1997
The temperature dependence of the small-angle neutron scattering from aqueous multilammellar DMPC lipid bilayers, containing small amounts of cholesterol, is analyzed near the main phase transition by means of a simple geometric model which yields the lamellar repeat distance, the hydrophobic thickness of the bilayer, the interlamellar aqueous spacing, as well as fluctuation parameters. The observation of anomalous swelling behavior in the transition region is interpreted as an indication of bilayer softening and thermally reduced bending rigidity. Our results indicate that the effect of small amounts of cholesterol, e3 mole%, is a softening of the bilayers in the transition region, whereas cholesterol contents above this range lead to the well-known effect of rigidification. The possible biological relevance of this result is discussed.
Anomalous swelling in phospholipid bilayers is not coupled to the formation of a ripple phase
Physical review. E, Statistical, nonlinear, and soft matter physics, 2001
Aligned stacks of monomethyl and dimethyl dimyristoyl phosphatidylethanolamine (DMPE) lipid bilayers, like the much studied dimyristoyl PC (DMPC) bilayers, swell anomalously in a critical fashion as the temperature is decreased within the fluid phase towards the main transition temperature, T(M). Unlike DMPC bilayers, both monomethyl and dimethyl DMPE undergo transitions into a gel phase rather than a rippled phase below T(M). Although it is not fully understood why there is anomalous swelling, our present results should facilitate theory by showing that the formation of the phase below T(M) is not related to critical phenomena above T(M).
Faraday Discuss., 2013
Using a microscopic molecular theory, we determine the bending and saddle-splay constants of three-component lipid bilayers. The membrane contains cholesterol, dipalmitoylphophatidylcholine (DPPC), and dioleoylphosphatidylcholine (DOPC) and the predictions of the theory have been shown to qualitatively reproduce phase diagrams of giant unilamellar vesicles (GUVs) of the same three components. The bending and saddle-splay constants were calculated for gel, liquid-ordered (lo), and liquid-disordered (ld) phases. By proper expansion of the free energy, the molecular theory enables us to determine the effects of the mode of membrane bending deformation on the value of the elastic constants for different phases. In particular, we refer to the ability of the molecules to arrange the composition between the two monolayers upon deformation. The bending and saddle-splay constants obtained from the free energy expansion can be expressed in terms of moments of the local lateral pressures and their derivatives all evaluated for a symmetric planar bilayer. The effect of blocked vs free exchange of lipids across the two monolayers on the values of the bending constant is as high as 50 k B T in the ld phase to as high as 200 k B T in the lo phase. These results show that one must strongly consider the mode of deformation in determining the mechanical properties of lipid bilayers. We discuss how the different contributions to the lateral pressures affect the values of the elastic constants including the effects of cholesterol concentration and temperature on the membrane elastic constants. We also calculate the equilibrium binding concentrations of lipid tail anchors as a function of membrane curvature by explicitly determining the chemical potential difference of species across a curved bilayer. Our results are in excellent agreement with recent experimental results.
Biophysical Journal, 2005
Quantitative structures of the fully hydrated fluid phases of dimyristoylphosphatidylcholine (DMPC) and dilauroylphosphatidylcholine (DLPC) were obtained at 30°C. Data for the relative form factors F(q z ) for DMPC were obtained using a combination of four methods. 1), Volumetric data provided F(0). 2), Diffuse x-ray scattering from oriented stacks of bilayers provided relative form factors jF(q z )j for high q z , 0.22 , q z , 0.8 Å ÿ1 . 3), X-ray scattering from extruded unilamellar vesicles with diameter 600 Å provided jF(q z )j for low q z , 0.1 , q z , 0.3 Å ÿ1 . 4), Previous measurements using a liquid crystallographic x-ray method provided jF(2ph/D)j for h ¼ 1 and 2 for a range of nearly fully hydrated D-spacings. The data from method 4 overlap and validate the new unilamellar vesicles data for DMPC, so method 4 is not required for DLPC or future studies. We used hybrid electron density models to obtain structural results from these form factors. Comparison of the model electron density profiles with that of gel phase DMPC provides areas per lipid A, 60.6 6 0.5 Å 2 for DMPC and 63.2 6 0.5 Å 2 for DLPC. Constraints on the model provided by volume measurements and component volumes obtained from simulations put the electron density profiles r(z) and the corresponding form factors F(q z ) on absolute scales. Various thicknesses, such as the hydrophobic thickness and the steric thickness, are obtained and compared to literature values.
Phase Behavior of Model Lipid Bilayers †
The Journal of Physical Chemistry B, 2005
We investigated the phase behavior of double-tail lipids, as a function of temperature, headgroup interaction and tail length. At low values of the head-head repulsion parameter a hh , the bilayer undergoes with increasing temperature the transitions from the subgel phase L c via the flat gel phase L to the fluid phase L R. For higher values of a hh , the transition from the L c to the L R phase occurs via the tilted gel phase L ′ and the rippled phase P ′. The occurrence of the L ′ phase depends on tail length. We find that the rippled structure (P ′) occurs if the headgroups are sufficiently surrounded by water and that the ripple is a coexistence between the L c or L ′ phase and the L R phase. The anomalous swelling, observed at the P ′ f L R transition, is not directly related to the rippled phase, but a consequence of conformational changes of the tails.
We investigate the structure of cholesterol-containing membranes composed of either short-chain (diC14:1PC) or long-chain (diC22:1PC) monounsaturated phospholipids. Bilayer structural information is derived from all-atom molecular dynamics simulations, which are validated via direct comparison to x-ray scattering experiments. We show that the addition of 40 mol % cholesterol results in a nearly identical increase in the thickness of the two different bilayers. In both cases, the chain ordering dominates over the hydrophobic matching between the length of the cholesterol molecule and the hydrocarbon thickness of the bilayer, which one would expect to cause a thinning of the diC22:1PC bilayer. For both bilayers there is substantial headgroup rearrangement for lipids directly in contact with cholesterol, supporting the so-called umbrella model. Importantly, in diC14:1PC bilayers, a dynamic network of hydrogen bonds stabilizes long-lived reorientations of some cholesterol molecules, during which they are found to lie perpendicular to the bilayer normal, deep within the bilayer's hydrophobic core. Additionally, the simulations show that the diC14:1PC bilayer is significantly more permeable to water. These differences may be correlated with faster cholesterol flip-flop between the leaflets of short-chain lipid bilayers, resulting in an asymmetric distribution of cholesterol molecules. This asymmetry was observed experimentally in a case of unilamellar vesicles (ULVs), and reproduced through a set of novel asymmetric simulations. In contrast to ULVs, experimental data for oriented multilamellar stacks does not show the asymmetry, suggesting that it results from the curvature of the ULV bilayers.
Lipid bilayers: thermodynamics, structure, fluctuations, and interactions
Chemistry and Physics of Lipids, 2004
This article, adapted from our acceptance speech of the Avanti Award in Lipids at the 47th Biophysical Society meeting in San Antonio, 2003, summarizes over 30 years of research in the area of lipid bilayers. Beginning with a theoretical model of the phase transition (J.F.N.), we have proceeded experimentally using dilatometry and density centrifugation to study volume, differential scanning calorimetry