Thermal transitions of DMPG bilayers in aqueous solution: SAXS structural studies

Abstract

Dimyristoylphosphatidylglycerol (DMPG) has been extensively studied as a model for biological membranes, since phosphatidylglycerol is the most abundant anionic phospholipid in prokaryotic cells. At low ionic strengths, this lipid presents a peculiar thermal behavior, with two sharp changes in the light scattering profile, at temperatures named here T(on)(m) and T(off)(m). Structural changes involved in the DMPG thermal transitions are here investigated by small angle X-ray scattering (SAXS), and compared to the results yielded by differential scanning calorimetry (DSC) and electron spin resonance (ESR). The SAXS results show a broad peak, indicating that DMPG is organized in single bilayers, for the range of temperature studied (10-45 degrees C). SAXS intensity shows an unusual effect, starting to decrease at T(on)(m), and presenting a sharp increase at T(off)(m). The bilayer electron density profiles, obtained from modeling the SAXS curves, show a gradual decrease in electron density contrast (attributed to separation between charged head groups) and in bilayer thickness between T(on)(m) and T(off)(m). Results yielded by SAXS, DSC and ESR indicate that a chain melting process starts at T(on)(m), but a complete fluid phase exists only for temperatures above T(off)(m), with structural changes occurring at the bilayer level in the intermediate region.

Rheological characterization of thermal phase behavior of anionic lipid DMPG dispersions

“…SAXS patterns in the gel and fluid phases show an isotropic ring suggesting that DMPG forms spherical vesicles as expected [3,7,17]. Broad peak is a characteristic of single bilayer membranes [3,18]. In the intermediate phase at T = 22 and 24°C, on the other hand, anisotropic rheo-SAXS patterns are obviously observed.…”

The Single Transmembrane Segment of Minimal Sensor DesK Senses Temperature via a Membrane-Thickness Caliper

“…The calculated SAXS curves are similar because the structure of the bilayered membrane is maintained at different temperatures. Nevertheless, the widening of the curves and the consequent shift to higher q values for q ϭ Ͼ2 nm Ϫ1 indicates a thinning of the membrane upon heating (19,20). This analysis showed that when Bacillus membranes are cooled from 37 to 25°C, the hydrophobic thickness increases by 1 Å.…”

“…The data were fitted to the commonly used three-layer model, in which the three layers represent (i) the end methyl group of the acyl chains (low electron density), (ii) the central core of the acyl chains (medium electron density), and (iii) the head groups (high electron density). This method allows estimation of lengths perpendicular to the membrane, electron density, and roughness for each slab (19,20). The roughness or smearing at each slab interface, thickness, and electron density were fitted with starting values for diacylphosphyatidylglycerol (19), which is the major lipid of the ensemble.…”

“…This method allows estimation of lengths perpendicular to the membrane, electron density, and roughness for each slab (19,20). The roughness or smearing at each slab interface, thickness, and electron density were fitted with starting values for diacylphosphyatidylglycerol (19), which is the major lipid of the ensemble. Hydrophobic thickness was calculated from the addition of the thicknesses from layers corresponding to the methyl and core acyl-chain layers.…”

NaCl-dependent formation of the highly crystalline phase in sufficiently hydrated dimyristoylphosphatidylglycerol bilayers

“…Dimyristoylphosphatidylglycerol (DMPG) bilayers have been extensively studied as a model for the negatively charged biomembrane (Eklund et al, 1987;Lotta et al, 1988;Kodama et al, 1993;Zhang et al, 1997;Garidel et al, 2000;Toca-Herrera et al, 2000;Riske et al, 2001;Lamy-Freund and Riske, 2003;Lewis et al, 2005). Recently, it has been reported that DMPG bilayers show a unique low-temperature phase behavior depending on environmental conditions.…”