Supramolecular organization of α-galactosylceramide in pure dispersions and in cationic DODAB bilayers

Thermotropic Behavior and Structural Organization of C24:1 Sulfatide Dispersions and Its Mixtures with Cationic Bilayers

“…In contrast to SF, pure DODAB dispersions have a narrow endothermic transition around 47 °C when heated (Figure A) and a narrow exothermic peak around 41.5 °C when cooled (Figure B). The narrow peaks indicate that these phase transitions are cooperative, i.e., the conformational changes of one molecule are transmitted to the other molecules of the array, leading to a collective change of all molecules. , Similar thermograms, with narrow peaks and a hysteresis of 5.4 °C between heating and cooling, have been described for diluted DODAB dispersions in water. , These samples prepared in water have transition peaks upon heating and cooling around 44 and 39 °C, respectively. , A narrow peak around 47 °C has been described upon heating buffered samples, , suggesting that the increase in transition temperature results from the electrostatic shielding of the cationic DODAB headgroups.…”

“…25 αGalCer is structurally very different from SF, not only because it lacks the sulfate group at the galactoside residue but also because this residue is α-linked to a ceramide that is made of a phytosphingosine base linked to a large saturated acyl chain. 25 However, SF and αGalCer share an important structural feature: an amide bond that connects the sphingoid base (sphingosine in SF, phytosphingosine in αGalCer) to the acyl chain (Figure 1). 25 The amide bond has a planar and rigid trans configuration and adopts a perpendicular orientation toward the axes of the sphingoid and acyl chains.…”

“…25 However, SF and αGalCer share an important structural feature: an amide bond that connects the sphingoid base (sphingosine in SF, phytosphingosine in αGalCer) to the acyl chain (Figure 1). 25 The amide bond has a planar and rigid trans configuration and adopts a perpendicular orientation toward the axes of the sphingoid and acyl chains. 48 In order to accommodate the polar headgroup into this rigid perpendicular orientation, the torsion angles spread out the sphingoid and acyl chains, resulting in a V-shaped molecular conformation.…”

“…This V-shaped conformation would result in a large lateral area requirement that would decrease the packing of the DODAB gel phase, as observed in Figure . The V-shaped conformation would also explain the increase in DODAB fluid-phase rigidity: the larger S eff and smaller h –1 / h 0 values in Figure indicate that the acyl chains of DODAB are more ordered and have less freedom of movement in the presence of SF, as they do in the presence of βGlcCer and αGalCer. , Paramagnetic-labeled galactosylceramides were also shown to increase the rigidity of membranes in the fluid phase …”

“…Lipid dispersions were prepared as previously described . Briefly, lipid films were prepared by drying chloroform/methanol 2:1 (v/v) solutions.…”