Wetting properties of dioleoyl-phosphatidyl-choline bilayers in the presence of trehalose: an X-ray diffraction study

The combined effect of trehalose and temperature on the wetting properties of L-dioleoylphosphatidyl-choline (DOPC) model membranes in excess aqueous solutions has been analyzed by X-ray diffraction and extended electron density map reconstruction. At room temperature, DOPC in excess water forms a fluid lamellar L phase. In the presence of trehalose, no phase transitions occur, but repeat and intermembrane distances increase considerably. Electron density maps show that trehalose in solution promotes a straightening of the hydrocarbon chain packing and a reduction of the molecular average area at the polar-apolar interface. Accordingly, the increased intermembrane distance is interpreted as a clear indication of a sugar screening effect of the van der Waals attractive contribution in the lamellar stacks, which overcomes the eventual decreasing of the repulsive fluctuations due to the hardening of the bilayer. By contrast to the thermally induced membrane swelling observed in excess water, in the presence of trehalose the DOPC bilayer thickness and repeat and intermembrane distances decrease continuously with temperature. While the thermal dependence of bilayer thickness is a consequence of the chain conformational disorder promoted by temperature, the changes in the intermembrane distance can be explained only assuming a trehalose-induced re-setting of the long-range force balance. The final results confirm the complex mechanism by which trehalose stabilize lipid bilayers.