Mode of organization of galactolipids: a conformational analysis.

Despite the fact that photosynthetic membranes show the conventional bilayer structure, their major lipid component monogalactosyldiacylglycerol does not form lamellar structure but takes up an hexagonal-II structure when dispersed alone in water and forms inverted lipids micelle structures when dispersed together with other lipid components of the photosynthetic membrane. We present here evidence that the mode of organization of these lipids can be predicted from a conformational approach allowing to describe the configuration of assembled amphiphilic molecules. The minimal conformational energy is calculated as the sum of the contributions resulting from the Van der Waals interactions, the torsional potentials, the electrostatic interaction and the transfer energy. Because of its calculated "cone shaped" structure monogalactosyldiacylglycerol forms inverted lipid structure with the hydrophilic groups pointing inward; for digalactosyldiacylglycerol, an other essential lipid constituent of photosynthetic membrane, its calculated cylindrical shape induces an organization in bilayer structures.