A cubic DNA-lipid complex

DNA-lipid interactions play a significant biological and biotechnological role but remain poorly understood. In investigations of mixed lipid-DNA systems a novel bicontinuous cubic phase, composed of lecithin, water and dodecyltrimethylammonium with DNA as the counterion (DNA-DTA), was identified. The cubic phase is stable only in a narrow composition range and in the temperature range 20-65 degrees C. The samples have a transparent rubber-like morphology, are rigid, optically isotropic and show a shear-induced optical birefringence. The NMR spectrum consists of a broadened singlet. Upon increasing the lecithin content the phase transforms to lamellar phase. The liquid crystal (LC) is determined to be in Ia3d symmetry from investigations by small angle X-ray scattering (SAXS). Model calculations indicate that the cubic phase is normal, i.e. being composed of DNA chains and water incorporated in polar group bilayers separating two hydrophobic domains containing hydrocarbon tails of lipids.