Thermally Stable Multilamellar Structure of DNA/Cationic Lipid Complex in the Bulk State

The effect of temperature on the two types of multilamellar structures, L I and L II , formed by the complexes of DNA with a cationic lipid, cholesteryl 3β-N-(dimethylamionethyl) carbamate (DC-Chol), in the bulk state has been investigated by small angle X-ray scattering (SAXS). L I phase composing of A-DNA intercalated between the lipid bilayers with tilted tails was formed at lower lipid-to-base pair molar ratio (x 2. In addition to the differences in lipid packing state and DNA conformation, these two lamellar phases also displayed different thermal stability. L I phase was highly thermally stable as its interlamellar distance remained essentially unperturbed even after the denaturation of A-DNA in the complex at elevated temperature. By contrast, the interlamellar distance of L II phase decreased with increasing temperature due to the release of bound water and B-DNA denaturation.