Mel'nikova Y S, Mel'nikov S M, Löfroth J E
Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, Box 124, S-22100 Lund, Sweden.
Biophys Chem. 1999 Oct 4;81(2):125-41. doi: 10.1016/s0301-4622(99)00088-5.
The mechanism of complex formation between DNA and oppositely charged dioctadecyldimethylammonium bromide/dioleoyl phosphatidylethanolamine (DODAB/DOPE) and 1,2-dioleoyl-3-trimethylammonium propane (DOTAP)/DOPE mixed liposomes, as well as the physico-chemical properties of DNA-mixed liposome complexes, were examined. Fluorescence microscopy showed that the interaction between DNA and oppositely charged mixed liposomes started at very low liposome concentrations and induced a discrete coil-globule transition in individual DNA molecules. The DNA size distribution was bimodal in a wide range of liposome concentrations. The critical concentration of the cationic lipid needed for the complete compaction of single DNA molecules depended on the composition of the charged mixed DODAB/DOPE and DOTAP/DOPE liposomes. Cryogenic transmission electron microscopy (cryo-TEM) observations of DNA complexes with mixed liposomes revealed that the lamellar packing of lipid molecules was typical for the complexes formed from the cationic lipid-enriched mixtures, while inverted hexagonal arrays were found for the neutral lipid-enriched complexes. The microstructures of the complexes were also examined with the use of the small-angle X-ray scattering (SAXS) technique, which confirmed the results obtained by cryo-TE microscopy and enabled the quantitative characterization of lipid packaging in the complexes with DNA macromolecules. We also found that the introduction of the neutral lipid into the complexes between DNA and oppositely charged lipids, DODAB and DOTAP, moderately increased the thermal stability of the complexes and changed the quantitative characteristics of the melting profiles of the complexes.
研究了DNA与带相反电荷的二辛基二甲基溴化铵/二油酰磷脂酰乙醇胺（DODAB/DOPE）以及1,2-二油酰-3-三甲基铵丙烷（DOTAP）/DOPE混合脂质体之间形成复合物的机制，以及DNA-混合脂质体复合物的物理化学性质。荧光显微镜显示，DNA与带相反电荷的混合脂质体之间的相互作用在非常低的脂质体浓度下就开始了，并在单个DNA分子中诱导了离散的线圈-球体转变。在广泛的脂质体浓度范围内，DNA大小分布呈双峰。单个DNA分子完全压缩所需的阳离子脂质的临界浓度取决于带电荷的混合DODAB/DOPE和DOTAP/DOPE脂质体的组成。对DNA与混合脂质体复合物的低温透射电子显微镜（cryo-TEM）观察表明，脂质分子的层状堆积对于由富含阳离子脂质的混合物形成的复合物是典型的，而对于富含中性脂质的复合物则发现了反相六角形阵列。还使用小角X射线散射（SAXS）技术检查了复合物的微观结构，该技术证实了cryo-TE显微镜获得的结果，并能够对与DNA大分子的复合物中的脂质包装进行定量表征。我们还发现，将中性脂质引入DNA与带相反电荷的脂质DODAB和DOTAP之间的复合物中，适度提高了复合物的热稳定性，并改变了复合物熔解曲线的定量特征。
