Calabresi L, Vecchio G, Frigerio F, Vavassori L, Sirtori C R, Franceschini G
Center E. Grossi Paoletti, Institute of Pharmacological Sciences, University of Milano, Italy.
Biochemistry. 1997 Oct 14;36(41):12428-33. doi: 10.1021/bi970505a.
The apolipoprotein A-IMilano (apoA-IM) is a molecular variant of apoA-I characterized by the Arg173-->Cys substitution, resulting in the formation of homodimers (A-IM/A-IM) and heterodimers with apoA-II. In order to examine the effects of the introduction of an interchain disulfide bridge on the lipid-binding properties of apoA-I, the present studies compare the kinetics of association of A-IM/A-IM and apoA-I with dimyristoylphosphatidylcholine (DMPC), and the structure and properties of reconstituted HDL containing palmitoyloleoylphosphatidylcholine (POPC) and either A-IM/A-IM or apoA-I. The results show that apoA-I dimerization does not affect the rate of association with DMPC. Apolipoprotein-POPC complexes instead, when analyzed by nondenaturing gradient gel electrophoresis, demonstrate that, differently from apoA-I, A-IM/A-IM forms only two species of rHDL particles despite a wide range of initial lipid to protein ratios. These two rHDL species contain one or two A-IM/A-IM molecules and have a diameter of 7.8 nm and 12.5 nm. Investigations of the A-IM/A-IM structure in these two rHDL, by circular dichroism, fluorescence, and second-derivative UV spectroscopy, suggest that the secondary and tertiary structures of A-IM/A-IM are remarkably similar in both small and large particles. These results suggest that the introduction of an interchain disulfide bridge does not affect the association of apoA-I with lipids but restricts HDL particle size heterogeneity, thus possibly affecting HDL function in lipid metabolism and atherosclerosis protection.
载脂蛋白A-米兰（apoA-IM）是载脂蛋白A-I的一种分子变体，其特征在于第173位精氨酸被半胱氨酸取代，导致形成同二聚体（A-IM/A-IM）以及与载脂蛋白A-II的异二聚体。为了研究引入链间二硫键对载脂蛋白A-I脂质结合特性的影响，本研究比较了A-IM/A-IM和载脂蛋白A-I与二肉豆蔻酰磷脂酰胆碱（DMPC）结合的动力学，以及含有棕榈酰油酰磷脂酰胆碱（POPC）和A-IM/A-IM或载脂蛋白A-I的重组高密度脂蛋白（HDL）的结构和特性。结果表明，载脂蛋白A-I二聚化不影响其与DMPC的结合速率。相反，当通过非变性梯度凝胶电泳分析载脂蛋白-POPC复合物时发现，与载脂蛋白A-I不同，尽管初始脂质与蛋白质的比例范围很广，但A-IM/A-IM仅形成两种重组HDL颗粒。这两种重组HDL颗粒含有一个或两个A-IM/A-IM分子，直径分别为7.8纳米和12.5纳米。通过圆二色性、荧光和二阶导数紫外光谱对这两种重组HDL中的A-IM/A-IM结构进行研究表明，A-IM/A-IM在小颗粒和大颗粒中的二级和三级结构非常相似。这些结果表明，引入链间二硫键不影响载脂蛋白A-I与脂质的结合，但限制了HDL颗粒大小的异质性，从而可能影响HDL在脂质代谢和动脉粥样硬化保护中的功能。
