Silver E T, Scraba D G, Ryan R O
Department of Biochemistry, University of Alberta, Edmonton, Canada.
J Biol Chem. 1990 Dec 25;265(36):22487-92.
Incubation of human high density lipoprotein (HDL) particles (density = 1.063-1.21 g/ml) with catalytic amounts of Manduca sexta lipid transfer particle (LTP) resulted in alteration of the density distribution of HDL protein such that the original HDL particles were transformed into new particles with an equilibrium density = 1.05 g/ml. Concomitantly, substantial amounts of protein were recovered in the bottom fraction of the density gradient. The LTP-induced alteration in HDL protein density distribution was dependent on the LTP concentration and incubation time. Electrophoretic analysis revealed that the lower density fraction contained apolipoprotein A-II (apoA-II) as the major apoprotein component while nearly all of the apoA-I was recovered in the bottom fraction. Lipid analysis of the HDL substrate and product fractions revealed that the apoA-I-rich fraction was nearly devoid of lipid (less than 1%, w/w). The lipid originally associated with HDL was recovered in the low density, apoA-II-rich, lipoprotein fraction, and the ratios of individual lipid classes were the same as in control HDL. Electron microscopy and gel permeation chromatography experiments revealed that the LTP-induced product lipoprotein population comprised particles of larger size (19.7 +/- 1.4-nm diameter) than control HDL (10.6 +/- 1.4-nm diameter). The results suggest that facilitated net lipid transfer between HDL particles altered the distribution of lipid such that apoprotein migration occurred and donor particles disintegrated. Similar results were obtained when human HDL3 or HDL2 density subclasses were employed as substrates for LTP. The lower surface area to core volume ratio of the larger, product lipoprotein particles compared with the substrate HDL requires that there be a decrease in the total exposed lipid/water interface which requires stabilization by apolipoprotein. Selective displacement of apoA-I by apoA-II or apoC, due to their greater surface binding affinity, dictates that apoA-I is preferentially lost from the lipoprotein surface and is therefore recovered as lipid-free apoprotein. Thus, it is conceivable that the structural arrangement of HDL particle lipid and apoprotein components isolated from human plasma may not represent the most thermodynamically stable arrangement of lipid and protein.
将人高密度脂蛋白（HDL）颗粒（密度 = 1.063 - 1.21 g/ml）与催化量的烟草天蛾脂质转运颗粒（LTP）一起孵育，导致HDL蛋白质的密度分布发生改变，使得原始的HDL颗粒转变为平衡密度 = 1.05 g/ml的新颗粒。同时，在密度梯度的底部级分中回收了大量蛋白质。LTP诱导的HDL蛋白质密度分布变化取决于LTP浓度和孵育时间。电泳分析表明，较低密度级分包含载脂蛋白A-II（apoA-II）作为主要载脂蛋白成分，而几乎所有的apoA-I都在底部级分中回收。对HDL底物和产物级分的脂质分析表明，富含apoA-I的级分几乎不含脂质（小于1%，w/w）。最初与HDL相关的脂质在低密度、富含apoA-II的脂蛋白级分中回收，并且各个脂质类别的比例与对照HDL中的相同。电子显微镜和凝胶渗透色谱实验表明，LTP诱导的产物脂蛋白群体由尺寸比对照HDL（直径10.6 +/- 1.4 nm）更大（直径19.7 +/- 1.4 nm）的颗粒组成。结果表明，HDL颗粒之间促进的净脂质转移改变了脂质分布，从而发生了载脂蛋白迁移并且供体颗粒解体。当使用人HDL3或HDL2密度亚类作为LTP的底物时，获得了类似的结果。与底物HDL相比，较大的产物脂蛋白颗粒的表面积与核心体积之比更低，这要求总暴露脂质/水界面减少，而这需要载脂蛋白进行稳定。由于apoA-II或apoC具有更高的表面结合亲和力，它们对apoA-I的选择性取代表明apoA-I优先从脂蛋白表面丢失，因此作为无脂质载脂蛋白回收。因此，可以想象，从人血浆中分离的HDL颗粒脂质和载脂蛋白成分的结构排列可能不代表脂质和蛋白质最热力学稳定的排列。
