Pownall Henry J, Hosken Brian D, Gillard Baiba K, Higgins Catherine L, Lin Hu Yu, Massey John B
Section of Atherosclerosis and Vascular Medicine, Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA.
Biochemistry. 2007 Jun 26;46(25):7449-59. doi: 10.1021/bi700496w. Epub 2007 May 27.
The distribution of apolipoprotein (apo) A-I between human high-density lipoproteins (HDL) and water is an important component of reverse cholesterol transport and the atheroprotective effects of HDL. Chaotropic perturbation (CP) with guanidinium chloride (Gdm-Cl) reveals HDL instability by inducing the unfolding and transfer of apo A-I but not apo A-II into the aqueous phase while forming larger apo A-I deficient HDL-like particles and small amounts of cholesteryl ester-rich microemulsions (CERMs). Our kinetic and hydrodynamic studies of the CP of HDL species separated according to size and density show that (1) CP mediated an increase in HDL size, which involves quasi-fusion of surface and core lipids, and release of lipid-free apo A-I (these processes correlate linearly), (2) >94% of the HDL lipids remain with an apo A-I deficient particle, (3) apo A-II remains associated with a very stable HDL-like particle even at high levels of Gdm-Cl, and (4) apo A-I unfolding and transfer from HDL to water vary among HDL subfractions with the larger and more buoyant species exhibiting greater stability. Our data indicate that apo A-I's on small HDL (HDL-S) are highly dynamic and, relative to apo A-I on the larger more mature HDL, partition more readily into the aqueous phase, where they initiate the formation of new HDL species. Our data suggest that the greater instability of HDL-S generates free apo A-I and an apo A-I deficient HDL-S that readily fuses with the more stable HDL-L. Thus, the presence of HDL-L drives the CP remodeling of HDL to an equilibrium with even larger HDL-L and more lipid-free apo A-I than with either HDL-L or HDL-S alone. Moreover, according to dilution studies of HDL in 3 M Gdm-Cl, CP of HDL fits a model of apo A-I partitioning between HDL phospholipids and water that is controlled by the principal of opposing forces. These findings suggest that the size and relative amount of HDL lipid determine the HDL stability and the fraction of apo A-I that partitions into the aqueous phase where it is destined for interaction with ABCA1 transporters, thereby initiating reverse cholesterol transport or, alternatively, renal clearance.
载脂蛋白（apo）A-I在人高密度脂蛋白（HDL）与水之间的分布是逆向胆固醇转运以及HDL抗动脉粥样硬化作用的一个重要组成部分。用氯化胍（Gdm-Cl）进行的离液剂扰动（CP）通过诱导apo A-I而非apo A-II展开并转移到水相中，同时形成更大的缺乏apo A-I的类HDL颗粒和少量富含胆固醇酯的微乳液（CERMs），揭示了HDL的不稳定性。我们对根据大小和密度分离的HDL种类进行的CP动力学和流体动力学研究表明：（1）CP介导了HDL大小的增加，这涉及表面和核心脂质的准融合以及无脂质apo A-I的释放（这些过程呈线性相关）；（2）>94%的HDL脂质保留在缺乏apo A-I的颗粒中；（3）即使在高浓度Gdm-Cl下，apo A-II仍与非常稳定的类HDL颗粒相关联；（4）apo A-I从HDL展开并转移到水相的情况在HDL亚组分中有所不同，较大且浮力更大的种类表现出更高的稳定性。我们的数据表明，小HDL（HDL-S）上的apo A-I高度动态，相对于较大、更成熟的HDL上的apo A-I，更容易分配到水相中，在那里它们启动新HDL种类的形成。我们的数据表明，HDL-S更大的不稳定性产生了游离apo A-I和缺乏apo A-I的HDL-S，其很容易与更稳定的HDL-L融合。因此，HDL-L的存在驱使HDL的CP重塑达到一种平衡，形成比单独的HDL-L或HDL-S更大的HDL-L和更多的无脂质apo A-I。此外，根据在3 M Gdm-Cl中对HDL的稀释研究，HDL的CP符合一种由相反力原理控制的apo A-I在HDL磷脂和水之间分配的模型。这些发现表明，HDL脂质的大小和相对量决定了HDL的稳定性以及分配到水相中的apo A-I的比例，在水相中它将与ABCA1转运蛋白相互作用，从而启动逆向胆固醇转运或肾脏清除。
