Cholesterol Determines and Limits rHDL Formation from Human Plasma Apolipoprotein A-II and Phospholipid Membranes
Cholesterol Determines and Limits rHDL Formation from Human Plasma Apolipoprotein A-II and Phospholipid Membranes
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DOI：
10.1021/bi3011994
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发表时间：
2012-10-30
期刊：
影响因子：
2.9
通讯作者：
Pownall, Henry J.
中科院分区：
文献类型：
--
作者：
Bassett, G. Randall;Gillard, Baiba K.;Pownall, Henry J.
载脂蛋白（apo） A-II是人类血浆高密度脂蛋白（HDL）中含量仅次于载脂蛋白A-I的第二丰富蛋白，是可交换的载脂蛋白中亲脂性最强的。当膜游离胆固醇（FC）水平增加到20 mol %时，载脂蛋白A-I对二myristoyl磷脂酰胆碱（DMPC）膜的微增溶速率增加，而反应水平降低到零。鉴于其更大的亲脂性，我们测试了载脂蛋白a - ii及其还原和羧甲基化单体（rcm载脂蛋白a - ii）在膜FC含量为bb0 20 mol %时形成rHDL的假设。根据浊度滴定，DMPC/apo A-II的化学计量为65/1（摩尔比摩尔）。在这个化学计量中，载脂蛋白A-II从DMPC和FC形成rHDL。与我们的假设相反，载脂蛋白A-II与载脂蛋白A-I一样，与含有>= 20 mol % FC的DMPC反应不良。在所有FC摩尔百分比下，rcm载脂蛋白A-H和DMPC形成rHDL的速度都比载脂蛋白A-II快，但在20摩尔百分比FC时为零。在平行反应中，单体和二聚体载脂蛋白A-II形成大的富含fc的rHDL与小的缺乏fc的rHDL共存；增加FC摩尔百分比增加富FC rHDL的数量和大小。根据大小rHDL共存的组成，FC从最小粒子到最大粒子的自由传递能约为-1.2 kJ。基于我们的数据，我们提出了一个载脂蛋白a - i和载脂蛋白a - ii通过表面缺陷与DMPC结合的模型，这些缺陷在20mol % FC时消失。这些数据表明，肝内形成的含载脂蛋白a - ii的HDL与细胞内较小的低脂载脂蛋白A-I HDL相比，可能富含胆固醇。
Apolipoprotein (apo) A-II, the second most abundant protein after apo A-I of human plasma high-density lipoproteins (HDL), is the most lipophilic of the exchangeable apolipoproteins. The rate of microsolubilization of dimyristoylphosphatidylcholine (DMPC) membranes by apo A-I to give rHDL increases as the level of membrane free cholesterol (FC) increases up to 20 mol % when the level of reaction decreases to nil. Given its greater lipophilicity, we tested the hypothesis that apo A-II and its reduced and carboxymethylated monomer (rcm apo A-II) would form rHDL at a membrane FC content of > 20 mol %. According to turbidimetric titrations, the DMPC/apo A-II stoichiometry is 65/1 (moles to moles). At this stoichiometry, apo A-II forms rHDL from DMPC and FC. Contrary to our hypothesis, apo A-II, like apo A-I, reacts poorly with DMPC containing >= 20 mol % FC. The rate of formation of rHDL from rcm apo A-H and DMPC at all FC mole percentages is faster than that of apo A-II but nil at 20 mol % FC. In parallel reactions, monomeric and dimeric apo A-II form large FC-rich rHDL coexisting with smaller FC-poor rHDL; increasing the FC mole percentage increases the number and size of FC-rich rHDL. On the basis of the compositions of coexisting large and small rHDL, the free energy of transfer of FC from the smallest to the largest particle is approximately -1.2 kJ. On the basis of our data, we propose a model in which apo A-I and apo A-II bind to DMPC via surface defects that disappear at 20 mol % FC. These data suggest apo A-II-containing HDL formed intrahepatically are likely cholesterol-rich compared to the smaller intracellular lipid-poor apo A-I HDL.