Dissociation of Apolipoprotein E Oligomers to Monomer Is Required for High-Affinity Binding to Phospholipid Vesicles
Dissociation of Apolipoprotein E Oligomers to Monomer Is Required for High-Affinity Binding to Phospholipid Vesicles
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DOI：
10.1021/bi1020106
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发表时间：
2011-04-05
期刊：
影响因子：
2.9
通讯作者：
Frieden, Carl
中科院分区：
文献类型：
--
作者：
Garai, Kanchan;Baban, Berevan;Frieden, Carl
载脂蛋白apoE在胆固醇和脂质代谢中起关键作用。这种蛋白质有三种亚型，其中之一apoE 4是阿尔茨海默病的主要危险因素。在微摩尔浓度下，所有无脂质apoE亚型主要以单体、二聚体和四聚体形式存在。然而，与脂质结合的apoE的分子量形式尚未明确定义。我们已经研究了apoE与磷脂相互作用的自相关作用。在加入apoE后，二肉豆蔻酰-sn-甘油-3-磷酸胆碱（DMPC）的小单层囊泡的浊度清除率的时间依赖性的测量表明，较高分子量的低聚物结合较差，如果有的话。动力学数据可以通过反应模型来描述，其中apoE的四聚体和二聚体必须首先解离成单体，然后以快速和可逆的方式结合到脂质体表面。然后发生单体的缓慢但不容易可逆的构象转化。结合解离过程的速率常数的先验知识使我们能够确定构象转化的速率常数。该速率常数是亚型依赖性的，并且似乎与apoE亚型的稳定性相关，其中apoE寡聚体解离成单体的速率是脂化的限速过程。载脂蛋白E异构体之间的脂化动力学的差异源于它们的自缔合行为的差异，从而得出自缔合行为可能以异构体依赖性方式影响载脂蛋白E的生物学功能的结论。
The apolipoprotein apoE plays a key role in cholesterol and lipid metabolism. There are three isoforms of this protein, one of which, apoE4, is the major risk factor for Alzheimer's disease. At micromolar concentrations all lipid-free apoE isoforms exist primarily as monomers, dimers, and tetramers. However, the molecular weight form of apoE that binds to lipid has not been clearly defined. We have examined the role of self-association of apoE with respect to interactions with phospholipids. Measurements of the time dependence of turbidity clearance of small unilamellar vesicles of dimyristoyl-sn-glycero-3-phosphocholine (DMPC) upon addition of apoE show that higher molecular weight oligomers bind poorly if at all. The kinetic data can be described by a reaction model in which tetramers and dimers of apoE must first dissociate to monomers which then bind to the liposome surface in a fast and reversible manner. A slow but not readily reversible conformational conversion of the monomer then occurs. Prior knowledge of the rate constants for the association dissociation process allows us to determine the rate constant of the conformational conversion. This rate constant is isoform dependent and appears to correlate with the stability of the apoE isoforms with the rate of dissociation of the apoE oligomers to monomers being the rate-limiting process for lipidation. Differences in the lipidation kinetics between the apoE isoforms arise from their differences in the self-association behavior leading to the conclusion that self-association behavior may influence biological functions of apoE in an isoform-dependent manner.