J Phys Chem B. 2021 May 13;125(18):4746-4756. doi: 10.1021/acs.jpcb.1c00271. Epub 2021 May 3.
Protein-lipid interactions govern the structure and function of lipoprotein particles, which transport neutral lipids and other hydrophobic cargo through the blood stream. Apolipoproteins cover the surface of lipoprotein particles, including low-density (LDL) and high-density (HDL) lipoproteins, and determine their function. Previous work has focused on small peptides derived from these apolipoproteins or used such artificial lipid systems as Langmuir monolayers or the lipid disc assay to determine how apolipoproteins interact with the neutral lipid interface. Here, we focus on a recurring protein domain found in many neutral lipid-binding proteins, the amphipathic α-helix bundle. We use liquid droplet tensiometry to investigate protein-lipid interactions on an oil droplet, which mimics the real lipoprotein interface. The N-terminus of apoE 3 and full-length apoLp-III serve as model proteins. We find that each protein interacts with lipid monolayers at the oil-aqueous interface in unique ways. For the first time, we show that helix bundle unfolding is critical for proper protein insertion into the lipid monolayer at the oil-aqueous interface and that specific membrane lipids promote the rebinding of protein upon fluctuation in droplet size. These results shed new light on how amphipathic apolipoprotein α-helix bundles interact with neutral lipid particles.
蛋白质-脂质相互作用控制脂蛋白颗粒的结构和功能，这些颗粒通过血液运输中性脂质和其他疏水性货物。载脂蛋白覆盖在脂蛋白颗粒的表面，包括低密度脂蛋白（LDL）和高密度脂蛋白（HDL），并决定其功能。以前的工作主要集中在这些载脂蛋白衍生的小肽上，或使用 Langmuir 单分子层或脂质盘测定等人工脂质系统来确定载脂蛋白如何与中性脂质界面相互作用。在这里，我们关注的是许多中性脂质结合蛋白中存在的一个重复出现的蛋白质结构域，即两亲性α-螺旋束。我们使用液滴张力计在油滴上研究蛋白质-脂质相互作用，油滴模拟真实的脂蛋白界面。载脂蛋白 E3 的 N 端和全长载脂蛋白 Lp-III 用作模型蛋白。我们发现，每种蛋白质与油-水界面处的脂质单层以独特的方式相互作用。我们首次表明，螺旋束展开对于蛋白质在油-水界面处正确插入脂质单层是至关重要的，并且特定的膜脂质促进了蛋白在液滴大小波动时的重新结合。这些结果为两亲性载脂蛋白α-螺旋束与中性脂质颗粒的相互作用提供了新的认识。
