Rathnayake Sewwandi S, Mirheydari Mona, Schulte Adam, Gillahan James E, Gentit Taylor, Phillips Ashley N, Okonkwo Rose K, Burger Koert N J, Mann Elizabeth K, Vaknin David, Bu Wei, Agra-Kooijman Dena Mae, Kooijman Edgar E
Department of Biological Sciences, Kent State University, Kent, OH 44242, USA.
Biochim Biophys Acta. 2014 Jan;1838(1 Pt B):482-92. doi: 10.1016/j.bbamem.2013.09.020. Epub 2013 Oct 4.
Neutral lipid transport in mammals is complicated involving many types of apolipoprotein. The exchangeable apolipoproteins mediate the transfer of hydrophobic lipids between tissues and particles, and bind to cell surface receptors. Amphipathic α-helices form a common structural motif that facilitates their lipid binding and exchangeability. ApoLp-III, the only exchangeable apolipoprotein found in insects, is a model amphipathic α-helix bundle protein and its three dimensional structure and function mimics that of the mammalian proteins apoE and apoAI. Even the intracellular exchangeable lipid droplet protein TIP47/perilipin 3 contains an α-helix bundle domain with high structural similarity to that of apoE and apoLp-III. Here, we investigated the interaction of apoLp-III from Locusta migratoria with lipid monolayers. Consistent with earlier work we find that insertion of apoLp-III into fluid lipid monolayers is highest for diacylglycerol. We observe a preference for saturated and more highly ordered lipids, suggesting a new mode of interaction for amphipathic α-helix bundles. X-ray reflectivity shows that apoLp-III unfolds at a hydrophobic interface and flexible loops connecting the amphipathic α-helices stay in solution. X-ray diffraction indicates that apoLp-III insertion into diacylglycerol monolayers induces additional ordering of saturated acyl-chains. These results thus shed important new insight into the protein-lipid interactions of a model exchangeable apolipoprotein with significant implications for its mammalian counterparts.
哺乳动物中的中性脂质转运很复杂，涉及多种载脂蛋白。可交换载脂蛋白介导疏水脂质在组织和颗粒之间的转移，并与细胞表面受体结合。两亲性α-螺旋形成一种常见的结构基序，有助于它们与脂质的结合和可交换性。ApoLp-III是在昆虫中发现的唯一可交换载脂蛋白，是一种典型的两亲性α-螺旋束蛋白，其三维结构和功能类似于哺乳动物蛋白apoE和apoAI。甚至细胞内可交换脂质滴蛋白TIP47/ perilipin 3也包含一个与apoE和ApoLp-III具有高度结构相似性的α-螺旋束结构域。在这里，我们研究了来自飞蝗的ApoLp-III与脂质单层的相互作用。与早期工作一致，我们发现ApoLp-III插入流体脂质单层中对二酰基甘油的插入率最高。我们观察到对饱和且更有序脂质的偏好，这表明两亲性α-螺旋束存在一种新的相互作用模式。X射线反射率表明，ApoLp-III在疏水界面处展开，连接两亲性α-螺旋的柔性环保留在溶液中。X射线衍射表明，ApoLp-III插入二酰基甘油单层会诱导饱和酰基链产生额外的有序排列。因此，这些结果为一种典型可交换载脂蛋白的蛋白质-脂质相互作用提供了重要的新见解，对其哺乳动物对应物具有重要意义。
