Department of Molecular Biology, University of Bergen, Pb. 7803, N-5020 Bergen, Norway; Computational Biology Unit, Department of Informatics, University of Bergen, Pb. 7803, N-5020, Norway; Flemish Institute for Technological Research, VITO, Mol B-2400, Belgium.
Department of Molecular Biology, University of Bergen, Pb. 7803, N-5020 Bergen, Norway; Computational Biology Unit, Department of Informatics, University of Bergen, Pb. 7803, N-5020, Norway.
Biochim Biophys Acta Biomembr. 2017 Jul;1859(7):1200-1210. doi: 10.1016/j.bbamem.2017.03.019. Epub 2017 Apr 1.
The human phospholipid scramblase 1 (SCR) distributes lipids non-selectively between the cellular membrane leaflets. SCR has long been thought to be mostly localized in the cytoplasm (amino acids 1-287) and anchored to the membrane via the insertion of a 19 amino acid long transmembrane C-terminal helix (CTH, 288-306), which further extends to the exoplasmic side with a 12 amino acid long tail (307-318). Little is known about the structure of this protein, but recent experimental data on two CTH peptides (288-306 and 288-318) show that they insert through phospholipid bilayers and that the presence of cholesterol improves their affinity for lipid vesicles. Yet the sequence of the CTH (KMKAVMIGACFLIDFMFFE) contains an aspartic acid (D301), which is not exactly a prototypical amino acid for single-pass transmembrane helices. In this study, we investigate how the polar aspartate residue is accommodated in lipid bilayers containing POPC with and without cholesterol, using all-atom molecular dynamics simulations. We identify two cholesterol-binding sites: (i) A291, F298 and L299 and (ii) L299, F302 and E306 and suggest that cholesterol plays a role in stabilizing the helix in a transmembrane position. We suggest that the presence of the aspartate could be functionally relevant for the scramblase protein activity.
人源磷脂酶 SCR 可在细胞膜的双层之间非选择性地分配脂质。长期以来，人们一直认为 SCR 主要定位于细胞质中（氨基酸 1-287），通过插入一个长 19 个氨基酸的跨膜 C 端螺旋（CTH，288-306）锚定在膜上，该螺旋进一步延伸到细胞外侧面，带有一个长 12 个氨基酸的尾巴（307-318）。关于这种蛋白质的结构知之甚少，但最近关于两个 CTH 肽（288-306 和 288-318）的实验数据表明，它们插入磷脂双层，胆固醇的存在可以提高它们与脂质体的亲和力。然而，CTH 的序列（KMKAVMIGACFLIDFMFFE）包含一个天冬氨酸（D301），它不完全是单次跨膜螺旋的典型氨基酸。在这项研究中，我们使用全原子分子动力学模拟研究了带或不带胆固醇的 POPC 脂质双层中如何容纳极性天冬氨酸残基。我们确定了两个胆固醇结合位点：（i）A291、F298 和 L299 和（ii）L299、F302 和 E306，并提出胆固醇在稳定跨膜位置的螺旋方面发挥作用。我们认为天冬氨酸的存在可能对 scramblase 蛋白的活性具有功能相关性。
