Center for Membrane Biology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, USA.
J Mol Biol. 2012 Apr 20;418(1-2):3-15. doi: 10.1016/j.jmb.2012.02.010. Epub 2012 Feb 17.
The human immunodeficiency virus (HIV) gp41 fusion domain plays a critical role in membrane fusion during viral entry. A thorough understanding of the relationship between the structure and the activity of the fusion domain in different lipid environments helps to formulate mechanistic models on how it might function in mediating membrane fusion. The secondary structure of the fusion domain in small liposomes composed of different lipid mixtures was investigated by circular dichroism spectroscopy. The fusion domain formed an α-helix in membranes containing less than 30 mol% cholesterol and formed β-sheet secondary structure in membranes containing ≥30 mol% cholesterol. EPR spectra of spin-labeled fusion domains also indicated different conformations in membranes with and without cholesterol. Power saturation EPR data were further used to determine the orientation and depth of α-helical fusion domains in lipid bilayers. Fusion and membrane perturbation activities of the gp41 fusion domain were measured by lipid mixing and contents leakage. The fusion domain fused membranes in both its helical form and its β-sheet form. High cholesterol, which induced β-sheets, promoted fusion; however, acidic lipids, which promoted relatively deep membrane insertion as an α-helix, also induced fusion. The results indicate that the structure of the HIV gp41 fusion domain is plastic and depends critically on the lipid environment. Provided that their membrane insertion is deep, α-helical and β-sheet conformations contribute to membrane fusion.
人类免疫缺陷病毒（HIV）的 gp41 融合域在病毒进入过程中的膜融合中起着关键作用。深入了解融合域在不同脂质环境中的结构与活性之间的关系有助于构建关于其介导膜融合的作用机制模型。通过圆二色性光谱研究了由不同脂质混合物组成的小脂质体中融合域的二级结构。融合域在胆固醇含量低于 30 mol%的膜中形成α-螺旋，在胆固醇含量≥30 mol%的膜中形成β-折叠二级结构。自旋标记融合域的 EPR 谱也表明胆固醇存在与否的膜中存在不同构象。功率饱和 EPR 数据进一步用于确定脂质双层中α-螺旋融合域的取向和深度。通过脂质混合和内容物泄漏测量 gp41 融合域的融合和膜扰动活性。融合域以其螺旋形式和β-折叠形式融合膜。高胆固醇诱导β-折叠，促进融合；然而，促进相对深膜插入作为α-螺旋的酸性脂质也诱导融合。结果表明，HIV gp41 融合域的结构具有可塑性，并且严重依赖于脂质环境。只要其膜插入深，α-螺旋和β-折叠构象有助于膜融合。
