Kim Sunghwan, Pang Hong-Bo, Kay Michael S
Department of Biochemistry, University of Utah School of Medicine, 15 North Medical Drive East, Room 4100, Salt Lake City, UT 84112-5650, USA.
J Mol Biol. 2008 Feb 22;376(3):786-97. doi: 10.1016/j.jmb.2007.12.001. Epub 2007 Dec 7.
The human immunodeficiency virus envelope glycoprotein (Env) is composed of surface (gp120) and transmembrane (gp41) subunits, which are noncovalently associated on the viral surface. Human immunodeficiency virus Env mediates viral entry after undergoing a complex series of conformational changes induced by interaction with cellular CD4 and a chemokine coreceptor. These changes propagate from gp120 to gp41 via the gp120-gp41 interface, ultimately exposing gp41 and allowing it to form the trimer-of-hairpins structure that provides the driving force for membrane fusion. Key unresolved questions about the gp120-gp41 interface include the specific regions of gp41 and gp120 involved, the mechanism by which receptor and coreceptor-binding-induced conformational changes in gp120 are communicated to gp41, how trimer-of-hairpins formation is prevented in the prefusogenic gp120-gp41 complex, and, ultimately, the structure of the prefusion gp120-gp41 complex. Here, we develop a biochemical model system that mimics a key portion of the gp120-gp41 interface in the prefusogenic state. We find that a gp41 fragment containing the disulfide bond loop and C-peptide region binds primarily to the gp120 C5 region and that this interaction is incompatible with trimer-of-hairpins formation. Based on these data, we propose that in prefusogenic Env, gp120 sequesters the gp41 C-peptide region away from the N-trimer region, preventing trimer-of-hairpins formation until coreceptor binding disrupts this interface. This model system is a valuable tool for studying the gp120-gp41 complex, conformational changes induced by CD4 and coreceptor binding, and the mechanism of membrane fusion.
人类免疫缺陷病毒包膜糖蛋白（Env）由表面亚基（gp120）和跨膜亚基（gp41）组成，二者在病毒表面非共价结合。人类免疫缺陷病毒Env在与细胞CD4和趋化因子共受体相互作用诱导一系列复杂的构象变化后介导病毒进入。这些变化通过gp120 - gp41界面从gp120传播到gp41，最终暴露gp41并使其形成发夹三聚体结构，该结构为膜融合提供驱动力。关于gp120 - gp41界面尚未解决的关键问题包括涉及gp-41和gp120的特定区域、受体和共受体结合诱导的gp120构象变化传递给gp41的机制、在融合前gp120 - gp41复合物中如何防止发夹三聚体形成，以及最终融合前gp120 - gp41复合物的结构。在此，我们开发了一种生化模型系统，该系统模拟融合前状态下gp120 - gp41界面的关键部分。我们发现，包含二硫键环和C肽区域的gp41片段主要与gp120 C5区域结合，并且这种相互作用与发夹三聚体形成不相容。基于这些数据，我们提出，在融合前Env中，gp120将gp41 C肽区域与N三聚体区域隔离，防止发夹三聚体形成，直到共受体结合破坏该界面。该模型系统是研究gp120 - gp41复合物、CD4和共受体结合诱导的构象变化以及膜融合机制的宝贵工具。
