Salzwedel K, Berger E A
Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 2000 Nov 7;97(23):12794-9. doi: 10.1073/pnas.230438497.
The envelope glycoprotein (Env) of HIV-1 is displayed on the surface of the virion or infected cell as an oligomer of multiple gp120/gp41 complexes. We sought to unravel the relationships between this oligomeric structure and the requirements for sequential interactions with CD4 and coreceptor (CCR5 or CXCR4). We used a quantitative cell fusion assay to examine the effects of coexpressing pairs of Envs, each nonfunctional because of a specific defect in one of the essential properties. We observed efficient fusion activity upon coexpression of two Env variants, one containing a gp41 subunit with a mutated fusion peptide and the other containing a gp120 subunit with a mutated CD4 binding site or a mismatched coreceptor specificity. We also observed fusion upon coexpression of two Env variants with distinct gp120 defects, i.e., a CD4 binding site mutation and the incorrect coreceptor specificity determinants. Coimmunoprecipitation experiments verified the efficient formation of mixed oligomers, suggesting that the observed fusion reflected subunit complementation within the oligomeric complex. These results support a model in which cooperative subunit interactions within the Env oligomer result in concerted conformational changes upon receptor binding, resulting in activation for fusion. The implications of these findings for Env function and virus neutralization are discussed.
HIV-1的包膜糖蛋白（Env）以多个gp120/gp41复合物的寡聚体形式展示在病毒粒子或感染细胞的表面。我们试图阐明这种寡聚体结构与与CD4和共受体（CCR5或CXCR4）顺序相互作用的要求之间的关系。我们使用定量细胞融合试验来检测共表达成对Env的效果，每对Env由于其中一个基本特性的特定缺陷而无功能。我们观察到，当共表达两个Env变体时具有高效的融合活性，其中一个变体的gp41亚基带有突变的融合肽，另一个变体的gp120亚基带有突变的CD4结合位点或错配的共受体特异性。我们还观察到，当共表达两个具有不同gp120缺陷的Env变体时会发生融合，即一个CD4结合位点突变体和具有不正确共受体特异性决定簇的变体。免疫共沉淀实验证实了混合寡聚体的有效形成，这表明观察到的融合反映了寡聚复合物内的亚基互补。这些结果支持了一个模型，即Env寡聚体内的协同亚基相互作用导致受体结合时发生协同构象变化，从而激活融合。本文讨论了这些发现对Env功能和病毒中和的影响。
