Laboratory of Structural Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland, USA.
J Virol. 2012 Nov;86(22):12129-37. doi: 10.1128/JVI.01880-12. Epub 2012 Aug 29.
Retrovirus infection starts with the binding of envelope glycoproteins to host cell receptors. Subsequently, conformational changes in the glycoproteins trigger fusion of the viral and cellular membranes. Some retroviruses, such as avian sarcoma/leukosis virus (ASLV), employ a two-step mechanism in which receptor binding precedes low-pH activation and fusion. We used cryo-electron tomography to study virion/receptor/liposome complexes that simulate the interactions of ASLV virions with cells. Binding the soluble receptor at neutral pH resulted in virions capable of binding liposomes tightly enough to alter their curvature. At virion-liposome interfaces, the glycoproteins are ∼3-fold more concentrated than elsewhere in the viral envelope, indicating specific recruitment to these sites. Subtomogram averaging showed that the oblate globular domain in the prehairpin intermediate (presumably the receptor-binding domain) is connected to both the target and the viral membrane by 2.5-nm-long stalks and is partially disordered, compared with its native conformation. Upon lowering the pH, fusion took place. Fusion is a stochastic process that, once initiated, must be rapid, as only final (postfusion) products were observed. These fusion products showed glycoprotein spikes on their surface, with their interiors occupied by patches of dense material but without capsids, implying their disassembly. In addition, some of the products presented a density layer underlying and resolved from the viral membrane, which may represent detachment of the matrix protein to facilitate the fusion process.
逆转录病毒感染始于包膜糖蛋白与宿主细胞受体的结合。随后，糖蛋白构象的变化引发病毒和细胞膜的融合。一些逆转录病毒，如禽肉瘤/白血病病毒（ASLV），采用两步机制，其中受体结合先于低 pH 值激活和融合。我们使用冷冻电子断层扫描研究模拟 ASLV 病毒与细胞相互作用的病毒/受体/脂质体复合物。在中性 pH 下结合可溶性受体会导致病毒颗粒能够紧密结合脂质体，从而改变其曲率。在病毒-脂质体界面处，糖蛋白的浓度比病毒包膜的其他部位高约 3 倍，表明它们特异性地募集到这些部位。亚体素平均法显示，发夹前中间体中的扁球形结构域（推测为受体结合域）通过 2.5nm 长的柄与靶标和病毒膜相连，并且与天然构象相比部分无序。降低 pH 值后，融合发生。融合是一个随机过程，一旦启动，必须迅速进行，因为只观察到最终（融合后）产物。这些融合产物在其表面显示出糖蛋白刺突，内部有密集物质的斑块，但没有衣壳，这意味着它们的解体。此外，一些产物呈现出位于病毒膜下方并与其分离的密度层，这可能代表基质蛋白的脱离以促进融合过程。
