Department of Infectious Diseases and Immunology, Virology Division, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
J Virol. 2012 Dec;86(24):13642-52. doi: 10.1128/JVI.01973-12. Epub 2012 Oct 3.
The entry of the enveloped Rift Valley fever virus (RVFV) into its host cell is mediated by the viral glycoproteins Gn and Gc. We investigated the RVFV entry process and, in particular, its pH-dependent activation mechanism using our recently developed nonspreading-RVFV-particle system. Entry of the virus into the host cell was efficiently inhibited by lysosomotropic agents that prevent endosomal acidification and by compounds that interfere with dynamin- and clathrin-dependent endocytosis. Exposure of plasma membrane-bound virions to an acidic pH (<pH 6) equivalent to the pH of late endolysosomal compartments allowed the virus to bypass the endosomal route of infection. Acid exposure of virions in the absence of target membranes triggered the class II-like Gc fusion protein to form extremely stable oligomers that were resistant to SDS and temperature dissociation and concomitantly compromised virus infectivity. By targeted mutagenesis of conserved histidines in Gn and Gc, we demonstrated that mutation of a single histidine (H857) in Gc completely abrogated virus entry, as well as acid-induced Gc oligomerization. In conclusion, our data suggest that after endocytic uptake, RVFV traffics to the acidic late endolysosomal compartments, where histidine protonation drives the reorganization of the Gc fusion protein that leads to membrane fusion.
包膜型裂谷热病毒（RVFV）进入宿主细胞是由病毒糖蛋白 Gn 和 Gc 介导的。我们使用最近开发的非扩散型 RVFV 颗粒系统研究了 RVFV 的进入过程，特别是其 pH 依赖性激活机制。溶酶体靶向剂可有效抑制病毒进入宿主细胞，这些溶酶体靶向剂可阻止内体酸化，还可干扰网格蛋白和胞吞作用依赖的内吞作用。将细胞膜结合的病毒颗粒暴露于酸性 pH（<pH 6），相当于晚期内体溶酶体区室的 pH，可使病毒绕过内体感染途径。在没有靶膜的情况下，病毒颗粒的酸性暴露会触发 II 类 Gc 融合蛋白形成极其稳定的寡聚体，这些寡聚体对 SDS 和温度解离具有抗性，同时降低病毒感染性。通过 Gn 和 Gc 中保守组氨酸的靶向突变，我们证明 Gc 中的单个组氨酸（H857）突变完全阻断了病毒进入以及酸诱导的 Gc 寡聚化。总之，我们的数据表明，RVFV 在进入细胞后会转运到酸性的晚期内体溶酶体区室，组氨酸质子化驱动 Gc 融合蛋白的重排，从而导致膜融合。
