Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA.
Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA.
J Virol. 2018 Aug 16;92(17). doi: 10.1128/JVI.01034-18. Print 2018 Sep 1.
Herpes simplex virus (HSV) is an important human pathogen with a high worldwide seroprevalence. HSV enters epithelial cells, the primary site of infection, by a low-pH pathway. HSV glycoprotein B (gB) undergoes low pH-induced conformational changes, which are thought to drive membrane fusion. When neutralized back to physiological pH, these changes become reversible. Here, HSV-infected cells were subjected to short pulses of radiolabeling, followed by immunoprecipitation with a panel of gB monoclonal antibodies (MAbs), demonstrating that gB folds and oligomerizes rapidly and cotranslationally in the endoplasmic reticulum. Full-length gB from transfected cells underwent low-pH-triggered changes in oligomeric conformation in the absence of other viral proteins. MAbs to gB neutralized HSV entry into cells regardless of the pH dependence of the entry pathway, suggesting a conservation of gB function in distinct fusion mechanisms. The combination of heat and acidic pH triggered irreversible changes in the antigenic conformation of the gB fusion domain, while changes in the gB oligomer remained reversible. An elevated temperature alone was not sufficient to induce gB conformational change. Together, these results shed light on the conformation and function of the HSV-1 gB oligomer, which serves as part of the core fusion machinery during viral entry. Herpes simplex virus (HSV) causes infection of the mouth, skin, eyes, and genitals and establishes lifelong latency in humans. gB is conserved among all herpesviruses. HSV gB undergoes reversible conformational changes following exposure to acidic pH which are thought to mediate fusion and entry into epithelial cells. Here, we identified cotranslational folding and oligomerization of newly synthesized gB. A panel of antibodies to gB blocked both low-pH and pH-neutral entry of HSV, suggesting conserved conformational changes in gB regardless of cell entry route. Changes in HSV gB conformation were not triggered by increased temperature alone, in contrast to results with EBV gB. Acid pH-induced changes in the oligomeric conformation of gB are related but distinct from pH-triggered changes in gB antigenic conformation. These results highlight critical aspects of the class III fusion protein, gB, and inform strategies to block HSV infection at the level of fusion and entry.
单纯疱疹病毒 (HSV) 是一种重要的人类病原体，具有很高的全球血清流行率。HSV 通过低 pH 途径进入感染的主要部位上皮细胞。HSV 糖蛋白 B (gB) 经历低 pH 诱导的构象变化，这些变化被认为驱动膜融合。当中和回生理 pH 时，这些变化变得可逆。在这里，用放射性标记短暂脉冲处理感染 HSV 的细胞，然后用一组 gB 单克隆抗体 (MAb) 进行免疫沉淀，证明 gB 在粗面内质网中快速折叠和翻译共组装。转染细胞的全长 gB 在没有其他病毒蛋白的情况下经历低 pH 触发的寡聚构象变化。针对 gB 的 MAbs 中和了 HSV 进入细胞的过程，无论进入途径的 pH 依赖性如何，这表明 gB 功能在不同的融合机制中是保守的。热和酸性 pH 的组合触发 gB 融合结构域的抗原构象发生不可逆变化，而 gB 寡聚体的变化仍然是可逆的。单独升高温度不足以诱导 gB 构象变化。总之，这些结果阐明了 HSV-1 gB 寡聚体的构象和功能，它作为病毒进入时核心融合机制的一部分。单纯疱疹病毒 (HSV) 引起口腔、皮肤、眼睛和生殖器感染，并在人类中建立终身潜伏。gB 在所有疱疹病毒中都保守。HSV gB 在暴露于酸性 pH 后经历可逆的构象变化，被认为介导融合和进入上皮细胞。在这里，我们鉴定了新合成的 gB 的共翻译折叠和寡聚化。一组针对 gB 的抗体阻断了 HSV 的低 pH 和 pH 中性进入，这表明 gB 存在保守的构象变化，无论细胞进入途径如何。与 EBV gB 的结果相反，仅升高温度不会引发 HSV gB 构象的变化。gB 寡聚构象的酸诱导变化与 pH 触发的 gB 抗原构象变化有关但不同。这些结果突出了 III 类融合蛋白 gB 的关键方面，并为在融合和进入水平阻断 HSV 感染提供了策略。
