Department of Microbiology, University of Pennsylvania, 4010 Locust St., Levy Rm. 233, Philadelphia, PA 19104, USA.
J Virol. 2011 Jul;85(13):6175-84. doi: 10.1128/JVI.00119-11. Epub 2011 Apr 20.
Herpes simplex virus (HSV) entry requires the core fusion machinery of gH/gL and gB as well as gD and a gD receptor. When gD binds receptor, it undergoes conformational changes that presumably activate gH/gL, which then activates gB to carry out fusion. gB is a class III viral fusion protein, while gH/gL does not resemble any known viral fusion protein. One hallmark of fusion proteins is their ability to bind lipid membranes. We previously used a liposome coflotation assay to show that truncated soluble gB, but not gH/gL or gD, can associate with liposomes at neutral pH. Here, we show that gH/gL cofloats with liposomes but only when it is incubated with gB at pH 5. When gB mutants with single amino acid changes in the fusion loops (known to inhibit the binding of soluble gB to liposomes) were mixed with gH/gL and liposomes at pH 5, gH/gL failed to cofloat with liposomes. These data suggest that gH/gL does not directly associate with liposomes but instead binds to gB, which then binds to liposomes via its fusion loops. Using monoclonal antibodies, we found that many gH and gL epitopes were altered by low pH, whereas the effect on gB epitopes was more limited. Our liposome data support the concept that low pH triggers conformational changes to both proteins that allow gH/gL to physically interact with gB.
单纯疱疹病毒（HSV）进入需要 gH/gL 和 gB 以及 gD 和 gD 受体的核心融合机制。当 gD 结合受体时，它会发生构象变化，推测这种变化会激活 gH/gL，然后激活 gB 进行融合。gB 是一种 III 类病毒融合蛋白，而 gH/gL 与任何已知的病毒融合蛋白都不相似。融合蛋白的一个标志是它们能够结合脂质膜。我们之前使用脂质体共漂浮测定法表明，截断的可溶性 gB，但不是 gH/gL 或 gD，可以在中性 pH 下与脂质体结合。在这里，我们表明 gH/gL 与脂质体共漂浮，但仅当它在 pH5 下与 gB 孵育时才会与脂质体共漂浮。当融合环中单个氨基酸变化的 gB 突变体（已知抑制可溶性 gB 与脂质体的结合）与 gH/gL 和脂质体在 pH5 下混合时，gH/gL 未能与脂质体共漂浮。这些数据表明 gH/gL 不会直接与脂质体结合，而是与 gB 结合，然后通过其融合环与脂质体结合。使用单克隆抗体，我们发现许多 gH 和 gL 表位在低 pH 下发生改变，而 gB 表位的影响则更为有限。我们的脂质体数据支持这样一种概念，即低 pH 会引发两种蛋白的构象变化，从而使 gH/gL 能够与 gB 进行物理相互作用。
