Cell entry of enveloped viruses requires specialized viral proteins that mediate fusion with the host membrane by substantial structural rearrangements from a metastable pre- to a stable postfusion conformation. This metastability renders the herpes simplex virus 1 (HSV-1) fusion glycoprotein B (gB) highly unstable such that it readily converts into the postfusion form, thereby precluding structural elucidation of the pharmacologically relevant prefusion conformation. By identification of conserved sequence signatures and molecular dynamics simulations, we devised a mutation that stabilized this form. Functionally locking gB allowed the structural determination of its membrane-embedded prefusion conformation at sub-nanometer resolution and enabled the unambiguous fit of all ectodomains. The resulting pseudo-atomic model reveals a notable conservation of conformational domain rearrangements during fusion between HSV-1 gB and the vesicular stomatitis virus glycoprotein G, despite their very distant phylogeny. In combination with our comparative sequence-structure analysis, these findings suggest common fusogenic domain rearrangements in all class III viral fusion proteins.

有包膜病毒进入细胞需要专门的病毒蛋白，这些蛋白通过从亚稳态融合前构象到稳定融合后构象的实质性结构重排来介导与宿主膜的融合。这种亚稳定性使得单纯疱疹病毒 1 (HSV-1) 融合糖蛋白 B (gB) 高度不稳定，因此很容易转化为融合后形式，从而妨碍了药理学相关的融合前构象的结构阐明。通过识别保守序列特征和分子动力学模拟，我们设计了一种稳定这种形式的突变。功能锁定 gB 允许以亚纳米分辨率确定其膜嵌入预融合构象，并实现所有胞外域的明确拟合。由此产生的伪原子模型揭示了 HSV-1 gB 和水泡性口炎病毒糖蛋白 G 融合过程中构象域重排的显着保守性，尽管它们的系统发育非常遥远。结合我们的比较序列结构分析，这些发现表明所有 III 类病毒融合蛋白中存在常见的融合结构域重排。