The HIV-1 envelope glycoprotein (Env) trimer, composed of gp120 and gp41 subunits, mediates viral entry into cells. Recombinant Env trimers have been studied structurally, but characterization of Env embedded in intact virus membranes has been limited to low resolution. Here, we deploy cryo-electron tomography and subtomogram averaging to determine the structures of Env trimers on aldrithiol-2 (AT-2)-inactivated virions in ligand-free, antibody-bound and CD4-bound forms at subnanometer resolution. Tomographic reconstructions document molecular features consistent with high-resolution structures of engineered soluble and detergent-solubilized Env trimers. One of three conformational states previously predicted by smFRET was not observed by cryo-ET, potentially owing to AT-2 inactivation. We did observe Env trimers to open in situ in response to CD4 binding, with an outward movement of gp120-variable loops and an extension of a critical gp41 helix. Overall features of Env trimer embedded in AT-2-treated virions appear well-represented by current engineered trimers.

HIV-1 包膜糖蛋白 (Env) 三聚体由 gp120 和 gp41 亚基组成，介导病毒进入细胞。重组 Env 三聚体已在结构上进行了研究，但嵌入完整病毒膜中的 Env 的表征仅限于低分辨率。在这里，我们采用冷冻电子断层扫描和亚断层扫描平均技术，以亚纳米分辨率确定无配体、抗体结合和 CD4 结合形式的 aldrithiol-2 (AT-2) 灭活病毒粒子上的 Env 三聚体结构。断层扫描重建记录了与工程可溶性和去污剂溶解的 Env 三聚体的高分辨率结构一致的分子特征。冷冻电子断层扫描 (cryo-ET) 未观察到先前由 smFRET 预测的三种构象状态之一，这可能是由于 AT-2 失活所致。我们确实观察到 Env 三聚体响应 CD4 结合而原位打开，同时 gp120 可变环向外移动，并且关键的 gp41 螺旋延伸。嵌入 AT-2 处理的病毒体中的 Env 三聚体的总体特征似乎可以很好地代表当前工程化的三聚体。