Dynamin assembles as a helical polymer at the neck of budding endocytic vesicles, constricting the underlying membrane as it progresses through the GTPase cycle to sever vesicles from the plasma membrane. Although atomic models of the dynamin helical polymer bound to guanosine triphosphate (GTP) analogs define earlier stages of membrane constriction, there are no atomic models of the assembled state post-GTP hydrolysis. Here, we used cryo-EM methods to determine atomic structures of the dynamin helical polymer assembled on lipid tubules, akin to necks of budding endocytic vesicles, in a guanosine diphosphate (GDP)-bound, super-constricted state. In this state, dynamin is assembled as a 2-start helix with an inner lumen of 3.4 nm, primed for spontaneous fission. Additionally, by cryo-electron tomography, we trapped dynamin helical assemblies within HeLa cells using the GTPase-defective dynamin K44A mutant and observed diverse dynamin helices, demonstrating that dynamin can accommodate a range of assembled complexes in cells that likely precede membrane fission.

Dynamin 在出芽的内吞囊泡颈部组装成螺旋聚合物，在 GTP 酶循环中收缩底层膜，从而将囊泡与质膜分离。尽管与三磷酸鸟苷 (GTP) 类似物结合的动力螺旋聚合物的原子模型定义了膜收缩的早期阶段，但没有 GTP 水解后组装状态的原子模型。在这里，我们使用冷冻电镜方法来确定组装在脂质小管上的动力螺旋聚合物的原子结构，脂质小管类似于出芽的内吞囊泡的颈部，处于鸟苷二磷酸（GDP）结合的超收缩状态。在这种状态下，动力蛋白组装成内腔为 3.4 nm 的 2 头螺旋，为自发裂变做好准备。此外，通过冷冻电子断层扫描，我们使用 GTPase 缺陷型动力 K44A 突变体捕获 HeLa 细胞内的动力螺旋组件，并观察到不同的动力螺旋，证明动力可以在细胞中容纳一系列可能在膜裂变之前组装的复合物。