Cryo-EM structures of membrane-bound dynamin in a post-hydrolysis state primed for membrane fission.

Abstract

Dynamin assembles as a helical polymer at the neck of budding endocytic vesicles, constricting the underlyingmembrane as it progresses through the GTPase cycle to sever vesicles from the plasmamembrane.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 theassembled 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 assembledas a 2-start helix with an inner lumen of 3.4nm, primed for spontaneous fission. Additionally, by cryo-electron tomography, we trapped dynamin helical assemblies within HeLa cells using theGTPase-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.