The dynamin A ring complex: molecular organization and nucleotide-dependent conformational changes

Here we show that Dictyostelium discoideum dynamin A is a fast GTPase, binds to negatively charged lipids, and self‐assembles into rings and helices in a nucleotide‐dependent manner, similar to human dynamin‐1. Chemical modification of two cysteine residues, positioned in the middle domain and GTPase effector domain (GED), leads to altered assembly properties and the stabilization of a highly regular ring complex. Single particle analysis of this dynamin A* ring complex led to a three‐dimensional map, which shows that the nucleotide‐free complex consists of two layers with 11‐fold symmetry. Our results reveal the molecular organization of the complex and indicate the importance of the middle domain and GED for the assembly of dynamin family proteins. Nucleotide‐dependent changes observed with the unmodified and modified protein support a mechanochemical action of dynamin, in which tightening and stretching of a helix contribute to membrane fission.