Just-right spirals

The canonical protein in the family, dynamin-1, constricts the necks of clathrin-coated pits during endocytosis. In the process, it assembles into rings that are 50 nm in diameter. By contrast, Ingerman et al. saw that Dnm1, a yeast protein required for mitochondrial fission, assembles into rings that are 109 nm across. That size closely matches the diameter of mitochondrial constrictions in vivo.

As in dynamin-1 assembly, GTP binding is required for Dnm1 ring formation. In the absence of GTP, Dnm1 assembles into long, slightly curved filaments, whereas in the presence of a nonhydrolyzable GTP analogue, it forms the spirals used in fission. There is a substantial lag...