GTP-dependent packing of a three-helix bundle is required for atlastin-mediated fusion.

The mechanisms governing atlastin-mediated membrane fusion are unknown. Here we demonstrate that a three-helix bundle (3HB) within the middle domain is required for oligomerization. Mutation of core hydrophobic residues within these helices inactivates atlastin function by preventing membrane tethering and the subsequent fusion.

Membrane fusion by the GTPase atlastin requires a conserved C-terminal cytoplasmic tail and dimerization through the middle domain.

The biogenesis and maintenance of the endoplasmic reticulum (ER) requires membrane fusion. ER homotypic fusion is driven by the large GTPase atlastin. Domain analysis of atlastin shows that a conserved region of the C-terminal cytoplasmic tail is absolutely required for fusion activity.