title: GTP-dependent packing of a three-helix bundle is required for atlastin-mediated fusion.
abstract: 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. GTP binding induces a conformational change that reorients the GTPase domain relative to the 3HB to permit self-association, but the ability to hydrolyze GTP is required for full fusion, indicating that nucleotide binding and hydrolysis play distinct roles. Oligomerization of atlastin stimulates its ability to hydrolyze GTP, and the energy released drives lipid bilayer merger. Mutations that prevent atlastin self-association also abolish oligomerization-dependent stimulation of GTPase activity. Furthermore, increasing the distance of atlastin complex formation from the membrane inhibits fusion, suggesting that this distance is crucial for atlastin to promote fusion.
authors.affiliation: Eugenio Medea Scientific Institute, 31015 Conegliano,  Italy.
authors.forename: Diana
authors.initials: D
authors.lastname: Pendin
authors.forename: Jessica
authors.initials: J
authors.lastname: Tosetto
authors.forename: Tyler J
authors.initials: TJ
authors.lastname: Moss
authors.forename: Camilla
authors.initials: C
authors.lastname: Andreazza
authors.forename: Stefano
authors.initials: S
authors.lastname: Moro
authors.forename: James A
authors.initials: JA
authors.lastname: McNew
authors.forename: Andrea
authors.initials: A
authors.lastname: Daga
mesh_terms: D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D004330:Drosophila; D019204:GTP-Binding Proteins / Q000502:physiology*; D006160:Guanosine Triphosphate / Q000378:metabolism / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D006868:Hydrolysis; D008565:Membrane Proteins / Q000502:physiology*
chemical_list: D017931:DNA Primers; D008565:Membrane Proteins; D006160:Guanosine Triphosphate; C440006:ATL1 protein, human; D019204:GTP-Binding Proteins