ATLs maintain the ER tubular network via homotypic fusion. ATLs have a conserved domain structure consisting of a globular G domain, a three-helix bundle, two transmembrane domains, and an amphipathic helix. The ATL fusion cycle consists of two ATL monomers in opposing membranes binding GTP, which induces trans G domain dimerization and a crossing over of the three-helix bundle. Crossover and subsequent insertion of the amphipathic helix into the lipid bilayer triggers lipids to mix for fusion. Lastly, GTP is hydrolyzed driving the dimer to disassembly and resetting the fusion machinery. While most of the human ATL protein structure is conserved between paralogs, the proteins have non-conserved N- and C-termini with the C-termini of ATL1 and ATL2 being autoinhibitory. ATL1 has been shown to interact with a range of proteins including spastin and REEP1, with spastin enhancing ATL1 fusion activity in vitro. ATL1 and ATL2 have also been observed as interacting with ER protein TMCC3, and ATL3 with nonstructural viral proteins, however it is not currently known how these interactions modulate protein function.