Reconstitution of human atlastin fusion activity reveals autoinhibition by the C terminus

• Published in: The Journal of cell biology 2022-02, Vol.221 (2), p.1
• Main Authors: Crosby, Daniel, Mikolaj, Melissa R, Nyenhuis, Sarah B, Bryce, Samantha, Hinshaw, Jenny E, Lee, Tina H
• Format: Article
• Language: English
• Subjects: Alternative splicing; Animals; Biochemistry; C-Terminus; Charge reversal; Chlorocebus aethiops; COS Cells; Domains; Endoplasmic Reticulum - metabolism; GTP-Binding Proteins - antagonists & inhibitors; GTP-Binding Proteins - chemistry; GTP-Binding Proteins - metabolism; Humans; Isoforms; Membrane Fusion; Membrane Proteins - antagonists & inhibitors; Membrane Proteins - chemistry; Membrane Proteins - metabolism; Mutation - genetics; Network formation; Organelles; Protein Structure, Secondary; Splicing
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.202107070

ER network formation depends on membrane fusion by the atlastin (ATL) GTPase. In humans, three paralogs are differentially expressed with divergent N- and C-terminal extensions, but their respective roles remain unknown. This is partly because, unlike Drosophila ATL, the fusion activity of human ATLs has not been reconstituted. Here, we report successful reconstitution of fusion activity by the human ATLs. Unexpectedly, the major splice isoforms of ATL1 and ATL2 are each autoinhibited, albeit to differing degrees. For the more strongly inhibited ATL2, autoinhibition mapped to a C-terminal α-helix is predicted to be continuous with an amphipathic helix required for fusion. Charge reversal of residues in the inhibitory domain strongly activated its fusion activity, and overexpression of this disinhibited version caused ER collapse. Neurons express an ATL2 splice isoform whose sequence differs in the inhibitory domain, and this form showed full fusion activity. These findings reveal autoinhibition and alternate splicing as regulators of atlastin-mediated ER fusion.