Abstract
Fusion of tubular membranes is required to form three-way junctions found in reticular subdomains of the endoplasmic reticulum. The large GTPase Atlastin has recently been shown to drive endoplasmic reticulum membrane fusion and three-way junction formation. The mechanism of Atlastin-mediated membrane fusion is distinct from SNARE-mediated membrane fusion, and many details remain unclear. In particular, the role of the amphipathic C-terminal tail of Atlastin is still unknown. We found that a peptide corresponding to the Atlastin C-terminal tail binds to membranes as a parallel α helix, induces bilayer thinning, and increases acyl chain disorder. The function of the C-terminal tail is conserved in human Atlastin. Mutations in the C-terminal tail decrease fusion activity in vitro, but not GTPase activity, and impair Atlastin function in vivo. In the context of unstable lipid bilayers, the requirement for the C-terminal tail is abrogated. These data suggest that the C-terminal tail of Atlastin locally destabilizes bilayers to facilitate membrane fusion.
Highlights
Atlastin is large GTPase that catalyzes the homotypic fusion of ER membranes
The Atlastin C-terminal Tail Is an Amphipathic Helix and Interacts with Membranes—We have shown recently that the Atlastin C-terminal 23 amino acids are required for membrane fusion in vitro and in vivo [11]
We used a native tryptophan residue in the C-terminal peptide (C23) to examine the propensity of the peptide to associate with membranes
Summary
Atlastin is large GTPase that catalyzes the homotypic fusion of ER membranes. Results: In vitro and in vivo studies reveal that the C-terminal tail of Atlastin affects its function. This result is likely because of alterations in the lipid composition of native membranes versus synthetic membranes used in in vitro fusion We tested this directly by altering the lipid composition of synthetic proteoliposomes and found that phosphatidylethanolamine, which promotes non-bilayer-forming structures, can help alleviate the requirement for the C-terminal tail. These results establish that the Atlastin C-terminal tail is a membrane-perturbing ␣ helix that participates in membrane fusion by destabilizing the bilayer structure and promoting the mechanics of lipid mixing
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have