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

Department of Biochemistry and Cell Biology, Rice University, Houston, TX 77005, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 06/2011; 108(27):11133-8. DOI: 10.1073/pnas.1105056108
Source: PubMed


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. Atlastin in adjacent membranes must associate to bring the ER membranes into molecular contact. Drosophila atlastin dimerizes in the presence of GTPγS but is monomeric with GDP or without nucleotide. Oligomerization requires the juxtamembrane middle domain three-helix bundle, as does efficient GTPase activity. A soluble version of the N-terminal cytoplasmic domain that contains the GTPase domain and the middle domain three-helix bundle serves as a potent, concentration-dependent inhibitor of membrane fusion both in vitro and in vivo. However, atlastin domains lacking the middle domain are without effect. GTP-dependent dimerization of atlastin generates an enzymatically active protein that drives membrane fusion after nucleotide hydrolysis and conformational reorganization.

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    • "However, the structures depict only GDP-bound states, hence, the exact catalytic mechanism for atlastin and the concurrent conformational switching upon GTP hydrolysis remained unknown. It has also been established that the middle domain is required for dimerization and GTPase activity (Morin-Leisk et al, 2011; Moss et al, 2011; Pendin et al, 2011), the reason for which is not obvious from the initial models. In addition, a recent report demonstrated, using single-particle electron microscopy, that atlastin-2 bound to the GTP-mimic GppNHp adopts both the presumed pre-and post-fusion conformations, the latter of which depends on an intramolecular salt bridge between the middle domain and the adjacent linker (Morin-Leisk et al, 2011). "
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