Article

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

ABSTRACT

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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    • "Atlastin also forms a high molecular mass oligomer (Liu et al., 2012). Atlastin self-assembles through its middle domain (Pendin et al., 2011) and/or its transmembrane domain (Moss et al., 2011;Liu et al., 2012). We found that the oligomerization of RHD3 was promoted by kinase treatment (Fig. 10). "
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    • "Unlabeled liposomes consisted of palmitoyloleoylphosphatidylcholine (POPC):dioleoyl phosphatidylserine (DOPS; 85:15), and labeled liposomes had POPC:DOPS:1,2-di- palmitoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3- benzoxadiazol-4-yl (DPPE-NBD):rhodamine-DPPE (82:15:1.5:1.5). Drosophila atlastin in 0.1% Anapoe-X 100 was reconstituted into preformed 100-nm liposomes as previously described (Moss et al., 2011). In brief, reconstitutions were carried out at a protein-to-lipid "
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    • "By a similar mechanism, the same proteins are also involved in generating the highly curved edges of ER sheets (Shibata et al. 2010). Two additional classes of proteins act in concert with RTNs and REEPs during ER morphogenesis: atlastins, large GTPases that mediate homotypic fusion of ER tubules, and spastin, an ATPase that separates microtubules, particularly in relation to membrane modeling events (Errico et al. 2002; Orlacchio et al. 2004; Connell et al. 2009; Hu et al. 2009; Bian et al. 2011; Morin-Leisk et al. 2011; Moss et al. 2011; Liu et al. 2012; Lumb et al. 2012). In line with this, the expression of an ATPase-defective spastin results in extensive tubulation of the ER, highlighting its role as a microtubule-severing protein during ER shaping (Connell et al. 2009). "
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