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

摘要

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 con served region of the C-terminal cytoplasmic tail is absolutely re quired for fusion activity. Atlastin in adjacent membranes must associate to bring the ER membranes into molecular contact. Dro sophila atlastin dimerizes in the presence of GTPγS but is mono meric 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 cyto plasmic 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 enzy matically active protein that drives membrane fusion after nucle otide hydrolysis and conformational reorganization.