期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：15
页码：E1851-E1860
DOI：10.1073/pnas.1504368112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThe membrane-anchored GTPase atlastin (ATL) mediates the fusion of endoplasmic reticulum membranes into a network of tubules and sheets, but the mechanism of ATL function is still poorly understood. Here we show that vesicle fusion is preceded by GTP hydrolysis-dependent tethering, caused by the interaction of ATL molecules in opposing membranes. GTP hydrolysis also dissociates ATL dimers sitting in the same membrane (cis dimers), generating a pool of ATL monomers that can dimerize with molecules on a different (trans) membrane. Multiple rounds of GTP hydrolysis and the cooperation of several ATL molecules in each membrane are required for a successful fusion event. These results lead to a model of ATL-mediated fusion that also may have implications for SNARE-mediated fusion. Atlastin (ATL), a membrane-anchored GTPase that mediates homotypic fusion of endoplasmic reticulum (ER) membranes, is required for formation of the tubular network of the peripheral ER. How exactly ATL mediates membrane fusion is only poorly understood. Here we show that fusion is preceded by the transient tethering of ATL-containing vesicles caused by the dimerization of ATL molecules in opposing membranes. Tethering requires GTP hydrolysis, not just GTP binding, because the two ATL molecules are pulled together most strongly in the transition state of GTP hydrolysis. Most tethering events are futile, so that multiple rounds of GTP hydrolysis are required for successful fusion. Supported lipid bilayer experiments show that ATL molecules sitting on the same (cis) membrane can also undergo nucleotide-dependent dimerization. These results suggest that GTP hydrolysis is required to dissociate cis dimers, generating a pool of ATL monomers that can dimerize with molecules on a different (trans) membrane. In addition, tethering and fusion require the cooperation of multiple ATL molecules in each membrane. We propose a comprehensive model for ATL-mediated fusion that takes into account futile tethering and competition between cis and trans interactions.
