Comparison of human and Drosophila atlastin GTPases

Abstract

Formation of the endoplasmic reticulum (ER) network requires homotypic membrane fusion, which involves a class of atlastin (ATL) GTPases. Purified Drosophila ATL is capable of mediating vesicle fusion in vitro, but such activity has not been reported for any other ATLs. Here, we determined the preliminary crystal structure of the cytosolic segment of Drosophila ATL in a GDP-bound state. The structure reveals a GTPase domain dimer with the subsequent three-helix bundles associating with their own GTPase domains and pointing in opposite directions. This conformation is similar to that of human ATL1, to which GDP and high concentrations of inorganic phosphate, but not GDP only, were included. Drosophila ATL restored ER morphology defects in mammalian cells lacking ATLs, and measurements of nucleotide-dependent dimerization and GTPase activity were comparable for Drosophila ATL and human ATL1. However, purified and reconstituted human ATL1 exhibited no in vitro fusion activity. When the cytosolic segment of human ATL1 was connected to the transmembrane (TM) region and C-terminal tail (CT) of Drosophila ATL, the chimera still exhibited no fusion activity, though its GTPase activity was normal. These results suggest that GDP-bound ATLs may adopt multiple conformations and the in vitro fusion activity of ATL cannot be achieved by a simple collection of functional domains.

Keywords

endoplasmic reticulum / membrane fusion / atlastin / GTPase / X-ray crystallography

References

[1] Anwar K, Klemm RW, Condon A, Severin KN, Zhang M, Ghirlando R, Hu J, Rapoport TA, Prinz WA (2012) The dynamin-like GTPase Sey1p mediates homotypic ER fusion in S. cerevisiae. J Cell Biol197: 209-217

[2] Bian X, Klemm RW, Liu TY, Zhang M, Sun S, Sui X, Liu X, Rapoport TA, Hu J (2011) Structures of the atlastin GTPase provide insight into homotypic fusion of endoplasmic reticulum membranes. Proc Natl Acad Sci108: 3976-3981

[3] Byrnes LJ, Sondermann H (2011) Structural basis for the nucleotidedependent dimerization of the large G protein atlastin-1/SPG3A. Proc Natl Acad Sci108: 2216-2221

[4] Byrnes LJ, Singh A, Szeto K, Benvin NM, O’Donnell JP, Zipfel WR, Sondermann H (2013) Structural basis for conformational switching and GTP loading of the large G protein atlastin. EMBO J32 (3): 369-384

[5] Fassier C, Hutt JA, Scholpp S, Lumsden A, Giros B, Nothias F, Schneider-Maunoury S, Houart C, Hazan J (2010) Zebrafish atlastin controls motility and spinal motor axon architecture via inhibition of the BMP pathway. Nat Neurosci13: 1380-1387

[6] Hu J, Shibata Y, Zhu P-P, Voss C, Rismanchi N, Prinz WA, Rapoport TA, Blackstone C (2009) A class of dynamin-like GTPases involved in the generation of the tubular ER network. Cell138: 549-561

[7] Hu J, Prinz WA, Rapoport TA (2011) Weaving the web of ER tubules. Cell147: 1226-1231

[8] Lee Y, Paik D, Bang S, Kang J, Chun B, Lee S, Bae E, Chung J, Kim J (2008) Loss of spastic paraplegia gene atlastin induces agedependent death of dopaminergic neurons in Drosophila. Neurobiol Aging29: 84-94

[9] Lee M, Paik SK, Lee MJ, Kim YJ, Kim S, Nahm M, Oh SJ, Kim HM, Yim J, Lee CJ (2009) Drosophila atlastin regulates the stability of muscle microtubules and is required for synapse development. Dev Biol330: 250-262

[10] Lin S, Sun S, Hu J (2012) Molecular basis for sculpting the endoplasmic reticulum membrane. Int J Biochem Cell Biol44: 1436-1443

[11] Liu TY, Bian X, Sun S, Hu X, Klemm RW, Prinz WA, Rapoport TA, Hu J (2012) Lipid interaction of the C terminus and association of the transmembrane segments facilitate atlastin-mediated homotypic endoplasmic reticulum fusion. Proc Natl Acad Sci109: E2146-E2154

[12] Moss TJ, Andreazza C, Verma A, Daga A, McNew JA (2011) Membrane fusion by the GTPase atlastin requires a conserved C-terminal cytoplasmic tail and dimerization through the middle domain. Proc Natl Acad Sci108: 11133-11138

[13] Orso G, Pendin D, Liu S, Tosetto J, Moss TJ, Faust JE, Micaroni M, Egorova A, Martinuzzi A, McNew JA (2009) Homotypic fusion of ER membranes requires the dynamin-like GTPase atlastin. Nature460: 978-983

[14] Salinas S, Proukakis C, Crosby A, Warner TT (2008) Hereditary spastic paraplegia: clinical features and pathogenetic mechanisms. Lancet Neurol7: 1127-1138

[15] Schiefelbein JW, Somerville C (1990) Genetic control of root hair development in Arabidopsis thaliana. Plant Cell2: 235-243

[16] Shibata Y, Voeltz GK, Rapoport TA (2006) Rough sheets and smooth tubules. Cell126: 435-439

[17] Stefano G, Renna L, Moss T, McNew JA, Brandizzi F (2012) In Arabidopsis, the spatial and dynamic organization of the endoplasmic reticulum and Golgi apparatus is influenced by the integrity of the C-terminal domain of RHD3, a non-essential GTPase. Plant J69: 957-966

[18] Wang H, Lockwood SK, Hoeltzel MF, Schiefelbein JW (1997) The ROOT HAIR DEFECTIVE3 gene encodes an evolutionarily conserved protein with GTP-binding motifs and is required for regulated cell enlargement in Arabidopsis. Genes Dev11: 799-811

[19] Zhang M, Wu F, Shi J, Zhu Y, Zhu Z, Gong Q, Hu J (2013) ROOT HAIR DEFECTIVE3 family of dynamin-like GTPases mediates homotypic endoplasmic reticulum fusion and is essential for Arabidopsis development. Plant Physiol163: 713-720

[20] Zhao X, Alvarado D, Rainier S, Lemons R, Hedera P, Weber CH, Tukel T, Apak M, Heiman-Patterson T, Ming L (2001) Mutations in a newly identified GTPase gene cause autosomal dominant hereditary spastic paraplegia. Nat Genet29: 326-331

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