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The membrane-anchored atlastin GTPase couples nucleotide hydrolysis to the catalysis of homotypic membrane fusion to form a branched endoplasmic reticulum network. Trans dimerization between atlastins anchored in opposing membranes, accompanied by a cross-over conformational change, is thought to draw the membranes together for fusion. Previous studies on the conformational coupling of atlastin to its GTP hydrolysis cycle have been carried out largely on atlastins lacking a membrane anchor. Consequently, whether fusion involves a discrete tethering step and, if so, the potential role of GTP hydrolysis and cross-over in tethering remain unknown. In this study, we used membrane-anchored atlastins in assays that separate tethering from fusion to dissect the requirements for each. We found that tethering depended on GTP hydrolysis, but, unlike fusion, it did not depend on cross-over. Thus GTP hydrolysis initiates stable head-domain contact in trans to tether opposing membranes, whereas cross-over formation plays a more pivotal role in powering the lipid rearrangements for fusion.

Original publication

DOI

10.1091/mbc.E14-08-1284

Type

Journal article

Journal

Mol Biol Cell

Publication Date

01/12/2014

Volume

25

Pages

3942 - 3953

Keywords

Animals, COS Cells, Cell Membrane, Cercopithecus aethiops, Cryoelectron Microscopy, Drosophila Proteins, Endoplasmic Reticulum, GTP Phosphohydrolases, Guanosine Triphosphate, Hydrolysis, Membrane Fusion, Microscopy, Fluorescence, Models, Biological, Models, Molecular, Mutation, Protein Binding, Protein Conformation, Protein Multimerization, Protein Structure, Tertiary