Cis and trans interactions between atlastin molecules during membrane fusion

Proc Natl Acad Sci U S A. 2015 Apr 14;112(15):E1851-60. doi: 10.1073/pnas.1504368112. Epub 2015 Mar 30.

Abstract

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.

Keywords: GTPase; endoplasmic reticulum; lipid bilayer; membrane docking; spastic paraplegia type 3A gene.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Algorithms
  • Animals
  • Drosophila Proteins / chemistry
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism*
  • Drosophila melanogaster / genetics
  • Drosophila melanogaster / metabolism
  • Fluorescence Resonance Energy Transfer
  • GTP Phosphohydrolases / chemistry
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism*
  • Guanosine Triphosphate / metabolism
  • Hydrolysis
  • Lipid Bilayers / chemistry
  • Lipid Bilayers / metabolism
  • Membrane Fusion*
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Microscopy, Confocal
  • Microscopy, Fluorescence
  • Models, Biological
  • Models, Molecular
  • Mutation
  • Protein Binding
  • Protein Multimerization
  • Protein Structure, Tertiary
  • Time-Lapse Imaging
  • Transport Vesicles / chemistry
  • Transport Vesicles / metabolism*

Substances

  • Drosophila Proteins
  • Lipid Bilayers
  • Membrane Proteins
  • Guanosine Triphosphate
  • GTP Phosphohydrolases
  • atl protein, Drosophila