Structures of the yeast dynamin-like GTPase Sey1p provide insight into homotypic ER fusion

J Cell Biol. 2015 Sep 14;210(6):961-72. doi: 10.1083/jcb.201502078.


Homotypic membrane fusion of the endoplasmic reticulum is mediated by dynamin-like guanosine triphosphatases (GTPases), which include atlastin (ATL) in metazoans and Sey1p in yeast. In this paper, we determined the crystal structures of the cytosolic domain of Sey1p derived from Candida albicans. The structures reveal a stalk-like, helical bundle domain following the GTPase, which represents a previously unidentified configuration of the dynamin superfamily. This domain is significantly longer than that of ATL and critical for fusion. Sey1p forms a side-by-side dimer in complex with GMP-PNP or GDP/AlF4(-) but is monomeric with GDP. Surprisingly, Sey1p could mediate fusion without GTP hydrolysis, even though fusion was much more efficient with GTP. Sey1p was able to replace ATL in mammalian cells, and the punctate localization of Sey1p was dependent on its GTPase activity. Despite the common function of fusogenic GTPases, our results reveal unique features of Sey1p.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis Inducing Factor / chemistry
  • Apoptosis Inducing Factor / metabolism
  • COS Cells
  • Candida albicans / enzymology*
  • Candida albicans / genetics
  • Chlorocebus aethiops
  • Crystallization
  • Crystallography, X-Ray
  • Endoplasmic Reticulum / enzymology*
  • Fungal Proteins / chemistry*
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism
  • GTP Phosphohydrolases / chemistry*
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism
  • Guanosine Diphosphate / chemistry
  • Guanosine Diphosphate / metabolism
  • Guanosine Triphosphate / chemistry
  • Guanosine Triphosphate / metabolism
  • Guanylyl Imidodiphosphate / chemistry
  • Guanylyl Imidodiphosphate / metabolism
  • Hydrolysis
  • Membrane Fusion*
  • Models, Molecular
  • Protein Binding
  • Protein Multimerization
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / metabolism
  • Structure-Activity Relationship
  • Transfection
  • Vesicular Transport Proteins / chemistry
  • Vesicular Transport Proteins / metabolism


  • Apoptosis Inducing Factor
  • Fungal Proteins
  • SEY1 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Vesicular Transport Proteins
  • Guanosine Diphosphate
  • Guanylyl Imidodiphosphate
  • Guanosine Triphosphate
  • GTP Phosphohydrolases

Associated data

  • PDB/5CA8
  • PDB/5CA9
  • PDB/5CB2