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Structure of the Sec23/24-Sar1 pre-budding complex of the COPII vesicle coat.

COPII-coated vesicles form on the endoplasmic reticulum by the stepwise recruitment of three cytosolic components: Sar1-GTP to initiate coat formation, Sec23/24 heterodimer to select SNARE and cargo molecules, and Sec13/31 to induce coat polymerization and membrane deformation. Crystallographic analysis of the Saccharomyces cerevisiae Sec23/24-Sar1 complex reveals a bow-tie-shaped structure, 15 nm long, with a membrane-proximal surface that is concave and positively charged to conform to the size and acidic-phospholipid composition of the COPII vesicle. Sec23 and Sar1 form a continuous surface stabilized by a non-hydrolysable GTP analogue, and Sar1 has rearranged from the GDP conformation to expose amino-terminal residues that will probably embed in the bilayer. The GTPase-activating protein (GAP) activity of Sec23 involves an arginine side chain inserted into the Sar1 active site. These observations establish the structural basis for GTP-dependent recruitment of a vesicular coat complex, and for uncoating through coat-controlled GTP hydrolysis.

Pubmed ID: 12239560


  • Bi X
  • Corpina RA
  • Goldberg J



Publication Data

September 19, 2002

Associated Grants


Mesh Terms

  • Amino Acid Sequence
  • Binding Sites
  • Biological Transport
  • COP-Coated Vesicles
  • Crystallography, X-Ray
  • Dimerization
  • GTPase-Activating Proteins
  • Guanosine Diphosphate
  • Guanosine Triphosphate
  • Hydrolysis
  • Macromolecular Substances
  • Membrane Proteins
  • Models, Molecular
  • Molecular Sequence Data
  • Monomeric GTP-Binding Proteins
  • Protein Binding
  • Protein Isoforms
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Vesicular Transport Proteins