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

Nature. 2002 Sep 19;419(6904):271-7. doi: 10.1038/nature01040.

Abstract

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.

Publication types

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

MeSH terms

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

Substances

  • GTPase-Activating Proteins
  • Macromolecular Substances
  • Membrane Proteins
  • Protein Isoforms
  • SEC23 protein, S cerevisiae
  • SEC24 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Vesicular Transport Proteins
  • Guanosine Diphosphate
  • Guanosine Triphosphate
  • Monomeric GTP-Binding Proteins
  • SAR1 protein, S cerevisiae

Associated data

  • PDB/1M2O
  • PDB/1M2V