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Structure and organization of coat proteins in the COPII cage.

COPII-coated vesicles export newly synthesized proteins from the endoplasmic reticulum. The COPII coat consists of the Sec23/24-Sar1 complex that selects cargo and the Sec13/31 assembly unit that can polymerize into an octahedral cage and deform the membrane into a bud. Crystallographic analysis of the assembly unit reveals a 28 nm long rod comprising a central alpha-solenoid dimer capped by two beta-propeller domains at each end. We construct a molecular model of the COPII cage by fitting Sec13/31 crystal structures into a recently determined electron microscopy density map. The vertex geometry involves four copies of the Sec31 beta-propeller that converge through their axial ends; there is no interdigitation of assembly units of the kind seen in clathrin cages. We also propose that the assembly unit has a central hinge-an arrangement of interlocked alpha-solenoids-about which it can bend to adapt to cages of variable curvature.

Pubmed ID: 17604721


  • Fath S
  • Mancias JD
  • Bi X
  • Goldberg J



Publication Data

June 29, 2007

Associated Grants


Mesh Terms

  • Animals
  • COP-Coated Vesicles
  • Cells, Cultured
  • Clathrin
  • Crystallography, X-Ray
  • Endoplasmic Reticulum
  • Golgi Apparatus
  • Macromolecular Substances
  • Membrane Proteins
  • Models, Molecular
  • Nuclear Pore Complex Proteins
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Protein Transport
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Vesicular Transport Proteins