Abstract
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.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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COP-Coated Vesicles / chemistry*
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COP-Coated Vesicles / ultrastructure*
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Cells, Cultured
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Clathrin / metabolism
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Crystallography, X-Ray
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Endoplasmic Reticulum / metabolism*
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Endoplasmic Reticulum / ultrastructure
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Golgi Apparatus / metabolism
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Golgi Apparatus / ultrastructure
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Macromolecular Substances
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Membrane Proteins / chemistry*
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Membrane Proteins / metabolism
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Models, Molecular
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Nuclear Pore Complex Proteins / chemistry*
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Nuclear Pore Complex Proteins / metabolism
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Protein Structure, Secondary / physiology
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Protein Structure, Tertiary / physiology
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Protein Transport / physiology
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Saccharomyces cerevisiae
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Saccharomyces cerevisiae Proteins / chemistry*
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Saccharomyces cerevisiae Proteins / metabolism
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Vesicular Transport Proteins / chemistry*
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Vesicular Transport Proteins / metabolism
Substances
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Clathrin
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Macromolecular Substances
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Membrane Proteins
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Nuclear Pore Complex Proteins
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SEC13 protein, S cerevisiae
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SEC31 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
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Vesicular Transport Proteins