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
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Binding Sites
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Biological Transport
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COP-Coated Vesicles / chemistry*
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Crystallography, X-Ray
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Dimerization
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GTPase-Activating Proteins
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Guanosine Diphosphate / metabolism
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Guanosine Triphosphate / metabolism
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Hydrolysis
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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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Molecular Sequence Data
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Monomeric GTP-Binding Proteins / chemistry*
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Monomeric GTP-Binding Proteins / metabolism
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Protein Binding
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Protein Isoforms / chemistry
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Protein Isoforms / metabolism
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Protein Structure, Secondary
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Protein Structure, Tertiary
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Saccharomyces cerevisiae / chemistry*
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Saccharomyces cerevisiae / cytology*
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Saccharomyces cerevisiae / metabolism
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Saccharomyces cerevisiae Proteins / chemistry*
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Saccharomyces cerevisiae Proteins / metabolism
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Vesicular Transport Proteins
Substances
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GTPase-Activating Proteins
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Macromolecular Substances
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Membrane Proteins
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Protein Isoforms
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SEC23 protein, S cerevisiae
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SEC24 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
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Vesicular Transport Proteins
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Guanosine Diphosphate
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Guanosine Triphosphate
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Monomeric GTP-Binding Proteins
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SAR1 protein, S cerevisiae