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.
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
Nature
Date: Sep. 19, 2002
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