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.
Pubmed ID: 12239560 RIS Download
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