title: Structure of the Sec23/24-Sar1 pre-budding complex of the COPII vesicle coat.
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.
authors.affiliation: Howard Hughes Medical Institute and the Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021, USA.
authors.forename: Xiping
authors.initials: X
authors.lastname: Bi
authors.forename: Richard A
authors.initials: RA
authors.lastname: Corpina
authors.forename: Jonathan
authors.initials: J
authors.lastname: Goldberg
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D001692:Biological Transport; D022181:COP-Coated Vesicles / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D020690:GTPase-Activating Proteins; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000166:cytology* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism; D033921:Vesicular Transport Proteins
chemical_list: D020690:GTPase-Activating Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D020033:Protein Isoforms; C079037:SEC23 protein, S cerevisiae; C118289:SEC24 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020559:Monomeric GTP-Binding Proteins; C077395:SAR1 protein, S cerevisiae