title: Structure of the Sec13/31 COPII coat cage.
abstract: Endomembranes of eukaryotic cells are dynamic structures that are in continuous communication through the activity of specialized cellular machineries, such as the coat protein complex II (COPII), which mediates cargo export from the endoplasmic reticulum (ER). COPII consists of the Sar1 GTPase, Sec23 and Sec24 (Sec23/24), where Sec23 is a Sar1-specific GTPase-activating protein and Sec24 functions in cargo selection, and Sec13 and Sec31 (Sec13/31), which has a structural role. Whereas recent results have shown that Sec23/24 and Sec13/31 can self-assemble to form COPII cage-like particles, we now show that Sec13/31 can self-assemble to form minimal cages in the absence of Sec23/24. We present a three-dimensional reconstruction of these Sec13/31 cages at 30 A resolution using cryo-electron microscopy and single particle analysis. These results reveal a novel cuboctahedron geometry with the potential to form a flexible lattice and to generate a diverse range of containers. Our data are consistent with a model for COPII coat complex assembly in which Sec23/24 has a non-structural role as a multivalent ligand localizing the self-assembly of Sec13/31 to form a cage lattice driving ER cargo export.
authors.affiliation: National Resource for Automated Molecular Microscopy, Departments of Cell, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Stagg
authors.forename: Cemal
authors.initials: C
authors.lastname: Gürkan
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Fowler
authors.forename: Paul
authors.initials: P
authors.lastname: LaPointe
authors.forename: Ted R
authors.initials: TR
authors.lastname: Foss
authors.forename: Clinton S
authors.initials: CS
authors.lastname: Potter
authors.forename: Bridget
authors.initials: B
authors.lastname: Carragher
authors.forename: William E
authors.initials: WE
authors.lastname: Balch
mesh_terms: D000818:Animals; D022181:COP-Coated Vesicles / Q000737:chemistry* / Q000648:ultrastructure*; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure*; D002352:Carrier Proteins; D002460:Cell Line; D020285:Cryoelectron Microscopy; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D008027:Light; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D012542:Scattering, Radiation; D033921:Vesicular Transport Proteins
chemical_list: D036022:Capsid Proteins; D002352:Carrier Proteins; C507456:SEC13 protein, human; C507455:SEC31A protein, human; C521195:SEC31B protein, human; D033921:Vesicular Transport Proteins