Structure and organization of coat proteins in the COPII cage.

Publication Type:

Journal Article

Authors:

Fath, Stephan; Mancias, Joseph D; Bi, Xiping; Goldberg, Jonathan

Source:

Cell, Volume 129, Issue 7, p.1325-36 (2007)

Keywords:

Animals, Cells, Cultured, Clathrin, COP-Coated Vesicles, Crystallography, X-Ray, Endoplasmic Reticulum, Golgi Apparatus, Macromolecular Substances, Membrane Proteins, Models, Molecular, Nuclear Pore Complex Proteins, Protein Structure, Secondary, Protein Structure, Tertiary, Protein Transport, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Vesicular Transport Proteins

Abstract:

<p>COPII-coated vesicles export newly synthesized proteins from the endoplasmic reticulum. The COPII coat consists of the Sec23/24-Sar1 complex that selects cargo and the Sec13/31 assembly unit that can polymerize into an octahedral cage and deform the membrane into a bud. Crystallographic analysis of the assembly unit reveals a 28 nm long rod comprising a central alpha-solenoid dimer capped by two beta-propeller domains at each end. We construct a molecular model of the COPII cage by fitting Sec13/31 crystal structures into a recently determined electron microscopy density map. The vertex geometry involves four copies of the Sec31 beta-propeller that converge through their axial ends; there is no interdigitation of assembly units of the kind seen in clathrin cages. We also propose that the assembly unit has a central hinge-an arrangement of interlocked alpha-solenoids-about which it can bend to adapt to cages of variable curvature.</p>