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Updated: May 9, 2026

Cargo Loading onto Kinesin Powered Molecular Shuttles
Published on: November 3, 2010
Structural basis for cargo regulation of COPII coat assembly
Scott M Stagg1, Paul LaPointe, Abbas Razvi
1National Resource for Automated Molecular Microscopy, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Abstract:
Using cryo-electron microscopy, we have solved the structure of an icosidodecahedral COPII coat involved in cargo export from the endoplasmic reticulum (ER) coassembled from purified cargo adaptor Sec23-24 and Sec13-31 lattice-forming complexes. The coat structure shows a tetrameric assembly of the Sec23-24 adaptor layer that is well positioned beneath the vertices and edges of the Sec13-31 lattice. Fitting the known crystal structures of the COPII proteins into the density map reveals a flexible hinge region stemming from interactions between WD40 beta-propeller domains present in Sec13 and Sec31 at the vertices. The structure shows that the hinge region can direct geometric cage expansion to accommodate a wide range of bulky cargo, including procollagen and chylomicrons, that is sensitive to adaptor function in inherited disease. The COPII coat structure leads us to propose a mechanism by which cargo drives cage assembly and membrane curvature for budding from the ER.
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