Surface structure of the COPII-coated vesicle
K Matsuoka1, R Schekman, L Orci
1Howard Hughes Medical Institute and Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3206, USA.
Summary
COPII coat proteins assemble in layers on vesicle surfaces, with inner subunits like Sar1p binding most efficiently. Outer subunits, such as Sec13/31p, form polygonal structures and are added last.
Area of Science:
- Cell Biology
- Protein Structure and Assembly
- Membrane Trafficking
Background:
- COPII (Coat Protein Complex II) is essential for vesicular transport from the endoplasmic reticulum.
- Understanding the precise spatial arrangement of COPII subunits is crucial for elucidating its assembly and function in cargo export.
Purpose of the Study:
- To investigate the spatial organization and structural features of COPII coat proteins.
- To determine the order and efficiency of COPII subunit recruitment and assembly on artificial membrane surfaces and vesicles.
Main Methods:
- Crosslinking of COPII subunits to artificial membrane surfaces.
- Electron microscopy, including deep-etch rotary shadowing, of isolated COPII proteins and coated vesicles.
- Analysis of subunit structure and vesicle coat architecture.
Main Results:
- Crosslinking efficiency to phospholipids decreased in the order Sar1p > Sec23/24p >> Sec13/31p, indicating differential membrane association.
- Structural analysis revealed distinct shapes for Sec23/24p (bow tie) and Sec13/31p (bilobed globular structures with a central rod).
- COPII vesicle coats are composed of polygonal units, with the Sec13/31p rod segment matching the unit size, and these proteins form outer layers.
Conclusions:
- COPII coat subunits assemble in layers, with the order of addition to the coat being the reverse of their displacement from the membrane surface.
- The structural data supports a model where Sec13/31p forms the outer lattice of the COPII coat.
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