Crystal structure of alpha-COP in complex with epsilon-COP provides insight into the architecture of the COPI vesicular coat.
The heptameric coatomer complex forms the protein shell of membrane-bound vesicles that are involved in transport from the Golgi to the endoplasmatic reticulum and in intraGolgi trafficking. The heptamer can be dissected into a heterotetrameric F-subcomplex, which displays similarities to the adapter complex of the "inner" coat in clathrin-coated vesicles, and a heterotrimeric B-subcomplex, which is believed to form an "outer" coat with a morphology distinct from that of clathrin-coated vesicles. We have determined the crystal structure of the complex between the C-terminal domain (CTD) of alpha-COP and full-length epsilon-COP, two components of the B-subcomplex, at a 2.9 A resolution. The alpha-COP(CTD) x epsilon-COP heterodimer forms a rod-shaped structure, in which epsilon-COP adopts a tetratricopeptide repeat (TPR) fold that deviates substantially from the canonical superhelical conformation. The alpha-COP CTD adopts a U-shaped architecture that complements the TPR fold of epsilon-COP. The epsilon-COP TPRs form a circular bracelet that wraps around a protruding beta-hairpin of the alpha-COP CTD, thus interlocking the two proteins. The alpha-COP(CTD) x epsilon-COP complex forms heterodimers in solution, and we demonstrate biochemically that the heterodimer directly interacts with the Dsl1 tethering complex. These data suggest that the heterodimer is exposed on COPI vesicles, while the remaining part of the B-subcomplex oligomerizes underneath into a cage.
Laboratory of Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
Kuo-Chiang
KC
Hsia
André
A
Hoelz
D022181:COP-Coated Vesicles / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D020755:Coat Protein Complex I / Q000737:chemistry*; D020756:Coatomer Protein / Q000737:chemistry*; D018360:Crystallography, X-Ray / Q000379:methods; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
D020755:Coat Protein Complex I; D020756:Coatomer Protein