PerspectiveStructural Biology

COPI gets a fancy new coat

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Science  10 Jul 2015:
Vol. 349, Issue 6244, pp. 142-143
DOI: 10.1126/science.aac6537

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A defining characteristic of eukaryotic cells is their numerous membrane-bound compartments, including the endoplasmic reticulum (ER), Golgi apparatus, and other organelles. Proteins and lipids are transported between these compartments and the cell surface by vesicles about 100 nm in diameter. Three canonical protein coat complexes facilitate the formation of these small vesicular carriers: the clathrin coat, coat protein 1 (COPI), and coat protein 2 (COPII) complexes. The COPII coat mediates vesicle formation at the ER for transport to the Golgi; the COPI coat forms vesicles at the cis-Golgi for transport to the ER; and clathrin has a dual role, forming vesicles at the trans-Golgi for transport to the plasma membrane and forming vesicles at the plasma membrane for endocytosis. Each of these coat complexes is composed of numerous proteins that bind to membrane, recognize cargo proteins, bend the parent membranes into a bud, and pinch the buds off into vesicles (1). On page 195 of this issue, Dodonova et al. (2) have created an atomic model of the COPI coat by using cryogenic electron tomography (cryo-ET) combined with labeling and cross-linking mass spectrometry. Their model gives new insights into the mechanisms by which the COPI proteins assemble into highly interconnected scaffoldings and work together to bend membrane.