COP-coated vesicles Current Biology Natalia Gomez-Navarro, Elizabeth A. Miller  Current Biology  Volume 26, Issue 2, Pages R54-R57 (January 2016) DOI: 10.1016/j.cub.2015.12.017 Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 1 Vesicles and tubules mediate traffic in the early secretory pathway. Schematic depiction of the compartments involved in ER-Golgi protein transport. Vesicles that bud from the ER to initiate anterograde transport are generated by COPII coat proteins (green and orange). COPII vesicles may fuse directly with the Golgi, as occurs in yeast or plants, or may fuse together on their way to the Golgi to generate a pleiomorphic compartment called the ER-Golgi intermediate compartment, or ERGIC. COPI proteins (blue and purple) generate retrograde vesicles from the Golgi complex or from the ERGIC, recycling escaped ER residents to ensure retrieval to the ER. The same proteins responsible for the formation of spherical vesicle targets probably also drive formation of tubular structures from the ER (COPII) and the Golgi (COPI). Current Biology 2016 26, R54-R57DOI: (10.1016/j.cub.2015.12.017) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 2 Structure and assembly of COPI and COPII coats. Representations of the hierarchical assembly of coat proteins on the membrane and of the structural units that form the coat complexes. Upper panel: the COPII coat can be divided into two layers. The GTPase Sar together with Sec23–Sec24 form the inner coat. Its bowtie-shaped structure lies flat on the membrane where it interacts with cargo proteins and triggers vesicle budding. Sec13–Sec31 forms the outer shell. Its rod-like structural unit consists of a heterotetramer composed of two Sec13 and two Sec31 polypeptides that self-assemble into a polyhedral cage. Lower panel: COPI coat proteins interact with the membrane predominantly through the GTPase Arf1 and via regions of β’- and α-COP that interact with cargo. The distal regions of both subcomplexes, β’–α-COP and γ–ζ–β–δ-COP, form arch-like structures. Three structural units seem to form a triangular structure called a ‘triad’, which is the building block of the vesicle coat that blankets the membrane. Current Biology 2016 26, R54-R57DOI: (10.1016/j.cub.2015.12.017) Copyright © 2016 Elsevier Ltd Terms and Conditions