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A structure of the COPI coat and the role of coat proteins in membrane vesicle assembly

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Science  10 Jul 2015:
Vol. 349, Issue 6244, pp. 195-198
DOI: 10.1126/science.aab1121

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A coat of many components

The formation of coated trafficking vesicles is among the most fundamental of cellular processes. COP1 transport vesicles are involved in retrograde membrane trafficking in the Golgi apparatus and endoplasmic reticulum. Dodonova et al. applied cryo–electron tomography to determine the structure of the COPI coat in its fully assembled form on budded vesicles (see the Perspective by Noble and Stagg). They combined structural data with cross-linking mass spectrometry to generate a complete molecular model. The model suggests a mechanism of coat assembly in which coat proteins cluster via flexible interactions instead of forming a protein cage on the membrane.

Science, this issue p. 195; see also p. 142

Abstract

Transport of material within cells is mediated by trafficking vesicles that bud from one cellular compartment and fuse with another. Formation of a trafficking vesicle is driven by membrane coats that localize cargo and polymerize into cages to bend the membrane. Although extensive structural information is available for components of these coats, the heterogeneity of trafficking vesicles has prevented an understanding of how complete membrane coats assemble on the membrane. We combined cryo–electron tomography, subtomogram averaging, and cross-linking mass spectrometry to derive a complete model of the assembled coat protein complex I (COPI) coat involved in traffic between the Golgi and the endoplasmic reticulum. The highly interconnected COPI coat structure contradicted the current “adaptor-and-cage” understanding of coated vesicle formation.

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