The structure of the COPI coat determined within the cell
- European Molecular Biology Laboratory, Germany
- Max Planck Institute of Biochemistry, Germany
Abstract
COPI-coated vesicles mediate trafficking within the Golgi apparatus and from the Golgi to the endoplasmic reticulum. The structures of membrane protein coats, including COPI, have been extensively studied with in vitro reconstitution systems using purified components. In a previous paper (Dodonova et al., 2017), we determined a complete structural model of the in vitro reconstituted COPI coat. Here, we applied cryo-focused ion beam milling, cryo-electron tomography and subtomogram averaging to determine the native structure of the COPI coat within vitrified Chlamydomonas reinhardtii cells. The native algal structure resembles the in vitro mammalian structure, but additionally reveals cargo bound beneath β'-COP. We find that all coat components disassemble simultaneously and relatively rapidly after budding. Structural analysis in situ, maintaining Golgi topology, shows that vesicles change their size, membrane thickness, and cargo content as they progress from cis to trans, but the structure of the coat machinery remains constant.
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Article and author information
Author details
Svetlana O Dodonova
Funding
Deutsche Forschungsgemeinschaft (SFB1129 (Z2))
- John AG Briggs
Deutsche Forschungsgemeinschaft (SFB-1035/Project A01)
- Wolfgang Baumeister
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2017, Bykov et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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The structure of the COPI coat determined within the cell
eLife 6:e32493.
https://doi.org/10.7554/eLife.32493
Further reading
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- Structural Biology and Molecular Biophysics
- Cell Biology
Advances in imaging techniques have shed new light on the structure of vesicles formed by COPI protein complexes.
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- Structural Biology and Molecular Biophysics
BTB (bric-a-brack, Tramtrack, and broad complex) is a diverse group of protein-protein interaction domains found within metazoan proteins. Transcription factors contain a dimerizing BTB subtype with a characteristic N-terminal extension. The Tramtrack group (TTK) is a distinct type of BTB domain, which can multimerize. Single-particle cryo-EM microscopy revealed that the TTK-type BTB domains assemble into a hexameric structure consisting of three canonical BTB dimers connected through a previously uncharacterized interface. We demonstrated that the TTK-type BTB domains are found only in Arthropods and have undergone lineage-specific expansion in modern insects. The Drosophila genome encodes 24 transcription factors with TTK-type BTB domains, whereas only four have non-TTK-type BTB domains. Yeast two-hybrid analysis revealed that the TTK-type BTB domains have an unusually broad potential for heteromeric associations presumably through a dimer-dimer interaction interface. Thus, the TTK-type BTB domains are a structurally and functionally distinct group of protein domains specific to Arthropodan transcription factors.
