An ER translocon for multi-pass membrane protein biogenesis
- University of Chicago, United States
- University of California, San Francisco, United States
Abstract
Membrane proteins with multiple transmembrane domains play critical roles in cell physiology, but little is known about the machinery coordinating their biogenesis at the endoplasmic reticulum. Here we describe a ~360 kDa ribosome-associated complex comprising the core Sec61 channel and five accessory factors: TMCO1, CCDC47 and the Nicalin-TMEM147-NOMO complex. Cryo-electron microscopy reveals a large assembly at the ribosome exit tunnel organized around a central membrane cavity. Similar to protein-conducting channels that facilitate movement of transmembrane segments, cytosolic and luminal funnels in TMCO1 and TMEM147, respectively, suggest routes into the central membrane cavity. High-throughput mRNA sequencing shows selective translocon engagement with hundreds of different multi-pass membrane proteins. Consistent with a role in multi-pass membrane protein biogenesis, cells lacking different accessory components show reduced levels of one such client, the glutamate transporter EAAT1. These results identify a new human translocon and provide a molecular framework for understanding its role in multi-pass membrane protein biogenesis.
Data availability
Annotated spectra corresponding to the reported ribosome-translocon cross-links are available at the MS-Viewer website (http://msviewer.ucsf.edu/prospector/cgi- bin/msform.cgi?form=msviewer) with the following accession keys: HCD data: 7s2yb4zfjw and ETD data: vdibnsypj7. Cryo-EM maps have been deposited in the Electron Microscopy Data Bank with accession codes: EMD-21426 (Map 1), EMD-21427 (Map 2) and EMD-21435 (Map 3). Coordinates for the human 60S-translocon complex have been deposited in the Protein Data Bank with accession code 6W6L. mRNA sequencing data have been deposited in Gene Expression Omnibus (GEO) under accession number GSE134027.
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Annotated spectra corresponding to ribosome-translocon cross-linksHCD data: 7s2yb4zfjw and ETD data: vdibnsypj7.
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Cryo-EM structure of the human ribosome-TMCO1 transloconProtein Data Bank, 6W6L.
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mRNA sequencing dataNCBI Gene Expression Omnibus, GSE134027.
Article and author information
Author details
Funding
National Institute of General Medical Sciences (NIH R01 GM130051)
- Robert J Keenan
National Eye Institute (NIH R21 EY026719)
- Robert J Keenan
Boehringer Ingelheim Fonds (PhD fellowship)
- S Andre Anghel
National Institute of General Medical Sciences (T32 GM007183)
- Philip T McGilvray
- Frank Zhong
Dr. Miriam and Sheldon G. Adelson Medical Research Foundation
- Alma L Burlingame
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2020, McGilvray 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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An ER translocon for multi-pass membrane protein biogenesis
eLife 9:e56889.
https://doi.org/10.7554/eLife.56889
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