Molecular view of ER membrane remodeling by the Sec61/TRAP translocon

Sudeep Karki; Matti Javanainen; Shahid Rehan; Dale Tranter; Juho Kellosalo; Juha Huiskonen; Lotta Happonen; Ville Paavilainen

doi:10.15252/embr.202357910

Molecular view of ER membrane remodeling by the Sec61/TRAP translocon

Sudeep Karki, Matti Javanainen, Shahid Rehan, Dale Tranter, Juho Kellosalo, Juha Huiskonen, Lotta Happonen, Ville Paavilainen

Research output: Contribution to journal › Article › peer-review

Abstract

Protein translocation across the endoplasmic reticulum (ER) membrane is an essential step during protein entry into the secretory pathway. The conserved Sec61 protein-conducting channel facilitates polypeptide translocation and coordinates cotranslational polypeptide-processing events. In cells, the majority of Sec61 is stably associated with a heterotetrameric membrane protein complex, the translocon-associated protein complex (TRAP), yet the mechanism by which TRAP assists in polypeptide translocation remains unknown. Here, we present the structure of the core Sec61/TRAP complex bound to a mammalian ribosome by cryogenic electron microscopy (cryo-EM). Ribosome interactions anchor the Sec61/TRAP complex in a conformation that renders the ER membrane locally thinner by significantly curving its lumenal leaflet. We propose that TRAP stabilizes the ribosome exit tunnel to assist nascent polypeptide insertion through Sec61 and provides a ratcheting mechanism into the ER lumen mediated by direct polypeptide interactions.

Original language	English
Journal	EMBO Reports
Volume	24
Issue number	12
DOIs	https://doi.org/10.15252/embr.202357910
Publication status	Published - 2023

Bibliographical note

Funding Information:
Research was supported by funding: VOP from the Academy of Finland (338836 and 314672), the Sigrid Juselius Foundation, and the Jane and Aatos Erkko Foundation. JTH from the Academy of Finland (314669). MJ from the Academy of Finland (338160). We are thankful to Pasi Laurinmaki and Benita Löflund (Cryo‐EM unit, Institute of Biotechnology, University of Helsinki) and Zane Dekere for the technical support. We thank members of Professor Timo Otonkoski's group for advice and help in carrying out the insulin secretion assays. We thank Jason van Rooyen (Beamline scientist, Diamond Light Source, UK) for the data collection. Support from the Swedish National Infrastructure for Biological Mass Spectrometry (BioMS) and the SciLifeLab, Integrated Structural Biology (ISB) platform, is gratefully acknowledged. We thank CSC–IT Center for Science for computational resources. We thank Professor Ramanujan Hegde (MRC Laboratory of Molecular Biology, Cambridge, UK) for the kind gift of anti‐TRAPα antibody and Professor Peter Arvan (University of Michigan Medical School, Ann Arbor, MI, USA) for the kind gift of INS‐1 832/13 cells. We thank Prof. Thomas Bell, Dr. Sarah O'Keefe, and Dr. Fabio Lolicato for constructive feedback on the manuscript.

Publisher Copyright:
© 2023 The Authors. Published under the terms of the CC BY 4.0 license.

Subject classification (UKÄ)

Biological Sciences

Free keywords

cryo-EM
membrane proteins
protein translocation
secretory proteins
structural biology

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.15252/embr.202357910Licence: CC BY

Cite this

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title = "Molecular view of ER membrane remodeling by the Sec61/TRAP translocon",

abstract = "Protein translocation across the endoplasmic reticulum (ER) membrane is an essential step during protein entry into the secretory pathway. The conserved Sec61 protein-conducting channel facilitates polypeptide translocation and coordinates cotranslational polypeptide-processing events. In cells, the majority of Sec61 is stably associated with a heterotetrameric membrane protein complex, the translocon-associated protein complex (TRAP), yet the mechanism by which TRAP assists in polypeptide translocation remains unknown. Here, we present the structure of the core Sec61/TRAP complex bound to a mammalian ribosome by cryogenic electron microscopy (cryo-EM). Ribosome interactions anchor the Sec61/TRAP complex in a conformation that renders the ER membrane locally thinner by significantly curving its lumenal leaflet. We propose that TRAP stabilizes the ribosome exit tunnel to assist nascent polypeptide insertion through Sec61 and provides a ratcheting mechanism into the ER lumen mediated by direct polypeptide interactions.",

keywords = "cryo-EM, membrane proteins, protein translocation, secretory proteins, structural biology",

author = "Sudeep Karki and Matti Javanainen and Shahid Rehan and Dale Tranter and Juho Kellosalo and Juha Huiskonen and Lotta Happonen and Ville Paavilainen",

note = "Funding Information: Research was supported by funding: VOP from the Academy of Finland (338836 and 314672), the Sigrid Juselius Foundation, and the Jane and Aatos Erkko Foundation. JTH from the Academy of Finland (314669). MJ from the Academy of Finland (338160). We are thankful to Pasi Laurinmaki and Benita L{\"o}flund (Cryo‐EM unit, Institute of Biotechnology, University of Helsinki) and Zane Dekere for the technical support. We thank members of Professor Timo Otonkoski's group for advice and help in carrying out the insulin secretion assays. We thank Jason van Rooyen (Beamline scientist, Diamond Light Source, UK) for the data collection. Support from the Swedish National Infrastructure for Biological Mass Spectrometry (BioMS) and the SciLifeLab, Integrated Structural Biology (ISB) platform, is gratefully acknowledged. We thank CSC–IT Center for Science for computational resources. We thank Professor Ramanujan Hegde (MRC Laboratory of Molecular Biology, Cambridge, UK) for the kind gift of anti‐TRAPα antibody and Professor Peter Arvan (University of Michigan Medical School, Ann Arbor, MI, USA) for the kind gift of INS‐1 832/13 cells. We thank Prof. Thomas Bell, Dr. Sarah O'Keefe, and Dr. Fabio Lolicato for constructive feedback on the manuscript. Publisher Copyright: {\textcopyright} 2023 The Authors. Published under the terms of the CC BY 4.0 license.",

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doi = "10.15252/embr.202357910",

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AU - Karki, Sudeep

AU - Javanainen, Matti

AU - Rehan, Shahid

AU - Tranter, Dale

AU - Kellosalo, Juho

AU - Huiskonen, Juha

AU - Happonen, Lotta

AU - Paavilainen, Ville

N1 - Funding Information: Research was supported by funding: VOP from the Academy of Finland (338836 and 314672), the Sigrid Juselius Foundation, and the Jane and Aatos Erkko Foundation. JTH from the Academy of Finland (314669). MJ from the Academy of Finland (338160). We are thankful to Pasi Laurinmaki and Benita Löflund (Cryo‐EM unit, Institute of Biotechnology, University of Helsinki) and Zane Dekere for the technical support. We thank members of Professor Timo Otonkoski's group for advice and help in carrying out the insulin secretion assays. We thank Jason van Rooyen (Beamline scientist, Diamond Light Source, UK) for the data collection. Support from the Swedish National Infrastructure for Biological Mass Spectrometry (BioMS) and the SciLifeLab, Integrated Structural Biology (ISB) platform, is gratefully acknowledged. We thank CSC–IT Center for Science for computational resources. We thank Professor Ramanujan Hegde (MRC Laboratory of Molecular Biology, Cambridge, UK) for the kind gift of anti‐TRAPα antibody and Professor Peter Arvan (University of Michigan Medical School, Ann Arbor, MI, USA) for the kind gift of INS‐1 832/13 cells. We thank Prof. Thomas Bell, Dr. Sarah O'Keefe, and Dr. Fabio Lolicato for constructive feedback on the manuscript. Publisher Copyright: © 2023 The Authors. Published under the terms of the CC BY 4.0 license.

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N2 - Protein translocation across the endoplasmic reticulum (ER) membrane is an essential step during protein entry into the secretory pathway. The conserved Sec61 protein-conducting channel facilitates polypeptide translocation and coordinates cotranslational polypeptide-processing events. In cells, the majority of Sec61 is stably associated with a heterotetrameric membrane protein complex, the translocon-associated protein complex (TRAP), yet the mechanism by which TRAP assists in polypeptide translocation remains unknown. Here, we present the structure of the core Sec61/TRAP complex bound to a mammalian ribosome by cryogenic electron microscopy (cryo-EM). Ribosome interactions anchor the Sec61/TRAP complex in a conformation that renders the ER membrane locally thinner by significantly curving its lumenal leaflet. We propose that TRAP stabilizes the ribosome exit tunnel to assist nascent polypeptide insertion through Sec61 and provides a ratcheting mechanism into the ER lumen mediated by direct polypeptide interactions.

AB - Protein translocation across the endoplasmic reticulum (ER) membrane is an essential step during protein entry into the secretory pathway. The conserved Sec61 protein-conducting channel facilitates polypeptide translocation and coordinates cotranslational polypeptide-processing events. In cells, the majority of Sec61 is stably associated with a heterotetrameric membrane protein complex, the translocon-associated protein complex (TRAP), yet the mechanism by which TRAP assists in polypeptide translocation remains unknown. Here, we present the structure of the core Sec61/TRAP complex bound to a mammalian ribosome by cryogenic electron microscopy (cryo-EM). Ribosome interactions anchor the Sec61/TRAP complex in a conformation that renders the ER membrane locally thinner by significantly curving its lumenal leaflet. We propose that TRAP stabilizes the ribosome exit tunnel to assist nascent polypeptide insertion through Sec61 and provides a ratcheting mechanism into the ER lumen mediated by direct polypeptide interactions.

KW - cryo-EM

KW - membrane proteins

KW - protein translocation

KW - secretory proteins

KW - structural biology

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DO - 10.15252/embr.202357910

M3 - Article

C2 - 37983950

AN - SCOPUS:85177189274

SN - 1469-221X

VL - 24

JO - EMBO Reports

JF - EMBO Reports

IS - 12

ER -

Molecular view of ER membrane remodeling by the Sec61/TRAP translocon

Abstract

Bibliographical note

Subject classification (UKÄ)

Free keywords

UN SDGs

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Cite this