Crystal structure of a substrate-engaged SecY protein-translocation channel
Hydrophobic signal sequences target secretory polypeptides to a protein-conducting channel formed by a heterotrimeric membrane protein complex, the prokaryotic SecY or eukaryotic Sec61 complex. How signal sequences are recognized is poorly understood, particularly because they are diverse in sequenc...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | en_US |
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Springer Nature
2017
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| Online Access: | http://hdl.handle.net/1721.1/107210 https://orcid.org/0000-0002-0511-4280 https://orcid.org/0000-0002-1090-6071 |
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| author | Li, Long Park, Eunyong Rapoport, Tom A. Ling, Jingjing Ingram, Jessica Ploegh, Hidde |
| author2 | Massachusetts Institute of Technology. Department of Biology |
| author_facet | Massachusetts Institute of Technology. Department of Biology Li, Long Park, Eunyong Rapoport, Tom A. Ling, Jingjing Ingram, Jessica Ploegh, Hidde |
| author_sort | Li, Long |
| collection | MIT |
| description | Hydrophobic signal sequences target secretory polypeptides to a protein-conducting channel formed by a heterotrimeric membrane protein complex, the prokaryotic SecY or eukaryotic Sec61 complex. How signal sequences are recognized is poorly understood, particularly because they are diverse in sequence and length. Structures of the inactive channel show that the largest subunit, SecY or Sec61α, consists of two halves that form an hourglass-shaped pore with a constriction in the middle of the membrane and a lateral gate that faces lipid. The cytoplasmic funnel is empty, while the extracellular funnel is filled with a plug domain. In bacteria, the SecY channel associates with the translating ribosome in co-translational translocation, and with the SecA ATPase in post-translational translocation. How a translocating polypeptide inserts into the channel is uncertain, as cryo-electron microscopy structures of the active channel have a relatively low resolution (~10 Å) or are of insufficient quality. Here we report a crystal structure of the active channel, assembled from SecY complex, the SecA ATPase, and a segment of a secretory protein fused into SecA. The translocating protein segment inserts into the channel as a loop, displacing the plug domain. The hydrophobic core of the signal sequence forms a helix that sits in a groove outside the lateral gate, while the following polypeptide segment intercalates into the gate. The carboxy (C)-terminal section of the polypeptide loop is located in the channel, surrounded by residues of the pore ring. Thus, during translocation, the hydrophobic segments of signal sequences, and probably bilayer-spanning domains of nascent membrane proteins, exit the lateral gate and dock at a specific site that faces the lipid phase. |
| first_indexed | 2024-09-23T12:56:12Z |
| format | Article |
| id | mit-1721.1/107210 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T12:56:12Z |
| publishDate | 2017 |
| publisher | Springer Nature |
| record_format | dspace |
| spelling | mit-1721.1/1072102022-09-28T10:59:38Z Crystal structure of a substrate-engaged SecY protein-translocation channel Li, Long Park, Eunyong Rapoport, Tom A. Ling, Jingjing Ingram, Jessica Ploegh, Hidde Massachusetts Institute of Technology. Department of Biology Whitehead Institute for Biomedical Research Ling, Jingjing Ingram, Jessica Ploegh, Hidde Hydrophobic signal sequences target secretory polypeptides to a protein-conducting channel formed by a heterotrimeric membrane protein complex, the prokaryotic SecY or eukaryotic Sec61 complex. How signal sequences are recognized is poorly understood, particularly because they are diverse in sequence and length. Structures of the inactive channel show that the largest subunit, SecY or Sec61α, consists of two halves that form an hourglass-shaped pore with a constriction in the middle of the membrane and a lateral gate that faces lipid. The cytoplasmic funnel is empty, while the extracellular funnel is filled with a plug domain. In bacteria, the SecY channel associates with the translating ribosome in co-translational translocation, and with the SecA ATPase in post-translational translocation. How a translocating polypeptide inserts into the channel is uncertain, as cryo-electron microscopy structures of the active channel have a relatively low resolution (~10 Å) or are of insufficient quality. Here we report a crystal structure of the active channel, assembled from SecY complex, the SecA ATPase, and a segment of a secretory protein fused into SecA. The translocating protein segment inserts into the channel as a loop, displacing the plug domain. The hydrophobic core of the signal sequence forms a helix that sits in a groove outside the lateral gate, while the following polypeptide segment intercalates into the gate. The carboxy (C)-terminal section of the polypeptide loop is located in the channel, surrounded by residues of the pore ring. Thus, during translocation, the hydrophobic segments of signal sequences, and probably bilayer-spanning domains of nascent membrane proteins, exit the lateral gate and dock at a specific site that faces the lipid phase. National Institutes of Health (U.S.) (NIH Grant GM052586) National Institutes of Health (U.S.) (Pioneer Award) Howard Hughes Medical Institute (Investigator) 2017-03-07T16:15:19Z 2017-03-07T16:15:19Z 2016-03 2015-11 Article http://purl.org/eprint/type/JournalArticle 0028-0836 1476-4687 http://hdl.handle.net/1721.1/107210 Li, Long, Eunyong Park, JingJing Ling, Jessica Ingram, Hidde Ploegh, and Tom A. Rapoport. “Crystal Structure of a Substrate-Engaged SecY Protein-Translocation Channel.” Nature 531, no. 7594 (March 7, 2016): 395–399. https://orcid.org/0000-0002-0511-4280 https://orcid.org/0000-0002-1090-6071 en_US http://dx.doi.org/10.1038/nature17163 Nature Creative Commons Attribution-Noncommercial-Share Alike http://creativecommons.org/licenses/by-nc-sa/4.0/ application/pdf Springer Nature PMC |
| spellingShingle | Li, Long Park, Eunyong Rapoport, Tom A. Ling, Jingjing Ingram, Jessica Ploegh, Hidde Crystal structure of a substrate-engaged SecY protein-translocation channel |
| title | Crystal structure of a substrate-engaged SecY protein-translocation channel |
| title_full | Crystal structure of a substrate-engaged SecY protein-translocation channel |
| title_fullStr | Crystal structure of a substrate-engaged SecY protein-translocation channel |
| title_full_unstemmed | Crystal structure of a substrate-engaged SecY protein-translocation channel |
| title_short | Crystal structure of a substrate-engaged SecY protein-translocation channel |
| title_sort | crystal structure of a substrate engaged secy protein translocation channel |
| url | http://hdl.handle.net/1721.1/107210 https://orcid.org/0000-0002-0511-4280 https://orcid.org/0000-0002-1090-6071 |
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