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Title: Crystal structure of a substrate-engaged SecY protein-translocation channel

Journal Article · · Nature (London)
DOI:https://doi.org/10.1038/nature17163· OSTI ID:1243126
 [1];  [2];  [3];  [3];  [3];  [1]
  1. Howard Hughes Medical Institute and Harvard Medical School, Boston, MA (United States)
  2. The Rockefeller University and Howard Hughes Medical Inst., New York, NY (United States); Howard Hughes Medical Institute and Harvard Medical School, Boston, MA (United States)
  3. Whitehead Inst. for Biomedical Research, Cambridge, MA (United States)

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. Furthermore, 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.

Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Organization:
National Inst. of Health
Grant/Contract Number:
GM052586
OSTI ID:
1243126
Journal Information:
Nature (London), Vol. 531, Issue 7594; ISSN 0028-0836
Publisher:
Nature Publishing GroupCopyright Statement
Country of Publication:
United States
Language:
ENGLISH
Citation Metrics:
Cited by: 111 works
Citation information provided by
Web of Science

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Cited By (38)

Structure of the post-translational protein translocation machinery of the ER membrane journal December 2018
Structural considerations of folded protein import through the chloroplast TOC / TIC translocons journal March 2019
Variant Signal Peptides of Vaccine Antigen, FHbp, Impair Processing Affecting Surface Localization and Antibody-Mediated Killing in Most Meningococcal Isolates journal December 2019
Structure and topology around the cleavage site regulate post-translational cleavage of the HIV-1 gp160 signal peptide journal July 2017
A central cavity within the holo-translocon suggests a mechanism for membrane protein insertion. journalarticle January 2016
Use of a sequential high throughput screening assay to identify novel inhibitors of the eukaryotic SRP-Sec61 targeting/translocation pathway journal December 2018
Interaction mapping of the Sec61 translocon identifies two Sec61α regions interacting with hydrophobic segments in translocating chains journal September 2018
Structural Basis of the Sec Translocon and YidC Revealed Through X-ray Crystallography journal April 2019
Archaeal cell surface biogenesis journal June 2018
The molecular mechanism of cotranslational membrane protein recognition and targeting by SecA journal September 2019
SecY-SecA fusion protein retains the ability to mediate protein transport journal August 2017
Post-Translational Protein Transport by the Sec Complex journal June 2019
Structurally detailed coarse-grained model for Sec-facilitated co-translational protein translocation and membrane integration journal March 2017
Insertion of proteins and lipopolysaccharide into the bacterial outer membrane journal June 2017
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Quality control of nonstop membrane proteins at the ER membrane and in the cytosol journal August 2016
An alternate mode of oligomerization for E. coli SecA journal September 2017
Structure-based working model of SecDF, a proton-driven bacterial protein translocation factor journal April 2018
HDX-MS reveals nucleotide-dependent, anti-correlated opening and closure of SecA and SecY channels of the bacterial translocon journal July 2019
Structure of the posttranslational Sec protein-translocation channel complex from yeast journal December 2018
Structure of the substrate-engaged SecA-SecY protein translocation machine journal June 2019
Tracking Proteins Secreted by Bacteria: What's in the Toolbox? journal May 2017
A clearer picture of the ER translocon complex journal February 2020
Molecular Mimicry of SecA and Signal Recognition Particle Binding to the Bacterial Ribosome journal August 2019
Protein translocation by the SecA ATPase occurs by a power‐stroke mechanism journal March 2019
ATP-induced asymmetric pre-protein folding as a driver of protein translocation through the Sec machinery journal January 2019
EMC Is Required to Initiate Accurate Membrane Protein Topogenesis journal November 2018
Voltage Sensing in Bacterial Protein Translocation text January 2020
Atomic structures of anthrax toxin protective antigen channels bound to partially unfolded lethal and edema factors journal February 2020
The way is the goal: how SecA transports proteins across the cytoplasmic membrane in bacteria journal April 2018
Protein export through the bacterial Sec pathway journal November 2016
The Dynamic ATP-Driven Mechanism of Bacterial Protein Translocation and the Critical Role of Phospholipids journal June 2019
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Two-way communication between SecY and SecA suggests a Brownian ratchet mechanism for protein translocation journal May 2016
ZMPSTE24 missense mutations that cause progeroid diseases decrease prelamin A cleavage activity and/or protein stability journal May 2018

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