1. Biochemistry and Chemical Biology
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Sec17/Sec18 can support membrane fusion without help from completion of SNARE zippering

  1. Hongki Song
  2. Thomas L Torng
  3. Amy S Orr
  4. Axel T Brunger
  5. William T Wickner  Is a corresponding author
  1. Geisel School of Medicine at Dartmouth, United States
  2. Stanford University, United States
Research Article
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Cite this article as: eLife 2021;10:e67578 doi: 10.7554/eLife.67578

Abstract

Membrane fusion requires R-, Qa-, Qb-, and Qc-family SNAREs that zipper into RQaQbQc coiled coils, driven by the sequestration of apolar amino acids. Zippering has been thought to provide all the force driving fusion. Sec17/aSNAP can form an oligomeric assembly with SNAREs with the Sec17 C-terminus bound to Sec18/NSF, the central region bound to SNAREs, and a crucial apolar loop near the N-terminus poised to insert into membranes. We now report that Sec17 and Sec18 will drive robust fusion without requiring zippering completion. Zippering-driven fusion is blocked by deleting the C-terminal quarter of any Q-SNARE domain or by replacing the apolar amino acids of the Qa-SNARE which face the center of the 4-SNARE coiled coils with polar residues. These blocks, singly or combined, are bypassed by Sec17 and Sec18, and SNARE-dependent fusion is restored without help from completing zippering.

Data availability

All data generated or analyzed during this study are included in the manuscript and supporting files. Source data files have been provided for Figures 1, 2, 3 4, 5, and 6.

The following previously published data sets were used

Article and author information

Author details

  1. Hongki Song

    Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-3761-5434
  2. Thomas L Torng

    Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-2295-2777
  3. Amy S Orr

    Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, United States
    Competing interests
    No competing interests declared.
  4. Axel T Brunger

    Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States
    Competing interests
    Axel T Brunger, Reviewing editor, eLife.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-5121-2036
  5. William T Wickner

    Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, United States
    For correspondence
    William.T.Wickner@dartmouth.edu
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8431-0468

Funding

National Institutes of Health (R35GM118037)

  • William T Wickner

National Institutes of Health (R37MH63105)

  • Axel T Brunger

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Josep Rizo, University of Texas Southwestern Medical Center, United States

Publication history

  1. Received: February 16, 2021
  2. Accepted: April 30, 2021
  3. Accepted Manuscript published: May 4, 2021 (version 1)
  4. Version of Record published: May 24, 2021 (version 2)

Copyright

© 2021, Song 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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Further reading

    1. Biochemistry and Chemical Biology
    Josep Rizo et al.
    Insight

    Two proteins called Sec17 and Sec18 may have a larger role in membrane fusion than is commonly assumed in textbook models.

    1. Biochemistry and Chemical Biology
    2. Cell Biology
    Jasmin Mertins et al.
    Research Article Updated

    SNARE proteins have been described as the effectors of fusion events in the secretory pathway more than two decades ago. The strong interactions between SNARE domains are clearly important in membrane fusion, but it is unclear whether they are involved in any other cellular processes. Here, we analyzed two classical SNARE proteins, syntaxin 1A and SNAP25. Although they are supposed to be engaged in tight complexes, we surprisingly find them largely segregated in the plasma membrane. Syntaxin 1A only occupies a small fraction of the plasma membrane area. Yet, we find it is able to redistribute the far more abundant SNAP25 on the mesoscale by gathering crowds of SNAP25 molecules onto syntaxin clusters in a SNARE-domain-dependent manner. Our data suggest that SNARE domain interactions are not only involved in driving membrane fusion on the nanoscale, but also play an important role in controlling the general organization of proteins on the mesoscale. Further, we propose these mechanisms preserve active syntaxin 1A–SNAP25 complexes at the plasma membrane.