SM proteins Sly1 and Vps33 co-assemble with Sec17 and SNARE complexes to oppose SNARE disassembly by Sec18

  1. Braden T Lobingier
  2. Daniel P Nickerson
  3. Sheng-Ying Lo
  4. Alexey J Merz  Is a corresponding author
  1. University of Washington School of Medicine, United States

Abstract

Secretory and endolysosomal fusion events are driven by SNAREs and cofactors, including Sec17 (α-SNAP), Sec18 (NSF), and Sec1/Munc18 (SM) proteins. SMs are essential for fusion in vivo, but the basis of this requirement is enigmatic. We now report that, in addition to their established roles as fusion accelerators, SM proteins Sly1 and Vps33 directly shield SNARE complexes from Sec17- and Sec18-mediated disassembly. In vivo, wild-type Sly1 and Vps33 function are required to withstand overproduction of Sec17. In vitro, Sly1 and Vps33 impede SNARE complex disassembly by Sec18 and ATP. Unexpectedly, Sec17 directly promotes selective loading of Sly1 and Vps33 onto cognate SNARE complexes. A large thermodynamic barrier limits SM binding, implying that significant conformational rearrangements are involved. In a working model, Sec17 and SMs accelerate fusion mediated by cognate SNARE complexes and protect them from NSF-mediated disassembly, while mis-assembled or non-cognate SNARE complexes are eliminated through kinetic proofreading by Sec18.

Article and author information

Author details

  1. Braden T Lobingier

    University of Washington School of Medicine, Seattle, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Daniel P Nickerson

    University of Washington School of Medicine, Seattle, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Sheng-Ying Lo

    University of Washington School of Medicine, Seattle, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Alexey J Merz

    University of Washington School of Medicine, Seattle, United States
    For correspondence
    merza@uw.edu
    Competing interests
    The authors declare that no competing interests exist.

Reviewing Editor

  1. Reinhard Jahn, Max Planck Institute for Biophysical Chemistry, Germany

Publication history

  1. Received: January 12, 2014
  2. Accepted: May 13, 2014
  3. Accepted Manuscript published: May 16, 2014 (version 1)
  4. Version of Record published: June 17, 2014 (version 2)

Copyright

© 2014, Lobingier 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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  1. Braden T Lobingier
  2. Daniel P Nickerson
  3. Sheng-Ying Lo
  4. Alexey J Merz
(2014)
SM proteins Sly1 and Vps33 co-assemble with Sec17 and SNARE complexes to oppose SNARE disassembly by Sec18
eLife 3:e02272.
https://doi.org/10.7554/eLife.02272
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