SM proteins Sly1 and Vps33 co-assemble with Sec17 and SNARE complexes to oppose SNARE disassembly by Sec18
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
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.
Metrics
-
- 2,102
- views
-
- 302
- downloads
-
- 69
- citations
Views, downloads and citations are aggregated across all versions of this paper published by eLife.
Download links
Downloads (link to download the article as PDF)
Open citations (links to open the citations from this article in various online reference manager services)
Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)
Further reading
-
- Biochemistry and Chemical Biology
- Microbiology and Infectious Disease
Birnaviruses are a group of double-stranded RNA (dsRNA) viruses infecting birds, fish, and insects. Early endosomes (EE) constitute the platform for viral replication. Here, we study the mechanism of birnaviral targeting of EE membranes. Using the Infectious Bursal Disease Virus (IBDV) as a model, we validate that the viral protein 3 (VP3) binds to phosphatidylinositol-3-phosphate (PI3P) present in EE membranes. We identify the domain of VP3 involved in PI3P-binding, named P2 and localized in the core of VP3, and establish the critical role of the arginine at position 200 (R200), conserved among all known birnaviruses. Mutating R200 abolishes viral replication. Moreover, we propose a two-stage modular mechanism for VP3 association with EE. Firstly, the carboxy-terminal region of VP3 adsorbs on the membrane, and then the VP3 core reinforces the membrane engagement by specifically binding PI3P through its P2 domain, additionally promoting PI3P accumulation.
-
- Biochemistry and Chemical Biology
- Microbiology and Infectious Disease
In the bacterium M. smegmatis, an enzyme called MftG allows the cofactor mycofactocin to transfer electrons released during ethanol metabolism to the electron transport chain.