Abstract
Munc18-1 and Munc13-1 orchestrate assembly of the SNARE complex formed by syntaxin-1, SNAP-25 and synaptobrevin, allowing exquisite regulation of neurotransmitter release. Non-regulated neurotransmitter release might be prevented by αSNAP, which inhibits exocytosis and SNARE-dependent liposome fusion. However, distinct mechanisms of inhibition by αSNAP were suggested, and it is unknown how such inhibition is overcome. Using liposome fusion assays, FRET and NMR spectroscopy, here we provide a comprehensive view of the mechanisms underlying the inhibitory functions of αSNAP, showing that αSNAP potently inhibits liposome fusion by: binding to syntaxin-1, hindering Munc18-1 binding; binding to syntaxin-1-SNAP-25 heterodimers, precluding SNARE complex formation; and binding to trans-SNARE complexes, preventing fusion. Importantly, inhibition by αSNAP is avoided only when Munc18-1 binds first to syntaxin-1, leading to Munc18-1-Munc13-1-dependent liposome fusion. We propose that at least some of the inhibitory activities of αSNAP ensure that neurotransmitter release occurs through the highly-regulated Munc18-1-Munc13-1 pathway at the active zone.
Highlights
Munc[] and Munc[] orchestrate assembly of the SNARE complex formed by syntaxin-1, sensitive factor (NSF) attachment protein (SNAP)-25 and synaptobrevin, allowing exquisite regulation of neurotransmitter release
We propose that the ability of αSNAP to preclude transSNARE complex assembly and membrane fusion induced by assembled trans-SNARE complexes provides fundamental mechanisms to prevent synaptic vesicle fusion by constitutive pathways, ensuring that neurotransmitter release occurs through the highly regulated Munc18-1-Munc[] pathway
To investigate how NSF-independent αSNAP function is coupled to those of other core components of the release machinery, we used an assay that simultaneously monitors lipid and content mixing between synaptobrevin-containing liposomes (V-liposomes) and syntaxin-1-SNAP-25 liposomes (T-liposomes)[49,50] and that we have used extensively[16,18,29,51]
Summary
Munc[] and Munc[] orchestrate assembly of the SNARE complex formed by syntaxin-1, SNAP-25 and synaptobrevin, allowing exquisite regulation of neurotransmitter release. Core components of the release machinery[1,3,4,5] include the soluble N-ethylmaleimide (NEM)-sensitive factor (NSF) attachment protein (SNAP) receptors (SNAREs) syntaxin-1, SNAP-25, and synaptobrevin, which form a four-helix bundle called the SNARE complex that brings the vesicle and plasma membranes into close proximity and is key for membrane fusion[6,7,8,9]. This complex is disassembled by NSF and SNAPs to recycle the SNAREs for another round of fusion[6,10].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
