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. Author manuscript; available in PMC: 2018 Apr 1.
Published in final edited form as: Curr Opin Neurobiol. 2017 Jan 16;43:63–70. doi: 10.1016/j.conb.2016.12.012

Figure 3. Simplified, Munc13-centered model of exocytosis.

Figure 3

Munc13 participates in multiple steps of exocytosis, which raises the question at which step a vesicle becomes part of the RRP.

(a) RIM recruits and monomerizes Munc13 to activate a release site.

(b) Munc13, together with Munc18, opens syntaxin-1 to allow for the assembly of the SNARE complex.

(c) SNARE complexes may partially assemble under the molecular control of Munc13 and Munc18, and this assembly may be regulated by complexin, synaptotagmin, or other SNARE-binding proteins.

(d) Fusion proceeds when SNARE proteins fully assemble into a four-alpha-helical bundle that forces the vesicular and target membranes to fuse.