Figure 5. Working model of Munc13 in initiating ternary SNARE complex formation in synaptic exocytosis.

Colors are as follows: syntaxin‐1 H_abc domain, light gray; the H3 domain, dark gray; the C‐terminal extension of the H_c helix, yellow; the short linker helix, light green; the N‐terminal end of the H3 domain, magenta; Munc18‐1, cyan; the Munc13‐1 MUN domain, dark blue; SNAP‐25, green; synaptobrevin‐2, blue. The unstructured regions of the SNARE proteins are depicted by lines, and the structured regions are displayed by bold lines. The N‐terminal end of the H3 domain in the “intermediate” state is shown as a dashed line, implying a nucleation site for ternary SNARE complex formation.