Figure 9. The trans-SNARE complexes at phasic and tonic synapses are partially zippered under resting state.

The N-terminal end of the SNARE complex is zippered whereas the C-terminal end is exposed. The binding and cleavage sites of BoNT/B are exposed but the shared binding site for TeNT and BoNT/D, and possibly the cleavage site for BoNT/D, are occluded. Scissors and white lines indicate neurotoxin cleavage site. Gray arrow head indicates the location of the zero-layer across all three SNARE proteins.