Figure 2.

The SNARE complex zippers stepwise. (A) Force‐extension curves (FECs) obtained by first pulling and then relaxing single SNARE complexes in the absence (#1 and #2) and presence (#3) of SNAP‐25 in the solution. Regions of different states (red numbers, see B) are fit by the Marko‐Siggia formula (dashed red lines). Some transitions are marked: the reversible LD transition by a dashed oval, the reversible CTD transition by a solid oval, NTD unfolding by green arrows, t‐SNARE unfolding by cyan arrows, t‐SNARE refolding by the blue arrow, and full SNARE reassembly by red arrows. The inset shows the close‐up view of the CTD transition. (B) Derived SNARE assembly and disassembly states and pathway. The free energies of different states relative to the unzipped state (E) are indicated. Adapted from Gao et al. and Ma et al.48, 53