Fig. 2.

Complexin extends the lifetime of zippered SNARE complexes under tension. a–c The force-jump scheme used for serial measurements of τ_unzip and τ_rezip in the absence (a) or presence (b, c) of Cpx. The predicted locations of the fully zippered and the unzipped states are indicated with dashed and dotted lines, respectively. Gray vertical bars mark the force-jump periods. Inset in b shows the marked increase in lifetime of SNARE induced by Cpx, the red box of which is magnified above. Vertical scale bars represent 20 nm, and horizontal scale bars represent 0.5 s (main panels) and 30 s (inset in b). d, f Distributions of τ_unzip (d) and τ_rezip (f) at varying forces (N ≥ 19 for each panel). Red curves represent the fits to exponential distributions with their mean values indicated. e, g Force dependences of unzipping (e) and rezipping (g) rates in the absence (black) or presence (blue) of Cpx. Error bars represent the 95% confidence intervals for the mean parameter estimates in d and f. Dashed lines represent the fits to the Bell equation. h The energy diagram for the unzipping/zippering of a neuronal SNARE complex at 14 pN. The effect of Cpx is indicated in blue