Fig. 2: Equilibrium measurement of Csp at various constant forces.

a Extension time course of Csp at three constant forces of 5.5, 6.3, and 7 pN were recorded for 600 s. Corresponding relative frequency distributions of the extensions were shown in the right panel and fitted by Gauss functions. Raw data were recorded at 200 Hz (gray) and smoothed over a 5-s time window (red). b, c The Unfolding and folding probability of Csp at the three constant forces. Solid lines show exponential fitting curves to determine \(k_u\) and \(k_f\) of Csp. d The force-dependent folding/unfolding probability data points were fitted with Eq. (9).