Figure 4: Unfolding and refolding of αC_M in the presence of V_D1.

(a) Force-extension curve of αC_M in a typical stretch-relax force cycle in the presence of 10 nM V_D1. The inset shows a ~3 nm V_D1 dissociation unfolding step at ~37 pN. (b) Unfolding force histogram obtained from repeating stretch-relax force cycles on a single αC_M at different V_D1 concentrations. (c) Percentages of observed unfolding events at <7.5 pN and >7.5 pN unfolding cycles at different V_D1 concentrations. The significance indicated by the asterisks is based on P-value calculation from the χ² test with the null hypothesis that the percentages of the unfolding events are independent on the V_D1 concentration. Four asterisks denote a P-value smaller than 0.0001. The data were collected from eight independent tethers. The error bar denotes 95% confidence interval of probability estimation. (d) Three force-extension curves recorded during three sequential stretch processes between 1 and 9 pN in the presence of 0 nM V_D1 (coloured traces), where only the ~5 pN unfolding/refolding events occurred. After each stretch, force was jumped to 0.1 pN for 1 min for refolding before the next stretch was performed in the presence of 10 nM V_D1 (black and grey traces). The ~5 pN unfolding/refolding event was observed during the first stretch cycle (black), but was lost in the subsequent three stretches. Data in d are smoothed using 0.05-s time interval.