Supporting Information

Files in this Data Supplement:

Supporting Figure 6
Supporting Results and Discussion
Supporting Table 1
Supporting Figure 7

Fig. 6. Predicting force–clamp step size from worm-like chain model (WLC) fits to force-extension data. (A) Force-extension unfolding of I27_{(G32C–A75C)8} in the presence of DTT. Dashed lines indicate predicted step size for unfolding at a constant force as determined by WLC fits (solid lines) to force-extension data. FL, full-length unfolding; Un, unsequestered unfolding; D/T, disulfide reduction and trapped unfolding. (B) Force-extension unfolding of wild-type (I27)₈. (C) Experimentally determined step-size distribution for unsequestered unfolding at F = 130 pN in force–clamp. A Gaussian fit gives an average step size of 10.6 ± 0.7 nm. (D) Step-size distributions from force–clamp data for disulfide reduction/trapped unfolding at various second–pulse forces. Note that the average step sizes at each force are very similar to those predicted by WLC fits to force-extension data in A (see Table 1).

Fig. 7. Averaged traces of unsequestered unfolding at various forces. Each averaged trace is fit with a single exponential: 1/t_u = a_u. Recordings were obtained in the absence of DTT.

Table 1. Step sizes for thiol/disulfide exchange as a function of the applied force

*See Fig. 6A.