Figure 2.

Zigzag force ramp. (A) In the zigzag protocol, the position of the cantilever base (Z) repeatedly cycles back and forth vertically during a net slow retraction from the surface (magenta, upward motion; blue, downward motion). This protocol results in cyclically increasing and decreasing force (F) as a function of time. (B) A representative force-extension curve shows the application of the zigzag protocol to EF-cleaved bR. Colored bars indicate the helix pair or terminal helix being unfolded. (Inset) Local refolding occurred between three states, each separated by 4 aa or one helical turn. (C) A plot of Z(t) shows the pattern used to obtain these data.