FIG. 4.

Folding and unfolding trajectories observed for MtrC during approach (light blue) and retraction (dark blue) cycles. Here, the hematite-coated tip was not fully retracted as described for Fig. 3, but rather only to a distance of 275 nm (A) or 200 nm (B). Under these conditions, the MtrC molecule does not detach from the tip but rather maintains a physical bond with the hematite-functionalized tip (depicted in the bottom schematic), allowing the observation of unfolding and refolding pathways of the polypeptide.