FIGURE 4.

Disruption of protein dimer results in a peak of extremely high mechanical resistance. A and B, individual unfolding trajectories showing the rupture of a protein dimer under force. WLC fits to the data measure the increase in contour length before (green fits) and after (gray fits) the peak of high force (orange fit) takes place. C, histogram of the unfolding forces for the force peaks occurring before (green bars, 337 ± 84 pN, n = 152) or after (gray bars, 192 ± 48 pN, n = 303) the high-force peak. D, histogram of the measured persistence length for the force peaks occurring before (green bars, 0.22 ± 0.07 nm) or after (gray bars, 0.40 ± 0.09 nm) the high-force peak. These results demonstrate that before the high-force peak, the protein is in its dimeric form, converting into a protein monomer once after the high-force event occurs. The high-force event thus fingerprints the dimer-to-monomer transition.