Testing Kinetic Identities Involving Transition-Path Properties Using Single-Molecule Folding Trajectories.

Recent advances in single-molecule assays have allowed individual transition paths during the folding of single molecules to be observed directly. We used the transition paths of DNA hairpins having different sequences, measured with high-resolution optical tweezers, to test theoretical relations between the properties of the transition paths and the folding kinetics. We showed that folding and unfolding rates were related to the average transition-path times, as expected from theory, for all hairpins studied. We also found that the probability distribution of transition-path occupancies agreed with the profile of the average velocity along the transition paths for each of the hairpins, as expected theoretically. Finally, we used the latter result to show that the committor probability recovered from the velocity profile matches the committor measured empirically. These results validate the proposed kinetic identities.