Fig. 7.

Rate-limiting effect of the unkiss. (a) At high forces, the effective kinetic barrier for the overall unfolding is the one to break the kissing. (b) When a triple transition occurs at high force (blue), the first part of the rip is to unkiss; the rest is the unfolding of the hairpins. The area under the rip for unfolding the hairpins (green) equals the mechanical work done to unfold the two hairpins in the kissing complex, which is significantly larger than the mechanical work to fold the hairpins (orange areas). This difference and the hysteresis between the unfolding and refolding curves reflect the enhanced kinetic stability of the hairpins imposed by the rate-limiting kissing interaction.