Stretching of proteins in a force-clamp

Mechanically induced protein unfolding in the force-clamp apparatus is shown, in a coarse-grained model of ubiquitin, to have lognormal statistics above a threshold force and exponential statistics below it. Correspondingly, the mean unfolding time is slowly varying and exponentially decreases as a function of the force. The time dependences of the end-to-end distances are also distinct. The time sequence of unfolding events weakly depends on force and much of it resembles that for stretching at constant speed. A more complicated time dependence arises for integrin.