Lattice Model Studies of Force-Induced Unfolding of Proteins^†

We probe the general characteristics of force-induced unfolding of proteins using lattice models. The computations show that the experimental observations. such as the shape of the force-extension curves and hysteresis, are qualitatively reproduced using the coarse-grained models. Force hysteresis, which occurs because the structural relaxation times are longer than the time scales for dissipation of stored mechanical energy, strongly depends on the rate of application of force or the pulling speed. As a result, refolding is not spontaneous, when force is decreased after fully extending the polypeptide chain. Most importantly, we show that the distribution of unfolding free energy barriers in the absence of force can be obtained using the dynamics of force-induced unfolding. This key result immediately suggests that dynamic single molecule force spectroscopy can be used to directly measure the folding free energy landscape of proteins.