Protein unfolding free energy surfaces from Jaryznski's equality

COMP 106

Nathan Salwen, salwen@rice.edu, Ching-Hwa Kiang, chkiang@rice.edu, and Nolan C. Harris, nolanh@rice.edu. Physics, Rice University, 6100 Main St., MS61, Houston, TX 77005
An atomic force microscope is used to investigate the unfolding of individual molecules of titin I27 domain. Using the Jarzinski equality, we reconstruct the free energy of the molecule as a function of its extended distance. We also apply the Jarzinski relation to the calculation of the activation energy for the unfolding of this molecule. The Jarzinski equality allows the calculation of equilibrium free energy differences through multiple non-equilibrium measurements. While the existence of an exact relation between these two different regimes is interesting in itself, there has been some question as to its usefulness. In simulations, the increased speed of each simulation is offset by the increased number of necessary runs. In this single-molecule pulling experiment the stability of the experimental setup does not allow equilibrium measurements. Only because of the Jarzinski relation can the free energy be extracted.