Mechanical unfolding and refolding of proteins: an off-lattice model study.

Using an off-lattice model, we investigate the response of a protein molecule to external stretching and release. In particular we study the passive force in a protein as a function of the extension of the protein. These force-extension curves exhibit hysteresis loops, whose areas increase with the pulling rate and decrease with thermal noise. Most of these results seem to be appropriately described by a cusp catastrophe.