Unfolding proteins in an external field: Can we always observe the intermediate states?

A protein molecule under the stress of an external denaturing force acting on a terminal end or on the entire molecule is expected to unfold, possibly through a few intermediate stages depending on the magnitude of the denaturing force. We have investigated two protein minimal models under various types of denaturing force fields using the collision molecular-dynamics simulation, in order to critically examine the relationship between the folding pathways observed in different protein denaturing experiments.