Relevance of the Speed and Direction of Pulling in Simple Modular Proteins.

A theoretical framework capable of predicting the first unit that unfolds in pulled modular proteins has been recently introduced, for "fast enough" pulling velocities. Within this picture, we investigate the unfolding pathway in a chain of identical units and predict that the module closest to the pulled end opens first. Steered molecular dynamics of a simple construct, specifically a chain composed of two coiled-coil motives, shows that this is indeed the case. Notwithstanding, the unfolding behavior strongly depends on the terminus (C or N) from which this homopolyprotein is pulled. Therefore, anisotropic features are revealed and seem to play an important role for the observed unfolding pathway.