Steered Molecular Dynamics Simulations of the Electron Transfer Complex between Azurin and Cytochrome c551

The unbinding properties of the transient complex between the electron transfer proteins azurin and cytochrome c(551) have been investigated by steered molecular dynamics simulations by pulling four different atoms of cytochrome c(551). The atoms to be pulled have been chosen to closely match the conditions of a previous experimental study by atomic force spectroscopy. The temporal evolution of the distance between different Couples Of atoms of the intermolecular hydrogen bonds and of the unbinding force have been analyzed for the various setups and by applying seven different pulling speed values. The observed variability in the response of the system has been traced back to the occurrence of different pathways during the unbinding process. Furthermore, an analysis of the unbinding force as a function of the pulling speed analyzed in the framework of the thermally activated model has allowed the extraction of the dissociation rate constant at equilibrium. These results have been discussed in connection with the transient character of the system and with the available experimental data by atomic force spectroscopy.