Biological Relevance of Charge Transfer Branching Pathways in Photolyases

In PhrA, a class III CPD photolyase, two branching tryptophan charge transfer pathways have been characterized in the mechanism of FAD photoreduction. To provide a molecular explanation of the charge transfer abilities of both pathways, we performed simulations where the protein motion and the positive charge are simultaneously propagated. Our computational approach reveals that one pathway drives a very fast charge transfer whereas the other pathway provides a very good thermodynamic stabilization of the positive charge. During the simulations, the positive charge firstly moves on the fast triad, allowing the stabilization of reduced FAD. After one nanosecond, we observe a nearly equal probability to find the charge at ending tryptophan of either pathway. Our results highlight the role of the protein environment, which manages the association of a kinetic and a thermodynamic pathways to trigger a fast and efficient FAD photoreduction.