Theoretical analysis of photoinduced electron transfer in FMN binding protein : Effect of changes in one charge on electron transfer rate

Abstract

Photoinduced electron transfer (PET) is an important process due to its several applications, e.g. solar energy conversion. Flavoproteins are generally selected as a model for the study of PET. In this research, effect of charge at residue 13 on the PET from Trp32, Tyr35 and Try106 to an excited isoalloxazine (Iso*) in FMN binding protein (FBP) from Desulfovibrio vulgaris (Miyazaki F) was studied. A wild type (E13 with negative charge) and four mutations of FBP at residue 13, E13K and E13R (politive charge), E13T and E13Q (neutral charge), were subjected to molecular dynamics (MD) simulations, Snap shots obtained from the MD simulations were used to evaluate the PET rate using the Kakitani and Mataga theory. The PET rates were found to largely depend on the electrostatic energies between photo-products and other ionic groups but not on other physical quantities related to the PET rate such as solvent reorganization energies. A plot of the PET rates vs. total free energy gaps displayed a parabolic function. Similarly, the plot of the PET rates vs. the net electrostatic energies between photo-products and other ionic groups also displayed a parabolic function. This reveals that the net electrostatic energies are most influential upon the ET rate, in addition to the donor-acceptor distance.