Protein electron transfer rates set by the bridging secondary and tertiary structure.

The rate of long-distance electron transfer in proteins rapidly decreases with distance, which is indicative of an electron tunneling process. Calculations predict that the distance dependence of electron transfer in native proteins is controlled by the protein's structural motif. The helix and sheet content of a protein and the tertiary arrangement of these secondary structural units define the distance dependence of electronic coupling in that protein. The calculations use a tunneling pathway model applied previously with success to ruthenated proteins. The analysis ranks the average distance decay constant for electronic coupling in electron transfer proteins and identifies the amino acids that are coupled to the charge localization site more strongly or weakly than average for their distance.