Tuning the Intramolecular Electron Transfer in 2[4Fe-4S] Ferredoxin: A Molecular Dynamics Study

The 2[4Fe-4S] ferredoxins are found as a subunit of Photosystem I and of the respiratory complex I “wire” and as water-soluble proteins in bacteria. They are generally small (6 kDa) pseudosymmetric proteins containing two [4Fe-4S] clusters. The effects of protein and solvent on the intramolecular electron transfer direction and rate are studied. Interestingly, while the charged side chains overwhelmingly favor the reactant state and the rest of the polar groups of the protein only slightly favor the product state, the solvent and counterions overwhelmingly favor the product so that the net driving force slightly favors the product, in agreement with experiment.