The structure of Acidithiobacillus ferrooxidans c4-cytochrome:: A model for complex-induced electron transfer tuning

The study of electron transfer between the copper protein rusticyanin (RCy) and the c(4)-cytochrome CYC41 of the acidophilic bacterium Acidithiobacillus ferrooxidans has evidenced a remarkable decrease of RCy's redox potential upon complex formation. The structure of the CYC41 obtained at 2.2 Angstrom resolution highlighted a specific glutamate residue (E121) involved in zinc binding as potentially playing a central role in this effect, required for the electron transfer to occur. EPR and stopped-flow experiments confirmed the strong inhibitory effect of divalent cations on CYC41:RCy complex formation. A docking analysis of the CYC41 and RCy structure allows us to propose a detailed model for the complex-induced tuning of electron transfer in agreement with our experimental data, which could be representative of other copper proteins involved in electron transfer.