Mutation Effect Investigation on Cytochrome C552 Protein Instability and Electron Transfer Improvement in the Acidithiobacillus Ferrooxidans Bacteria Respiratory Chain

Abstract

Cytochrome c552 (Cyc1) is a protein in the electron transport chain of the Acidithiobacillus ferrooxidans (Af) bacteria which obtain their energy from oxidation Fe2+ to Fe+3. The electrons are directed through Cyc2, RCY (rusticyanin), Cytochrome c552, and Cox aa3 proteins to O2. Cytochrome c552 protein consists of two chains, A and B. In the present study, a new mutation (E121D) in the A chain of cytochrome c552 protein was selected due to electron receiving from Histidine 143 of RCY. Then, the changes performed in the E121D mutant were evaluated by MD simulations analyzes. Cytochrome c552 and RCY proteins were docked by a Patchdock server. By E121D mutation, the connection between the two chains in Cytochrome c552 was enhanced by an additional hydrogen bond between Zn1388 and aspartate 121. Asp 121 in chain A gets farther from Zn 1388 in chain B. Therefore, the aspartate gets closer to Cu 1156 of the RCY leading to the higher stability of the RCY/Cytochrome c552 complex. Further, an acidic residue (Glu121) becomes a more acidic residue (Asp121) and improving the electron transfer to Cytochrome c552 protein. The results of RMSF analysis showed further ligand flexibility in mutation. This leads to fluctuation of the active site and increases redox potential at the mutation point and the speed of electron transfer. This study also predicts that in all respiratory chain proteins, electrons probably enter the first active site via glutamate and exit through the second active site of each respiratory chain protein and through histidine.