The role of propionate heme side-chains in cytochrome c: molecular statistics and ab initio molecular dynamics

Protoporphyrin IX derivatives in biological systems have propionate side-chains. The negative charge of propionate groups interact with the iron center, with heme ligands and with protein side-chains close to the heme. By using semi-empirical and ab initio models, we show that the detailed balance of these interactions determines a switch fro the structural plasticity modulation caused by the change in oxidation state of Fe in cytochrome c. The oxidation of Fe in cytochrome c determines a cascade of events that increase the protein mobility and decrease the hydrophobic nature of the protein. This observation explains recent results obtained for cytochrome c in different environments.