Fine tuning of the redox function of Pseudomonas aeruginosa cytochrome c551 through structural properties of a polypeptide loop bearing an axial Met residue

► The redox function of P. aeruginosa cytochrome c. is finely tuned by the Ser52 residue. ► The structure of the loop near the heme is slightly altered by the S52G mutation. ► The structural change of the loop increases the polarity of the heme environment. ► As a result, the redox function of the protein is affected by the mutation. ► Thus, the protein function can be tuned through the structure of the loop.