Mimicking Tyrosine Phosphorylation in Human Cytochrome c by the Evolved tRNA Synthetase Technique

Phosphorylation of tyrosine 48 of cytochrome c is related to a wide range of human diseases due to the pleiotropic role of the heme‐protein in cell life and death. However, the structural conformation and physicochemical properties of phosphorylated cytochrome c are difficult to study as its yield from cell extracts is very low and its kinase remains unknown. Herein, we report a high‐yielding synthesis of a close mimic of phosphorylated cytochrome c, developed by optimization of the synthesis of the non‐canonical amino acid p‐carboxymethyl‐L ‐phenylalanine (pCMF) and its efficient site‐specific incorporation at position 48. It is noteworthy that the Y48pCMF mutation significantly destabilizes the Fe?Met bond in the ferric form of cytochrome c, thereby lowering the pK_a value for the alkaline transition of the heme‐protein. This finding reveals the differential ability of the phosphomimic protein to drive certain events. This modified cytochrome c might be an important tool to investigate the role of the natural protein following phosphorylation.