Structural basis of mitochondrial dysfunction in response to cytochrome phosphorylation at tyrosine 48.

Regulation of mitochondrial activity allows cells to adapt to changing conditions and to control oxidative stress, and its dysfunction can lead to hypoxia-dependent pathologies such as ischemia and cancer. Although cytochrome phosphorylation-in particular, at tyrosine 48-is a key modulator of mitochondrial signaling, its action and molecular basis remain unknown. Here we mimic phosphorylation of cytochrome by replacing tyrosine 48 with -carboxy-methyl-l-phenylalanine (CMF). The NMR structure of the resulting mutant reveals significant conformational shifts and enhanced dynamics around CMF that could explain changes observed in its functionality: The phosphomimetic mutation impairs cytochrome diffusion between respiratory complexes, enhances hemeprotein peroxidase and reactive oxygen species scavenging activities, and hinders caspase-dependent apoptosis. Our findings provide a framework to further investigate the modulation of mitochondrial activity by phosphorylated cytochrome and to develop novel therapeutic approaches based on its prosurvival effects.