NMR Study on the Mechanism of Cytochrome c Methionine Oxidation

Mitochondria generate reactive oxygen species (ROS) during respiration. Low levels of ROS are conducive to signal transduction, whereas excessive accumulation of ROS can lead to protein oxidative modification. Cytochrome c (cyt c) is a multifunctional metalloprotein located in mitochondria. The oxidative modification of cyt c, especially the Met80 has been found to result in conformational change, but the mechanism is still unclear. In this study, the terminal methyl group of methionine on cytochrome c was selectively labeled with 13C, and the modification of the methionine in cytochrome c under oxidative environments was tracked by NMR. It was observed that under oxidative environments, the protein was first converted from reduced state to oxidized state, then oxidatively modified. The oxidative modification of Met80 occurred under relatively high content of ROS, but did not result in distinctive conformation transition. The result suggests that the protein has high activity to resist ROS damage, therefore, plays a regulatory role in inhibiting apoptosis.