Protection and reactivation of human methylmalonyl-CoA mutase by MMAA protein

► Methylmalonyl-CoA mutase (MCM) undergoes oxidative inactivation during catalysis. ► mut and MMAA gene mutations generate a rare disorder called methylmalonic acidemia. ► Bacterial reactivases restore the activity of inactivated AdoCbl-dependent enzymes. ► We demonstrate that the function of MMAA protein is to protect/reactivate inactive MCM.