Involved in oxidative stress response. Confers protection against diverse stresses by binding both CSD1 and GPX2 and mediating the cytosolic activation of the Cu-Zn-dependent superoxide dismutase activity of CSD1. Homodimer (Probable). Interacts with CSD1 and GPX2. By high light, copper, hydrogen peroxide, methyl viologen and cis-jasmone, but not methyl jasmonate. No visible phenotype under normal growth conditions, but mutant plants have increased susceptibility to oxidative stress-induced cell death and accelerated cell death in aging plants. Belongs to the peptidase C56 family.