ROS, such as superoxide and hydrogen peroxide, are produced as natural byproducts of cellular metabolism and when cells are exposed to external stressors like radiation and toxins. While ROS play a role in cellular signaling and immunity, excessive levels can cause oxidative stress and damage proteins, lipids, and DNA, leading to cell death and various diseases.
One of the primary defense mechanisms against oxidative damage involves antioxidant enzymes such as superoxide dismutases (SODs). In particular, manganese superoxide dismutase (MnSOD), located in the mitochondrial matrix, is a critical enzyme that catalyzes the conversion of the superoxide radical into hydrogen peroxide and oxygen.
Despite the importance of MnSOD in protecting cells from oxidative damage, the detailed molecular mechanism by which it carries out this function remained unclear. To uncover these secrets, an international team of scientists led by researchers from the RIKEN Center for Sustainable Resource Science (CSRS) and the Institute of Molecular Biology and Genetics (IMBG) set out to determine the structure of human MnSOD.
Using state-of-the-art cryo-electron microscopy techniques, the researchers successfully visualized the structure of human MnSOD at a resolution of 2.8 Å. This high-resolution structure revealed the precise arrangement of the protein's atoms and provided a detailed understanding of its molecular architecture.
The researchers found that human MnSOD forms a homotetrameric structure, with four identical subunits arranged in a tetrahedral shape. This organization creates an active site at the interface of each pair of subunits, where the superoxide conversion reaction takes place.
Furthermore, the structure revealed a flexible loop region near the active site that undergoes conformational changes upon substrate binding. This conformational change allows the protein to efficiently capture superoxide molecules and catalyze their conversion, enhancing its protective function against oxidative stress.
The findings from this study provide important insights into the molecular mechanism of MnSOD in safeguarding cells against oxidative damage. Understanding these structural and mechanistic details could pave the way for the development of novel therapeutic strategies to enhance cellular resistance to oxidative stress and combat oxidative stress-related diseases.
The study, titled "Cryo-EM structure of human manganese superoxide dismutase reveals the molecular mechanism of superoxide conversion," was published in the journal Nature Communications.
