The nitration of Tyr34 in MnSOD is enough to block the entry of superoxide radicals into the active site

DIEGO MORENO; LEONARDO BOECHI; RAFAEL RADI; MARCELO A. MARTI; DAMIAN A. SCHERLIS; DARIO A. ESTRIN

Salta, Argentina

Congreso; 3rd Latin American Protein Society Meeting; 2010

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } --> Manganese Superoxide Dismutase (MnSOD) is an essential mitochondrial antioxidant enzyme that protects organisms against oxidative damage, dismutating free superoxide radical (O2) into H2O2 and O2. The active site of the protein presents a Mn ion in a distorted trigonal-bipyramidal environment, coordinated by different residues. The catalytic cycle of the enzyme is a “ping-pong” mechanism involving MnIII/MnII. Specificaly, the environment of the active-site is characterized by a hydrogen-bonded network between solvent molecules and residues such as Tyr34 and Gln143. It is known that nitration of Tyr34 is responsible for enzyme inactivation, and that this protein oxidative modification is found in tissues undergoing inflammatory and degenerative processes under oxidative stress conditions. However, the explanation about how MnSOD tyrosine nitration affects the protein catalytic function is still unsolved. In this work we performed different simulation techniques to study the accessibility of O2 from the solvent to Mn site. We studied the nitrated protein, together with different protein mutants, in order to achieve a complete understanding of the behavior of the active site in the entry of the ligand. The results show that the nitration of Tyr34 is enough to block the ligand entry, and they reveal that the OH of the Tyr is necessary for effective superoxide migration.