Unraveling the molecular basis of human manganese superoxide dismutase inactivation promoted by tyrosine 34 nitration

MORENO D.M.; MARTI, M.A.; DE BIASE, P.; ESTRIN, D.A.; DE MICHELI, V.; RADI, R.; BOECHI, L.

ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS

ELSEVIER SCIENCE INC

Año: 2011 vol. 507 p. 304 - 309

0003-9861

Manganese Superoxide Dismutase (MnSOD) is an essential mitochondrial antioxidant enzyme that pro-tects organisms against oxidative damage, dismutating superoxide radical (OÅÀ ) into H2O2 and O2. The2active site of the protein presents a Mn ion in a distorted trigonal–bipyramidal environment, coordinatedÀby H26, H74, H163, D159 and one OH ion or H2O molecule. The catalytic cycle of the enzyme is a ‘‘ping-pong’’ mechanism involving Mn3+/Mn2+. It is known that nitration of Y34 is responsible for enzyme inac-tivation, and that this protein oxidative modification is found in tissues undergoing inflammatory anddegenerative processes. However, the molecular basis about MnSOD tyrosine nitration affects the proteincatalytic function is mostly unknown.In this work we strongly suggest, using computer simulation tools, that Y34 nitration affects proteinfunction by restricting ligand access to the active site. In particular, deprotonation of 3-nitrotyrosineincreases drastically the energetic barrier for ligand entry due to the absence of the proton.Our results for the WT and selected mutant proteins confirm that the phenolic moiety of Y34 plays akey role in assisting superoxide migration.