Departamento de Química Inorgánica, Analítica y Química-Física and INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pab. 2, C1428EHA Buenos Aires, Argentina.
Arch Biochem Biophys. 2011 Mar 15;507(2):304-9. doi: 10.1016/j.abb.2010.12.011. Epub 2010 Dec 15.
Manganese Superoxide Dismutase (MnSOD) is an essential mitochondrial antioxidant enzyme that protects organisms against oxidative damage, dismutating 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 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 inactivation, and that this protein oxidative modification is found in tissues undergoing inflammatory and degenerative processes. However, the molecular basis about MnSOD tyrosine nitration affects the protein catalytic function is mostly unknown. In this work we strongly suggest, using computer simulation tools, that Y34 nitration affects protein function by restricting ligand access to the active site. In particular, deprotonation of 3-nitrotyrosine increases 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 a key role in assisting superoxide migration.
锰超氧化物歧化酶（MnSOD）是一种重要的线粒体抗氧化酶，可保护生物免受氧化损伤，将超氧自由基（O₂(.)⁻）歧化为 H₂O₂ 和 O₂。该蛋白的活性部位呈现出一种扭曲的三角双锥环境中的 Mn 离子，由 H26、H74、H163、D159 和一个 ⁻OH 离子或 H₂O 分子配位。该酶的催化循环是一种“乒乓”机制，涉及 Mn³⁺/Mn²⁺。已知 Y34 的硝化作用导致酶失活，并且这种蛋白质氧化修饰存在于经历炎症和退行性过程的组织中。然而，MnSOD 酪氨酸硝化影响蛋白质催化功能的分子基础在很大程度上尚不清楚。在这项工作中，我们强烈建议使用计算机模拟工具，Y34 的硝化作用通过限制配体进入活性部位来影响蛋白质功能。特别是，由于缺少质子，3-硝基酪氨酸的去质子化会极大地增加配体进入的能量障碍。我们对 WT 和选定的突变蛋白的研究结果证实，Y34 的酚部分在协助超氧迁移方面起着关键作用。
