Departmento de Bioquimica, Facultad de Medicina, Center for Free Radical and Biomedical Research, Universidad de la República, Montevideo, Uruguay.
Metallomics. 2018 May 23;10(5):679-695. doi: 10.1039/c7mt00348j.
Human MnSOD is a homotetramer and represents an essential mitochondrial antioxidant enzyme, which catalyzes the dismutation of superoxide radicals (O2˙-) at near diffusion-controlled rates. Under a variety of disease conditions and in the process of aging, nitric oxide (˙NO) can outcompete MnSOD and react with O2˙- to yield the potent oxidant peroxynitrite (ONOO-). Then, peroxynitrite can promote the regio-specific nitration of MnSOD at active site tyrosine 34, which turns the enzyme inactive. In this review we assess the kinetic aspects of the formation of peroxynitrite in the presence of MnSOD and the biochemical mechanisms of peroxynitrite-mediated MnSOD nitration. In particular, the central role of the Mn atom in the reaction of the enzyme with peroxynitrite (k = 1.0 × 105 M-1 s-1 per tetramer at pH = 7.4 and T = 37 °C) and the catalysis of nitration at the active site are disclosed. Then, we analyze at the atomic level of detail how a single oxidative post-translational modification in the enzyme, namely the nitration of tyrosine 34, results in enzyme inactivation. Herein, kinetic, molecular, structural biology and computational studies are integrated to rationalize the specificity and impact of peroxynitrite-dependent MnSOD tyrosine nitration in vitro and in vivo from both functional and structural perspectives.
人 MnSOD 是一个四聚体，代表着一种重要的线粒体抗氧化酶，它能以接近扩散控制的速率催化超氧自由基 (O2˙-)的歧化反应。在各种疾病条件下和衰老过程中，一氧化氮 (˙NO) 可以与 MnSOD 竞争并与 O2˙-反应生成强氧化剂过氧亚硝酸根 (ONOO-)。然后，过氧亚硝酸根可以促进 MnSOD 活性部位酪氨酸 34 的区域特异性硝化，从而使酶失活。在这篇综述中，我们评估了 MnSOD 存在下过氧亚硝酸根形成的动力学方面以及过氧亚硝酸根介导的 MnSOD 硝化的生化机制。特别是，Mn 原子在酶与过氧亚硝酸根反应中的中心作用（在 pH = 7.4 和 T = 37°C 时，每个四聚体的 k = 1.0×105 M-1 s-1）和活性部位硝化的催化作用被揭示。然后，我们在原子水平上详细分析了单个酶的翻译后氧化修饰，即酪氨酸 34 的硝化，如何导致酶失活。在这里，动力学、分子、结构生物学和计算研究被整合在一起，从功能和结构的角度来合理化体外和体内过氧亚硝酸根依赖性 MnSOD 酪氨酸硝化的特异性和影响。
