Deciphering the Enzymatic Mechanism of Superoxide Dismutase

摘要 超氧化物歧化酶(SOD)是氧化应激的主要调节者， 因此，保护生物体免受新陈代谢的第一道防线--以及 环境诱导的活性氧物种(ROS)。人线粒体 锰超氧化物歧化酶(MnSOD)的表达被调节以防止基于ROS的损伤， 促进氧化还原动态平衡，并维持适当的细胞信号。我们的研究目标是 了解MnSOD如何利用质子-电子耦合转移的分子基础 使超氧化物歧化。为此，最需要的是所有原子的3D排列 重要的是质子的位置。我们在中子方面的最新技术进展 橡树岭国家实验室的结晶学已经克服了X- 射线结晶学-以高细节揭示质子位置，同时还允许 金属电子态的控制。在这个研究项目中，MnSOD中子图将 揭示了质子对活性中心金属的传递和金属的质子化状态。 结合的配体。这项研究的科学假设是，MnSOD转移质子 从一小群水分子通过部分溶剂暴露的氨基酸到 超氧化物歧化为氢的近全埋锰 过氧化氢和分子氧通过循环金属氧化还原反应。具体目标是 用质子研究表征MnSOD型电子耦合质子继电器 环境(1)还原和氧化活性锰的休止状态 (2)产物抑制了锰-过氧物络合物；(3)超氧化物结合 酵素。将对晶体进行光谱分析，以帮助设计/理解 中子源的晶体实验和计算化学研究 全原子结构将有助于将结果联系在一起，并测试我们对 酶活性。由此产生的协议、方法和结构将是特定的 对结构生物学、抗氧化剂和金属酶学领域的人感兴趣 也是生物学家普遍感兴趣的。

Abstract Superoxide dismutases (SODs) are the major regulators of oxidative stress and therefore the first line of defense to protect organisms against metabolic- and environmentally-induced reactive oxygen species (ROS). Human mitochondrial manganese SOD (MnSOD) expression is modulated to prevent ROS-based damage, promote redox homeostasis, and maintain proper cell signaling. Our research goal is to understand the molecular basis of how MnSOD uses coupled proton-electron transfers to dismute superoxide. For this, the 3D arrangement of all atoms is needed, most importantly the position of protons. Our recent technical advancements with neutron crystallography at Oak Ridge National Laboratory have overcome the limitations of X- ray crystallography – revealing proton positions with high detail while also allowing control of the metal electronic state. In this research project, MnSOD neutron maps will reveal the proton relays to the active site metal and the protonation states of metal- bound ligands. The scientific hypothesis for this study is that MnSOD transfers protons from a small group of water molecules via partially solvent-exposed amino acids to the nearly completely buried manganese for the dismutation of superoxide to hydrogen peroxide and molecular oxygen via cyclic metal redox reactions. The specific aims are to characterize the electron-coupled proton relays of MnSOD by investigating the proton environment of (1) the resting states of the reduced and oxidized manganese active sites, (2) the product inhibited Mn-peroxo complex, and (3) the superoxide bound enzyme. Spectroscopy on crystals will be performed to help design/understand crystallographic experiments, and computational chemistry studies on neutron derived all-atom structures will help tie the results together and test our interpretations about the enzymatic activity. The resulting protocols, methods, and structures will be of specific interest to those in the fields of structural biology, antioxidants, and metallo-enzymology and of interest to biologists in general.