Structure/Function of Mn and Fe Superoxide Dismutases

描述（由申请人提供）：超氧化物歧化酶（SOD）是含有Mn、Fe、Cu/Zn或Ni活性位点的金属酶，其保护生物系统免受由超氧阴离子自由基（O2）介导的氧化损伤，O2是有氧代谢的产物。SOD还被证明可以防止炎症，并参与一系列抗癌和抗衰老机制。该提议集中在结构相似的Mn和Fe依赖的SOD上，其通过将O2还原为O2和H2 O2来实现其功能。该提案中概述的研究的长期目标是-确定对Mn和Fe依赖的SOD的反应性的关键几何和电子结构贡献，以及-获得分子-水平洞察这些酶的反应机制。考虑到这些目标，制定了以下具体目标：-生成氧化和还原Mn-和Fe-SOD活性位点的电子结构描述。探索负责SOD金属特异性的因素。评估第二球氨基酸在调节活性位点性质中的作用。定义Mn-和Fe-SOD的基质-金属相互作用的性质，并在实验和理论水平上评估相应催化循环中的关键步骤。（吸收、CD、MCD、EPR和rR）和计算方法（DFT和NBO）研究天然Mn和Fe-SOD蛋白，催化非活性金属取代的Mn和Fe-SOD物种，和几个突变蛋白。这些研究将系统地探索几何和电子因素对SOD活性的贡献。由于SOD酶在涉及超氧化物的疾病状态的动物模型中显示出治疗功效，因此已经提出了用于治疗各种疾病的低分子量SOD酶模拟物（合酶）。与天然SOD酶相比，合酶作为药剂具有明显的优势，例如细胞渗透性、缺乏免疫原性、寿命更长、口服递送的潜力和更低的生产成本。因此，理解Mn-和Fe-SOD酶实现其显着高催化速率的原理，特别是第二配位壳氨基酸对活性位点电子的影响，可以显着帮助SOD模拟物用于药物应用的合理设计。

DESCRIPTION (provided by applicant): Superoxide dismutases (SODs) are metalloenzymes containing Mn, Fe, Cu/Zn, or Ni active sites that defend biological systems against oxidative damage mediated by the superoxide radical anion (O2), a product of aerobic metabolism. SODs have also been shown to protect against inflammation and are involved in a range of anti-cancer and anti-aging mechanisms. This proposal focuses on the structurally similar Mn- and Fe-dependent SODs, which accomplish their function through disproportionation of O2 to 02 and H202.The long-term objectives of the research outlined in this proposal are- to identify key geometric and electronic structure contributions to the reactivities of Mn- and Fe-dependent SODs and- to obtain molecular-level insight into the reaction mechanisms of these enzymes.With these goals in mind, the following specific aims have been formulated:- Generate electronic structure descriptions of the oxidized and reduced Mn- and Fe-SOD active sites.- Explore the factors responsible for SOD metal specificity.- Assess the role of second-sphere amino acids in tuning active site properties.- Define the nature of the substrate-metal interaction for Mn- and Fe-SODs and evaluate key steps in the corresponding catalytic cycles on experimental and theoretical levels.Our approach involves using a combination of spectroscopic tools (absorption, CD, MCD, EPR, and rR) and computational methods (DFT and NBO) to study the native Mn- and Fe-SOD proteins, the catalytically inactive metal-substituted Mn- and Fe-SOD species, and several mutant proteins. These studies will systematically explore geometric and electronic factors contributing to SOD activity.As SOD enzymes demonstrate therapeutic efficacy in animal models of disease states involving superoxide, low molecular weight SOD enzyme mimics (synzymes) have been proposed for the treatment of a variety of diseases. Synzymes could have distinct advantages over natural SOD enzymes as pharmaceutical agents, such as cellular permeability, lack of immunogenicity, longer lifetimes, potential for oral delivery, and lower production costs. Thus, understanding the principles by which the Mn- and Fe-SOD enzymes achieve their remarkably high catalytic rates, in particular the influence of second coordination shell amino acids on active site electronics, could aid significantly in the rational design of SOD mimics for pharmaceutical applications.