The Biological and Chemical Function of Selenium in Enzymes

硒在酶中的生物和化学功能

基本信息

批准号：
8322774
负责人：
NICHOLAS H HEINTZ
金额：
$ 31.7万
依托单位：
UNIVERSITY OF VERMONT & ST AGRIC COLLEGE
依托单位国家：
美国
项目类别：
财政年份：
2010
资助国家：
美国
起止时间：
2010-09-01 至 2014-08-31
项目状态：
已结题

来源：
https://reporter.nih.gov/project-details/8322774
关键词：
Accounting Acidity Acids Active Sites Address Alzheimer&apos s Disease Amino Acids Antineoplastic Agents Apoptosis Apoptotic Back Biochemical Biochemical Reaction Biological Biological Process C-terminal C10 Cell Culture Techniques Cell Cycle Arrest Cell Proliferation Cell physiology Cells Chemicals Complex Cysteine Dissection Disulfides Dose Electron Transport Enzymes Epithelial Epithelial Cells Genetic Code Genome Goals Human Hydrogen Peroxide In Vitro Literature Lung Malignant Neoplasms Measures Mediating Methionine Methods Modeling Molecular Mus N-terminal Names Nature Neurodegenerative Disorders Nutritional Requirements Organism Oxidation-Reduction Oxidative Stress Oxygen Parents Parkinson Disease Pathogenesis Pathway interactions Play Process Property Proteins Reaction Reactive Oxygen Species Recovery Recycling Reduced Glutathione Relative (related person)Resistance Role Selenium Selenocysteine Sense Codon Speed Substrate Specificity Sulfhydryl Compounds Sulfinic Acids Sulfur System Terminator Codon Testing Thioredoxin Trace Elements Western Blotting antioxidant therapy base cancer cell chemical function chemical property cysteine sulfinic acid design dithiol enzyme mechanism human TXN protein in vivo methionine sulfoxide methionine sulfoxide reductase mutant oxidation pressure prevent public health relevance research study response selenoenzyme selenol therapeutic target thioredoxin reductase

项目摘要

DESCRIPTION (provided by applicant): Selenoenzymes use the rare amino acid selenocysteine, the so-called "21st" amino acid in the genetic code. Insertion of selenocysteine (Sec) into a protein is much more complicated than the other 20 amino acids because a UGA stop codon must be recoded as a sense codon for Sec and this process requires complex cellular machinery. Any explanation that accounts for the use of Sec in an enzyme must explain why it is needed relative to the use of the more commonly used cysteine (Cys) residue in order to justify maintaining the energetically costly Sec-insertion machinery. The most frequently given reasons for the use of Sec is that it is a type of "super-Cys" residue that can "speed reactions" due to selenium's superior chemical reactivity relative to sulfur. If this were true, then we might expect to find the use of Sec widely spread throughout nature instead of its observed rarity. We are pursuing a new hypothesis that explains the biological pressure to maintain the UGA recoding apparatus for Sec. This biological pressure is based upon the superior chemical property of selenium (relative to sulfur) to confer resistance to oxidation and we thus name it the "chemico-biological" rationale for the presence of Sec in enzymes. Sec can resist oxidation in two ways that Cys cannot. First when Sec is oxidized to seleninic acid (Sec-SeO2-) it can be converted back to the parent form (Sec-SeH) with relative ease compared to the extreme difficulty that the oxidized form of Cys (Cys-SO2-) can be converted to its parent form (Cys-SH). Second, it is much more difficult for Sec-SeO2- to be further oxidized to Sec-SeO3-, while Cys-SO2- can be oxidized to Cys-SO3- relatively easily. We believe both of these facts are unrecognized in the biochemical literature and our experiments will address the hypothesis that Sec only occurs in an enzyme when the enzyme needs to be very resistant to inactivation by oxidation. In other words Sec will substitute for Cys in an enzyme when this Cys-enzyme would otherwise be inactivated due to oxidation of its active-site Cys residue to sulfinic acid (Cys-SO2-). This major hypothesis will be addressed in this study by showing how the selenoenzymes thioredoxin reductase and methionine sulfoxide reductase resist oxidation using both in vitro and in vivo experiments. In the case of thioredoxin reductase we will show how the modular design of the enzyme is such that it carries within itself its own internal rescue system for reducing the Sec- SeO2- residue back to Sec-SeH. Thioredoxin reductase is a major therapeutic target for anti-cancer drugs due to its role in enhancing cell proliferation and regulating cellular apoptotic pathways. Oxidation of methionine to methionine sulfoxide is suspected to play a major role in neurodegenerative disorders such as Parkinson's and Alzheimer's diseases, and understanding how methionine sulfoxide reductase may become inactivated due to oxidation is critical to understanding how antioxidant therapies can best be used to prevent inactivation of the enzyme. The successful completion of the goals of this proposal will provide a universal chemical basis for the nutritional requirement of selenium in humans and other organisms. PUBLIC HEALTH RELEVANCE: Selenium is an essential trace element because it is required for incorporation into a specialized set of enzymes - selenoenzymes that use the rare amino acid selenocysteine. The primary selenoenzyme in this study, thioredoxin reductase is a major cancer target due to its role in preventing apoptosis (which cancer cells must avoid) and promoting cell proliferation. Cancer cells must divide rapidly to cause pathogenesis and require increased expression of thioredoxin reductase to survive.

描述（由申请人提供）：硒酶使用稀有氨基酸硒代半胱氨酸，即遗传密码中所谓的“第 21 个”氨基酸。将硒代半胱氨酸 (Sec) 插入蛋白质比其他 20 个氨基酸复杂得多，因为必须将 UGA 终止密码子重新编码为 Sec 的有义密码子，并且此过程需要复杂的细胞机制。任何关于在酶中使用 Sec 的解释都必须解释为什么相对于更常用的半胱氨酸 (Cys) 残基的使用需要它，以便证明维护能量昂贵的 Sec 插入机制是合理的。使用 Sec 最常见的原因是，它是一种“超级半胱氨酸”残留物，由于硒相对于硫具有优异的化学反应性，因此可以“加速反应”。如果这是真的，那么我们可能会发现 Sec 的使用在自然界中广泛传播，而不是观察到的稀有性。我们正在寻求一个新的假设，该假设可以解释维持 Sec 的 UGA 记录装置的生物压力。这种生物压力基于硒（相对于硫）优异的化学性质，具有抗氧化性，因此我们将其命名为酶中存在 Sec 的“化学生物学”原理。 Sec 可以通过两种方式抵抗氧化，而 Cys 则不能。首先，当 Sec 被氧化为硒酸 (Sec-SeO2-) 时，与半胱氨酸 (Cys-SO2-) 的氧化形式 (Cys-SO2-) 极其困难相比，它可以相对容易地转化回母体形式 (Sec-SeH)。转化为其母体形式 (Cys-SH)。其次，Sec-SeO2- 更难进一步氧化为 Sec-SeO3-，而 Cys-SO2- 则相对容易氧化为 Cys-SO3-。我们相信这两个事实在生化文献中都未被认识到，我们的实验将解决这样的假设：当酶需要非常抵抗氧化失活时，Sec 仅出现在酶中。换句话说，当这种半胱氨酸酶由于其活性位点半胱氨酸残基氧化成亚磺酸（Cys-SO2-）而失活时，Sec 将取代酶中的半胱氨酸。本研究将通过体外和体内实验展示硒酶硫氧还蛋白还原酶和甲硫氨酸亚砜还原酶如何抵抗氧化来解决这一主要假设。就硫氧还蛋白还原酶而言，我们将展示该酶的模块化设计如何使其自身携带其自身的内部救援系统，以将 Sec-SeO2- 残基还原回 Sec-SeH。硫氧还蛋白还原酶由于其在增强细胞增殖和调节细胞凋亡途径中的作用而成为抗癌药物的主要治疗靶点。甲硫氨酸氧化成甲硫氨酸亚砜被怀疑在帕金森病和阿尔茨海默病等神经退行性疾病中起重要作用，了解甲硫氨酸亚砜还原酶如何因氧化而失活对于了解如何最好地使用抗氧化疗法来防止甲硫氨酸亚砜失活至关重要酶。该提案目标的成功完成将为人类和其他生物体对硒的营养需求提供通用的化学基础。公共健康相关性：硒是一种必需的微量元素，因为它是融入一组专门的酶（使用稀有氨基酸硒代半胱氨酸的硒酶）中所必需的。作为本研究中的主要硒酶，硫氧还蛋白还原酶是主要的癌症靶标，因为它在防止细胞凋亡（癌细胞必须避免细胞凋亡）和促进细胞增殖方面发挥作用。癌细胞必须快速分裂才能引起发病，并且需要增加硫氧还蛋白还原酶的表达才能生存。