The Biological and Chemical Function of Selenium in Enzymes

硒在酶中的生物和化学功能

• 批准号: 7943593
• 负责人: NICHOLAS H HEINTZ
• 金额: $ 31.85万
• 依托单位: UNIVERSITY OF VERMONT & ST AGRIC COLLEGE
• 依托单位国家: 美国
• 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/7943593
• 关键词: Accounting; Acidity; Acids; Active Sites; Address; Alzheimer' 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; Proteome; 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

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.

说明(申请人提供)：硒酶使用稀有的氨基酸--硒半胱氨酸，即遗传密码中所谓的“第21”氨基酸。在蛋白质中插入硒半胱氨酸(Sec)比其他20个氨基酸复杂得多，因为UGA终止密码子必须被重新编码为SEC的正义密码子，这一过程需要复杂的细胞机制。任何解释在酶中使用SEC的解释都必须解释为什么相对于使用更常用的半胱氨酸(Cys)残基，为什么需要它，以证明维护耗费巨大的SEC插入机械是合理的。使用SEC的最常见的理由是，由于相对于硫，硒具有更好的化学反应活性，因此它是一种“超半胱氨酸”残基，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存在，而不是它被观察到的稀有性。我们正在寻求一个新的假说来解释维持SEC的UGA记录设备的生物压力。这种生物压力是基于硒(相对于硫)具有优越的抗氧化性的化学性质，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，与将氧化形式的Cys(Cys-SO2-)转化为其母形式(Cys-SH)相比，可以相对容易地将其转化回母体形式(Sec-SeH)。其次，Sec-SeO2-更难被进一步氧化成Sec-SeO3-，而Cys-SO2-相对容易被氧化成Cys-SO3-。我们相信这两个事实在生化文献中都没有得到承认，我们的实验将解决这样的假设，即SEC仅在酶需要非常抵抗氧化失活的情况下才会出现。换句话说，当半胱氨酸酶因其活性部位半胱氨酸残基氧化成亚磺酸(Cys-SO2-)而失活时，SEC将取代该酶中的半胱氨酸。这一主要假说将在这项研究中通过体外和体内实验显示硒酶硫氧还蛋白还原酶和蛋氨酸亚砜还原酶如何抵抗氧化。在硫氧还蛋白还原酶的情况下，我们将展示酶的模块化设计如何使其内部携带自己的内部救援系统，以将SEC-SeO2-残基还原为SEC-Seh。硫氧还蛋白还原酶具有促进细胞增殖和调节细胞凋亡途径的作用，是抗癌药物的主要治疗靶点。蛋氨酸氧化成蛋氨酸亚砜被怀疑在帕金森氏症和阿尔茨海默病等神经退行性疾病中起主要作用，了解蛋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剂疗法来防止酶失活至关重要。这项提议的目标的成功完成将为人类和其他生物对硒的营养需求提供普遍的化学基础。 与公共健康相关：硒是一种必需的微量元素，因为它是加入一组专门的酶--使用稀有氨基酸硒半胱氨酸的硒酶--中所必需的。硫氧还蛋白还原酶是本研究中的主要硒酶，由于其在防止细胞凋亡(癌细胞必须避免)和促进细胞增殖方面的作用，它是一个主要的癌症靶点。癌细胞必须迅速分裂才能导致发病，并需要增加硫氧还蛋白还原酶的表达才能存活。