Heme and Protein Radical-Mediated Remote Enzyme Catalysis

描述（由申请人提供）：血红素和蛋白质自由基介导的远程酶催化项目描述了解酶如何特异性氧化比酶本身大得多的蛋白质底物，将阐明蛋白质通过酶介导的翻译后修饰成熟的机制。鉴于蛋白质翻译后修饰、代谢化学和疾病之间的相互联系，酶如何保持对大蛋白底物的特异性的问题是酶学的基础。我们正在研究的远程远程酶催化机制所需的生物合成的蛋白质衍生的色氨酸甲萘醌（TTQ）辅因子。TTQ是甲胺脱氢酶的催化中心。该提案旨在确定两个反应中间体的化学性质，一个前所未有的双-FeIV状态的二血红素酶MauG和一个新的基于双自由基的底物蛋白preMADH。两者都是在TTQ生物合成的催化循环中顺序发生的关键催化中间体。这些关键中间体的表征将导致理解TTQ的生物合成机制，这反过来又将提供洞察远程酶介导的远程氧化和氧合化学修饰策略。这些研究将开始检查两个血红素之间的电子相互作用的性质和化学反应性，稳定性和光谱特征的高价双FeIV状态的MauG。然后，我们将跟进与光谱，结构和理论表征的底物蛋白质中的基于双自由基的中间体，以阐明的耦合性质的双自由基物种和必要的交联和随后的氧化反应的质子释放机制。

DESCRIPTION (provided by applicant): Heme and Protein Radical-Mediated Remote Enzyme Catalysis Project Description Understanding how an enzyme specifically oxidizes a protein substrate that is much larger than the enzyme itself will illuminate the mechanism by which proteins mature through enzyme-mediated posttranslational modifications. Given the interconnectedness of protein posttranslational modification, metabolic chemistry, and diseases, the question of how enzymes preserve specificity for large protein substrates is fundamental to enzymology. We are studying the long-range remote enzyme catalysis mechanism required for the biogenesis of a protein-derived tryptophan tryptophylquinone (TTQ) cofactor. TTQ is the catalytic center of methylamine dehydrogenase. This proposal seeks to determine the chemical properties of two reactive intermediates, an unprecedented bis-FeIV state of a di-heme enzyme MauG and a novel tryptophan-based di-radical in the substrate protein preMADH. Both are critical catalytic intermediates that occur sequentially in the catalytic cycle of TTQ biogenesis. Characterization of these key intermediates will lead to comprehension of the TTQ biogenesis mechanism, which in turn will provide insight into long-range enzyme-mediated remote oxidative and oxygenation chemical modification strategies. These studies will begin with examining the nature of the electronic interactions between the two hemes and the chemical reactivity, stability, and spectroscopic signature of the high-valent bis-FeIV state of MauG. Then, we will follow up with spectroscopic, structural, and theoretical characterizations of the tryptophan-based di-radical intermediate in the substrate protein to elucidate the coupling nature of the di-radical species and the proton release mechanism necessary for cross-linking and subsequent oxidation reactions.