Heme and Protein Radical-Mediated Remote Enzyme Catalysis

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是酶学的基础问题。我们正在研究蛋白质衍生色氨酸色氨酸醌（TTQ）辅助因子生物生成所需的远程远程酶催化机制。TTQ是甲胺脱氢酶的催化中心。本研究旨在确定两种活性中间体的化学性质，一种是二血红素酶mag前所未有的双feiv状态，另一种是底物蛋白preMADH中基于色氨酸的新型二自由基。两者都是TTQ生物发生催化循环中依次发生的关键催化中间体。这些关键中间体的表征将有助于理解TTQ的生物发生机制，从而为远程酶介导的远程氧化和氧合化学修饰策略提供见解。这些研究将从检查两种血红素之间电子相互作用的性质以及MauG的高价双feiv态的化学反应性、稳定性和光谱特征开始。然后，我们将对底物蛋白中基于色氨酸的双自由基中间体进行光谱、结构和理论表征，以阐明双自由基的偶联性质以及交联和随后的氧化反应所需的质子释放机制。

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.