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.
Free radicals and reactive oxygen species are double-edged swords. On one hand, they are the primary culprits for non-specific oxidative damage to cell components, leading to oxidative stress, aging, and mitochondrial disease states. On the other hand, many critical metabolic events depend on protein-based free radicals and reactive oxygen species that are produced and consumed in a controlled manner. The proposed research will elucidate how an iron-dependent enzyme generates protein-based radicals in a tightly controlled manner to produce cofactors necessary for sustaining life.
|Davis, Ian; Yang, Yu; Wherritt, Daniel et al. (2018) Reassignment of the human aldehyde dehydrogenase ALDH8A1 (ALDH12) to the kynurenine pathway in tryptophan catabolism. J Biol Chem 293:9594-9603|
|Wang, Yifan; Griffith, Wendell P; Li, Jiasong et al. (2018) Cofactor Biogenesis in Cysteamine Dioxygenase: C-F Bond Cleavage with Genetically Incorporated Unnatural Tyrosine. Angew Chem Int Ed Engl 57:8149-8153|
|Yang, Yu; Liu, Fange; Liu, Aimin (2018) Adapting to oxygen: 3-Hydroxyanthrinilate 3,4-dioxygenase employs loop dynamics to accommodate two substrates with disparate polarities. J Biol Chem 293:10415-10424|
|Davis, Ian; Koto, Teruaki; Liu, Aimin (2018) Radical Trapping Study of the Relaxation of bis-Fe(IV) MauG. React Oxyg Species (Apex) 5:46-55|
|Davis, Ian; Koto, Teruaki; Terrell, James R et al. (2018) High-Frequency/High-Field Electron Paramagnetic Resonance and Theoretical Studies of Tryptophan-Based Radicals. J Phys Chem A 122:3170-3176|
|Krishnan, V Mahesh; Davis, Ian; Baker, Tessa M et al. (2018) Backbone Dehydrogenation in Pyrrole-Based Pincer Ligands. Inorg Chem 57:9544-9553|
|Li, Jiasong; Griffith, Wendell P; Davis, Ian et al. (2018) Cleavage of a carbon-fluorine bond by an engineered cysteine dioxygenase. Nat Chem Biol 14:853-860|
|Shin, Inchul; Ambler, Brett R; Wherritt, Daniel et al. (2018) Stepwise O-Atom Transfer in Heme-Based Tryptophan Dioxygenase: Role of Substrate Ammonium in Epoxide Ring Opening. J Am Chem Soc 140:4372-4379|
|Dornevil, Kednerlin; Davis, Ian; Fielding, Andrew J et al. (2017) Cross-linking of dicyclotyrosine by the cytochrome P450 enzyme CYP121 from Mycobacterium tuberculosis proceeds through a catalytic shunt pathway. J Biol Chem 292:13645-13657|
|Ferreira, Patrick; Shin, Inchul; Sosova, Iveta et al. (2017) Hypertryptophanemia due to tryptophan 2,3-dioxygenase deficiency. Mol Genet Metab 120:317-324|
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