Mechanistic and spectroscopic investigation of sulfur-oxidizing non-heme iron enzymes

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In this award from the Chemistry of Life Processes Program in the Division of Chemistry, Dr. Brad Pierce, from the University of Texas at Arlington, will study the mechanism and regulation of mammalian thiol dioxygenase (TDO) enzymes. Characterization of transient non-heme iron [Fe-O] intermediates has historically attracted considerable interest within the area of bioinorganic chemistry. This intense focus of research efforts can largely be explained by the vast number of functionally (and structurally) diverse non-heme iron enzymes and the incredible versatility exhibited in chemical oxidations they initiate. In contrast to the canonical 2-His-1-carboxylate facial triad motif exhibited by nearly all members of this enzyme class, the active site of mammalian TDO enzymes utilize a neutral, all-His (3-His) facial triad motif. Furthermore, TDO enzymes also have an unusual covalently cross-linked cysteine-tyrosine pair in close proximity to the non-heme iron active site. One objective for this proposal is to identify and spectroscopically characterize transient intermediates produced during TDO-catalyzed thiol-oxidation. An additional area of focus is the role of a rare post-transcriptional cysteine-tyrosine covalent modification within the active site of TDO enzymes. Specifically, steady-state O2-coupling efficiency of TDO enzymes will be determined for comparison to C93 and Y157 mutants. These results will be correlated to specific molecular interactions within the active site as observed by spectroscopy to evaluate the role of outer-sphere interactions on native TDO catalysis. In contrast to oxygenase/oxidase enzymes, synthetic non-heme iron model complexes are unable to gate O2-reactivity through substrate-binding. As a consequence, model systems are poor catalysts for oxidative transformations. Currently, this poorly understood aspect of non-heme iron catalysis represents one of the most significant hurdles in the development of industrially useful O2-dependent iron catalysts. Therefore, an additional area of investigation will focus on the mechanism by which TDO enzymes modulate O2-reactivity through protein-substrate interactions. Dr. Pierce's research is potentially technology-enabling in that results obtained could be applied to the design of biologically inspired catalysts for oxidative transformations. The award will contribute significantly to the University of Texas at Arlington's strategic plan of becoming a national research university and a source of well-prepared STEM students. Furthermore, given the high population of first-generation students at the University, a significant impact can be made toward increasing diversity within STEM fields by sponsoring undergraduate and graduate research opportunities. Mentoring future scientists is a significant priority, and this award will provide continued research opportunities and support for both local area high school students and undergraduates at the University. The interdisciplinary nature of the proposed research will provide a wide breadth of research training for students at every level (high school, undergraduate, and graduate).