title: Mechanistic Investigation of the Radical S-Adenosyl-L-methionine Enzyme DesII Using Fluorinated Analogues.
abstract: DesII is a radical S-adenosyl-l-methionine (SAM) enzyme that can act as a deaminase or a dehydrogenase depending on the nature of its TDP-sugar substrate. Previous work has implicated a substrate-derived, C3-centered α-hydroxyalkyl radical as a key intermediate during catalysis. Although deprotonation of the α-hydroxyalkyl radical has been shown to be important for dehydrogenation, much less is known regarding the course of the deamination reaction. To investigate the role played by the C3 hydroxyl during deamination, 3-deutero-3-fluoro analogues of both substrates were prepared and characterized with DesII. In neither case was deamination or oxidation observed; however, in both cases deuterium was efficiently exchanged between the substrate analogues and SAM. These results imply that the C3 hydroxyl plays a key role in both reactions—thereby arguing against a 1,2-migration mechanism of deamination—and that homolysis of SAM concomitant with H atom abstraction from the substrate is readily reversible when forward partitioning is inhibited.
authors.affiliation: †Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Geng-Min
authors.initials: GM
authors.lastname: Lin
authors.affiliation: †Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Sei-Hyun
authors.initials: SH
authors.lastname: Choi
authors.affiliation: ‡Division of Medicinal Chemistry, College of Pharmacy, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Ruszczycky
authors.affiliation: †Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States.|‡Division of Medicinal Chemistry, College of Pharmacy, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Hung-wen
authors.initials: HW
authors.lastname: Liu
mesh_terms: D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D054879:Halogenation; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000737:chemistry / Q000378:metabolism*
chemical_list: D005609:Free Radicals; D006845:Hydrocarbons, Fluorinated; D012436:S-Adenosylmethionine; D010088:Oxidoreductases
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