title: Direct observation of a deoxyadenosyl radical in an active enzyme environment.
abstract: 5'-deoxyadenosyl radicals have been proposed as the first common intermediate in the molecular reaction mechanism of the family of radical S-adenosyl-l-methionine (SAM) enzymes. However, this radical species has not yet been directly observed in a catalytically active enzyme environment. In a reduced and SAM-containing C140A mutant of the spore photoproduct lyase from Geobacillus thermodenitrificans, a mutant with altered catalytic activity, we were able to identify an organic radical with pronounced hyperfine structure using electron paramagnetic resonance spectroscopy. Guided by quantum-chemical computations at the density functional theory level of theory, this radical could be tentatively assigned to a deoxyadenosyl radical, which provides first experimental evidence for this intermediate in the reaction mechanism of radical SAM enzymes.
authors.affiliation: Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Germany.
authors.forename: Lorenz
authors.initials: L
authors.lastname: Heidinger
authors.affiliation: Department für Chemie, Ludwig-Maximilians-Universität München, Germany.|Institute of Biophysics and Physical Biochemistry, University of Regensburg, Germany.
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Kneuttinger
authors.affiliation: Department für Chemie, Ludwig-Maximilians-Universität München, Germany.
authors.forename: Gengo
authors.initials: G
authors.lastname: Kashiwazaki
authors.affiliation: Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weber
authors.affiliation: Department für Chemie, Ludwig-Maximilians-Universität München, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Carell
authors.affiliation: Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Germany.
authors.forename: Erik
authors.initials: E
authors.lastname: Schleicher
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D055162:Biocatalysis; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D015870:Gene Expression; D056506:Geobacillus / Q000737:chemistry* / Q000201:enzymology; D008958:Models, Molecular; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D011789:Quantum Theory; D013171:Spores, Bacterial / Q000737:chemistry / Q000201:enzymology
chemical_list: D001426:Bacterial Proteins; D005609:Free Radicals; D011506:Proteins; C088014:spore photoproduct lyase
keywords: EPR spectroscopy; deoxyadenosyl radical; radical SAM enzymes; radical intermediate; spore photoproduct lyase