Spectroscopic and Computational Evaluation of the Structure of the High-Spin Fe(IV)-Oxo Intermediates in Taurine: α-Ketoglutarate Dioxygenase from Escherichia coli and Its His99Ala Ligand Variant

• DOI: 10.1021/ja067899q
• Publication Date: 2007-04-24T16:38:35Z
• Authors: Sebastian Sinnecker; Nina Svensen; Eric W. Barr; Shengfa Ye; J. Martin Bollinger; Frank Neese; Carsten Krebs
• Keywords: Dioxygenase; Site-directed spin labeling

The Fe(II)- and α-ketoglutarate (αKG)-dependent dioxygenases activate O2 for cleavage of unactivated C−H bonds in their substrates. key intermediate that abstracts hydrogen the reaction taurine:αKG dioxygenase (TauD), a member this enzyme family, was recently characterized. intermediate, denoted J, shown to contain an iron(IV)-oxo unit. Other important structural features such as number, identity, disposition ligands Fe(IV) coordination sphere, are not yet understood. To probe these features, series models J with ion coordinated by expected two imidazole (from His99 His255), carboxylate (succinate Asp101), oxo have been generated density functional theory (DFT) calculations, spectroscopic parameters (Mössbauer isomer shift, quadrupole splitting, asymmetry parameter, 57Fe hyperfine coupling tensor, zero field splitting parameters, D E/D) calculated each model. distorted octahedral which one carboxylates serves monodentate ligand other bidentate ligand, trigonal bipyramidal model, both serve ligands, agree well experimental whereas square pyramidal is equatorial plane, inconsistent data. Similar analysis complex variant protein His99, residue contributes cis group, replaced alanine suggests deleted water ligand. This work lends credence idea combination Mössbauer spectroscopy DFT calculations can provide detailed information reactive intermediates catalytic cycles iron enzymes.