| Autor: |
Srnec M; Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305-5080, United States.; J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejškova 3, Prague 8 182 23, Czech Republic., Iyer SR; Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305-5080, United States., Dassama LMK; Department of Chemistry and Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States., Park K; Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305-5080, United States., Wong SD; Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305-5080, United States., Sutherlin KD; Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305-5080, United States., Yoda Y; Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan., Kobayashi Y; Research Reactor Institute, Kyoto University, Osaka 590-0494, Japan., Kurokuzu M; Research Reactor Institute, Kyoto University, Osaka 590-0494, Japan., Saito M; Research Reactor Institute, Kyoto University, Osaka 590-0494, Japan., Seto M; Research Reactor Institute, Kyoto University, Osaka 590-0494, Japan., Krebs C; Department of Chemistry and Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States., Bollinger JM Jr; Department of Chemistry and Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States., Solomon EI; Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305-5080, United States. |
| Abstrakt: |
The α-ketoglutarate (αKG)-dependent oxygenases catalyze a diverse range of chemical reactions using a common high-spin Fe IV ═O intermediate that, in most reactions, abstract a hydrogen atom from the substrate. Previously, the Fe IV ═O intermediate in the αKG-dependent halogenase SyrB2 was characterized by nuclear resonance vibrational spectroscopy (NRVS) and density functional theory (DFT) calculations, which demonstrated that it has a trigonal-pyramidal geometry with the scissile C-H bond of the substrate calculated to be perpendicular to the Fe-O bond. Here, we have used NRVS and DFT calculations to show that the Fe IV ═O complex in taurine dioxygenase (TauD), the αKG-dependent hydroxylase in which this intermediate was first characterized, also has a trigonal bipyramidal geometry but with an aspartate residue replacing the equatorial halide of the SyrB2 intermediate. Computational analysis of hydrogen atom abstraction by square pyramidal, trigonal bipyramidal, and six-coordinate Fe IV ═O complexes in two different substrate orientations (one more along [σ channel] and another more perpendicular [π channel] to the Fe-O bond) reveals similar activation barriers. Thus, both substrate approaches to all three geometries are competent in hydrogen atom abstraction. The equivalence in reactivity between the two substrate orientations arises from compensation of the promotion energy (electronic excitation within the d manifold) required to access the π channel by the significantly larger oxyl character present in the pπ orbital oriented toward the substrate, which leads to an earlier transition state along the C-H coordinate. |
