Download MendeleyActive Site Threonine Facilitates Proton Transfer during Dioxygen Activation at the Diiron Center of Toluene/o-Xylene Monooxygenase Hydroxylase.
Song, W.J., McCormick, M.S., Behan, R.K., Sazinsky, M.H., Jiang, W., Lin, J., Krebs, C., Lippard, S.J.(2010) J Am Chem Soc 132: 13582-13585
- PubMed: 20839885
- DOI: https://doi.org/10.1021/ja1063795
- Primary Citation of Related Structures:
3N1X, 3N1Y, 3N1Z, 3N20 - PubMed Abstract:
Toluene/o-xylene monooxygenase hydroxylase (ToMOH), a diiron-containing enzyme, can activate dioxygen to oxidize aromatic substrates. To elucidate the role of a strictly conserved T201 residue during dioxygen activation of the enzyme, T201S, T201G, T201C, and T201V variants of ToMOH were prepared by site-directed mutagenesis. X-ray crystal structures of all the variants were obtained. Steady-state activity, regiospecificity, and single-turnover yields were also determined for the T201 mutants. Dioxygen activation by the reduced T201 variants was explored by stopped-flow UV-vis and Mössbauer spectroscopy. These studies demonstrate that the dioxygen activation mechanism is preserved in all T201 variants; however, both the formation and decay kinetics of a peroxodiiron(III) intermediate, T201(peroxo), were greatly altered, revealing that T201 is critically involved in dioxygen activation. A comparison of the kinetics of O(2) activation in the T201S, T201C, and T201G variants under various reaction conditions revealed that T201 plays a major role in proton transfer, which is required to generate the peroxodiiron(III) intermediate. A mechanism is postulated for dioxygen activation, and possible structures of oxygenated intermediates are discussed.
Organizational Affiliation:
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
