Geometric and electronic structure of the Mn(IV)Fe(III) cofactor in class Ic ribonucleotide reductase: Correlation to the class ia binuclear non-heme iron enzyme

Yeonju Kwak, Wei Jiang, Laura M.K. Dassama, Kiyoung Park, Caleb B. Bell, Lei V. Liu, Shaun D. Wong, Makina Saito, Yasuhiro Kobayashi, Shinji Kitao, Makoto Seto, Yoshitaka Yoda, E. Ercan Alp, Jiyong Zhao, J. Martin Bollinger, Carsten Krebs, Edward I. Solomon

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Abstract

The class Ic ribonucleotide reductase (RNR) from Chlamydia trachomatis (Ct) utilizes a Mn/Fe heterobinuclear cofactor, rather than the Fe/Fe cofactor found in the β (R2) subunit of the class Ia enzymes, to react with O 2. This reaction produces a stable MnIVFeIII cofactor that initiates a radical, which transfers to the adjacent α (R1) subunit and reacts with the substrate. We have studied the Mn IVFeIII cofactor using nuclear resonance vibrational spectroscopy (NRVS) and absorption (Abs)/circular dichroism (CD)/magnetic CD (MCD)/variable temperature, variable field (VTVH) MCD spectroscopies to obtain detailed insight into its geometric/electronic structure and to correlate structure with reactivity; NRVS focuses on the FeIII, whereas MCD reflects the spin-allowed transitions mostly on the MnIV. We have evaluated 18 systematically varied structures. Comparison of the simulated NRVS spectra to the experimental data shows that the cofactor has one carboxylate bridge, with MnIV at the site proximal to Phe127. Abs/CD/MCD/VTVH MCD data exhibit 12 transitions that are assigned as d-d and oxo and OH- to metal charge-transfer (CT) transitions. Assignments are based on MCD/Abs intensity ratios, transition energies, polarizations, and derivative-shaped pseudo-A term CT transitions. Correlating these results with TD-DFT calculations defines the MnIVFeIII cofactor as having a μ-oxo, μ-hydroxo core and a terminal hydroxo ligand on the MnIV. From DFT calculations, the MnIV at site 1 is necessary to tune the redox potential to a value similar to that of the tyrosine radical in class Ia RNR, and the OH- terminal ligand on this Mn IV provides a high proton affinity that could gate radical translocation to the α (R1) subunit.

Original languageEnglish (US)
Pages (from-to)17573-17584
Number of pages12
JournalJournal of the American Chemical Society
Volume135
Issue number46
DOIs
StatePublished - Nov 20 2013

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All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Kwak, Y., Jiang, W., Dassama, L. M. K., Park, K., Bell, C. B., Liu, L. V., Wong, S. D., Saito, M., Kobayashi, Y., Kitao, S., Seto, M., Yoda, Y., Alp, E. E., Zhao, J., Bollinger, J. M., Krebs, C., & Solomon, E. I. (2013). Geometric and electronic structure of the Mn(IV)Fe(III) cofactor in class Ic ribonucleotide reductase: Correlation to the class ia binuclear non-heme iron enzyme. Journal of the American Chemical Society, 135(46), 17573-17584. https://doi.org/10.1021/ja409510d