Density Functional Theory Analysis of Structure, Energetics, and Spectroscopy for the Mn−Fe Active Site of Chlamydia trachomatis Ribonucleotide Reductase in Four Oxidation States

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• 作者：Wen-Ge Han ; Debra Ann Giammona ; Donald Bashford ; Louis Noodleman
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：August 16, 2010
• 年：2010
• 卷：49
• 期：16
• 页码：7266-7281
• 全文大小：1333K
• 年卷期：v.49,no.16(August 16, 2010)
• ISSN：1520-510X

文摘

Models for the Mn−Fe active site structure of ribonucleotide reductase (RNR) from pathogenic bacteria Chlamydia trachomatis (Ct) in different oxidation states have been studied in this paper, using broken-symmetry density functional theory (DFT) incorporated with the conductor like screening (COSMO) solvation model and also with finite-difference Poisson−Boltzmann self-consistent reaction field (PB-SCRF) calculations. The detailed structures for the reduced Mn(II)−Fe(II), the met Mn(III)−Fe(III), the oxidized Mn(IV)−Fe(III) and the superoxidized Mn(IV)−Fe(IV) states are predicted. The calculated properties, including geometries, ⁵⁷Fe Mssbauer isomer shifts and quadrupole splittings, and ⁵⁷Fe and ⁵⁵Mn electron nuclear double resonance (ENDOR) hyperfine coupling constants, are compared with the available experimental data. The Mssbauer and energetic calculations show that the (μ-oxo, μ-hydroxo) models better represent the structure of the Mn(IV)−Fe(III) state than the di-μ-oxo models. The predicted Mn(IV)−Fe(III) distances (2.95 and 2.98 Å) in the (μ-oxo, μ-hydroxo) models are in agreement with the extended X-ray absorption fine structure (EXAFS) experimental value of 2.92 Å (Younker et al. J. Am. Chem. Soc. 2008, 130, 15022−15027). The effect of the protein and solvent environment on the assignment of the Mn metal position is examined by comparing the relative energies of alternative mono-Mn(II) active site structures. It is proposed that if the Mn(II)−Fe(II) protein is prepared with prior addition of Mn(II) or with Mn(II) richer than Fe(II), Mn is likely positioned at metal site 2, which is further from Phe127.