Geometrical properties of the manganese(iv)/iron(iii) cofactor of Chlamydia trachomatis ribonucleotide reductase unveiled by simulations of XAS spectra.

Using simulations of Mn/Fe K-edge X-ray absorption spectroscopy (XAS), combined with DFT-optimized structural models and direct comparisons with available experimental data, we determine geometrical and electronic properties of the Mn-Fe active site of Chlamydia trachomatis (Ct) of ribonucleotide reductase (RNR). In the post-edge XAS energy range, we use extended X-ray absorption fine structure (EXAFS) data, to acquire absorber-scatterer geometrical information around each absorber metal center. For this task, we apply a protocol that evaluates Debye-Waller factors in scattering paths instead of scattering shells to fit the experimental EXAFS. The model of the manganese(iv)/iron(iii) cofactor that best fit Mn and Fe K-edge EXAFS experimental data is a structure with Mn at metal site 1 (proximal to Phe-127), a μ-oxo/μ-hydroxo/μ-1,3-carboxylato core, and a terminal hydroxo ligand, i.e. OH-Mn1(iv)-(μ-O)(μ-OH)-Fe2(iii).