title: A manganese(IV)/iron(IV) intermediate in assembly of the manganese(IV)/iron(III) cofactor of Chlamydia trachomatis ribonucleotide reductase.
abstract: We recently showed that the class Ic ribonucleotide reductase from the human pathogen Chlamydia trachomatis uses a Mn(IV)/Fe(III) cofactor to generate protein and substrate radicals in its catalytic mechanism [Jiang, W., Yun, D., Saleh, L., Barr, E. W., Xing, G., Hoffart, L. M., Maslak, M.-A., Krebs, C., and Bollinger, J. M., Jr. (2007) Science 316, 1188-1191]. Here, we have dissected the mechanism of formation of this novel heterobinuclear redox cofactor from the Mn(II)/Fe(II) cluster and O2. An intermediate with a g = 2 EPR signal that shows hyperfine coupling to both 55Mn and 57Fe accumulates almost quantitatively in a second-order reaction between O2 and the reduced R2 complex. The otherwise slow decay of the intermediate to the active Mn(IV)/Fe(III)-R2 complex is accelerated by the presence of the one-electron reductant, ascorbate, implying that the intermediate is more oxidized than Mn(IV)/Fe(III). Mössbauer spectra show that the intermediate contains a high-spin Fe(IV) center. Its chemical and spectroscopic properties establish that the intermediate is a Mn(IV)/Fe(IV)-R2 complex with an S = 1/2 electronic ground state arising from antiferromagnetic coupling between the Mn(IV) (S(Mn) = 3/2) and high-spin Fe(IV) (S(Fe) = 2) sites.
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Jiang
authors.forename: Lee M
authors.initials: LM
authors.lastname: Hoffart
authors.forename: Carsten
authors.initials: C
authors.lastname: Krebs
authors.forename: J Martin
authors.initials: JM
authors.lastname: Bollinger
mesh_terms: D000942:Antigens, Bacterial; D002692:Chlamydia trachomatis / Q000737:chemistry* / Q000201:enzymology; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005296:Ferrous Compounds / Q000737:chemistry* / Q000378:metabolism; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007501:Iron / Q000737:chemistry* / Q000378:metabolism; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000378:metabolism; D015204:Spectroscopy, Mossbauer
chemical_list: D000942:Antigens, Bacterial; D005296:Ferrous Compounds; D005609:Free Radicals; D008345:Manganese; D007501:Iron; D012264:Ribonucleotide Reductases; C108427:ribonucleotide reductase R2 subunit; D010100:Oxygen