title: Evidence for a Di-μ-oxo Diamond Core in the Mn(IV)/Fe(IV) Activation Intermediate of Ribonucleotide Reductase from Chlamydia trachomatis.
abstract: High-valent iron and manganese complexes effect some of the most challenging biochemical reactions known, including hydrocarbon and water oxidations associated with the global carbon cycle and oxygenic photosynthesis, respectively. Their extreme reactivity presents an impediment to structural characterization, but their biological importance and potential chemical utility have, nevertheless, motivated extensive efforts toward that end. Several such intermediates accumulate during activation of class I ribonucleotide reductase (RNR) β subunits, which self-assemble dimetal cofactors with stable one-electron oxidants that serve to initiate the enzyme's free-radical mechanism. In the class I-c β subunit from Chlamydia trachomatis, a heterodinuclear Mn(II)/Fe(II) complex reacts with dioxygen to form a Mn(IV)/Fe(IV) intermediate, which undergoes reduction of the iron site to produce the active Mn(IV)/Fe(III) cofactor. Herein, we assess the structure of the Mn(IV)/Fe(IV) activation intermediate using Fe- and Mn-edge extended X-ray absorption fine structure (EXAFS) analysis and multifrequency pulse electron paramagnetic resonance (EPR) spectroscopy. The EXAFS results reveal a metal-metal vector of 2.74-2.75 Å and an intense light-atom (C/N/O) scattering interaction 1.8 Å from the Fe. Pulse EPR data reveal an exchangeable deuterium hyperfine coupling of strength |T| = 0.7 MHz, but no stronger couplings. The results suggest that the intermediate possesses a di-μ-oxo diamond core structure with a terminal hydroxide ligand to the Mn(IV).
authors.affiliation: Department of Chemistry and ‡Department of Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Ryan J
authors.identifier: 0000-0003-1257-2850
authors.initials: RJ
authors.lastname: Martinie
authors.affiliation: Department of Chemistry and ‡Department of Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Blaesi
authors.affiliation: Department of Chemistry and ‡Department of Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Carsten
authors.identifier: 0000-0002-3302-7053
authors.initials: C
authors.lastname: Krebs
authors.affiliation: Department of Chemistry and ‡Department of Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: J Martin
authors.initials: JM
authors.lastname: Bollinger
authors.affiliation: Department of Chemistry and ‡Department of Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Alexey
authors.initials: A
authors.lastname: Silakov
authors.affiliation: Department of Chemistry and ‡Department of Biochemistry and Molecular Biology, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Christopher J
authors.identifier: 0000-0001-5736-513X
authors.initials: CJ
authors.lastname: Pollock
mesh_terms: D002692:Chlamydia trachomatis / Q000201:enzymology*; D004578:Electron Spin Resonance Spectroscopy; D058085:Iron Compounds / Q000737:chemistry / Q000378:metabolism*; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D012264:Ribonucleotide Reductases / Q000737:chemistry / Q000378:metabolism*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D058085:Iron Compounds; D008345:Manganese; D012264:Ribonucleotide Reductases; D010100:Oxygen