Variable Coordination Geometries at the Diiron(II) Active Site of Ribonucleotide Reductase R2

Walter C. Voegtli, Monika Sommerhalter, Lana Saleh, Jeffrey Baldwin, J. Martin Bollinger*, Amy C Rosenzweig

*Corresponding author for this work

Research output: Contribution to journalArticle

36 Scopus citations

Abstract

The R2 subunit of Escherichia coli ribonucleotide reductase contains a dinuclear iron center that generates a catalytically essential stable tyrosyl radical by one electron oxidation of a nearby tyrosine residue. After acquisition of Fe(II) ions by the apo protein, the resulting diiron(II) center reacts with O2 to initiate formation of the radical. Knowledge of the structure of the reactant diiron(II) form of R2 is a prerequisite for a detailed understanding of the O2 activation mechanism. Whereas kinetic and spectroscopic studies of the reaction have generally been conducted at pH 7.6 with reactant produced by the addition of Fe(II) ions to the apo protein, the available crystal structures of diferrous R2 have been obtained by chemical or photoreduction of the oxidized diiron(III) protein at pH 5-6. To address this discrepancy, we have generated the diiron(II) states of wildtype R2 (R2-wt), R2-D84E, and R2-D84E/W48F by infusion of Fe(II) ions into crystals of the apo proteins at neutral pH. The structures of diferrous R2-wt and R2-D48E determined from these crystals reveal diiron(II) centers with active site geometries that differ significantly from those observed in either chemically or photoreduced crystals. Structures of R2-wt and R2-D48E/W48F determined at both neutral and low pH are very similar, suggesting that the differences are not due solely to pH effects. The structures of these "ferrous soaked" forms are more consistent with circular dichroism (CD) and magnetic circular dichroism (MCD) spectroscopic data and provide alternate starting points for consideration of possible O2 activation mechanisms.

Original languageEnglish (US)
Pages (from-to)15822-15830
Number of pages9
JournalJournal of the American Chemical Society
Volume125
Issue number51
DOIs
StatePublished - Dec 24 2003

ASJC Scopus subject areas

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

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