PMID:15634667
| Citation |
Kolberg, M, Logan, DT, Bleifuss, G, Pötsch, S, Sjöberg, BM, Gräslund, A, Lubitz, W, Lassmann, G and Lendzian, F (2005) A new tyrosyl radical on Phe208 as ligand to the diiron center in Escherichia coli ribonucleotide reductase, mutant R2-Y122H. Combined x-ray diffraction and EPR/ENDOR studies. J. Biol. Chem. 280:11233-46 |
|---|---|
| Abstract |
The R2 protein subunit of class I ribonucleotide reductase (RNR) belongs to a structurally related family of oxygen bridged diiron proteins. In wild-type R2 of Escherichia coli, reductive cleavage of molecular oxygen by the diferrous iron center generates a radical on a nearby tyrosine residue (Tyr122), which is essential for the enzymatic activity of RNR, converting ribonucleotides into deoxyribonucleotides. In this work, we characterize the mutant E. coli protein R2-Y122H, where the radical site is substituted with a histidine residue. The x-ray structure verifies the mutation. R2-Y122H contains a novel stable paramagnetic center which we name H, and which we have previously proposed to be a diferric iron center with a strongly coupled radical, Fe(III)Fe(III)R.. Here we report a detailed characterization of center H, using 1H/2H -14N/15N- and 57Fe-ENDOR in comparison with the Fe(III)Fe(IV) intermediate X observed in the iron reconstitution reaction of R2. Specific deuterium labeling of phenylalanine residues reveals that the radical results from a phenylalanine. As Phe208 is the only phenylalanine in the ligand sphere of the iron site, and generation of a phenyl radical requires a very high oxidation potential, we propose that in Y122H residue Phe208 is hydroxylated, as observed earlier in another mutant (R2-Y122F/E238A), and further oxidized to a phenoxyl radical, which is coordinated to Fe1. This work demonstrates that small structural changes can redirect the reactivity of the diiron site, leading to oxygenation of a hydrocarbon, as observed in the structurally similar methane monoxygenase, and beyond, to formation of a stable iron-coordinated radical. |
| Links |
PubMed Online version:10.1074/jbc.M414634200 |
| Keywords |
Electron Spin Resonance Spectroscopy; Escherichia coli/enzymology; Escherichia coli Proteins/chemistry; Free Radicals; Ligands; Models, Molecular; Ribonucleotide Reductases/chemistry; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Tyrosine; X-Ray Diffraction |
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