The class Ib ribonucleotide reductase from Mycobacterium tuberculosis has two active R2F subunits
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Ribonucleotide reductases (RNRs) catalyze the reduction of ribonucleotides to their corresponding deoxyribonucleotides, playing a crucial role in DNA repair and replication in all living organisms. Class Ib RNRs require either a diiron–tyrosyl radical (Y·) or a dimanganese–Y· cofactor in their R2F subunit to initiate ribonucleotide reduction in the R1 subunit. Mycobacterium tuberculosis, the causative agent of tuberculosis, contains two genes, nrdF1 and nrdF2, encoding the small subunits R2F-1 and R2F-2, respectively, where the latter has been thought to serve as the only active small subunit in the M. tuberculosis class Ib RNR. Here, we present evidence for the presence of an active Fe 2 III –Y· cofactor in the M. tuberculosis RNR R2F-1 small subunit, supported and characterized by UV–vis, X-band electron paramagnetic resonance, and resonance Raman spectroscopy, showing features similar to those for the M. tuberculosis R2F-2–Fe 2 III –Y· cofactor. We also report enzymatic activity of Fe 2 III –R2F-1 when assayed with R1, and suggest that the active M. tuberculosis class Ib RNR can use two different small subunits, R2F-1 and R2F-2, with similar activity.
KeywordsRibonucleotide reductase R2 Tyrosyl radical Mycobacterium tuberculosis Iron
Electron paramagnetic resonance
This work was financially supported by the Norwegian Research Council through projects 214239/F20 and 218412/F50 (K.K.A.) and CMST COST Action CM1003 (K.K.A. and A.G.), the Swedish Research Council [2010-5061 (M.H.) and 2011-4850 (A.G.)], the Swedish Foundation for Strategic Research, and the Knut and Alice Wallenberg Foundation (M.H.) Travel grants were provided by the MLSUiO program for molecular life science research at the University of Oslo, and the National Graduate School in Structural Biology (BioStruct) (UiT/NorStruct). We thank Hans-Petter Hersleth (University of Oslo) for useful discussions.
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