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Publication Abstract from PubMed

Class Ib ribonucleotide reductases (RNRs) use a dimetal-tyrosyl radical (Y*) cofactor in their NrdF (beta2) subunit to initiate ribonucleotide reduction in the NrdE (alpha2) subunit. Contrary to the diferric tyrosyl radical (Fe(III)2-Y*) cofactor, which can self-assemble from Fe(II)2-NrdF and O2, generation of the Mn(III)2-Y* cofactor requires the reduced form of a flavoprotein, NrdIhq, and O2 for its assembly. Here we report the 1.8 A resolution crystal structure of Bacillus cereus Fe2-NrdF in complex with NrdI. Compared to the previously solved Escherichia coli NrdI-Mn(II)2-NrdF structure, NrdI and NrdF binds similarly in Bacillus cereus through conserved core interactions. This protein-protein association seems to be unaffected by metal ion type bound in the NrdF subunit. The Bacillus cereus Mn(II)2-NrdF and Fe2-NrdF structures, also presented here, show conformational flexibility of residues surrounding the NrdF metal ion site. The movement of one of the metal-coordinating carboxylates is linked to the metal type present at the dimetal site and not associated with NrdI-NrdF binding. This carboxylate conformation seems to be vital for the water network connecting the NrdF dimetal site and the flavin in NrdI. From these observations, we suggest that metal-dependent variations in carboxylate coordination geometries are important for active Y* cofactor generation in class Ib RNRs. Additionally, we show that binding of NrdI to NrdF would structurally interfere with the suggested alpha2beta2 (NrdE-NrdF) holoenzyme formation, suggesting the potential requirement for NrdI dissociation before NrdE-NrdF assembly after NrdI-activation. The mode of interactions between the proteins involved in the class Ib RNR system is, however, not fully resolved.

Crystal Structure of Bacillus cereus Class Ib Ribonucleotide Reductase Di-iron NrdF in Complex with NrdI.,Hammerstad M, Hersleth HP, Tomter AB, Rohr AK, Andersson KK ACS Chem Biol. 2014 Feb 21;9(2):526-37. doi: 10.1021/cb400757h. Epub 2013 Dec 11. PMID:24295378^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.