Structural Basis for Activation of Class Ib Ribonucleotide Reductase

Abstract

Two Ways to Nucleotide Reduction Ribonucleotide reductases (RNRs) are essential for DNA synthesis and repair in all organisms, initiating nucleotide reduction through a free-radical mechanism. The class Ib RNRs are the primary aerobic RNRs for many human pathogens. NrdF, the class Ib RNR of Escherichia coli , can initiate nucleotide reduction through either a Fe III 2 -Y• or a Mn III 2 -Y• cofactor. Whereas the Fe-based cofactor can self-assemble, assembly of the Mn-based free radical requires a reduced flavoprotein, NrdI. Boal et al. (p. 1526 , published online 5 August; see the Perspective by Sjöberg ) have gained insight into the mechanism of cofactor activation by determining structures of Mn II 2 -NrdF, Fe II 2 -NrdF, and Mn II 2 -NrdF in complex with reduced and oxidized NrdI. The structures show how a single protein, NrdF, can use two different oxidants to activate two different metallocofactors using distinct chemistries.