Ribonucleotide reductases (RNRs) catalyse the reductive synthesis of deoxyribonucleotides from their corresponding ribonucleotides. Providing the precursors necessary for DNA synthesis. This is a class III (anaerobic) RNR. The mechanism of the enzyme involves a glycine-centred radical (which is formed by the radical SAM superfamily protein NrdG).
Class III RNRs, found in strict or facultative anaerobic bacteria, bacteriophage, and archaea, use an FeS cluster and S-adenosylmethionine to generate a glycyl radical. The class III enzyme from phage T4 consists of two subunits, the larger of which contains the active and allosteric sites.
The protein binds a zinc ion in a position remote from the active site which has been shown to be critical for function. It is thought that this metal ion is responsible for protecting the enzyme from loss of its ground state radical.
Defined by 9 residues: ASN:A-78CYS:A-79MET:A-288CYS:A-290SER:A-292ASN:A-311TYR:A-441GLU:A-446ALA:A-580