Ribonucleotide reductases catalyze the conversion of nucleoside diphosphates to deoxynucleotides supplying and controlling both the amounts and ratios of dNTP pools essential for DNA replication and DNA repair.  Nucleotide reduction catalyzed by all RNR classes involves free radical chemistry involving protein thiyl and nucleotide radicals.  The class Ia RNRs involve an unprecedented reaction in biology, the reversible oxidation of an active site cysteine to a thiyl radical by a “stable” tyrosyl radical (residue 122) that occurs across two subunits (alpha and beta) over a distance of &gt;35 Å.  This long range RT involves in addition to the stable tyrosyl radical, three transient tyrosyl radicals.  These radicals have reduction potentials of 0.96 volts at pH 7.6.  Studies using F<sub>n</sub>Ys site specifically incorporated in place of the stable and transient tyrosyl radicals involved in RT have provided insight into how nature controls this unprecedented oxidation and prevents enzymatic self-destruction.  RNR provides a paradigm for how nature can harness the reactivity of radicals to carry out difficult chemistry with exquisite specificity and highlights the importance of proton coupled electron transfer in these interconversions.

Radicals: Your lIfe is in their hands

2019 Spring National Meeting

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