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Direct Measurement of the Radical Translocation Distance in the Class I Ribonucleotide Reductase from Chlamydia trachomatis

Livada, Jovan, Martinie, Ryan J., Dassama, Laura M. K., Krebs, Carsten, Bollinger, J. Martin, Silakov, Alexey
The Journal of physical chemistry 2015 v.119 no.43 pp. 13777-13784
Chlamydia trachomatis, active sites, manganese, ribonucleotide reductase, ribonucleotides
Ribonucleotide reductases (RNRs) catalyze conversion of ribonucleotides to deoxyribonucleotides in all organisms via a free-radical mechanism that is essentially conserved. In class I RNRs, the reaction is initiated and terminated by radical translocation (RT) between the α and β subunits. In the class Ic RNR from Chlamydia trachomatis (Ct RNR), the initiating event converts the active S = 1 Mn(IV)/Fe(III) cofactor to the S = 1/2 Mn(III)/Fe(III) “RT-product” form in the β subunit and generates a cysteinyl radical in the α active site. The radical can be trapped via the well-described decomposition reaction of the mechanism-based inactivator, 2′-azido-2′-deoxyuridine-5′-diphosphate, resulting in the generation of a long-lived, nitrogen-centered radical (N•) in α. In this work, we have determined the distance between the Mn(III)/Fe(III) cofactor in β and N• in α to be 43 ± 1 Å by using double electron–electron resonance experiments. This study provides the first structural data on the Ct RNR holoenzyme complex and the first direct experimental measurement of the inter-subunit RT distance in any class I RNR.