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Science. 2004 Jul 9;305(5681):245-8.

The radical site in chlamydial ribonucleotide reductase defines a new R2 subclass.

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  • 1Department of Biochemistry and Biophysics, Stockholm University, Roslagstullsbacken 15, Albanova University Center, SE-10691 Stockholm, Sweden.


Ribonucleotide reductase (RNR) synthesizes the deoxyribonucleotides for DNA synthesis. The R2 protein of normal class I ribonucleotide reductases contains a diiron site that produces a stable tyrosyl free radical, essential for enzymatic activity. Structural and electron paramagnetic resonance studies of R2 from Chlamydia trachomatis reveal a protein lacking a tyrosyl radical site. Instead, the protein yields an iron-coupled radical upon reconstitution. The coordinating structure of the diiron site is similar to that of diiron oxidases/monoxygenases and supports a role for this radical in the RNR mechanism. The specific ligand pattern in the C. trachomatis R2 metal site characterizes a new group of R2 proteins that so far has been found in eight organisms, three of which are human pathogens.

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