2xof | pdb_00002xof
Ribonucleotide reductase Y122NO2Y modified R2 subunit of E. coli
Structural highlights
FunctionRIR2_ECOLI Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides. R2 contains the tyrosyl radical required for catalysis. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedEscherichia coli ribonucleotide reductase is an alpha2beta2 complex that catalyzes the conversion of nucleotides to deoxynucleotides and requires a diferric-tyrosyl radical (Y(*)) cofactor to initiate catalysis. The initiation process requires long-range proton-coupled electron transfer (PCET) over 35 A between the two subunits by a specific pathway (Y(122)(*)-->W(48)-->Y(356) within beta to Y(731)-->Y(730)-->C(439) within alpha). The rate-limiting step in nucleotide reduction is the conformational gating of the PCET process, which masks the chemistry of radical propagation. 3-Nitrotyrosine (NO(2)Y) has recently been incorporated site-specifically in place of Y(122) in beta2. The protein as isolated contained a diferric cluster but no nitrotyrosyl radical (NO(2)Y(*)) and was inactive. In the present paper we show that incubation of apo-Y(122)NO(2)Y-beta2 with Fe(2+) and O(2) generates a diferric-NO(2)Y(*) that has a half-life of 40 s at 25 degrees C. Sequential mixing experiments, in which the cofactor is assembled to 1.2 NO(2)Y(*)/beta2 and then mixed with alpha2, CDP, and ATP, have been analyzed by stopped-flow absorption spectroscopy, rapid freeze quench EPR spectroscopy, and rapid chemical quench methods. These studies have, for the first time, unmasked the conformational gating. They reveal that the NO(2)Y(*) is reduced to the nitrotyrosinate with biphasic kinetics (283 and 67 s(-1)), that dCDP is produced at 107 s(-1), and that a new Y(*) is produced at 97 s(-1). Studies with pathway mutants suggest that the new Y(*) is predominantly located at 356 in beta2. In consideration of these data and the crystal structure of Y(122)NO(2)Y-beta2, a mechanism for PCET uncoupling in NO(2)Y(*)-RNR is proposed. A Hot Oxidant, 3-NO(2)Y(122) Radical, Unmasks Conformational Gating in Ribonucleotide Reductase.,Yokoyama K, Uhlin U, Stubbe J J Am Chem Soc. 2010 Oct 7. PMID:20929229[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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