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Semiquinone-Induced Maturation of Bacillus anthracis Ribonucleotide Reductase by a Superoxide Intermediate
2014 (English)In: Journal of Biological ChemistryArticle in journal (Refereed) Published
Abstract [en]

Ribonucleotide reductases (RNRs) catalyze the conversion of ribonucleotides to deoxyribonucleotides, and represent the only de novo pathway to provide DNA building blocks. Three different classes of RNR are known, denoted I-III. Class I RNRs are heteromeric proteins built up by α and β subunits and are further divided into different subclasses, partly based on the metal content of the β-subunit. In subclass Ib RNR the β-subunit is denoted NrdF, and harbors a manganese-tyrosyl radical cofactor. The generation of this cofactor is dependent on a flavodoxin-like maturase denoted NrdI, responsible for the formation of an active oxygen species suggested to be either a superoxide or a hydroperoxide. Herein we report on the magnetic properties of the manganese-tyrosyl radical cofactor of Bacillus anthracis NrdF and the redox properties of B. anthracis NrdI. The tyrosyl radical in NrdF is stabilized through its interaction with a ferromagnetically coupled manganese dimer. Moreover, we show through a combination of redox titration and protein electrochemistry that in contrast to hitherto characterized NrdIs, the B. anthracis NrdI is stable in its semiquinone form (NrdIsq) with a difference in electrochemical potential of approximately 110 mV between the hydroquinone and semiquinone state. The under anaerobic conditions stable NrdIsq is fully capable of generating the oxidized, tyrosyl radical-containing form of Mn-NrdF when exposed to oxygen. This latter observation strongly supports that a superoxide radical is involved in the maturation mechanism, and contradicts the participation of a peroxide species. Additionally, EPR spectra on whole cells revealed that a significant fraction of NrdI resides in its semiquinone form in vivo, underscoring that NrdIsq is catalytically relevant.

Place, publisher, year, edition, pages
2014.
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Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-251765OAI: oai:DiVA.org:uu-251765DiVA: diva2:807712
Available from: 2015-04-24 Created: 2015-04-24 Last updated: 2015-05-05

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http://www.jbc.org/content/early/2014/09/27/jbc.M114.592535.abstract

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Berggren, Gustav

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