Electronic structure of neutral tryptophan radicals in ribonucleotide reductase studied by epr and endor spectroscopy

Lassmann, G., Lendzian, F., MacMillan, F., Bittl, R., Pötsch, S., Sahlin, M., Sioberg, B.-M., Jjfäslund, A. and Lubitz, W. (1997) Electronic structure of neutral tryptophan radicals in ribonucleotide reductase studied by epr and endor spectroscopy. The FASEB Journal, 11 (9). ISSN 0892-6638

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Abstract

New transient protein-linked radicals have been analyzed by EPR and ENDOR spectroscopy in the radical enzyme ribonucteotide reductase of E coK, particularly in the mutant Y122F of the protein R2, during the reconstitution of the diiron center. Two different tryptophan radicals (Wa° and W0°) with life-times of several minutes are formed at room temperature. Wa° is freeze-trapped and investigated by EPR and ENDOR in normal and selectively deuterated proteins at 20K Two hyperfine couplings from the βmethylene protons, hyperfine tensors of two a-protons and the complete nitrogen hyperfine tensor are determined. Based on the absence of a large hyperfine coupling from the N-H proton, which could be expected for a cation radical, and on comparison of the experimental data with theoretical spin densities from density functional calculations, WV is assigned to an oxidized neutral tryptophan radical. A small anisotropic hyperfine coupling detected in selectively deuterated W." is tentatively assigned to a proton which is hydrogen bonded to the nitrogen of VW. A similar spin density distribution was obtained also for the second tryptophan radical. WV observed at room temperature by stopped-flow EPR is also assigned to an oxidized neutral radical. The site of Wa° and WtT in protein R2 has been determined from the comparison of the conformation of the βprotons (from EPR data) with X-ray structure data to W111 and W107, respectively, in close neighborhood to the iron center. For the first time, detailed hyperfine parameters are determined for protein-linked oxidized neutral tryptophan radicals. Using the same technique of iron reconstitution, in the mutant R2-Y122H, where the site of the catalytic essential stable tyrosyl radical has been replaced by a histidine, a new stable radical exhibiting a strong magnetic metal interaction is observed by EPR and ENDOR.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
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Depositing User: Pure Connector
Date Deposited: 21 Jan 2015 12:22
Last Modified: 21 Sep 2020 23:41
URI: https://ueaeprints.uea.ac.uk/id/eprint/51836
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