Function of the Diiron Cluster of Escherichia coli Class Ia Ribonucleotide Reductase in Proton-Coupled Electron Transfer
Author(s)
Wörsdörfer, Bigna; Conner, Denise A.; Yokoyama, Kenichi; Livada, Jovan; Jiang, Wei; Silakov, Alexey; Stubbe, JoAnne; Bollinger, J. Martin; Krebs, Carsten; Seyedsayamdost, Mohammad R.; ... Show more Show less
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The class Ia ribonucleotide reductase (RNR) from Escherichia coli employs a free-radical mechanism, which involves bidirectional translocation of a radical equivalent or “hole” over a distance of ~35 Å from the stable diferric/tyrosyl-radical (Y[subscript 122]•) cofactor in the β subunit to cysteine 439 (C[subscript 439]) in the active site of the α subunit. This long-range, intersubunit electron transfer occurs by a multistep “hopping” mechanism via formation of transient amino acid radicals along a specific pathway and is thought to be conformationally gated and coupled to local proton transfers. Whereas constituent amino acids of the hopping pathway have been identified, details of the proton-transfer steps and conformational gating within the β sununit have remained obscure; specific proton couples have been proposed, but no direct evidence has been provided. In the key first step, the reduction of Y[subscript 122]• by the first residue in the hopping pathway, a water ligand to Fe[subscript 1] of the diferric cluster was suggested to donate a proton to yield the neutral Y[subscript 122]. Here we show that forward radical translocation is associated with perturbation of the Mössbauer spectrum of the diferric cluster, especially the quadrupole doublet associated with Fe[subscript 1]. Density functional theory (DFT) calculations verify the consistency of the experimentally observed perturbation with that expected for deprotonation of the Fe[subscript 1]-coordinated water ligand. The results thus provide the first evidence that the diiron cluster of this prototypical class Ia RNR functions not only in its well-known role as generator of the enzyme’s essential Y[subscript 122]•, but also directly in catalysis.
Date issued
2013-05Department
Massachusetts Institute of Technology. Department of Biology; Massachusetts Institute of Technology. Department of ChemistryJournal
Journal of the American Chemical Society
Publisher
American Chemical Society (ACS)
Citation
Wörsdörfer, Bigna, Denise A. Conner, Kenichi Yokoyama, Jovan Livada, Mohammad Seyedsayamdost, Wei Jiang, Alexey Silakov, JoAnne Stubbe, J. Martin Bollinger, and Carsten Krebs. “ Function of the Diiron Cluster of Escherichia Coli Class Ia Ribonucleotide Reductase in Proton-Coupled Electron Transfer .” Journal of the American Chemical Society 135, no. 23 (June 12, 2013): 8585–8593.
Version: Author's final manuscript
ISSN
0002-7863
1520-5126