Iron Oxidation in Escherichia coli Bacterioferritin Ferroxidase Centre, a Site Designed to React Rapidly with H2O2 but Slowly with O2.

Jacob Pullin,Martin Clémancey,Geneviève Blondin,Michael T Wilson,Jonathan A R Worrall,Nick E Le Brun,Marina Lučić,Geoffrey R Moore,Justin M Bradley,Dimitri A Svistunenko

doi:10.1002/ange.202015964

Abstract

Both O2 and H2O2 can oxidize iron at the ferroxidase center (FC) of Escherichia coli bacterioferritin (EcBfr) but mechanistic details of the two reactions need clarification. UV/Vis, EPR, and Mössbauer spectroscopies have been used to follow the reactions when apo-EcBfr, pre-loaded anaerobically with Fe2+, was exposed to O2 or H2O2. We show that O2 binds di-Fe2+ FC reversibly, two Fe2+ ions are oxidized in concert and a H2O2 molecule is formed and released to the solution. This peroxide molecule further oxidizes another di-Fe2+ FC, at a rate circa 1000 faster than O2, ensuring an overall 1:4 stoichiometry of iron oxidation by O2. Initially formed Fe3+ can further react with H2O2 (producing protein bound radicals) but relaxes within seconds to an H2O2-unreactive di-Fe3+ form. The data obtained suggest that the primary role of EcBfr in vivo may be to detoxify H2O2 rather than sequester iron.

Highlights

Ferritins belong to the family of proteins and enzymes that exploit the chemistry of dinuclear iron complexes
We focus on Escherichia coli bacterioferritin (EcBfr) for which H2O2 was reported to compete with O2 very successfully in iron oxidation.[9]
The stoichiometries of Fe2+ binding to ferroxidase center (FC) under anaerobic conditions (2:1) and of its oxidation thereafter by added O2 (4:1) follow from the results reported in Figure 2 and Figure S1

Summary

Introduction

Ferritins belong to the family of proteins and enzymes that exploit the chemistry of dinuclear iron complexes. The di-iron complexes embedded in proteins have many biochemical functions including catalytic organic transformation (in ribonucleotide reductases,[1] RNR, methane monoxygenases[2] and desaturases[3]) as well as reversible O2 binding (in haemerythrins,[4] Hr). In addition to these roles, the di-iron centers in ferritins function as Fe2+ oxidases and iron transit sites involved in the formation of polynuclear iron minerals.[5]. Blondin UniversitØ Grenoble Alpes, CNRS, CEA, IRIG, Laboratoire de Chimie et Biologie des MØtaux, UMR 5249 17 rue des Martyrs, 38000 Grenoble (France)

Results

Discussion

Conclusion