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

Abstract

Both O 2 and H 2 O 2 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 Mçssbauer spectroscopies have been used to follow the reactions when apo-EcBfr, pre-loaded anaerobically with Fe 2+ , was exposed to O 2 or H 2 O 2. We show that O 2 binds di-Fe 2+ FC reversibly, two Fe 2+ ions are oxidized in concert and a H 2 O 2 molecule is formed and released to the solution. This peroxide molecule further oxidizes another di-Fe 2+ FC, at a rate circa 1000 faster than O 2 , ensuring an overall 1:4 stoichiometry of iron oxidation by O 2. Initially formed Fe 3+ can further react with H 2 O 2 (producing protein bound radicals) but relaxes within seconds to an H 2 O 2-unreactive di-Fe 3+ form. The data obtained suggest that the primary role of EcBfr in vivo may be to detoxify H 2 O 2 rather than sequester iron.

In Situ Monitoring of Hydrogen Peroxide Released from Living Cells Using a ZIF-8-Based Surface-Enhanced Raman Scattering Sensor

“…19−21 However, on the one hand, monitoring H 2 O 2 released from cells is challenging due to its rapid diffusion, self-transformation, and dilution to ultralow concentration in the cellular microenvironment. 7,22 On the other hand, it is difficult to detect molecules with low Raman scattering cross-sections or with poor affinity to the SERS-active substrates. 18,23 These problems severely limit the application of SERS in H 2 O 2 detection.…”

The Ferroxidase Centre of Escherichia coli Bacterioferritin Plays a Key Role in the Reductive Mobilisation of the Mineral Iron Core

“…[22] The observation that heme is seemingly unimportant for the rate at which Bfr is able to oxidise and mineralise iron [23] led to the proposal that the ferroxidase centres and hemes function as two independent cofactors involved in iron uptake and iron release, respectively. Under oxidative stress or iron-replete conditions the Bfr ferroxidase centre couples oxidation of Fe 2 + to the reduction of an external electron acceptor, most likely peroxide, [24] performing the dual roles of consuming ROS and converting the potentially toxic Fe 2 + into a chemically inert ferric mineral solubilized within the protein coat. Under low-iron conditions the heme cycles oxidation state by accepting electrons from reduced Bfd and passing them to the mineral core, mobilising the iron by reducing it to Fe 2 + , leading to release into the cytoplasm.…”

The Ferroxidase Centre of Escherichia coli Bacterioferritin Plays a Key Role in the Reductive Mobilisation of the Mineral Iron Core

“…The observation that heme is seemingly unimportant for the rate at which Bfr is able to oxidise and mineralise iron [23] led to the proposal that the ferroxidase centres and hemes function as two independent cofactors involved in iron uptake and iron release, respectively. Under oxidative stress or iron‐replete conditions the Bfr ferroxidase centre couples oxidation of Fe 2+ to the reduction of an external electron acceptor, most likely peroxide, [24] performing the dual roles of consuming ROS and converting the potentially toxic Fe 2+ into a chemically inert ferric mineral solubilized within the protein coat. Under low‐iron conditions the heme cycles oxidation state by accepting electrons from reduced Bfd and passing them to the mineral core, mobilising the iron by reducing it to Fe 2+ , leading to release into the cytoplasm [20] …”