title: Comparative Fe and Zn K-edge X-ray absorption spectroscopic study of the ferroxidase centres of human H-chain ferritin and bacterioferritin from Desulfovibrio desulfuricans.
abstract: Iron uptake by the ubiquitous iron-storage protein ferritin involves the oxidation of two Fe(II) ions located at the highly conserved dinuclear "ferroxidase centre" in individual subunits. We have measured X-ray absorption spectra of four mutants (K86Q, K86Q/E27D, K86Q/E107D, and K86Q/E27D/E107D, involving variations of Glu to Asp on either or both sides of the dinuclear ferroxidase site) of recombinant human H-chain ferritin (rHuHF) in their complexes with reactive Fe(II) and redox-inactive Zn(II). The results for Fe-rHuHf are compared with those for recombinant Desulfovibrio desulfuricans bacterioferritin (DdBfr) in three states: oxidised, reduced, and oxidised/Chelex-treated. The X-ray absorption near-edge region of the spectrum allows the oxidation state of the iron ions to be assessed. Extended X-ray absorption fine structure simulations have yielded accurate geometric information that represents an important refinement of the crystal structure of DdBfr; most metal-ligand bonds are shortened and there is a decrease in ionic radius going from the Fe(II) to the Fe(III) state. The Chelex-treated sample is found to be partly mineralised, giving an indication of the state of iron in the cycled-oxidised (reduced, then oxidised) form of DdBfr, where the crystal structure shows the dinuclear site to be only half occupied. In the case of rHuHF the complexes with Zn(II) reveal a surprising similarity between the variants, indicating that the rHuHf dinuclear site is rigid. In spite of this, the rHuHf complexes with Fe(II) show a variation in reactivity that is reflected in the iron oxidation states and coordination geometries.
authors.affiliation: Unité de Biochimie, Institut des Sciences de la Vie, Université Catholique de Louvain, Croix du Sud, 4-5, boite 3, 1348, Louvain-la-Neuve, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Toussaint
authors.forename: M G
authors.initials: MG
authors.lastname: Cuypers
authors.forename: L
authors.initials: L
authors.lastname: Bertrand
authors.forename: L
authors.initials: L
authors.lastname: Hue
authors.forename: C V
authors.initials: CV
authors.lastname: Romão
authors.forename: L M
authors.initials: LM
authors.lastname: Saraiva
authors.forename: M
authors.initials: M
authors.lastname: Teixeira
authors.forename: W
authors.initials: W
authors.lastname: Meyer-Klaucke
authors.forename: M C
authors.initials: MC
authors.lastname: Feiters
authors.forename: R R
authors.initials: RR
authors.lastname: Crichton