Interaction of Th(IV), Pu(IV) and iron(III) with ferritin protein : how similar ?

Ferritin is the main actor of Fe storage in eukaryote and prokaryote cells. It is a large multifunctional, multi-subunit protein consisting of heavy H and light L subunits. In the field of nuclear toxicology, it has been suggested that some actinide elements, such as thorium and plutonium at oxidation state +IV, have a comparable "biochemistry" as iron at oxidation state +III due to their very high tendency for hydrolysis and somehow comparable ionic radii. Therefore, the possible mechanisms of interaction of such actinide elements with Fe storage protein is a fundamental question of bio-actinidic chemistry. We have recently described the complexation of Pu(IV) and Th(IV) with horse spleen ferritin (composed mainly of L subunits). In this article we bring another viewpoint to this question by further combining modeling with our previous EXAFS data for Pu(IV) and Th(IV). As a result, the interaction between the L subunits and both actinides appears to be non-specific but only driven by the density of presence of Asp and Glu residues on the protein shell. The formation of an oxyhydroxide Th or Pu core has not been observed in our experimental condition, nor the interaction of Th or Pu with the ferric oxyhydroxide core.