Interaction between the transferrin protein and plutonium (and thorium), what’s new?

Transferrin (Tf) is a glycoprotein that transports iron from the serum to the various organs. Several studies have highlighted that Tf can interact with metals other than Fe(III), including actinides that are chemical and radiological toxics. We propose here to report on the behavior of Th(IV) and Pu(IV) in comparison with Fe(III) upon Tf complexation. We first considered UV-Vis and IR data of the M2Tf complex (M = Fe, Th, Pu) and combined experimental EXAFS data with MD models in order to better describe the metallic coordination site. EXAFS data of the first M-O coordination sphere are consistent with the MD model considering 1 synergistic carbonate. Further EXAFS data analysis strongly suggests that contamination by Th/Pu colloids seems to occur upon Tf complexation, but this contamination seems limited. SAXS data have also been recorded for all complexes and also after the addition of DFOB in the medium. The Rg values are very close for apoTf, ThTf and PuTf, but slightly larger than for holoTf. Data suggest that the structure of the protein is more ellipsoidal than spherical, with a flattened oblate form. From this data, the following order of conformation size might be considered : holoTf < M2Tf (M = Th, Pu) < apoTf < M2Tf-DFOB (M = Fe, Th, Pu).