If released into the environment during an event such as a nuclear power plant leak, radioactive actinide metals would be a potential health risk. But little is known about how cells take up these elements. A research team led by Rebecca J. Abergel of Lawrence Berkeley National Laboratory and Roland K. Strong of the Fred Hutchinson Cancer Research Center, in Seattle, has shown that actinides might get inside cells by hitching a ride on a protein called siderocalin that’s usually involved in iron trafficking (Proc. Natl. Acad. Sci. USA 2015, DOI: 10.1073/pnas.1508902112). Siderocalin captures iron indirectly by forming a complex with ligands that bind iron. Because these ligands can bind multiple metals, that means siderocalin can as well. To demonstrate such binding, Abergel and coworkers obtained six crystal structures of siderocalin bound to various lanthanide and actinide complexes. The overall structures were remarkably similar, with only four of siderocalin’s amino acids adjusting to accommodate the various complexes. The researchers showed that cultured kidney cells took up siderocalin complexed with the ligand enterobactin bound to plutonium.