Once released into the environment, radioactive materials pose risks to humans and animals. Scientists at Lawrence Berkeley National Laboratory found that siderocalin, an iron-transport protein, binds radioactive actinide elements, such as thorium, plutonium, americium, and curium. This discovery reveals a molecular mechanism to probe and possibly remediate a radioactively contaminated environment.
Discovery of the siderocalin transport mechanism provides scientists not only with the ability to develop treatments based on blocking the uptake of actinide elements, but also brings forth a novel coordination method that could be harnessed for energy applications and environmental cleanup. The siderocalin-actinide complexes are the first protein structures containing transuranic elements in the Protein Data Bank.
The threat of human exposure to synthetic radioactive elements, such as the actinides, has greatly increased over the last several decades, both from expansion of nuclear energy and development of advanced nuclear weapons. Once released, actinides pose health risks to humans and animals through environmental contamination. Although containment of actinides has been the goal of much research, methods to detect and remediate actinides from the environment are also needed. To explore new ligand platforms for chemical studies of actinides and discover remediation techniques, researchers at Lawrence Berkeley National Laboratory investigated siderocalin, a protein found in mammalian cells that typically binds and transports iron. The team discovered that, in addition to transporting iron, siderocalin could also bind several actinide elements. To function properly, siderocalin forms strong electrostatic interactions with a natural iron-chelating compound named Enterobactin. Because siderocalin interacts with Enterobactin instead of iron directly, the iron can be swapped for other metal ions, such as actinides. This finding provides a mechanism for reclaiming actinides released into the environment. Although the environmental implications of this research are of great importance, benefits also exist for many other areas of science. Using crystallography, the team identified complexes of siderocalin with thorium, plutonium, americium, and curium and submitted the complexes to the Protein Data Bank. These structures are the first in the Protein Data Bank to contain thorium and transuranic actinide elements and bring new fundamental information on the coordination properties of these elements. Additionally, the team found that the complex of siderocalin and the actinide elements have increased fluorescence compared to the element itself. Scientists could exploit this phenomenon in future technology to improve photoluminescence, diagnostic, and bio-imaging tools.
Rebecca J. Abergel
Lawrence Berkeley National Laboratory
This work was funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences under Contract DE-AC02-05CH11231, and by the National Institutes of Health under Award R01DK073462. The Advanced Light Source is a DOE user facility supported by the Office of Science, Office of Basic Energy Sciences under Contract DE-AC02-05CH11231.
B.E. Allred, P.B. Rupert, S.S. Gauny, D.D. An, C.Y. Ralston, M. Sturzbecher-Hoehne, R.K. Strong, and R.J. Abergel, "Siderocalin-mediated recognition, sensitization, and cellular uptake of actinides." Proceedings of the National Academy of Sciences USA 112, 10342 (2015). [DOI: 10.1073/pnas.1508902112]
Lawrence Berkeley National Laboratory news release: Cellular Contamination Pathway for Plutonium, Other Heavy Elements, Identified
C&EN Concentrates: Iron-Binding Protein Transports Actinides into Cells