Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United States.
Glenn T. Seaborg Institute, Lawrence Livermore National Laboratory, Livermore, California 94550, United States.
J Am Chem Soc. 2021 Sep 29;143(38):15769-15783. doi: 10.1021/jacs.1c07103. Epub 2021 Sep 20.
Anthropogenic radionuclides, including long-lived heavy actinides such as americium and curium, represent the primary long-term challenge for management of nuclear waste. The potential release of these wastes into the environment necessitates understanding their interactions with biogeochemical compounds present in nature. Here, we characterize the interactions between the heavy actinides, Am and Cm, and the natural lanthanide-binding protein, lanmodulin (LanM). LanM is produced abundantly by methylotrophic bacteria, including , that are widespread in the environment. We determine the first stability constant for an Am-protein complex (AmLanM) and confirm the results with CmLanM, indicating a ∼5-fold higher affinity than that for lanthanides with most similar ionic radius, Nd and Sm, and making LanM the strongest known heavy actinide-binding protein. The protein's high selectivity over Am's daughter nuclide Np enables lab-scale actinide-actinide separations as well as provides insight into potential protein-driven mobilization for these actinides in the environment. The luminescence properties of the Cm-LanM complex, and NMR studies of Gd-LanM, reveal that lanmodulin-bound f-elements possess two coordinated solvent molecules across a range of metal ionic radii. Finally, we show under a wide range of environmentally relevant conditions that lanmodulin effectively outcompetes desferrioxamine B, a hydroxamate siderophore previously proposed to be important in trivalent actinide mobility. These results suggest that natural lanthanide-binding proteins such as lanmodulin may play important roles in speciation and mobility of actinides in the environment; it also suggests that protein-based biotechnologies may provide a new frontier in actinide remediation, detection, and separations.
人为放射性核素，包括镅和锔等长寿命重放射性元素，是核废料管理的长期主要挑战。这些废物有可能释放到环境中，因此需要了解它们与自然界中存在的生物地球化学化合物的相互作用。在这里，我们描述了重放射性元素镅和锔与天然的镧系元素结合蛋白——蓝藻素（LanM）之间的相互作用。LanM 由包括 在内的甲基营养细菌大量产生，在环境中广泛存在。我们确定了第一个镅-蛋白复合物（AmLanM）的稳定常数，并通过 CmLanM 证实了这一结果，这表明其与最相似离子半径的镧系元素（Nd 和 Sm）的亲和力高约 5 倍，使其成为已知最强的重放射性元素结合蛋白。该蛋白对 Am 的子核素 Np 的高选择性使得可以进行实验室规模的锕系元素-锕系元素分离，并且深入了解了这些锕系元素在环境中可能的蛋白驱动的迁移。Cm-LanM 配合物的发光性质以及对 Gd-LanM 的 NMR 研究表明，蓝藻素结合的 f 族元素在一系列金属离子半径范围内具有两个配位的溶剂分子。最后，我们在广泛的环境相关条件下表明，蓝藻素有效地与去铁胺 B 竞争，而去铁胺 B 是一种羟肟酸铁载体，先前被认为在三价锕系元素的迁移中很重要。这些结果表明，天然的镧系元素结合蛋白，如蓝藻素，可能在环境中锕系元素的形态和迁移中发挥重要作用；这也表明基于蛋白质的生物技术可能为锕系元素的修复、检测和分离提供一个新的前沿。
