Department of Chemistry, The Pennsylvania State University, University Park, PA, USA.
Critical Materials Institute, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA, USA.
Nature. 2023 Jun;618(7963):87-93. doi: 10.1038/s41586-023-05945-5. Epub 2023 May 31.
Technologically critical rare-earth elements are notoriously difficult to separate, owing to their subtle differences in ionic radius and coordination number. The natural lanthanide-binding protein lanmodulin (LanM) is a sustainable alternative to conventional solvent-extraction-based separation. Here we characterize a new LanM, from Hansschlegelia quercus (Hans-LanM), with an oligomeric state sensitive to rare-earth ionic radius, the lanthanum(III)-induced dimer being >100-fold tighter than the dysprosium(III)-induced dimer. X-ray crystal structures illustrate how picometre-scale differences in radius between lanthanum(III) and dysprosium(III) are propagated to Hans-LanM's quaternary structure through a carboxylate shift that rearranges a second-sphere hydrogen-bonding network. Comparison to the prototypal LanM from Methylorubrum extorquens reveals distinct metal coordination strategies, rationalizing Hans-LanM's greater selectivity within the rare-earth elements. Finally, structure-guided mutagenesis of a key residue at the Hans-LanM dimer interface modulates dimerization in solution and enables single-stage, column-based separation of a neodymium(III)/dysprosium(III) mixture to >98% individual element purities. This work showcases the natural diversity of selective lanthanide recognition motifs, and it reveals rare-earth-sensitive dimerization as a biological principle by which to tune the performance of biomolecule-based separation processes.
技术关键的稀土元素由于其离子半径和配位数的细微差异，极难分离。天然镧系元素结合蛋白 Lanmodulin（LanM）是传统溶剂萃取分离的可持续替代方案。在这里，我们描述了一种新的 LanM，来自 Hansschlegelia quercus（Hans-LanM），其多聚状态对稀土离子半径敏感，镧（III）诱导的二聚体比镝（III）诱导的二聚体强 100 多倍。X 射线晶体结构说明了镧（III）和镝（III）之间皮米级半径差异如何通过羧酸转移传递到 Hans-LanM 的四级结构，从而重新排列第二球氢键网络。与来自 Methylorubrum extorquens 的原型 LanM 的比较揭示了不同的金属配位策略，合理化了 Hans-LanM 在稀土元素中的更高选择性。最后，对 Hans-LanM 二聚体界面上关键残基的结构引导突变调节了溶液中二聚体的形成，并能够在单级、基于柱的分离中，将钕（III）/镝（III）混合物分离到>98%的单个元素纯度。这项工作展示了选择性镧系元素识别基序的天然多样性，并揭示了稀土敏感二聚化作为一种生物原理，可用于调节基于生物分子的分离过程的性能。
