Technologically critical rare-earth elements are notoriously difficult to separate, owing to their subtle differences in ionic radius and coordination number^1,2,3. The natural lanthanide-binding protein lanmodulin (LanM)^4,5 is a sustainable alternative to conventional solvent-extraction-based separation⁶. 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.

众所周知，技术上关键的稀土元素很难分离，因为它们在离子半径和配位数^1,2,3方面存在细微差别。天然镧系元素结合蛋白 lanmodulin (LanM) ^4,5是传统溶剂萃取分离法的可持续替代品⁶ 。在这里，我们描述了一种来自Hansschlegelia quercus ( Hans -LanM)的新LanM，其具有对稀土离子半径敏感的低聚状态，镧(III)诱导的二聚体比镝(III)诱导的二聚体紧密100倍以上二聚体。 X 射线晶体结构说明了镧 (III) 和镝 (III) 之间的皮米级半径差异如何通过羧酸盐位移传播到Hans -LanM 的四级结构，从而重新排列第二球氢键网络。与来自Mmethylorubrum 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 在稀土元素中的更大选择性。最后，对Hans- LanM 二聚体界面的关键残基进行结构引导诱变，调节溶液中的二聚化，并实现基于柱的单级分离，将钕 (III)/镝 (III) 混合物分离至 >98% 的单元素纯度。这项工作展示了选择性镧系元素识别基序的自然多样性，并揭示了稀土敏感二聚化作为一种​​生物学原理，通过该原理来调整基于生物分子的分离过程的性能。