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难以分离，因为它们在离子半径和配位数^1,2,3上存在细微差别。天然镧系元素结合蛋白 lanmodulin (LanM) ^{4,5是传统基于溶剂萃取的分离6}的可持续替代品。在这里，我们描述了一种新的 LanM，它来自Hansschlegelia quercus ( Hans -LanM)，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 倍二聚体。X 射线晶体结构说明镧 (III) 和镝 (III) 之间的皮米级半径差异如何传播到汉斯-LanM 的四级结构通过重排第二球氢键网络的羧酸盐转变。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 在稀土元素中的更大选择性。最后， Hans-关键残基的结构引导诱变LanM 二聚体界面调节溶液中的二聚作用，并使钕 (III)/镝 (III) 混合物的单级、基于柱的分离达到 >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，可以通过该原理调整基于生物分子的分离过程的性能。