Near-Adjacent Heavy Lanthanide Separation and Sensing Using Dimerizing Lanmodulins

Abstract

Protein-based recovery, detection, and separation of rare earth elements (REs) have accelerated since the discovery of the lanmodulin (LanM) proteins. While exceptional at total RE recovery, prior proteins, like most ligands, exhibited limited ability to differentiate REs, whether in detection or separations. Here we report two dimerizing LanMs (Al-LanM and Xan-LanM) that address these challenges. Uniquely among biomolecules, these proteins promote luminescence of up to six specific REs, enabling their use as biosensors to prospect for bacteria that accumulate the valuable heavy RE, terbium. The average adjacent-element separation factor (SF) for Al-LanM and structure-guided variants over the range of 11 REs, Nd–Lu, is 2.1, among the best for any ligand, protein or otherwise. By construction and immobilization of tandem dimers of Al-LanM competent to self-dimerize, we nearly double SF(Nd/Dy) relative to the immobilized monomer, establishing that protein dimerization amplifies RE discrimination. Leveraging this on-column dimerization behavior, we achieve separation of Y, Dy, Gd, Sm, and Nd from one another to >95% purities from a mixed-RE leachate derived from allanite ore, with just one pH step per element. In achieving robust protein-based separations with the simplest desorption scheme to date, our work highlights the many knobs biology uses to tune metal ion selectivity and introduces high-performance bioligands to identify heavy RE-accumulating organisms and to separate the most valuable REs, NdIII–LuIII.