Reducing Binding Site Heterogeneity via Truncation of the RTX Domain Enhances Selectivity for Rare Earth Element Separation

Rare earth elements (REEs) are critical components of modern technologies but present a notoriously difficult separation challenge. Here, we report a rationally truncated variant of the calcium-binding RTX domain that improves REE selectivity by reducing binding site heterogeneity. The engineered scaffold, RTX(2), exhibits improved binding affinity, structure stability, pH-tunable elution, and enhanced chromatographic resolution, achieving over 200-fold selectivity within the REE series.