Metal-Triggered Rheological Switching in Engineered Lanmodulin Condensates

Reliable recovery of rare earth elements (REEs) is increasingly important for energy and communication technologies, yet current separation methods rely on harsh chemistries and are difficult to scale sustainably. Biological strategies offer a promising alternative but typically require immobilized proteins, introducing diffusion limitations and regeneration challenges. Here, we engineer a phase-separating variant of the high-affinity lanthanide-binding protein Lanmodulin (LanM) by fusing it to an encapsulation peptide (EP) microdomain. The resulting chimera, EP-LanM, undergoes liquid–liquid phase separation upon REE binding, forming condensates whose formation and dynamic properties are governed by metal stoichiometry and temperature. These condensates enable selective capture and release of La³⁺ and Nd³⁺ and support efficient recovery and reuse of the protein. Our findings show that metal-triggered protein condensation can be harnessed as an aqueous, reversible mechanism for REE enrichment, establishing a generalizable biophysical approach for designing functional phase-separating proteins for selective metal separation.