Identification, characterization and optimization of lanthanide ion binding peptides for the recovery of rare earth elements

Lanthanides are indispensable in times of modern technology and of extremely high relevance for the future due to their special properties. They provide essential components for high tech products and are used in environmental technology and the green tech industry, which focuses on sustainable products. The growing demand for these valuable metals and the existing high supply risk at the same time, as well as climate and environmental protection policies, are increasingly driving the search for alternative lanthanide extraction solutions. Therefore, a central issue is the recycling of lanthanides from end-of-life products as well as wastewater from agriculture, industry, hospitals and mining, for example. However, efficient recovery currently appears difficult to impossible, as their separation is associated with high costs – not least because of their chemically and physically very similar properties and their relatively low concentration in the product material and waste streams. For these reasons, there is intensive research into new recycling processes to enable a cost effective and environmentally friendly separation of these metals from electronic waste and wastewater, as well as conservation of and independence from primary resources.
Biocollectors and biohybrid separation platforms are promising novel recycling approaches, which are developed in our team of the Helmholtz Institute Freiberg for Resource Technology and the Institute for Resource Ecology of the Helmholtz-Zentrum Dresden-Rossendorf. The new approaches are composed of an appropriate carrier material and target specific peptides immobilized on it and are intended to extract the critical metals from electronic scrap, process waste streams or primary raw material mixtures in this way (Figure 1).
Phage surface display technology was applied for the identification and enrichment of those peptides that show an affinity for europium ions. In a competitive binding experiment, the selected peptide motifs were further reduced and non-specific sequences were discarded. The resulting best europium binding peptide variants were characterized by time-resolved laser fluorescence spectroscopy with respect to their affinity for europium ions and, if necessary, are optimized by site-directed mutagenesis. The four EF-hand peptides from the protein calmodulin will serve as a reference system.