(515b) Probing Molecular Conformations of Lanthanide Binding Peptides at Air-Water Interface

Lanthanides, or rare earth elements (REEs) are critical materials with unique luminescent, magnetic and catalytic properties that are exploited in a wide range of clean energy technologies which require REEs in high purity. However, REEs are difficult to separate from each other due to their similar size and electric valence. Thus, there is a growing need for green methods to separate these elements from mixtures. Lanthanide-binding tags (LBTs), engineered from the calcium-binding motif of bacterial proteins have been designed to bind selectively to Tb³⁺. Furthermore, LBT adsorb at air-water interfaces, and thus can used as peptide surfactant for REE recovery by froth flotation methods. In order to understand the selective binding mechanism of LBT variants to different REEs (such as La³⁺, Tb³⁺ and Lu³⁺), here we have performed enhanced-sampling molecular dynamics simulations (Metadynamics) to investigate the binding free energy landscape of LBT peptides and various trivalent REE cations in aqueous solution and at air-water interface. For each LBT-REE system, we have identified 5 to 6 different metastable binding structures with small free energy differences (∆∆G ≤1 kcal/mol), revealing the hidden complexity of the LBT-REE binding complex conformations. Importantly, we were able to quantify the influence of air-water interface on the molecular conformations of LBT-REE complexes, which is difficulty to probe from macroscopic experiments. This work paves road for determining quantitative structure-activity relationship of lanthanide binding peptides, as well as designing novel peptide surfactants for green and efficient REE extractions.