(304e) Improving Cerium (III) Ion Binding Affinity of Designed Peptides Based on EF-1 Hand Loop of Lanmodulin

In recent years, the demand for rare earth elements (REEs) has drastically increased due to their applications in several advanced technologies such as wind turbines, satellites, electric cars, and biomedical devices, etc. However, the growing demand along with limited national resources and the high environmental impact of mining highlights the need for novel low-cost, efficient, and environmentally friendly technologies to recover and recycle these materials from end-of-life products and industrial waste streams. Among several methods that have been proposed, bio-based technologies have gained excessive attention because of their eco-friendly nature, low cost, high selectivity, high regeneration, and fast kinetics. Lanmodulin is a highly selective lanthanide binding protein found in Methylobacterium extorquens. It has four sequences characterized as EF-hand loops which are known to bind to REEs. Peptides based on these EF-hand sequences are potentially attractive in REE capture. Peptides are smaller than the whole protein counterpart, which makes them easier to tune, and could result in increased binding capacity. Other advantages of peptides include ease of synthesis, robustness, and low production cost.

In the present work, we designed several peptides based on the EF-1 hand loop of Lanmodulin to improve the REE ion binding affinity, specifically targeting modulation of entropy in the process. Circular dichroism (CD) and isothermal titration calorimetry (ITC) experiments were performed to confirm binding and estimate the thermodynamic properties such as ΔG, ΔH, ΔS, dissociation constant (K_d), and binding sites (N). It is found that all designed peptides have REE ion binding affinity, where ΔG is negative and ΔH and ΔS are positive, confirming the binding is entropy-driven. The estimated dissociation constant (K_D) values range from around 1.0 µM and 10 µM by sequence-defined tuning of ΔS. A significant structure-function mathematical relationship can be drawn between amino acid content and ΔS. The insights captured in this study will help design peptides that span an order of magnitude in K_d which is important in developing peptide-grafted polymeric membranes for REE separation processes.