Cadmium detection by a thermally responsive elastin copolymer with metal-binding functionality

Heavy metals are of great concern to environmental safety because of their adverse effects on the environment and human health, even at very low levels. In particular, cadmium and several cadmium-containing compounds are carcinogens and induce many types of cancer. Biological extracts of cadmium have been given greater attention recently because they are considered to be environmentally benign and economically acceptable. Among promising candidates, one emerging technology is the use of tunable, metal-binding biopolymers based on elastin-like polypeptides (ELPs). An ELP consists of the repeating pentapeptide of specific amino acids, Val-Pro-Gly-Xaa-Gly (where the "guest residue" Xaa is any amino except proline) that undergoes a reversible phase transition at a specific temperature (transition temperature, Tt). However, the ELP itself is relatively non-selective. A biopolymer with metal-binding domains that have stronger affinity, capacity, and selectivity would have distinct advantages. We investigated the use of a new generation of ELP biopolymers, EC18-ELP containing synthetic phytochelatin (EC), which is a metal-binding protein with a repetitive motif (Glu-Cys)nGly, as the metal-binding domain. In this study, an EC18-ELP fusion protein was expressed in Escherichia coli and the metal binding ability of EC to cadmium was examined quantitatively. In addition, transition temperature variation was analyzed when the fusion protein bound to cadmium.