Experimental and theoretical studies of cadmium ions absorption by a new reduced recombinant defensin

Heavy metal pollutants such as Cd, Hg, Pb, As, and Se are considered as both a global problem and a growing threat to the humanity. Being strongly poisonous to the metal-sensitive enzymes and leading to the growth inhibition and death of organisms, these metals have a toxic impact on the plants and animals. Inducing the metal-binding cysteine-rich peptides such as metallothioneins, phytochelatins, and defensins, higher organisms like plants and animals usually react to the heavy metal stress. In this study, a recombinant defensin protein was expressed in bean and its ability in the cadmium absorption was determined. Experimental studies revealed that this protein was able to absorb cadmium ions in reduced form more than oxide one. Molecular dynamics simulations were carried out in order to evaluation of experimental studies, using a model of Cd²⁺ or Na⁺ and Cl^- ions enclosed in a fully hydrated simulation box with the recombinant defensin. The theoretical results also suggested that the reduced recombinant defensin was more powerful in the absorption of Cd²⁺ than its oxide form. The present study is the first report of Cd²⁺ absorption potential of this new reduced recombinant defensin. The results unraveled that this recombinant defensin can be adopted as a molecular switch in the cadmium pollution of the environment and also the important role of sulfur groups in the absorption of cadmium ions.