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 Cd 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 Cd than its oxide form. The present study is the first report of Cd 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.

Background: Defensin peptide isolated from plants are often heterogeneous in length, sequence and structure, but they are mostly small, cationic and amphipathic. Plant defensins exhibit broad-spectrum antibacterial and antifungal activities against Gram-positive and Gram-negative bacteria, fungi and etc. Plant defensins also play an important role in innate immunity, such as heavy metal and some abiotic stresses tolerance. Objectives: In this paper, in vitro broad-spectrum activities, antimicrobial and heavy metal absorption, of a recombinant plant defensin were studied. Material and Methods: SDmod gene, a modified plant defensin gene, was cloned in pBISN1-IN (EU886197) plasmid, recombinant protein was produced by transient expression via Agroinfiltration method in common bean. The recombinant protein was tested for antibacterial activity against Gram-negative, Gram-positive bacteria and Fusarium sp. the effects of different treatments on heavy metal zinc absorption by this peptide were tested. Results: We confirmed the antibacterial activities of this peptide against Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus and Bacillus cereus) bacteria, and antifungal activities of this peptide against Fusarium spp. (Fusarium oxysporum and Fusarium solani). High metal absorption coefficient for this peptide was also observed. Results: Out of six actinobacterial isolates, VITVAMB 1 possessed the most efficient RO-16 decolorization property. It decolorized 85.6% of RO-16 (250 mg L -1 ) within 24hrs. Isolate VITVAMB 1 was identified to be Nocardiopsis sp. Maximum dye decolorization occurred at pH 8, temperature 35 o C, 3% salt concentration and a dye concentration of 50 mg L -1 . Conclusions: Results suggesting that modified defensin peptide facilitates a broader range of defense activities. dedefensins are an important part of the innate immune system in eukaryotes. These molecules have multidimensional properties that making them promising agents for therapeutic drugs.