Metal-binding Peptides Research Articles

Designing Gold Binding Peptides: Modelling and Experiment at the Bio-Abiotic Interface

The interface of biological and abiological material is an area of intense interest, touching on a widespread application space of sensors, bioelectronics, designer coatings, self-healing materials. Building upon our work in reconfigurable electronic devices, part of our efforts were focused on engineering E. coli to display metal binding peptides using a bacterial display system, eCPX. Here, we present our efforts in understanding cell binding to Au(111) surfaces as well as gold nanoparticles (AuNPs) through a series of known and designed gold binding peptides (GBPs) that have been engineered into eCPX. First, we demonstrate that integration of specific GBPs into the E. coli outer membrane protein increases binding to both Au(111) surfaces and AuNPs, that the binding to gold is selective, and is influenced by interactions with specific amino acids. Second, from molecular dynamics (MD) simulations of select GBPs on Au(111), we show that interaction energies between the peptides and surface correlate with experimental data, and that both thermodynamic and entropic effects play a role in binding. And finally, we demonstrate a novel fragment-based computer-aided biomaterial design approach using Au(111) as a proof of concept. These findings will be discussed in the greater context of our work in transformational synthetic biology for military environments.

Isolation and Sequencing of Cu-, Fe-, and Zn-Binding Whey Peptides for Potential Neuroprotective Applications as Multitargeted Compounds.

This study aims to isolate metal-binding peptides and synthesize promising amino acid sequences to potentially act as neuroprotective compounds in the future, targeting different mechanisms. Fractions of whey metal-binding peptides (Cu, Fe, and Zn) isolated by immobilized metal affinity chromatography showed different amino acid profiles according to the metal. The Cu-binding peptides presented roughly twofold increase in the in vitro antioxidant, as assessed by oxygen radical absorbance capacity and anticholinesterase activities over the hydrolysate. This is probably because of the higher concentration of aromatic and basic residues, the latter being crucial for binding to the anionic sites of acetylcholinesterase. Six peptide sequences were synthesized based on the metal-binding sites, molecular mass, hydrophobicity, and bioactivity probability. Among the synthetic peptides, the VF dipeptide stood out both for its in vitro antioxidant and anticholinesterase activities. This peptide, as well as the fraction of Cu-binding peptides, should be further studied because it may act through different mechanisms related to neurodegenerative diseases, in addition to the chelation of the excess of metals in the central nervous system.

Self-Immobilized Putrescine Oxidase Biocatalyst System Engineered with a Metal Binding Peptide.

Flavin oxidases are valuable biocatalysts for the oxidative synthesis of a wide range of compounds, while at the same time reduce oxygen to hydrogen peroxide. Compared to other redox enzymes, their ability to use molecular oxygen as an electron acceptor offers a relatively simple system that does not require a dissociable coenzyme. As such, they are attractive targets for adaptation as cost-effective biosensor elements. Their functional immobilization on surfaces offers unique opportunities to expand their utilization for a wide range of applications. Genetically engineered peptides have been demonstrated as enablers of the functional assembly of biomolecules at solid material interfaces. Once identified as having a high affinity for the material of interest, these peptides can provide a single step bioassembly process with orientation control, a critical parameter for functional immobilization of the enzymes. In this study, for the first time, we explored the bioassembly of a putrescine oxidase enzyme using a gold binding peptide tag. The enzyme was genetically engineered to incorporate a gold binding peptide with an expectation of an effective display of the peptide tag to interact with the gold surface. In this work, the functional activity and expression were investigated, along with the selectivity of the binding of the peptide-tagged enzyme. The fusion enzyme was characterized using multiple techniques, including protein electrophoresis, enzyme activity, and microscopy and spectroscopic methods, to verify the functional expression of the tagged protein with near-native activity. Binding studies using quartz crystal microbalance (QCM), nanoparticle binding studies, and atomic force microscopy studies were used to address the selectivity of the binding through the peptide tag. Surface binding AFM studies show that the binding was selective for gold. Quartz crystal microbalance studies show a strong increase in the affinity of the peptide-tagged protein over the native enzyme, while activity assays of protein bound to nanoparticles provide evidence that the enzyme retained catalytic activity when immobilized. In addition to showing selectivity, AFM images show significant differences in the height of the molecules when immobilized through the peptide tag compared to immobilization of the native enzyme, indicating differences in orientation of the bound enzyme when attached via the affinity tag. Controlling the orientation of surface-immobilized enzymes would further improve their enzymatic activity and impact diverse applications, including oxidative biocatalysis, biosensors, biochips, and biofuel production.

The Impact of Using some Adjunct Cultures on the Quality of Fermented Camel Milk Fortified with Iron

Lipid oxidation is one of the key determinants of the quality of iron-fortified dairy products. In this study, using starter cultures possessing a high ability to release metal-binding peptides during fermentation and storage was proposed to address the quality problems related to fortification of fermented milk with iron. For this purpose, a combination of commercial yogurt starter (CS) with Lactobacillus plantarum B-4496 (LP) or Lactobacillus paracasei subsp . paracasei B-4560(LPC)wasused to ferment camel milk, which was fortified with ferrous sulphate at a level of 40 mg iron/kg milk. Fermented milk was stored at 4±1°C for 14 days. Proteolysis degree and thiobarbituric acid (TBA) value were evaluated for all treatments, while iron chelating activity (ICA) and fatty acids composition were determined for the iron-free treatments. The results revealed that starter culture combinations had a significant influence (p˂0.05) on all studied parameters. Samples containing CS-LPC showed the highest proteolysis degree, ICA and TBA values as compared to CS or CS-LP samples. The presence of iron significantly increased TBA value of fermented milk. Proteolysis degree, ICA and TBA values increased significantly in all treatments with increasing storage time except for the TBA values of iron-free samples and iron-fortified samples containing CS that remained stable during storage. Differences in fatty acids composition were observed among fermented milks and ranged from little to remarkable. The high ICA, particularly in CS-LPC treatment did not prevent the development of lipid oxidation during storage. This study suggests that the ability to chelate iron in fermented milk is likely to be less important than the effect related to the fatty acids composition. Therefore, evaluating the ability of starter cultures to alter the fatty acids composition of dairy products is critical to determine their suitability for use in iron-fortified milks.

PH dependent chelation study of Zn(II) and Ni(II) by a series of hexapeptides using electrospray ionization – Ion mobility – Mass spectrometry

Presented here are the results of a study characterizing the selective metal chelating performance of the alternative metal binding (amb) peptide: acetyl-His1-Cys2-Gly3-Pro4-His5-Cys6-OH, and eight ambs with systematic modifications to His, Cys, and carboxyl C-terminus metal chelating sites. The results show that from the divalent metal ions of zinc, nickel, cobalt, magnesium and calcium, the ambs most extensively formed complexes with zinc and nickel. The ambs, which retained both Cys2 and Cys6 in their primary structure, exhibited the greatest formation of zinc complexes. The replacement of His1 and His5 residues with two additional Cys with the amidation of the C-terminus also increased the zinc chelation at pH 7.0. Density functional theory indicated that these modifications might be disrupting the hydrogen bonding between the His-Cys and carboxylate terminus making the 4Cys more available for chelation. Nickel chelation was generally lower than zinc because of competition from the Cys to form disulfide bonds in the presence of nickel. The two ambs that formed the highest number of nickel complexes both included the amidated C-termini and either 4Cys or 2Cys-2His. Comparison with recent published results of six heptapeptide ambs, which have the same primary structures, but with the inclusion of Tyr5 before the final two residues, indicates the inclusion of the Tyr5 residue increases the zinc chelation at pH 7.0 from 25%, of total observed species, to 70%. These types of studies may pave the way to discoveries of new therapeutics suitable as enzyme inhibitors or chelators for diseases associated with metal homeostasis misbalances, or as new peptide tags for recombinant protein purification.

Front Cover: Recombinant Peptide Fusion Protein‐Templated Palladium Nanoparticles for Suzuki‐Miyaura and Stille Coupling Reactions (ChemCatChem 11/2020)

The Front Cover shows recombinant peptide fusion protein-directed palladium nanoparticles that are catalytically active for Suzuki-Miyaura and Stille coupling reactions in green solvent. In their Communication, I. Mosleh et al. show that metal-binding peptides remain functional after fusing to a green fluorescent protein (GFPuv). This work opens the possibility to use inexpensive peptide sources and shows their ability with palladium to synthesize the anticancer drug Tykerb® precursor. We are grateful to M. A. Ziba Rajabi for designing the cover image. More information can be found in the Communication by I. Mosleh et al.

Identification of Metal-Binding Peptides and Their Conjugation onto Nanoparticles of Superparamagnetic Iron Oxides and Liposomes.

Metallic materials are used for clinical medical devices such as vascular stents and coils to treat both ischemic and hemorrhagic vascular diseases. An antiplatelet drug is required to avoid thromboembolic complication until metallic surface is covered with a neo-endothelial cell layer. It is important to identify endothelial cell coverage on the metallic surface. However, it is difficult since there are no selective ligands. Here, we used the phage display method to identify peptide ligands that had high affinity for the metallic surface of Ni-Ti stents, Pt-W coils, and Co-Cr stents. The binding assay using fluorescence labeling revealed that several synthetic peptides could bind onto those surfaces. We also chose some oligopeptides for the conjugation onto superparamagnetic iron oxide (SPIO) nanoparticles and liposome-encapsulating SPIO nanoparticles and studied their ability to bind to the stent and coils. By SEM and fluorophotometry, we found that those modified SPIOs and liposomes were selectively bound onto those surfaces. In addition, both treated stents and coils could be detected by magnetic resonance imaging due to the magnetic artifact through the SPIOs and liposomes that were immobilized onto the surface. Thus, we identified metal-binding peptides which may enable to stop antiplatelet therapy after vascular stenting or coiling.

Microalgal Metallothioneins and Phytochelatins and Their Potential Use in Bioremediation.

The persistence of heavy metals (HMs) in the environment causes adverse effects to all living organisms; HMs accumulate along the food chain affecting different levels of biological organizations, from cells to tissues. HMs enter cells through transporter proteins and can bind to enzymes and nucleic acids interfering with their functioning. Strategies used by microalgae to minimize HM toxicity include the biosynthesis of metal-binding peptides that chelate metal cations inhibiting their activity. Metal-binding peptides include genetically encoded metallothioneins (MTs) and enzymatically produced phytochelatins (PCs). A number of techniques, including genetic engineering, focus on increasing the biosynthesis of MTs and PCs in microalgae. The present review reports the current knowledge on microalgal MTs and PCs and describes the state of art of their use for HM bioremediation and other putative biotechnological applications, also emphasizing on techniques aimed at increasing the cellular concentrations of MTs and PCs. In spite of the broad metabolic and chemical diversity of microalgae that are currently receiving increasing attention by biotechnological research, knowledge on MTs and PCs from these organisms is still limited to date.

A new approach to biomining: Bioengineering surfaces for metal recovery from aqueous solutions

Electronics waste production has been fueled by economic growth and the demand for faster, more efficient consumer electronics. The glass and metals in end-of-life electronics components can be reused or recycled; however, conventional extraction methods rely on energy-intensive processes that are inefficient when applied to recycling e-waste that contains mixed materials and small amounts of metals. To make e-waste recycling economically viable and competitive with obtaining raw materials, recovery methods that lower the cost of metal reclamation and minimize environmental impact need to be developed. Microbial surface adsorption can aid in metal recovery with lower costs and energy requirements than traditional metal-extraction approaches. We introduce a novel method for metal recovery by utilizing metal-binding peptides to functionalize fungal mycelia and enhance metal recovery from aqueous solutions such as those found in bioremediation or biomining processes. Using copper-binding as a proof-of-concept, we compared binding parameters between natural motifs and those derived in silico, and found comparable binding affinity and specificity for Cu. We then combined metal-binding peptides with chitin-binding domains to functionalize a mycelium-based filter to enhance metal recovery from a Cu-rich solution. This finding suggests that engineered peptides could be used to functionalize biological surfaces to recover metals of economic interest and allow for metal recovery from metal-rich effluent with a low environmental footprint, at ambient temperatures, and under circumneutral pH.

Peptide-Induced Biomineralization of Tin Oxide (SnO2) Nanoparticles for Antibacterial Applications

Recently, there has been growing attention and effort to search for new microbicidal drugs which present different mode of action from those already existing, as an alternative to the global threat of fungal and bacterial multi drug resistance (MDR). Here we propose biological synthesis of SnO₂ nanoparticles using mammalian cells as an economic and ecofriendly platform. This presents a novel biogenic method for SnO₂ synthesis using metal binding peptides extracted from MCF-7 human cancer cells, which induces the biomineralization of SnO₂ nanoparticles. A series of electron donor functional groups and metal binding sites in these peptides reacts with Sn2+ ions and directs the growth of SnO₂ nanoparticles without addition of toxic redox and capping agents in the reaction system. Since peptides present reactive sites in aqueous solution at room temperature, a facile reaction environment can be easily achieved. Furthermore, by tuning the reactants' concentration and pH, the size, shape and 3D-structures of SnO₂ nanoparticles can be controlled. Peptides also ensure biocompatibility, and SnO₂ nanoparticles provide antibacterial properties, which broadens their applications in biomedical fields.

Reduction of the Cytotoxicity of Copper (II) Oxide Nanoparticles by Coating with a Surface-Binding Peptide.

Copper (II) oxide nanoparticles (CuO-NPs) have been studied as potential antimicrobial agents, similar to silver or platinum nanoparticles. However, the use of excess NPs is limited by their safety and toxicity in beneficial microflora and human cells. In this study, we evaluated the cytotoxicity of CuO-NPs by coating with a novel cyclic peptide, CuO binding peptide 1 (CuBP1), cyclic-SCATPFSPQVCS, which binds to the surface of CuO-NPs. CuBP1 was identified using biopanning of a T7 phage display system and was found to promote the aggregation of CuO-NPs under mild conditions. The treated CuO-NPs with CuBP1 caused the reduction of the cytotoxicity against Escherichia coli, Lactobacillus helveticus, and five other microorganisms, including bacteria and eukaryotes. Similar effects were also demonstrated against human embryonic kidney (HEK293) cells in vitro. Our findings suggested that the CuO-NPs coated with a surface-binding peptide may have applications as a safe antimicrobial agent without excessive cytotoxic activity against beneficial microflora and human cells. Moreover, a similar tendency may be achieved with other metal particles, such as silver or platinum NPs, by using optimal metal binding peptides.

Overexpression of phytochelatin synthase AtPCS2 enhances salt tolerance in Arabidopsis thaliana

Phytochelatin synthase (PCS) is an enzyme that synthesizes phytochelatins, which are metal-binding peptides. Despite the important role of PCS in heavy metal detoxification or tolerance, the functional role of PCS with respect to other abiotic stresses remains largely unknown. In this study, we determined the function of Arabidopsis thaliana phytochelatin synthase 2 (AtPCS2) in the salt stress response. Expression of AtPCS2 was significantly increased in response to 100 and 200 mM NaCl treatment. AtPCS2-overexpressing transgenic Arabidopsis and tobacco plants displayed increased seed germination rates and seedling growth under high salt stress. In addition, transgenic Arabidopsis subjected to salt stress exhibited enhanced proline accumulation and reduced Na+/K+ ratios compared to wild type plants. Furthermore, decreased levels of hydrogen peroxide (H2O2) and lipid peroxidation were observed in transgenic Arabidopsis compared to wild type specimens. Salt stress greatly reduced transcript levels of CuSOD2, FeSOD2, CAT2, and GR2 in wild type but not transgenic Arabidopsis. Notably, levels of CAT3 in transgenic Arabidopsis were markedly increased upon salt stress, suggesting that low accumulation of H2O2 in transgenic Arabidopsis is partially achieved through induction of CAT. Collectively, these results suggest that AtPCS2 plays a positive role in seed germination and seedling growth under salt stress through a series of indirect effects that are likely involved in H2O2 scavenging, regulation of osmotic adjustment and ion homeostasis.

A Facile Method to Prepare a Hydrophilic/Hydrophobic Metal Surface by Peptide.

A facile method to prepare a hydrophilic/hydrophobic metal surface by metal-binding peptide was proposed in this article. Metal-binding peptide sequenced NLNPNTASAMHV was taken as the target peptide to interact with stainless steel. The surface morphology, roughness and Fourier-Transform Infrared spectroscopy (FTIR) showed that some changes occurred on the modified stainless steel surface. Not only were the surfaces coarser but also some organic groups appeared on the modified sample surfaces. By comparing the CAs of all the samples, the most suitable concentration of peptide and treating time were determined. A new and facile way to endow some metals surfaces with hydrophobicity or hydrophilicity has been developed, which is useful especially for antibiofouling.

Recombinant Escherichia coli as a biofactory for various single- and multi-element nanomaterials

Nanomaterials (NMs) are mostly synthesized by chemical and physical methods, but biological synthesis is also receiving great attention. However, the mechanisms for biological producibility of NMs, crystalline versus amorphous, are not yet understood. Here we report biosynthesis of 60 different NMs by employing a recombinant Escherichia coli strain coexpressing metallothionein, a metal-binding protein, and phytochelatin synthase that synthesizes a metal-binding peptide phytochelatin. Both an in vivo method employing live cells and an in vitro method employing the cell extract are used to synthesize NMs. The periodic table is scanned to select 35 suitable elements, followed by biosynthesis of their NMs. Nine crystalline single-elements of Mn3O4, Fe3O4, Cu2O, Mo, Ag, In(OH)3, SnO2, Te, and Au are synthesized, while the other 16 elements result in biosynthesis of amorphous NMs or no NM synthesis. Producibility and crystallinity of the NMs are analyzed using a Pourbaix diagram that predicts the stable chemical species of each element for NM biosynthesis by varying reduction potential and pH. Based on the analyses, the initial pH of reactions is changed from 6.5 to 7.5, resulting in biosynthesis of various crystalline NMs of those previously amorphous or not-synthesized ones. This strategy is extended to biosynthesize multi-element NMs including CoFe2O4, NiFe2O4, ZnMn2O4, ZnFe2O4, Ag2S, Ag2TeO3, Ag2WO4, Hg3TeO6, PbMoO4, PbWO4, and Pb5(VO4)3OH NMs. The strategy described here allows biosynthesis of NMs with various properties, providing a platform for manufacturing various NMs in an environmentally friendly manner.

Peptides and their Metal Complexes in Neurodegenerative Diseases: from Structural Studies to Nanomedicine Prospects.

The metal ions dyshomeostasis is increasingly recognized to play a crucial role in the development of aging-related neurodegenerative diseases. Metal trafficking in the brain is related to proteins regulating both uptake and efflux of metals in neurons. Different pathways may occur, depending on specific binding features of metallo-protein complexes. In particular, copper, zinc and iron are recognized to influence the biochemistry of proteins involved in neurodegeneration (for instance Aβ and α-synuclein), as well as those playing a crucial role in neuronal development and efficiency (neurotrophins). Nowadays the application of peptide-based drugs is widespread for different pathologies, but the short lifetime in vivo due to proteolysis and other shortcomings still limit their use. A structured search was performed about the state of the art on: i) peptidomimetic approaches used to obtain peptides mimicking the metal binding activities of proteins involved in neurons survival, ii) peptide-based nanostructures, as promising biomaterials in tissue engineering and substrates for neurites outgrowth and synapses formation. Recent developments on metal-binding peptides and peptide nanostructures for therapeutic application in neurodegenerative diseases are reviewed, showing as metal ions interaction may affect structural and biological properties of different proteins involved in neurodegenerative diseases. This review provides a survey on peptides able to mimic some biofunctional activities of the whole protein, e.g., the binding features to metal ions, thus highlighting their promising potentialities as new, more effective, therapeutics. The integration of such peptides into multifunctional nanoplatforms can be a smart route for the development of biomaterials scaffolds and nanomedicine applications.

Manganese and cobalt recovery by surface display of metal binding peptide on various loops of OmpC in Escherichia coli.

In a cell-surface display (CSD) system, successful display of a protein or peptide is highly dependent on the anchoring motif and the position of the display in that anchoring motif. In this study, a recombinant bacterial CSD system for manganese (Mn) and cobalt (Co) recovery was developed by employing OmpC as an anchoring motif on three different external loops. A portion of Cap43 protein (TRSRSHTSEG)3 was employed as a manganese and cobalt binding peptide (MCBP), which was fused with OmpC at three different external loops. The fusions were made at the loop 2 [fusion protein-2 (FP2)], loop 6 (FP6), and loop 8 (FP8) of OmpC, respectively. The efficacy of the three recombinant strains in the recovery of Mn and Co was evaluated by varying the concentration of the respective metal. Molecular modeling studies showed that the short trimeric repeats of peptide probably form a secondary structure with OmpC, thereby giving rise to a difference in metal recovery among the three recombinant strains. Among the three recombinant strains, FP6 showed increased metal recovery with both Mn and Co, at 1235.14 (1mM) and 379.68 (0.2mM) µmol/g dry cell weight (DCW), respectively.

Binding Selectivity of Methanobactin from Methylosinus trichosporium OB3b for Copper(I), Silver(I), Zinc(II), Nickel(II), Cobalt(II), Manganese(II), Lead(II), and Iron(II).

Methanobactin (Mb) from Methylosinus trichosporium OB3b is a member of a class of metal binding peptides identified in methanotrophic bacteria. Mb will selectively bind and reduce Cu(II) to Cu(I), and is thought to mediate the acquisition of the copper cofactor for the enzyme methane monooxygenase. These copper chelating properties of Mb make it potentially useful as a chelating agent for treatment of diseases where copper plays a role including Wilson's disease, cancers, and neurodegenerative diseases. Utilizing traveling wave ion mobility-mass spectrometry (TWIMS), the competition for the Mb copper binding site from Ag(I), Pb(II), Co(II), Fe(II), Mn(II), Ni(II), and Zn(II) has been determined by a series of metal ion titrations, pH titrations, and metal ion displacement titrations. The TWIMS analyses allowed for the explicit identification and quantification of all the individual Mb species present during the titrations and measured their collision cross-sections and collision-induced dissociation patterns. The results showed Ag(I) and Ni(II) could irreversibly bind to Mb and not be effectively displaced by Cu(I), whereas Ag(I) could also partially displace Cu(I) from the Mb complex. At pH ≈ 6.5, the Mb binding selectivity follows the order Ag(I)≈Cu(I)>Ni(II)≈Zn(II)>Co(II)>>Mn(II)≈Pb(II)>Fe(II), and at pH 7.5 to 10.4 the order is Ag(I)>Cu(I)>Ni(II)>Co(II)>Zn(II)>Mn(II)≈Pb(II)>Fe(II). Breakdown curves of the disulfide reduced Cu(I) and Ag(I) complexes showed a correlation existed between their relative stability and their compact folded structure indicated by their CCS. Fluorescence spectroscopy, which allowed the determination of the binding constant, compared well with the TWIMS analyses, with the exception of the Ni(II) complex. Graphical abstract ᅟ.

In Planta Synthesis of Designer-Length Tobacco Mosaic Virus-Based Nano-Rods That Can Be Used to Fabricate Nano-Wires.

We have utilized plant-based transient expression to produce tobacco mosaic virus (TMV)-based nano-rods of predetermined lengths. This is achieved by expressing RNAs containing the TMV origin of assembly sequence (OAS) and the sequence of the TMV coat protein either on the same RNA molecule or on two separate constructs. We show that the length of the resulting nano-rods is dependent upon the length of the RNA that possesses the OAS element. By expressing a version of the TMV coat protein that incorporates a metal-binding peptide at its C-terminus in the presence of RNA containing the OAS we have been able to produce nano-rods of predetermined length that are coated with cobalt-platinum. These nano-rods have the properties of defined-length nano-wires that make them ideal for many developing bionanotechnological processes.

Simplified Expression and Production of Small Metal Binding Peptides

Phage display for discovery of specific binding peptides is nowadays widely used in the pharmaceutical industry and in many biotechnological applications. Using state-of-the-art cloning techniques we developed an easy-to-use cloning and expression system, allowing the fast production of identified peptides while avoiding proteolysis.

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.