Engineering Short Peptide Sequences for Uranyl Binding

DRGD-linked charged EKKE dimeric dodecapeptide: pH-based amyloid nanostructures and their application in lead and uranium binding

Peptides have been reported to undergo self-assembly into diverse nanostructures, influenced by several parameters, including their amino acid sequence, pH, charge, solvent, and temperature. Inspired by natural systems, researchers have developed biomimetic peptides capable of self-assembling into supramolecular functional structures. The present study explored a newly designed peptide sequence, EKKEDRGDEKKE, where E = glutamic acid, K = lysine, D = aspartic acid, G = glycine, and R = arginine, with a metal binding DRGD sequence incorporated between the exclusively charged EKKE peptide. We investigated the formation and the potential of the EKKEDRGDEKKE peptide in retaining the structure and morphology adopted by the individual EKKE peptide. According to a combination of experimental techniques such as thioflavin T fluorescence, field emission-scanning electron microscopy, atomic force microscopy, and circular dichroism, it was evident that the EKKEDRGDEKKE peptide displayed a pH-dependent propensity to adopt amyloid-like structures. Furthermore, the self-assembled entities formed under acidic, basic, and neutral conditions exhibited morphological variations, which resembled that observed for the exclusively charged EKKE peptide. Furthermore, the incorporation of the functional DRGD motif resulted in promising binding to two toxic metal ions, lead (Pb) and uranium (U), as evidenced by a range of spectroscopic techniques, including UV-visible spectroscopy, atomic absorption spectroscopy, fluorescence spectroscopy, and X-ray photoelectron spectroscopy. The use of the amyloid-forming EKKEDRGDEKKE scaffold can also be extended to potential biomedical applications.

Determining the selectivity of a tetra-phosphorylated biomimetic peptide towards uranium in the presence of competing cations through the simultaneous coupling of HILIC to ESI-MS and ICP-MS

A cyclic tetra-phosphorylated biomimetic peptide (pS1368) has been proposed as a promising starting structure to design a decorporating agent of uranyl (UO22+) due to its affinity being similar to that of osteopontin (OPN), a target UO22+ protein in vivo. The determination of this peptide's selectivity towards UO22+ in the presence of competing endogenous elements is also crucial to validate this hypothesis. In this context, the selectivity of pS1368 towards UO22+ in the presence of Ca2+, Cu2+ and Zn2+ was determined by applying the simultaneous coupling of hydrophilic interaction chromatography (HILIC) to electrospray ionization (ESI-MS) and inductively coupled plasma (ICP-MS) mass spectrometry. Sr2+ was used as Ca2+ simulant, providing less challenging ICP-MS measurements. The separation of the complexes by HILIC was first set up. The selectivity of pS1368 towards UO22+ was determined in the presence of Sr2+, by adding several proportions of the latter to UO2(pS1368). UO22+ was not displaced from UO2(pS1368) even in the presence of a ten-fold excess of Sr2+. The same approach has been undertaken to demonstrate the selectivity of pS1368 towards UO22+ in the presence of Cu2+, Zn2+ and Sr2+ as competing endogenous cations. Hence, we showed that pS1368 was selective towards UO22+ in the presence of Sr2+, but also in the presence of Cu2+ and Zn2+. This study highlights the performance of HILIC-ESI-MS/ICP-MS simultaneous coupling to assess the potential of molecules as decorporating agents of UO22+.

A novel fluorescence sensor for uranyl ion detection based on a dansyl-modified peptide

It is of great significance to sensitively and selectively detect uranyl ion (UO₂²⁺) in environmental and biological samples due to the high risks of UO₂²⁺ to human health. However, such suitable sensors are still scarce. A novel fluorescence sensor based on a dansyl-modified peptide, Dansyl-Glu-Glu-Pro-Glu-Trp-COOH (D-P5), was efficiently synthesized by Fmoc solid phase peptide synthesis. As the first linear peptide-based fluorescence sensor for UO₂²⁺, D-P5 exhibited high selectivity and sensitivity to UO₂²⁺ over 27 metal ions (UO₂²⁺, Cr³⁺, Cu²⁺, Ba²⁺, Hg²⁺, Pb²⁺, Co²⁺, Ag⁺, Fe³⁺, Ca²⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Cd²⁺, Zn²⁺, Al³⁺, Dy³⁺, Er³⁺, Gd²⁺, Ho³⁺, La³⁺, Lu³⁺, Pr³⁺, Sm³⁺, Tm³⁺) by a turn-off fluorescence response in 10 mM HEPES buffer (pH 6.3). The effects of anions such as S^2-, NO₃^-, SO₄^2- CO₃^2-, HCOO^-, antioxidant ascorbic acid and 4-nitrophenyl acetate on the selectivity for UO₂²⁺ detection were also studies. D-P5 sensor could be used for detecting UO₂²⁺ in a good linear relationship with concentration in the range of 0-8.0 μM with a low limit of detection of 83.2 nM. Furthermore, the interaction of the sensor with UO₂²⁺ was characterized by ESI-MS, IR, XPS and ITC measurements. The 1:1 binding stoichiometry between the sensor and UO₂²⁺ was measured by the job's plot and further verified by ESI-MS. The binding constant of the sensor with UO₂²⁺ was calculated to be 9.8 × 10⁴ M^-1 by modified Benesi-Hildebrand equation. ITC results showed that theΔH^θ andΔS^θ for the interaction of D-P5 with UO₂²⁺ were -(7.167 ± 1.25) kJ·mol^-1 and 66.5 J·mol^-1·K^-1, respectively. Time-resolved fluorescence spectroscopy indicated that the mechanism of fluorescence quenching of D-P5 by UO₂²⁺ ion was static quenching process. In addition, this sensor displayed a good practicality for UO₂²⁺ detection in lake water sample without tedious sample pretreatment.

The plasma membrane-associated cation-binding protein PCaP1 of Arabidopsis thaliana is a uranyl-binding protein

Uranium (U) is a naturally-occurring radionuclide that is toxic to living organisms. Given that proteins are primary targets of U(VI), their identification is an essential step towards understanding the mechanisms of radionuclide toxicity, and possibly detoxification. Here, we implemented a chromatographic strategy including immobilized metal affinity chromatography to trap protein targets of uranyl in Arabidopsis thaliana. This procedure allowed the identification of 38 uranyl-binding proteins (UraBPs) from root and shoot extracts. Among them, UraBP25, previously identified as plasma membrane-associated cation-binding protein 1 (PCaP1), was further characterized as a protein interacting in vitro with U(VI) and other metals using spectroscopic and structural approaches, and in planta through analyses of the fate of U(VI) in Arabidopsis lines with altered PCaP1 gene expression. Our results showed that recombinant PCaP1 binds U(VI) in vitro with affinity in the nM range, as well as Cu(II) and Fe(III) in high proportions, and that Ca(II) competes with U(VI) for binding. U(VI) induces PCaP1 oligomerization through binding at the monomer interface, at both the N-terminal structured domain and the C-terminal flexible region. Finally, U(VI) translocation in Arabidopsis shoots was affected in pcap1 null-mutant, suggesting a role for this protein in ion trafficking in planta.

Determination of the affinity of biomimetic peptides for uranium through the simultaneous coupling of HILIC to ESI-MS and ICP-MS

Several proteins have been identified in the past decades as targets of uranyl (UO₂²⁺) in vivo. However, the molecular interactions responsible for this affinity are still poorly known which requires the identification of the UO₂²⁺ coordination sites in these proteins. Biomimetic peptides are efficient chemical tools to characterize these sites. In this work, we developed a dedicated analytical method to determine the affinity of biomimetic, synthetic, multi-phosphorylated peptides for UO₂²⁺ and evaluate the effect of several structural parameters of these peptides on this affinity at physiological pH. The analytical strategy was based on the implementation of the simultaneous coupling of hydrophilic interaction chromatography (HILIC) with electrospray ionization mass spectrometry (ESI-MS) and inductively coupled plasma mass spectrometry (ICP-MS). An essential step had been devoted to the definition of the best separation conditions of UO₂²⁺ complexes formed with di-phosphorylated peptide isomers and also with peptides of different structure and degrees of phosphorylation. We performed the first separations of several sets of UO₂²⁺ complexes by HILIC ever reported in the literature. A dedicated method had then been developed for identifying the separated peptide complexes online by ESI-MS and simultaneously quantifying them by ICP-MS, based on uranium quantification using external calibration. Thus, the affinity of the peptides for UO₂²⁺ was determined and made it possible to demonstrate that (i) the increasing number of phosphorylated residues (pSer) promotes the affinity of the peptides for UO₂²⁺, (ii) the position of the pSer in the peptide backbone has very low impact on this affinity (iii) and finally the cyclic structure of the peptide favors the UO₂²⁺ complexation in comparison with the linear structure. These results are in agreement with those previously obtained by spectroscopic techniques, which allowed to validate the method. Through this approach, we obtained essential information to better understand the mechanisms of toxicity of UO₂²⁺ at the molecular level and to further develop selective decorporating agents by chelation.

Chelating decorporation agents for internal contamination by actinides: Designs, mechanisms, and advances

During the wide utilization of the actinides in medicine, energy, military, and other fields, internal contaminations can profoundly endanger human health and public security. Chelating decorporation agents are the most effective therapies to reduce internal contamination that includes radiological and chemical toxicities. This review introduces the structures of chelating decorporation agents including inorganic salts, polyaminocarboxylic acids, peptides, polyphosphonates, siderophores, calixarenes, polyethylenimines, and fullerenes, and highlights ongoing advances in their designs and mechanisms. However, there are still numerous challenges that block their applications including coordination properties, pharmacokinetic properties, oral bioavailability, limited timing of administration, and toxicity. Therefore, additional efforts are needed to push novel decorporation agents with high efficiency and low toxicity for the treatment of internal contamination by actinides.

Inter-Site Cooperativity of Calmodulin N-Terminal Domain and Phosphorylation Synergistically Improve the Affinity and Selectivity for Uranyl

Uranyl-protein interactions participate in uranyl trafficking or toxicity to cells. In addition to their qualitative identification, thermodynamic data are needed to predict predominant mechanisms that they mediate in vivo. We previously showed that uranyl can substitute calcium at the canonical EF-hand binding motif of calmodulin (CaM) site I. Here, we investigate thermodynamic properties of uranyl interaction with site II and with the whole CaM N-terminal domain by spectrofluorimetry and ITC. Site II has an affinity for uranyl about 10 times lower than site I. Uranyl binding at site I is exothermic with a large enthalpic contribution, while for site II, the enthalpic contribution to the Gibbs free energy of binding is about 10 times lower than the entropic term. For the N-terminal domain, macroscopic binding constants for uranyl are two to three orders of magnitude higher than for calcium. A positive cooperative process driven by entropy increases the second uranyl-binding event as compared with the first one, with ΔΔG = -2.0 ± 0.4 kJ mol-1, vs. ΔΔG = -6.1 ± 0.1 kJ mol-1 for calcium. Site I phosphorylation largely increases both site I and site II affinity for uranyl and uranyl-binding cooperativity. Combining site I phosphorylation and site II Thr7Trp mutation leads to picomolar dissociation constants Kd1 = 1.7 ± 0.3 pM and Kd2 = 196 ± 21 pM at pH 7. A structural model obtained by MD simulations suggests a structural role of site I phosphorylation in the affinity modulation.

Threonine Phosphorylation of an Electrochemical Peptide-Based Sensor to Achieve Improved Uranyl Ion Binding Affinity

We have successfully designed a uranyl ion (U(VI)-specific peptide and used it in the fabrication of an electrochemical sensor. The 12-amino acid peptide sequence, (n) DKDGDGYIpTAAE (c), originates from calmodulin, a Ca(II)-binding protein, and contains a phosphothreonine that enhances the sequence's affinity for U(VI) over Ca(II). The sensing mechanism of this U(VI) sensor is similar to other electrochemical peptide-based sensors, which relies on the change in the flexibility of the peptide probe upon interacting with the target. The sensor was systematically characterized using alternating current voltammetry (ACV) and cyclic voltammetry. Its limit of detection was 50 nM, which is lower than the United States Environmental Protection Agency maximum contaminant level for uranium. The signal saturation time was ~40 min. In addition, it showed minimal cross-reactivity when tested against nine different metal ions, including Ca(II), Mg(II), Pb(II), Hg(II), Cu(II), Fe(II), Zn(II), Cd(II), and Cr(VI). Its reusability and ability to function in diluted aquifer and drinking water samples were further confirmed and validated. The response of the sensor fabricated with the same peptide sequence but with a nonphosphorylated threonine was also analyzed, substantiating the positive effects of threonine phosphorylation on U(VI) binding. This study places emphasis on strategic utilization of non-standard amino acids in the design of metal ion-chelating peptides, which will further diversify the types of peptide recognition elements available for metal ion sensing applications.

A Simple Fluorescence Affinity Assay to Decipher Uranyl-Binding to Native Proteins

Determining the affinity of proteins for uranyl is key to understand the toxicity of this cation and to further develop decorporation strategies. However, usual techniques to achieve that goal often require specific equipment and expertise. Here, we propose a simple, efficient, fluorescence‐based method to assess the affinity of proteins and peptides for uranyl, at equilibrium and in buffered solution. We first designed and characterized an original uranyl‐binding fluorescent probe. We then built a reference scale for uranyl affinity in solution, relying on signal quenching of our fluorescent probe in presence of high‐affinity uranyl‐binding peptides. We finally validated our approach by re‐evaluating the uranyl‐binding affinity of four native proteins. We envision that this tool will facilitate the reliable and reproducible assessment of affinities of peptides and proteins for uranyl.

Hydrophobic core formation and secondary structure elements in uranyl(VI)-binding peptides

Cyclic peptides as well as a modified EF-hand motif of calmodulin have been newly designed to achieve high affinity towards uranyl(VI). Cyclic peptides may be engineered to bind uranyl(VI) to its backbone under acidic conditions, which may enhance its selectivity. For the modified EF-hand motif of calmodulin, strong electrostatic interactions between uranyl(VI) and negatively charged side chains play an important role in achieving high affinity; however, it is also essential to have a secondary structure element and formation of hydrophobic cores in the metal-bound state of the peptide.

Separation of multiphosphorylated cyclopeptides and their positional isomers by hydrophilic interaction liquid chromatography (HILIC) coupled to electrospray ionization mass spectrometry (ESI-MS)

Peptides are efficient models used in different fields such as toxicology to study the interactions of several contaminants at the molecular scale, requiring the development of bio-analytical strategies. In this context, Hydrophilic interaction liquid chromatography (HILIC) coupled to electrospray ionization mass spectrometry (ESI-MS) was used to separate synthetic multiphosphorylated cyclopeptides and their positional isomers at physiological pH. We assessed (i) the selectivity of eleven HILIC columns, from different manufacturers and packed with diverse polar sorbents, and (ii) the effect of mobile phase composition on the separation selectivity. The best selectivity and baseline resolution were achieved with the columns grafted by neutral sorbents amide and diol. Furthermore, we investigated the HILIC retention mechanism of these peptides by examining the effect of the number of phosphorylated residues in the peptide scaffold on their retention. The peptide behavior followed the classical hydrophilic partitioning mechanism exclusively on amide and diol columns. This trend was not fully respected on bare and hybrid silica due to the attractive/repulsive interactions of the deprotonated surface silanol groups with the Arginine or Glutamate residues in the peptide scaffold according to the peptide sequence. The position of the phosphorylated amino acid in the peptide backbone also showed to have an impact on the retention, making possible the separation of positional isomers of these multiphosphorylated cyclic peptides using HILIC.

Uranyl Binding to Proteins and Structural-Functional Impacts

The widespread use of uranium for civilian purposes causes a worldwide concern of its threat to human health due to the long-lived radioactivity of uranium and the high toxicity of uranyl ion (UO₂²⁺). Although uranyl–protein/DNA interactions have been known for decades, fewer advances are made in understanding their structural-functional impacts. Instead of focusing only on the structural information, this article aims to review the recent advances in understanding the binding of uranyl to proteins in either potential, native, or artificial metal-binding sites, and the structural-functional impacts of uranyl–protein interactions, such as inducing conformational changes and disrupting protein-protein/DNA/ligand interactions. Photo-induced protein/DNA cleavages, as well as other impacts, are also highlighted. These advances shed light on the structure-function relationship of proteins, especially for metalloproteins, as impacted by uranyl–protein interactions. It is desired to seek approaches for biological remediation of uranyl ions, and ultimately make a full use of the double-edged sword of uranium.

Recent advances in uranyl binding in proteins thanks to biomimetic peptides

Uranium is an element belonging to the actinide series. It is ubiquitous in rock, soil, and water. Uranium is found in the ecosystem due to mining and milling industrial activities and processing to nuclear fuel, but also to the extensive use of phosphate fertilizers. Understanding uranium binding in vivo is critical, first to deepen our knowledge of molecular events leading to chemical toxicity, but also to provide new mechanistic information useful for the development of efficient decorporation treatments to be applied in case of intoxication. The most stable form in physiological conditions is the uranyl cation (UO₂²⁺), in which uranium oxidation state is +VI. This short review presents uranyl coordination properties and chelation, and what is currently known about uranium binding to proteins. Although several target proteins have been identified, the UO₂²⁺ binding sites have barely been identified. Biomimetic approaches using model peptides are good options to shed light on high affinity uranyl binding sites in proteins. A strategy based on constrained cyclodecapeptides allowed recently to propose a tetraphosphate binding site for uranyl that provides an affinity similar to the one measured with the phosphoprotein osteopontin.

Phosphate-Rich Biomimetic Peptides Shed Light on High-Affinity Hyperphosphorylated Uranyl Binding Sites in Phosphoproteins

Some phosphoproteins such as osteopontin (OPN) have been identified as high-affinity uranyl targets. However, the binding sites required for interaction with uranyl and therefore involved in its toxicity have not been identified in the whole protein. The biomimetic approach proposed here aimed to decipher the nature of these sites and should help to understand the role of the multiple phosphorylations in UO₂ ²⁺ binding. Two hyperphosphorylated cyclic peptides, pS₁₆₈ and pS₁₃₆₈ containing up to four phosphoserine (pSer) residues over the ten amino acids present in the sequences, were synthesized with all reactions performed in the solid phase, including post-phosphorylation. These β-sheet-structured peptides present four coordinating residues from four amino acid side chains pointing to the metal ion, either three pSer and one glutamate in pS₁₆₈ or four pSer in pS₁₃₆₈ . Significantly, increasing the number of pSer residues up to four in the cyclodecapeptide scaffolds produced molecules with an affinity constant for UO₂ ²⁺ that is as large as that reported for osteopontin at physiological pH. The phosphate-rich pS₁₃₆₈ can thus be considered a relevant model of UO₂ ²⁺ coordination in this intrinsically disordered protein, which wraps around the metal ion to gather four phosphate groups in the UO₂ ²⁺ coordination sphere. These model hyperphosphorylated peptides are highly selective for UO₂ ²⁺ with respect to endogenous Ca²⁺ , which makes them good starting structures for selective UO₂ ²⁺ complexation.

A review on nanomaterial-based electrochemical, optical, photoacoustic and magnetoelastic methods for determination of uranyl cation

This review (with 177 refs) gives an overview on nanomaterial-based methods for the determination of uranyl ion (UO₂²⁺) by different types of transducers. Following an introduction into the field, a first large section covers the fundamentals of selective recognition of uranyl ion by receptors such as antibodies, aptamers, DNAzymes, peptides, microorganisms, organic ionophores (such as salophens, catechols, phenanthrolines, annulenes, benzo-substituted macrocyclic diamides, organophosphorus receptors, calixarenes, crown ethers, cryptands and β-diketones), by ion imprinted polymers, and by functionalized nanomaterials. A second large section covers the various kinds of nanomaterials (NMs) used, specifically on NMs for electrochemical signal amplification, on NMs acting as signal tags or carriers for signal tags, on fluorescent NMs, on NMs for colorimetric assays, on light scattering NMs, on NMs for surface enhanced Raman scattering (SERS)-based assays and wireless magnetoelastic detection systems. We then discuss detection strategies, with subsections on electrochemical methods (including ion-selective and potentiometric systems, voltammetric systems and impedimetric systems). Further sections treat colorimetric, fluorometric, resonance light scattering-based, SERS-based and photoacoustic methods, and wireless magnetoelastic detection. The current state of the art is summarized, and current challenges are discussed at the end. Graphical abstract An overview is given on nanomaterial-based methods for the detection of uranyl ion by different types of transducers (such as electrochemical, optical, photoacoustic, magnetoelastic, etc) along with a critical discussion of their limitations, benefits and application to real samples.

Strong Uranium(VI) Binding onto Bovine Milk Proteins, Selected Protein Sequences, and Model Peptides

Hexavalent uranium is ubiquitous in the environment. In view of the chemical and radiochemical toxicity of uranium(VI), a good knowledge of its possible interactions in the environment is crucial. The aim of this work was to identify typical binding and sorption characteristics of uranium(VI) with both the pure bovine milk protein β-casein and diverse related protein mixtures (caseins, whey proteins). For comparison, selected model peptides representing the amino acid sequence 13-16 of β-casein and dephosphorylated β-casein were also studied. Complexation studies using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy revealed that the phosphoryl-containing proteins form uranium(VI) complexes of higher stability than the structure-analog phosphoryl-free proteins. That is in agreement with the sorption experiments showing a significantly higher affinity of caseins toward uranium(VI) in comparison to whey proteins. On the other hand, the total sorption capacity of caseins is lower than that of whey proteins. The discussed binding behavior of milk proteins to uranium(VI) might open up interesting perspectives for sustainable techniques of uranium(VI) removal from aqueous solutions. This was further demonstrated by batch experiments on the removal of uranium(VI) from mineral water samples.

Structural features of uranium-protein complexes

Uranium toxicity depends on its chemical properties rather than on its radioactivity and involves its interaction with macromolecules. Here, a systematic survey of the structural features of the uranyl sites observed in protein crystal structures deposited in the Protein Data Bank is reported. Beside the two uranyl oxygens, which occupy the axial positions, uranium tends to be coordinated by five other oxygen atoms, which occupy the equatorial vertices of a pentagonal bipyramid. Even if one or more of these equatorial positions are sometime empty, they can be occupied only by oxygen atoms that belong to the carboxylate groups of Glu and Asp side-chains, usually acting as monodentate ligands, to water molecules, or to acetate anions. Although several uranium sites appear undefined or unrefined, with a single uranium atom that lacks the two uranyl oxygen atoms, this problem seems to become less frequent in recent years. However, it is clear that the crystallographic refinements of the uranyl sites are not always well restrained and a better parametrization of these restraints seems to be necessary.

A Trishistidine Pseudopeptide with Ability to Remove Both CuΙ and CuΙΙ from the Amyloid-β Peptide and to Stop the Associated ROS Formation

The pseudopeptide L, derived from a nitrilotriacetic acid scaffold and functionalized with three histidine moieties, is reminiscent of the amino acid side chains encountered in the Alzheimer's peptide (Aβ). Its synthesis and coordination properties for CuΙ and CuΙΙ are described. L efficiently complex CuΙΙ in a square-planar geometry involving three imidazole nitrogen atoms and an amidate-Cu bond. By contrast, CuΙ is coordinated in a tetrahedral environment. The redox behavior is irreversible and follows an ECEC mechanism in accordance with the very different environments of the two redox states of the Cu center. This is in line with the observed resistance of the CuΙ complex to oxidation by oxygen and the CuΙΙ complex reduction by ascorbate. The affinities of L for CuΙΙ and CuΙ at physiological pH are larger than that reported for the Aβ peptide. Therefore, due to its peculiar Cu coordination properties, the ligand L is able to target both redox states of Cu, redox silence them and prevent reactive oxygen species production by the CuAβ complex. Because reactive oxygen species contribute to the oxidative stress, a key issue in Alzheimer's disease, this ligand thus represents a new strategy in the long route of finding molecular concepts for fighting Alzheimer's disease.

Peptide nucleic acid as a selective recognition element for electrochemical determination of Hg2

A novel electrochemical PNA-based biosensor for the determination of Hg²⁺ is described. The receptor layer, containing single strands of polythymine PNA (peptide nucleic acid), was formed at the surface of gold electrode. Due to the presence of thymine bases and peptide bonds, an interaction between Hg²⁺ ion and receptor layer occurs. The influence of chain modification - PNA vs. DNA - and type of redox marker - anionic AQMS-Na (sodium salt of anthraquinone-2-sulfonic acid) and Fe^II/III (potassium ferri/ferrocyanide) or cationic MB (methylene blue) and RuHex (hexaammineruthenium(III) chloride) - were studied. Proposed PNA-based biosensor with anionic AQMS-Na as a redox marker demonstrated significantly better analytical parameters, as compared to results obtained for other tested redox markers (for measurements at pH6.0). The linear response towards Hg²⁺ was in the range from 5 to 500nmol·L^-1 with the detection limit of 4.5nmol·L^-1. The developed sensor distinguishes itself with high selectivity towards Hg²⁺, even for solutions containing several interfering cations. Interactions between Hg²⁺ and PNA receptor layer were studied using square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS).

Uranyl Photocleavage of Phosphopeptides Yields Truncated C-Terminally Amidated Peptide Products

The uranyl ion (UO₂²⁺) binds phosphopeptides with high affinity, and when irradiated with UV‐light, it can cleave the peptide backbone. In this study, high‐accuracy tandem mass spectrometry and enzymatic assays were used to characterise the photocleavage products resulting from the uranyl photocleavage reaction of a tetraphosphorylated β‐casein model peptide. We show that the primary photocleavage products of the uranyl‐catalysed reaction are C‐terminally amidated. This could be of great interest to the pharmaceutical industry, as efficient peptide amidation reactions are one of the top challenges in green pharmaceutical chemistry.

Cyclic Phosphopeptides to Rationalize the Role of Phosphoamino Acids in Uranyl Binding to Biological Targets

The specific molecular interactions responsible for uranium toxicity are not yet understood. The uranyl binding sites in high-affinity target proteins have not been identified yet and the involvement of phosphoamino acids is still an important question. Short cyclic peptide sequences, with three glutamic acids and one phosphoamino acid, are used as simple models to mimic metal binding sites in phosphoproteins and to help understand the mechanisms involved in uranium toxicity. A combination of peptide design and synthesis, analytical chemistry, extended X-ray absorption fine structure (EXAFS) spectroscopy, and DFT calculations demonstrates the involvement of the phosphate group in the uranyl coordination sphere together with the three carboxylates of the glutamate moieties. The affinity constants measured with a reliable analytical competitive approach at physiological pH are significantly enhanced owing to the presence of the phosphorous moiety. These findings corroborate the importance of phosphoamino acids in uranyl binding in proteins and the relevance of considering phosphoproteins as potential uranyl targets in vivo.

The enhanced uranyl–amidoxime binding by the electron-donating substituents

This work describes the enhanced binding between uranyl and amidoxime ligands due to the electron-donating effect of the substituents.

Entirely recombinant protein-based hydrogels for selective heavy metal sequestration

Green mining and heavy metal remediation enabled by metalloprotein hydrogels.

A Combined Experimental and Theoretical Study on the Extraction of Uranium by Amino-Derived Metal-Organic Frameworks through Post-Synthetic Strategy

A novel carboxyl-functionalized metal-organic framework for highly efficient uranium sorption was prepared through a generic postsynthetic strategy, and this MOF's saturation sorption capacity is found to be as high as 314 mg·g^-1. The preliminary application illustrated that the grafted free-standing carboxyl groups have notably enhanced the sorption of uranyl ions on MIL-101. In addition, we have performed molecular dynamics simulation combined with density functional theory calculations to investigate the molecular insights of uranyl ions binding on MOFs. The high selectivity and easy separation of the as-prepared material have shown tremendous potential for practical applications in the nuclear industry or radioactive water treatment, and the functionalized MOF can be extended readily upon the versatility of click chemistry. This work provides a facile and purposeful approach for developing MOFs toward a highly efficient and selective extraction of uranium(VI) in aqueous solution, and it further facilitates the structure-based design of nanomaterials for radionuclide-containing-medium pretreatment.

Engineering Short Preorganized Peptide Sequences for Metal Ion Coordination: Copper(II) a Case Study

Peptides are multidentate chiral ligands capable of coordinating different metal ions. Nowadays, they can be obtained with high yield and purity, thanks to the advances on peptide/protein chemistry as well as in equipment (peptide synthesizers). Based on the identity and length of their amino acid sequences, peptides can present different degrees of flexibility and folding. Although short peptide sequences (<20 amino acids) usually lack structure in solution, different levels of structural preorganization can be induced by introducing conformational constraints, such as β-turn/loop template sequences and backbone cyclization. For all these reasons, and the fact that one is not restricted to use proteinogenic amino acids, small peptidic scaffolds constitute a simple and versatile platform for the development of inorganic systems with tailor-made properties and functions. Here we outline a general approach to the design of short preorganized peptide sequences (10-16 amino acids) for metal ion coordination. Based on our experience, we present a general scheme for the design, synthesis, and characterization of these peptidic scaffolds and provide protocols for the study of their metal ion coordination properties.

Density functional theory investigations on the binding modes of amidoximes with uranyl ions

η¹-O of tautomerized amidoximes and η¹-O/η²-N–O of anionic amidoximes are all plausible coordination modes for amidoximes in ligating uranyl ions.

The impact of structural variation in simple lanthanide binding peptides

A series of di-, tri- and tetra-peptides were synthesised using l- and d-glutamic acid in order to determine the effects of peptide length and stereochemistry on lanthanide binding affinity.

Theoretical insight into the binding affinity enhancement of serine with the uranyl ion through phosphorylation

Various type complexes of uranyl ion with serine and phosphoserine were investigated which showed phosphorylation induced binding affinity enhancement of serine with the uranyl ion.

Interactions between uranium(vi) and phosphopeptide: experimental and theoretical investigations

A phosphorylated pentapeptide (WpTPpTW, P¹) motif was designed as a model to mimic possible U(vi) coordination sites of genuine phosphorylated proteins.

Preorganized Peptide Scaffolds as Mimics of Phosphorylated Proteins Binding Sites with a High Affinity for Uranyl

Cyclic peptides with two phosphoserines and two glutamic acids were developed to mimic high-affinity binding sites for uranyl found in proteins such as osteopontin, which is believed to be a privileged target of this ion in vivo. These peptides adopt a β-sheet structure that allows the coordination of the latter amino acid side chains in the equatorial plane of the dioxo uranyl cation. Complementary spectroscopic and analytical methods revealed that these cyclic peptides are efficient uranyl chelating peptides with a large contribution from the phosphorylated residues. The conditional affinity constants were measured by following fluorescence tryptophan quenching and are larger than 10(10) at physiological pH. These compounds are therefore promising models for understanding uranyl chelation by proteins, which is relevant to this actinide ion toxicity.

Fluorescent recognition of uranyl ions by a phosphorylated cyclic peptide

Fluorescent recognition of uranyl ions was achieved using a phosphorylated cyclic peptide, which can be used as a fluorescent sensor.