Lanmodulin: A Highly Selective Lanthanide-Binding Protein from a Lanthanide-Utilizing Bacterium

Constraints on lanthanide separation by selective biosorption

Lanthanides, key components of sustainable energy technologies, can be separated using microorganisms with selective biosorption capabilities that sometimes rival traditional solvent extraction methods. Recent discoveries show that single genetic mutations in Shewanella oneidensis can improve lanthanide biosorption selectivity, while larger genomic modifications in Vibrio natriegens yield greater improvements. To evaluate whether these enhancements are sufficient for industrial implementation, we developed three theoretical models of lanthanide separation by biosorption and desorption. Model 1 suggests that single-locus genetic changes could reduce separation time by 25%, while multi-locus modifications could achieve up to 90% reduction. Model 2 indicates that with multiple binding sites, larger genetic modifications would be necessary for high-purity separation. Model 3 proposes an alternative approach using multiple microbes with modest selectivity improvements: initial microbes enrich the target lanthanide, while subsequent ones remove contaminants.

Design and Evolution of a Phosphorescent Protein via the Proximal Encoding of Lanthanide and the Antenna Chromophore

Genetically encoded phosphorescent proteins with extended luminescence lifetimes provide an orthogonal channel for biological imaging and detection. While conventional fluorescent proteins typically exhibit nanosecond-scale lifetimes, the development of proteins with longer lifetimes enables time-resolved detection and enhanced signal-to-noise ratios. Here, we designed a novel phosphorescent protein system by incorporating photosensitizing unnatural amino acids (UAAs) proximal to the metal center of a lanthanide binding protein (LanM). Through systematic optimization of the incorporation sites, we achieved considerable enhancement in lanthanide phosphorescence compared with that of the wild-type LanM protein. The subsequent directed evolution of LanM and chemical evolution of UAA yielded variants with an additional muti-fold increase in signal intensity. This iterative optimization strategy generated phosphorescent proteins with extended lifetimes of up to 500 μs and significantly increased brightness. Using this phosphorescence protein platform, a europium sensor with a signal-to-noise ratio of more than 100 for 200 nM Eu(III) and a detection limit of less than 10 nM was developed. In addition, a protease sensor was further designed by inserting a cleavage site into a loop of the phosphorescent protein, achieving remarkable signal-to-noise ratios at nanomolar concentrations. Finally, this phosphorescent protein was fused to the affibody and further used for immunofluorescence imaging. These applications demonstrated a novel platform for developing genetically encoded sensors with enhanced detection sensitivity through time-resolved measurements.

Rare-Earth Element Adsorption to Membranes Functionalized with Lanmodulin-Derived Peptides

Rare-earth elements (REEs) are important components of modern technology and require highly selective separation for recovery and purification. Biosorbents are an emerging class of materials for REE separation that take advantage of the natural affinity and selectivity of proteins or peptides for REE metals. Increasing the capacity while maintaining selectivity is an important practical challenge for the adoption of this technology. This contribution presents a peptide-functionalized membrane adsorber and characterizes peptide loading, REE affinity, and REE binding capacity. A hydrophilic monomer, 2-hydroxyethyl methacrylate, was copolymerized with hydrophobic allyl methacrylate and grafted from poly(vinylbenzyl chloride) electrospun membranes. Hydrophilicity, membrane morphology, and equilibrium adsorption isotherms for La and Nd in pH 5.2 solutions were measured to compare the grafted allyl methacrylate homopolymer and the copolymer containing 2-hydroxyethyl methacrylate. Ultimately, the addition of a hydrophilic comonomer improves the accessibility for peptide loading and increases the level of REE binding in aqueous solutions; however, it reduces the selectivity from 2.3 to 1.1 for Nd/La.

Lanthanides Gd and Tm Can Inhibit Carnitine/Acylcarnitine Transporter: Insights from All-Atoms Simulations

Recent experimental evidence highlighted the inhibition of carnitine/acylcarnitine carrier (CAC), an important mitochondrial transmembrane protein for living organisms, by the early lanthanide Pr3+. A possible explanation of such a behaviour was found in the preference of the cation for amino acids like aspartate and glutamate containing a carboxylate in the side chain, laying in the inter-membrane space. Interaction of the cation with these residues can cause halt the transfer of the protein's substrates between the matrix and cytoplasm thus opening to new scenarios concerning the CAC-metal interactions and its relative inhibition. In the present work, the panel of metals binding the CAC protein is predictively expanded including Gd3+ and Tm3+, selected as representative species of middle and late lanthanides, respectively. A more realistic membrane-containing model of the protein was built and the comparative analysis of the molecular dynamics (MD) simulations of CAC apo-form with its complexed systems, named CAC-Pr, CAC-Gd and CAC-Tm, was performed. The analysis of the trajectories revealed that the inhibition is caused by the coordination of D132 and E179 to the cations and that such interactions generate a reorganization of important salt-bridges inside the framework of CAC. In detail, MD simulations highlighted that a spontaneous conformational change from cytoplasmatic-state (c-state) to matrix-state (m-state) induced by cations and that, in this condition, the protein channel is occluded, thus explaining the inhibition.

A novel protein for bioremediation of gadolinium waste

Several hundreds of tons of gadolinium-based contrast agents (GBCAs) are being dumped into the environment every year. Although macrocyclic GBCAs exhibit superior stability compared to their linear counterparts, we have found that the structural integrity of chelates is susceptible to ultraviolet light, regardless of configuration. In this study, we present a synthetic protein termed GLamouR that binds and reports gadolinium in an intensiometric manner. We then explore the extraction of gadolinium from MRI patient urine as a preventative measure for gadolinium pollution and investigate the viability of employing cost-effective bioremediation techniques for treating contaminated water bodies. Based on promising results, we anticipate proteins such as GLamouR can be used for detecting and mining rare earth elements beyond gadolinium and hope to expand the biological toolbox for such applications.

High-Fidelity In Vitro Packaging of Diverse Synthetic Cargo into Encapsulin Protein Cages

Cargo-filled protein cages are powerful tools in biotechnology with demonstrated potential as catalytic nanoreactors and vehicles for targeted drug delivery. While endogenous biomolecules can be packaged into protein cages during their expression and self-assembly inside cells, synthetic cargo molecules are typically incompatible with live cells and must be packaged in vitro. Here, we report a fusion-based in vitro assembly method for packaging diverse synthetic cargo into encapsulin protein cages that outperforms standard in cellulo assembly, producing cages with superior uniformity and thermal stability. Fluorescent dyes, proteins and cytotoxic drug molecules can all be selectively packaged with high efficiency via a peptide-mediated targeting process. The exceptional fidelity and broad compatibility of our in vitro assembly platform enables generalisable access to cargo-filled protein cages that host novel synthetic functionality for diverse biotechnological applications.

Lanmodulin-Decorated Microbes for Efficient Lanthanide Recovery

Rare earth elements (REEs) are essential for many clean energy technologies. Yet, they are a limited resource currently obtained through carbon-intensive mining. Here, bio-scaffolded proteins serve as simple, effective materials for the recovery of REEs. Surface expression of the protein lanmodulin (LanM) on E. coli, followed by freeze-drying of the microbes, yields a displayed protein material for REE recovery. Four REE cations (Y3+, La3+, Gd3+, and Tb3+) are captured efficiently, with over 80% recovery even in the presence of competitive ions at one-hundred-fold excess. Moreover, these materials are readily integrated into a filter with high capture capacity (12 mg g-1 dry cell weight) for the selective isolation and recovery of REEs from complex matrices. Further, the proteins in the filter remain stable over ten bind-and-release cycles and a week of storage. To improve the deployability of this filter material, a simple colorimetric assay with the dye alizarin-3-methyliminodiacetic acid is incorporated. The assay can be performed in under 5 min, enabling rapid monitoring of REE recovery and filter efficiency. Overall, this low-cost, robust material will enable environmentally friendly recycling and recovery of critical elements.

Lanthanide-Controlled Protein Switches: Development and In Vitro and In Vivo Applications

Lanthanides, which are part of the rare earth elements group have numerous applications in electronics, medicine and energy storage. However, our ability to extract them is not meeting the rapidly increasing demand. The discovery of the bacterial periplasmic lanthanide-binding protein lanmodulin spurred significant interest in developing biotechnological routes for lanthanide detection and extraction. Here we report the construction of β-lactamase-lanmodulin chimeras that function as lanthanide-controlled enzymatic switches. Optimized switches demonstrated dynamic ranges approaching 3000-fold and could accurately quantify lanthanide ions in simple colorimetric or electrochemical assays. E.coli cells expressing such chimeras grow on β-lactam antibiotics only in the presence of lanthanide ions. The developed lanthanide-controlled protein switches represent a novel platform for engineering metal-binding proteins for biosensing and microbial engineering.

Evaluation of Metal Accumulation in Escherichia coli Expressing SPL2 by Single-Cell Inductively Coupled Plasma Mass Spectrometry

Rare earth elements, comprising 17 elements including 15 lanthanides, are essential components in numerous high-tech applications. While physicochemical methods are commonly employed to remove toxic heavy metals (e.g., cadmium and mercury) from industrial wastewater, biological approaches offer increasingly attractive alternatives. Biomining, which utilizes microorganisms to extract valuable metals from ores and industrial wastes, and bioremediation, which leverages microorganisms to adsorb and transport metal ions into cells via active transport, provide eco-friendly solutions for resource recovery and environmental remediation. In this study, we investigated the potential of three recently identified lanthanide-binding proteins-SPL2, lanpepsy, and lanmodulin-for applications in these areas using single-cell inductively coupled plasma mass spectrometry (scICP-MS). Our results demonstrate that SPL2 exhibits superior characteristics for lanthanide and cadmium bioremediation. Heterologous expression of a cytosolic fragment of SPL2 in bacteria resulted in high expression levels and solubility. Single-cell ICP-MS analysis revealed that these recombinant bacteria accumulated lanthanum, cobalt, nickel, and cadmium, effectively sequestering lanthanum and cadmium from the culture media. Furthermore, SPL2 expression conferred enhanced bacterial tolerance to cadmium exposure. These findings establish SPL2 as a promising candidate for developing recombinant bacterial systems for heavy metal bioremediation and rare earth element biomining.

Application of phage surface display for the identification of Eu3+-binding peptides

Europium as one of the rare earth elements (REE) has outstanding properties in terms of its application for high-tech and renewable energy products. The high supply risk of REE, coupled with their low recovery rates from secondary sources, necessitates innovative recycling approaches. We introduce a phage display-based peptide biosorbent recycling technology that offers a cost-effective and environmentally friendly solution for recovering metal ions, supporting circular economy goals. In this study, we used phage surface display to screen for peptides with high affinity for europium (III) ions (Eu3+). Performing several independent biopanning experiments with the Ph.D.-12 Phage Display Peptide Library and different elution methods as well as combining them with next-generation sequencing, we identified eight peptides with moderate to good affinities for Eu3+ ions, verified by time-resolved laser fluorescence spectroscopy. The peptides EALTVNIKREME as well as DVHHVDGNDLQPFEGGGS and DSIHSDVTKDGRYPVEGGGS, the latter are variants of enriched dodecamers, proved to be the best candidates for future biosorption and selectivity studies. This study underscores the potential of phage surface display for peptide-based REE recovery, laying the foundation for selective recycling technologies from secondary raw materials.

Conformationally Adaptable Extractant Flexes Strong Lanthanide Reverse-Size Selectivity

Chemical selectivity is traditionally understood in the context of rigid molecular scaffolds with precisely defined local coordination and chemical environments that ultimately facilitate a given transformation of interest. By contrast, nature leverages dynamic structures and strong coupling to enable specific interactions with target species in otherwise complex media. Taking inspiration from nature, we demonstrate unconventional selectivity in the solvent extraction of light over heavy lanthanides using a conformationally flexible ligand called octadecyl acyclopa (ODA). This novel ligand forms pseudocyclic molecular complexes with lanthanide ions at organic/aqueous interfaces, revealed by vibrational sum frequency generation spectroscopy. These complexes are extracted into the organic phase, where femtosecond structural dynamics are probed by two-dimensional infrared spectroscopy and ab initio molecular dynamics simulations to mechanistically frame the macroscopic selectivity trends. We find larger-than-expected structural fluctuations and bond lengths for heavy Ln-ODA complexes that arise from an inability of ODA to contort around the smaller ions to satisfy all would-be bonding interactions, despite forming some individually strong bonds. This finding contrasts with the binding of ODA with lighter lanthanides where, despite individually weaker bonds, collective interactions manifest that minimize structural fluctuations and give rise to enhanced thermodynamic stability. These results point to a new paradigm where conformational dynamics and cumulative bonding interactions can be used to facilitate unconventional chemical transformations.

A lanmodulin-based fluorescent assay for the rapid and sensitive detection of rare earth elements

Sensitive and rapid detection methods for rare earth elements (REEs), including lanthanides (Lns), will facilitate the mining and recovery of these elements. Here, we innovated a rapid, highly selective and sensitive fluorescence detection method for Lns, based on Hans-Lanmodulin, a newly discovered protein with high selectivity and binding affinity for rare earth elements. By labelling the fluorescein moiety FITC onto Hans-Lanmodulin, named as FITC-Hans-LanM. When rare earth ions are present in solution, FITC-Hans-LanM will specifically bind rare earth ions undergoing a conformational change from a disordered state to a dimer, in which the FITC molecules come close to each other, resulting in decreasing fluorescence intensity or even quenching. The assay was responsive to light, medium and heavy rare earth ions. The fluorescence signal has a good linear relationship with Nd3+ concentration in the range of 1-20 nM. The detection limit of the method was 0.512 nM, within 1 min. This method could become a useful technique for the detection and quantification of rare earth elements in environmental and industrial samples.

Tuning the lanthanide binding tags for preferential actinide chelation: an all atom molecular dynamics study

The present study focuses on designing mutant peptides derived from the lanthanide binding tag (LBT) to enhance selectivity for trivalent actinide (An3+) ions over lanthanide (Ln3+) metal ions (M). The LBT is a short peptide consisting of only 17 amino acids, and is known for its high affinity towards Ln3+. LBT was modified by substituting hard-donor ligands like asparagine (ASN or N) and aspartic acid (ASP or D) with softer ligand cysteine (CYS or C) to create four mutant peptides: M-LBT (wild-type), M-N103C, M-D105C, and M-N103C-D105C. All atom molecular dynamics (MD) simulations were employed to analyze the binding dynamics and affinities of these mutants with Eu3+ and Am3+ as representatives for trivalent Ln and An ions, respectively. Hydrogen bond dynamics and short-range Coulomb interactions are evaluated from the equilibrium run for all the systems. The study utilized an enhanced sampling method, namely, well-tempered meta-dynamics (WT-MtD), to overcome sampling challenges and obtain converged free energy profiles for the metal-binding interactions. Our simulations studies indicate that both single and double mutations alter the coordination environment within the peptide's binding pocket, potentially increasing Am3+ selectivity over the Eu3+ ion. The binding of Eu3+ and Am3+ to LBT systems was analyzed, showing an unbinding energy barrier of ∼60 kJ mol-1 for the wild-type. The N103C variant increases the binding strength with a barrier over 100 kJ mol-1, while D105C shows a preference for Am3+ with a barrier around 70 kJ mol-1. The doubly mutated N103C-D105C variant favors Am3+ by more than 20 kJ mol-1. The findings suggest N103C for general chelation and N103C-D105C for preferential trivalent Ln/An separation. These insights contribute to the development of more effective and selective chelating agents for preferential actinide binding.

QM Investigation of Rare Earth Ion Interactions with First Hydration Shell Waters and Protein-Based Coordination Models

Conventional methods for extracting rare earth metals (REMs) from mined mineral ores are inefficient, expensive, and environmentally damaging. Recent discovery of lanmodulin (LanM), a protein that coordinates REMs with high-affinity and selectivity over competing ions, provides inspiration for new REM refinement methods. Here, we used quantum mechanical (QM) methods to investigate trivalent lanthanide cation (Ln3+) interactions with coordination systems representing bulk solvent water and protein binding sites. Energy decomposition analysis (EDA) showed differences in the energetic components of Ln3+ interaction with representatives of solvent (water, H2O) and protein binding sites (acetate, CH3COO-), highlighting the importance of accurate description of electrostatics and polarization in computational modeling of REM interactions with biological and bioinspired molecules. Relative binding free energies were obtained for Ln3+ with coordination complexes originating from binding sites in PDB structures of a lanthanum binding peptide (PDB entry 7CCO) and LanM, with explicit consideration of the first hydration shell waters, according to quasi-chemical theory (QCT). Beyond the first shell, the bulk solvent environment was represented with an implicit continuum model. Ln3+ interactions with (H2O)9 and both binding site models became more favorable, moving down the periodic series. This trend was more pronounced with the protein binding site models than with water, resulting in affinity increasing with periodic number, except for the last REM, Lu3+, which bound less favorably than the preceding element, Yb3+. Using the truncated 7CCO binding site model, the magnitude and trend of the experimental Ln3+ relative binding free energies for the whole 7CCO peptide were reproduced. Conversely, the previously reported experimental data for LanM show a preference for the earlier lanthanides; this is likely due to longer-range interactions and cooperative effects, which are not represented by the reduced models. Using the truncated 7CCO binding site model, the magnitude and trend of the experimental Ln3+ relative binding free energies for the whole 7CCO peptide were reproduced. In contrast to the previously reported experimental data for LanM, the peptide preferentially binds the earlier lanthanides. This difference likely arises due to longer-range interactions and cooperative effects not represented by the peptide. Further investigation of Ln3+ interactions with whole proteins using polarizable molecular mechanics models with explicit solvent is warranted to understand the influence of longer-ranged interactions, cooperativity, and bulk solvent. Nevertheless, the present work provides new insights into Ln3+ interactions with biomolecules and presents an effective computational platform for designing specific single-site REM binding peptides more efficiently.

Kinetic and Affinity Profiling Rare Earth Metals Using a DNA Aptamer

Rare earth elements (REEs) are widely used in various high-tech industries. Developing affinity ligands that can detect and distinguish REEs is at the forefront of analytical chemistry. It is also interesting to understand the limits of natural biomolecules for the recognition of REEs. In this study, Sc3+ was used as a target for the isolation of DNA aptamers, and an aptamer named Sc-1 was obtained. Using a thioflavin T (ThT) fluorescence assay, Sc-1 bound only to REEs, but not other metal ions. Additionally, the binding of Sc-1 to Sc3+ exhibited slow kinetics, and the binding complex resisted dissociation by EDTA. Furthermore, Sc-1 displayed varying binding kinetics with trivalent lanthanide ions, allowing for the discrimination of 17 REEs into three major groups: (1) La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, and Gd3+; (2) Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+, and Y3+; and (3) Sc3+. NMR spectroscopy confirmed binding-induced conformational changes in the aptamer. Using the fluorescence strand-displacement method, the true Kd of the aptamer was measured to range from 0.6 to 258.5 nM for the REE ions, and it showed effective detection of Sc3+ in real samples.

Extensive and diverse lanthanide-dependent metabolism in the ocean

To date, the only known Lanthanide (Ln)-dependent enzymes are pyrroloquinoline quinone-dependent alcohol dehydrogenases. When compared to their Ca dependent counterparts, there is an emerging picture that Ln-dependent versions of these enzymes are generally more efficient, are preferentially upregulated in the presence of Ln when there is functional redundancy, and may even be evolutionarily older. Ln-utilising microbes have furthermore evolved diverse means of solubilizing and acquiring Ln, enabling them to utilize Ln even at trace concentrations. The ocean is the largest dissolved organic carbon pool on Earth, yet the diversity and prevalence of Ln-dependent carbon metabolisms in the ocean is unknown. Here we show that Ln-utilising methanol-, ethanol- and putative sorbose- and glucose-dehydrogenase genes are ubiquitous in the ocean and are highly transcribed, despite extremely low concentrations of Ln in seawater. These enzymes occur in the genomes of 20% of marine microbes, with several individual organisms hosting dozens of unique Ln-utilising enzymes. We found that active microbial methanol oxidation in the ocean is almost entirely Ln-dependent. The widespread biological utility of Ln may help to explain the nutrient-like vertical concentration profiles of these elements in ocean waters and may exert an influence on rare earth element concentration patterns. Microbial Ln-utilisation is a poorly understood component of marine rare earth element biogeochemistry, with potentially important implications for the carbon cycle. The ocean microbiome will be a rich resource for future research into biologically inspired solutions to lanthanide extraction and purification.

Emerging role of rare earth elements in biomolecular functions

The importance of rare earth elements is increasingly recognized due to the increased demand for their mining and separation. This demand is driving research on the biology of rare earth elements. Biomolecules associated with rare earth elements include rare earth element-dependent enzymes (methanol dehydrogenase XoxF, ethanol dehydrogenase ExaF/PedH), rare earth element-binding proteins, and the relevant metallophores. Traditional (chemical) separation methods for rare earth elements harvesting and separation are typically inefficient, while causing environmental problems, whereas bioharvesting, potentially, offers more efficient, more green platforms. Here, we review the current state of research on the biological functions of rare earth element-dependent biomolecules, and the characteristics of the relevant proteins, including the specific amino acids involved in rare earth metal binding. We also provide an outlook at strategies for further understanding of biological processes and the potential applications of rare earth element-dependent enzymes and other biomolecules.

Living plastics from plasticizer-assisted thermal molding of silk protein

The pursuit of materials, particularly plastics, with a minimal ecological footprint throughout their circular lifecycle, is crucial for advancing sustainable materials development. Living materials composed of embedded yet active organisms can leverage endogenous biotic resources to achieve functional materials that align with sustainability goals. However, current living material systems face challenges such as weak mechanical properties, limited environmental adaptability, and restricted cellular functionality. In this study, we propose an approach to sustainable living materials by incorporating active organisms into silk-based plastics through a plasticizer-assisted thermal molding process. We investigate the mechanism of structure formation in these materials, correlating manufacturing performance to the resulting secondary structure. These silk-based plastics provide a protective matrix for probiotics, ensuring their survival through the harsh gastrointestinal tract and enhancing intestinal delivery. Similarly, soil rhizobacteria encapsulated within the plastics exhibit long-term protease activity, accelerating plastic degradation upon soil exposure. This work demonstrates the potential of sustainable plastics as a form of living materials, where active organisms are processed, entrapped, retain metabolic functions, and are protected in harsh environments.

From rock to living systems: Lanthanides toxicity and biological interactions

Since the discovery of lanthanides, the expanding range of applications and the growing demand for lanthanides in different aspects of life have escalated their dispersion in the environment, raising concerns about their impact on the living world. This review explores the interaction between lanthanides and different groups of living organisms (bacteria, algae, lichens, plants, invertebrates, and low vertebrates), reflecting the current state of scientific knowledge. We have aimed to provide a comprehensive overview of relevant studies, highlight existing gaps, and suggest potential areas for future research to enhance the understanding of this topic.

Bioinspired Metal-Ligand Networks with Enhanced Stability and Performance: Facile Preparation of Hydroxypyridinone (HOPO)-Functionalized Materials

Bioinspired hydroxypyridinone (HOPO)functionalized materials are shown to display a remarkable capacity for stability and for chelating a wide array of metal ions. This allows for the synthesis of multifunctional networks with diverse physical properties when compared to traditional catechol systems. In the present study, we report a facile, one-pot synthesis of an amino HOPO ligand and simple, scalable incorporation into PEG-acrylate based networks via active ester chemistry. This modular network approach allows for fabrication of patterned HOPO containing networks which can chelate a range of metal ions, such as transition metals (Fe3+) and lanthanides (Ho3+, Tb3+), leading to modulation of mechanical, magnetic, and fluorescent properties. Moreover, networks with tailored, heterogeneous properties can be prepared through localization of metal ion incorporation in 3-dimensions via masking techniques, creating distinctly soft, hard, magnetic, and fluorescent domains.

Lanthanide binding peptide surfactants at air-aqueous interfaces for interfacial separation of rare earth elements

Rare earth elements (REEs) are critical materials to modern technologies. They are obtained by selective separation from mining feedstocks consisting of mixtures of their trivalent cation. We are developing an all-aqueous, bioinspired, interfacial separation using peptides as amphiphilic molecular extractants. Lanthanide binding tags (LBTs) are amphiphilic peptide sequences based on the EF-hand metal binding loops of calcium-binding proteins which complex selectively REEs. We study LBTs optimized for coordination to Tb3+ using luminescence spectroscopy, surface tensiometry, X-ray reflectivity, and X-ray fluorescence near total reflection, and find that these LBTs capture Tb3+ in bulk and adsorb the complex to the interface. Molecular dynamics show that the binding pocket remains intact upon adsorption. We find that, if the net negative charge on the peptide results in a negatively charged complex, excess cations are recruited to the interface by nonselective Coulombic interactions that compromise selective REE capture. If, however, the net negative charge on the peptide is -3, resulting in a neutral complex, a 1:1 surface ratio of cation to peptide is achieved. Surface adsorption of the neutral peptide complexes from an equimolar mixture of Tb3+ and La3+ demonstrates a switchable platform dictated by bulk and interfacial effects. The adsorption layer becomes enriched in the favored Tb3+ when the bulk peptide is saturated, but selective to La3+ for undersaturation due to a higher surface activity of the La3+ complex.

Gravity-Driven Separation for Enrichment of Rare Earth Elements Using Lanthanide Binding Peptide-Immobilized Resin

Rare Earth Elements (REEs) constitute indispensable raw materials and are employed in a diverse range of devices, including but not limited to smartphones, electric vehicles, and clean energy technologies. While there is an increase in demand for these elements, there is a global supply challenge due to limited availability and geopolitical factors affecting their procurement. A crucial step in manufacturing these devices involves utilizing highly pure REEs, often obtained through complex and nonsustainable processes. These processes are vital in isolating individual REEs from mixtures containing non-REEs and other REEs. There exists an urgent requirement to explore alternative techniques that enable the selective recovery of REEs through more energy-efficient processes. To overcome the limitations mentioned above, we developed a microbead-based technology featuring immobilized lanthanide binding peptides (LBPs) for the selective adsorption of REEs. This technology does not require the utilization of external stimuli but uses gravity-based separation processes to separate the bound REE from the unbound REE. We demonstrate this technology's potential by enriching two relevant REEs (Europium and Terbium). Additionally, we propose a mechanism whereby REEs bind selectively to a particular LBP, leveraging the distinctive physicochemical characteristics of both the REE and the LBP. Moreover, these LBPs exhibit no binding affinity toward other frequently encountered industrial ions. Finally, we demonstrate the recovery of REEs through a change in system conditions and assess the reusability of the microbeads for subsequent adsorption cycles. We anticipate that this approach will address the challenges of REE recovery and demonstrate the potential of biomolecular strategies in advancing sustainable resource management.

Structure-Function Insights into Thermoresponsive Copolymers as Lanthanide Precipitants

The synthetic toolbox for stimuli-responsive polymers has broadened to include many tunable variables, making these materials applicable in diverse technologies. However, unraveling the key composition-structure-function relationships to facilitate ground-up design remains a challenge due to the inherent dispersity in sequence and conformations for synthetic polymers. We here present a systematic study of these relationships using a model system of copolymers with a thermoresponsive (N-isopropylacrylamide) backbone in addition to metal-chelating (acrylic acid) and hydrophobic structural comonomers and evaluate their efficiency at isolating technologically critical lanthanide ions. The efficiency of lanthanide ion extraction by precipitation was quantitated with a metallochromic dye to reveal trends relating copolymer hydrophobicity to improved separations. Further, we examined the role of different hydrophobic comonomers in dictating the solution-phase conformation of the polymer in the presence and absence of lanthanide ions, and we correlated key features of the hydrophobic comonomer to extraction efficiency. Finally, we identified how the local proximity of thermoresponsive, chelating, and hydrophobic subunits facilitates metal extraction by manipulating the copolymer sequence with multiblock polymerization. Through mechanistic analysis, we propose a binding-then-assembly process through which metal ions are coprecipitated with macromolecular chelators.

Pathway to industrial application of heterotrophic organisms in critical metals recycling from e-waste

The transition to renewable energies and electric vehicles has triggered an unprecedented demand for metals. Sustainable development of these technologies relies on effectively managing the lifecycle of critical raw materials, including their responsible sourcing, efficient use, and recycling. Metal recycling from electronic waste (e-waste) is of paramount importance owing to ore-exceeding amounts of critical elements and high toxicity of heavy metals and organic pollutants in e-waste to the natural ecosystem and human body. Heterotrophic microbes secrete numerous metal-binding biomolecules such as organic acids, amino acids, cyanide, siderophores, peptides, and biosurfactants which can be utilized for eco-friendly and profitable metal recycling. In this review paper, we presented a critical review of heterotrophic organisms in biomining, and current barriers hampering the industrial application of organic acid bioleaching and biocyanide leaching. We also discussed how these challenges can be surmounted with simple methods (e.g., culture media optimization, separation of microbial growth and metal extraction process) and state-of-the-art biological approaches (e.g., artificial microbial community, synthetic biology, metabolic engineering, advanced fermentation strategies, and biofilm engineering). Lastly, we showcased emerging technologies (e.g., artificially synthesized peptides, siderophores, and biosurfactants) derived from heterotrophs with the potential for inexpensive, low-impact, selective and advanced metal recovery from bioleaching solutions.

EF-Hand Battle Royale: Hetero-ion Complexation in Lanmodulin

The lanmodulin (LanM) protein has emerged as an effective means for rare earth element (REE) extraction and separation from complex feedstocks without the use of organic solvents. Whereas the binding of LanM to individual REEs has been well characterized, little is known about the thermodynamics of mixed metal binding complexes (i.e., heterogeneous ion complexes), which limits the ability to accurately predict separation performance for a given metal ion mixture. In this paper, we employ the law of mass action to establish a theory of perfect cooperativity for LanM-REE complexation at the two highest-affinity binding sites. The theory is then used to derive an equation that explains the nonintuitive REE binding behavior of LanM, where separation factors for binary pairs of ions vary widely based on the ratio of ions in the aqueous phase, a phenomenon that is distinct from single-ion-binding chemical chelators. We then experimentally validate this theory and perform the first quantitative characterization of LanM complexation with heterogeneous ion pairs using resin-immobilized LanM. Importantly, the resulting homogeneous and heterogeneous constants enable accurate prediction of the equilibrium state of LanM in the presence of mixtures of up to 10 REEs, confirming that the perfect cooperativity model is an accurate mechanistic description of REE complexation by LanM. We further employ the model to simulate separation performance over a range of homogeneous and heterogeneous binding constants, revealing important insights into how mixed binding differentially impacts REE separations based on the relative positioning of the ion pairs within the lanthanide series. In addition to informing REE separation process optimization, these results provide mathematical and experimental insight into competition dynamics in other ubiquitous and medically relevant, cooperative binding proteins, such as calmodulin.

Biogeochemistry of Actinides: Recent Progress and Perspective

Actinides are elements that are often feared because of their radioactive nature and potentially devastating consequences to humans and the environment if not managed properly. As such, their chemical interactions with the biosphere and geochemical environment, i.e., their "biogeochemistry," must be studied and understood in detail. In this Review, a summary of the past discoveries and recent advances in the field of actinide biogeochemistry is provided with a particular emphasis on actinides other than thorium and uranium (i.e., actinium, neptunium, plutonium, americium, curium, berkelium, and californium) as they originate from anthropogenic activities and can be mobile in the environment. The nuclear properties of actinide isotopes found in the environment and used in research are reviewed with historical context. Then, the coordination chemistry properties of actinide ions are contrasted with those of common metal ions naturally present in the environment. The typical chelators that can impact the biogeochemistry of actinides are then reviewed. Then, the role of metalloproteins in the biogeochemistry of actinides is put into perspective since recent advances in the field may have ramifications in radiochemistry and for the long-term management of nuclear waste. Metalloproteins are ubiquitous ligands in nature but, as discussed in this Review, they have largely been overlooked for actinide chemistry, especially when compared to traditional environmental chelators. Without discounting the importance of abundant and natural actinide ions (i.e., Th4+ and UO2 2+), the main focus of this review is on trivalent actinides because of their prevalence in the fields of nuclear fuel cycles, radioactive waste management, heavy element research, and, more recently, nuclear medicine. Additionally, trivalent actinides share chemical similarities with the rare earth elements, and recent breakthroughs in the field of lanthanide-binding chelators may spill into the field of actinide biogeochemistry, as discussed hereafter.

A novel in-silico model explores LanM homologs among Hyphomicrobium spp

Investigating microorganisms in metal-enriched environments holds the potential to revolutionize the sustainable recovery of critical metals such as lanthanides (Ln3+). We observe Hyphomicrobium spp. as part of a Fe2+/Mn2+-oxidizing consortia native to the ferruginous bottom waters of a Ln3+-enriched lake in Czechia. Notably, one species shows similarities to recently discovered bacteria expressing proteins with picomolar Ln3+ affinity. This finding was substantiated by developing an in-silico ionic competition model and recombinant expression of a homolog protein (Hm-LanM) from Hyphomicrobium methylovorum. Biochemical assays validate Hm-LanM preference for lighter Ln3+ ions (from lanthanum to gadolinium). This is comparable to established prototypes. Bioinformatics analyses further uncover additional H. methylovorum metabolic biomolecules in genomic proximity to Hm-LanM analogously dependent on Ln3+, including an outer membrane receptor that binds Ln3+-chelating siderophores. These combined observations underscore the remarkable strategy of Hyphomicrobium spp. for thriving in relatively Ln3+ enriched zones of metal-polluted environments.

Single-point mutated lanmodulin as a high-performance MRI contrast agent for vascular and kidney imaging

Magnetic resonance imaging contrast agents can enhance diagnostic precision but often face limitations such as short imaging windows, low tissue specificity, suboptimal contrast enhancement, or potential toxicity, which affect resolution and long-term monitoring. Here, we present a protein contrast agent based on lanmodulin, engineered with a single-point mutation at position 108 from N to D to yield maximum gadolinium binding sites. After loading with Gd3+ ions, the resulting protein complex, LanND-Gd, exhibits efficient renal clearance, high relaxivity, and prolonged renal retention compared to commercial agents. LanND-Gd enables high-performance visualization of whole-body structures and brain vasculature in male mice at a resolution finer than one hundred micrometers. In male ischemia mouse models, LanND-Gd also improves kidney dysfunction monitoring while minimizing risks of neural toxicity or immunogenic reactions. This protein-based contrast agent offers superior image quality, improved biocompatibility, and extended imaging timeframes, promising significant advancements in magnetic resonance-based diagnostics and patient outcomes.

Ultra-inert lanthanide chelates as mass tags for multiplexed bioanalysis

Coordination compounds of lanthanides are indispensable in biomedical applications as MRI contrast agents and radiotherapeutics. However, since the introduction of the chelator DOTA four decades ago, there has been only limited progress on improving their thermodynamic stability and kinetic inertness, which are essential for safe in vivo use. Here, we present ClickZip, an innovative synthetic strategy employing a coordination-templated formation of a 1,5-triazole bridge that improves kinetic inertness up to a million-fold relative to DOTA, expanding utility of lanthanide chelates beyond traditional uses. Acting as unique mass tags, the ClickZip chelates can be released from (biological) samples by acidic hydrolysis, chromatographically distinguished from interfering lanthanide species, and sensitively detected by mass spectrometry. Lanthanides enclosed in ClickZip chelates are chemically almost indistinguishable, providing a more versatile alternative to chemically identical isotopic labels for multiplexed analysis. The bioanalytical potential is demonstrated on tagged cell-penetrating peptides in vitro, and anti-obesity prolactin-releasing peptides in vivo.

Modulating metal-centered dimerization of a lanthanide chaperone protein for separation of light lanthanides

Elucidating details of biology's selective uptake and trafficking of rare earth elements, particularly the lanthanides, has the potential to inspire sustainable biomolecular separations of these essential metals for myriad modern technologies. Here, we biochemically and structurally characterize Methylobacterium (Methylorubrum) extorquens LanD, a periplasmic protein from a bacterial gene cluster for lanthanide uptake. This protein provides only four ligands at its surface-exposed lanthanide-binding site, allowing for metal-centered protein dimerization that favors the largest lanthanide, LaIII. However, the monomer prefers NdIII and SmIII, which are disfavored lanthanides for cellular utilization. Structure-guided mutagenesis of a metal-ligand and an outer-sphere residue weakens metal binding to the LanD monomer and enhances dimerization for PrIII and NdIII by 100-fold. Selective dimerization enriches high-value PrIII and NdIII relative to low-value LaIII and CeIII in an all-aqueous process, achieving higher separation factors than lanmodulins and comparable or better separation factors than common industrial extractants. Finally, we show that LanD interacts with lanmodulin (LanM), a previously characterized periplasmic protein that shares LanD's preference for NdIII and SmIII. Our results suggest that LanD's unusual metal-binding site transfers less-desirable lanthanides to LanM to siphon them away from the pathway for cytosolic import. The properties of LanD show how relatively weak chelators can achieve high selectivity, and they form the basis for the design of protein dimers for separation of adjacent lanthanide pairs and other metal ions.

Supercharged fluorescent proteins detect lanthanides via direct antennae signaling

A sustainable operation for harvesting metals in the lanthanide series is needed to meet the rising demand for rare earth elements across diverse global industries. However, existing methods are limited in their capacity for detection and capture at environmentally and industrially relevant lanthanide concentrations. Supercharged fluorescent proteins have solvent-exposed, negatively charged residues that potentially create multiple direct chelation pockets for free lanthanide cations. Here, we demonstrate that negatively supercharged proteins can bind and quantitatively report concentrations of lanthanides via an underutilized lanthanide-to-chromophore pathway of energy transfer. The top-performing sensors detect lanthanides in the micromolar to millimolar range and remain unperturbed by environmentally significant concentrations of competing metals. As a demonstration of the versatility and adaptability of this energy transfer method, we show proximity and signal transmission between the lanthanides and a supramolecular assembly of supercharged proteins, paving the way for the detection of lanthanides via programmable protein oligomers and materials.

A De Novo Metalloenzyme for Cerium Photoredox Catalysis

Cerium photoredox catalysis has emerged as a powerful strategy to activate molecules under mild conditions. Radical intermediates are formed using visible light and simple complexes of the earth-abundant lanthanide. Here, we report an artificial photoenzyme enabling this chemistry inside a protein. We utilize a de novo designed protein scaffold that tightly binds lanthanide ions in its central cavity. Upon visible-light irradiation, the cerium-dependent enzyme catalyzes the radical C-C bond cleavage of 1,2-diols in aqueous solution. Protein engineering led to variants with improved photostability and metal binding behavior. The photoenzyme cleaves a range of aromatic and aliphatic substrates, including lignin surrogates. Surface display of the protein scaffold on Escherichia coli facilitates whole-cell photobiocatalysis. Furthermore, we show that also natural lanthanide-binding proteins are suitable for this approach. Our study thus demonstrates a new-to-nature enzymatic photoredox activity with broad catalytic potential.

Microbial green synthesis of luminescent terbium sulfide nanoparticles using E. Coli: a rare earth element detoxification mechanism

BACKGROUND

Rare-earth sulfide nanoparticles (NPs) could harness the optical and magnetic features of rare-earth ions for applications in nanotechnology. However, reports of their synthesis are scarce and typically require high temperatures and long synthesis times.

RESULTS

Here we present a biosynthesis of terbium sulfide (TbS) NPs using microorganisms, identifying conditions that allow Escherichia coli to extracellularly produce TbS NPs in aqueous media at 37 °C by controlling cellular sulfur metabolism to produce a high concentration of sulfide ions. Electron microscopy revealed ultrasmall spherical NPs with a mean diameter of 4.1 ± 1.3 nm. Electron diffraction indicated a high degree of crystallinity, while elemental mapping confirmed colocalization of terbium and sulfur. The NPs exhibit characteristic absorbance and luminescence of terbium, with downshifting quantum yield (QY) reaching 28.3% and an emission lifetime of ~ 2 ms.

CONCLUSIONS

This high QY and long emission lifetime is unusual in a neat rare-earth compound; it is typically associated with rare-earth ions doped into another crystalline lattice to avoid non-radiative cross relaxation. This suggests a reduced role of nonradiative processes in these terbium-based NPs. This is, to our knowledge, the first report revealing the advantage of biosynthesis over chemical synthesis for Rare Earth Element (REE) based NPs, opening routes to new REE-based nanocrystals.

Virus-Based Separation of Rare Earth Elements

The utilization of biomaterials for the separation of rare earth elements (REEs) has attracted considerable interest due to their inherent advantages, including diverse molecular structures for selective binding and the use of eco-friendly materials for sustainable systems. We present a pioneering methodology for developing a safe virus to selectively bind REEs and facilitate their release through pH modulation. We engineered the major coat protein of M13 bacteriophage (phage) to incorporate a lanthanide-binding peptide. The engineered lanthanide-binding phage (LBPh), presenting ∼3300 copies of the peptide, serves as an effective biological template for REE separation. Our findings demonstrate the LBPh's preferential binding for heavy REEs over light REEs. Moreover, the LBPh exhibits remarkable robustness with excellent recyclability and stability across multiple cycles of separations. This study underscores the potential of genetically integrating virus templates with selective binding motifs for REE separation, offering a promising avenue for environmentally friendly and energy-efficient separation processes.

Structure-driven development of a biomimetic rare earth artificial metalloprotein

The 2011 discovery of the first rare earth-dependent enzyme in methylotrophic Methylobacterium extorquens AM1 prompted intensive research toward understanding the unique chemistry at play in these systems. This enzyme, an alcohol dehydrogenase (ADH), features a La3+ ion closely associated with redox-active coenzyme pyrroloquinoline quinone (PQQ) and is structurally homologous to the Ca2+-dependent ADH from the same organism. AM1 also produces a periplasmic PQQ-binding protein, PqqT, which we have now structurally characterized to 1.46-Å resolution by X-ray diffraction. This crystal structure reveals a Lys residue hydrogen-bonded to PQQ at the site analogously occupied by a Lewis acidic cation in ADH. Accordingly, we prepared K142A- and K142D-PqqT variants to assess the relevance of this site toward metal binding. Isothermal titration calorimetry experiments and titrations monitored by UV-Vis absorption and emission spectroscopies support that K142D-PqqT binds tightly (Kd = 0.6 ± 0.2 μM) to La3+ in the presence of bound PQQ and produces spectral signatures consistent with those of ADH enzymes. These spectral signatures are not observed for WT- or K142A-variants or upon addition of Ca2+ to PQQ ⸦ K142D-PqqT. Addition of benzyl alcohol to La3+-bound PQQ ⸦ K142D-PqqT (but not Ca2+-bound PQQ ⸦ K142D-PqqT, or La3+-bound PQQ ⸦ WT-PqqT) produces spectroscopic changes associated with PQQ reduction, and chemical trapping experiments reveal the production of benzaldehyde, supporting ADH activity. By creating a metal binding site that mimics native ADH enzymes, we present a rare earth-dependent artificial metalloenzyme primed for future mechanistic, biocatalytic, and biosensing applications.

Development of Broad-Range Microbial Minimal Culture Medium for Lanthanide Studies

Rare Earth Elements (REE), also known as Lanthanides (Ln3+), are a group of 17 elements showing peculiar physical and chemical properties. Unlike technological applications, very little is known about the physiological role and toxicity of Ln3+ on biological systems, in particular on microorganisms (e.g., bacteria), which represent the most abundant domains on our planet. Up to now, very limited studies have been conducted due to Ln3+ precipitation with some anions commonly present in the culture media. Therefore, the development of a minimal medium is essential to allow the study of Ln3+-microbial interactions, limiting considerably the precipitation of insoluble salts. In this regard, a new minimal culture medium capable of solubilizing large amounts of Ln3+ and allowing the growth of different microbial taxa was successfully developed. Assays have shown that the medium is capable of solubilizing Ln3+ up to 100 times more than other common culture media and allowing the growth of 63 bacteria and 5 fungi. The kinetic growth of one yeast and one Gram-positive bacterium has been defined, proving to support superior growth and biomass compared to other commonly used minimal media. Moreover, the sensitivity and uptake/absorption of a Bacillus stratosphericus strain were tested, highlighting its capability to tolerate concentrations up to 10 mM of either Cerium, Gadolinium or Lanthanum and accumulate different quantities of the three.

Rare Earth Element Binding and Recovery by a Beta Roll-Forming RTX Domain

The Block V of the RTX domain of the adenylate cyclase protein from Bordetella pertussis is disordered, and upon binding eight calcium ions, it folds into a beta roll domain with a C-terminal capping group. Due to their similar ionic radii and coordination geometries, trivalent lanthanide ions have been used to probe and identify calcium-binding sites in many proteins. Here, we report using a FRET-based assay that the RTX domain can bind rare earth elements (REEs) with higher affinities than calcium. The apparent disassociation constants for lanthanide ions ranged from 20 to 75 μM, which are an order of magnitude higher than the affinity for calcium, with a higher selectivity toward heavy REEs over light REEs. Most proteins release bound ions at mildly acidic conditions (pH 5-6), and the high affinity REE-binding lanmodulin protein can bind 3-4 REE ions at pH as low as ∼2.5. Circular dichroism (CD) spectra of the RTX domain demonstrate pH-induced folding of the beta roll domain in the absence of ions, indicating that protonation of key amino acids enables structure formation in low pH solutions. The beta roll domain coordinates up to four ions in extreme pH conditions (pH < 1), as determined by equilibrium ultrafiltration experiments. Finally, to demonstrate a potential application of the RTX domain, REE ions (Nd3+ and Dy3+) were recovered from other non-REEs (Fe2+ and Co2+) in a NdFeB magnet simulant solution (at pH 6).

High-efficiency dysprosium-ion extraction enabled by a biomimetic nanofluidic channel

Biological ion channels exhibit high selectivity and permeability of ions because of their asymmetrical pore structures and surface chemistries. Here, we demonstrate a biomimetic nanofluidic channel (BNC) with an asymmetrical structure and glycyl-L-proline (GLP) -functionalization for ultrafast, selective, and unidirectional Dy3+ extraction over other lanthanide (Ln3+) ions with very similar electronic configurations. The selective extraction mainly depends on the amplified chemical affinity differences between the Ln3+ ions and GLPs in nanoconfinement. In particular, the conductivities of Ln3+ ions across the BNC even reach up to two orders of magnitude higher than in a bulk solution, and a high Dy3+/Nd3+ selectivity of approximately 60 could be achieved. The designed BNC can effectively extract Dy3+ ions with ultralow concentrations and thereby purify Nd3+ ions to an ultimate content of 99.8 wt.%, which contribute to the recycling of rare earth resources and environmental protection. Theoretical simulations reveal that the BNC preferentially binds to Dy3+ ion due to its highest affinity among Ln3+ ions in nanoconfinement, which attributes to the coupling of ion radius and coordination matching. These findings suggest that BNC-based ion selectivity system provides alternative routes to achieving highly efficient lanthanide separation.

Yttrium immobilization through biomineralization with phosphate by the resistant strain Mesorhizobium qingshengii J19

AIMS

Yttrium (Y) holds significant industrial and economic importance, being listed as a critical element on the European list of critical elements, thus emphasizing the high priority for its recovery. Bacterial strategies play a crucial role in the biorecovery of metals, offering a promising and environmentally friendly approach. Therefore, gaining a comprehensive understanding of the underlying mechanisms behind bacterial resistance, as well as the processes of bioaccumulation and biotransformation, is of paramount importance.

METHODS AND RESULTS

A total of 207 Alphaproteobacteria strains from the University of Coimbra Bacteria Culture Collection were tested for Y-resistance. Among these, strain Mesorhizobium qingshengii J19 exhibited high resistance (up to 4 mM Y) and remarkable Y accumulation capacity, particularly in the cell membrane. Electron microscopy revealed Y-phosphate interactions, while X-ray diffraction identified Y(PO3)3·9H2O biocrystals produced by J19 cells.

CONCLUSION

This study elucidates Y immobilization through biomineralization within phosphate biocrystals using M. qingshengii J19 cells.

Constructing Two-Dimensional (2D) Heterostructure Channels with Engineered Biomembrane and Graphene for Precise Scandium Sieving

The special properties of rare earth elements (REE) have effectively broadened their application fields. How to accurately recognize and efficiently separate target rare earth ions with similar radii and chemical properties remains a formidable challenge. Here, precise two-dimensional (2D) heterogeneous channels are constructed using engineered E. coli membranes between graphene oxide (GO) layers. The difference in binding ability and corresponding conformational change between Lanmodulin (LanM) and rare earth ions in the heterogeneous channel allows for precisely recognizing and sieving of scandium ions (Sc3+). The engineered E. coli membranes not only can protect the integrity of structure and functionality of LanM, the rich lipids and sugars, but also help the Escherichia coli (E. coli) membranes closely tile on the GO nanosheets through interaction, preventing swelling and controlling interlayer spacing accurately down to the sub-nanometer. Apparently, the 2D heterogeneous channels showcase excellent selectivity for trivalent ions (SFFe /Sc≈3), especially for Sc3+ ions in REE with high selectivity (SFCe/Sc≈167, SFLa/Sc≈103). The long-term stability and tensile strain tests verify the membrane's outstanding stability. Thus, this simple, efficient, and cost-effective work provides a suggestion for constructing 2D interlayer heterogeneous channels for precise sieving, and this valuable strategy is proposed for the efficient extraction of Sc.

Critical Mineral Separations: Opportunities for Membrane Materials and Processes to Advance Sustainable Economies and Secure Supplies

Sustainable energy solutions and electrification are driving increased demand for critical minerals. Unfortunately, current mineral processing techniques are resource intensive, use large quantities of hazardous chemicals, and occur at centralized facilities to realize economies of scale. These aspects of existing technologies are at odds with the sustainability goals driving increased demand for critical minerals. Here, we argue that the small footprint and modular nature of membrane technologies position them well to address declining concentrations in ores and brines, the variable feed concentrations encountered in recycling, and the environmental issues associated with current separation processes; thus, membrane technologies provide new sustainable pathways to strengthening resilient critical mineral supply chains. The success of creating circular economies hinges on overcoming diverse barriers across the molecular to infrastructure scales. As such, solving these challenges requires the convergence of research across disciplines rather than isolated innovations.

Rare earth elements in biology: From biochemical curiosity to solutions for extractive industries

Rare earth elements (REEs) are critical for our modern lifestyles and the transition to a low-carbon economy. Recent advances in our understanding of the role of REEs in biology, particularly methylotrophy, have provided opportunities to explore biotechnological innovations to improve REE mining and recycling. In addition to bacterial accumulation and concentration of REEs, biological REE binders, including proteins (lanmodulin, lanpepsy) and small molecules (metallophores and cofactors) have been identified that enable REE concentration and separation. REE-binding proteins have also been used in several mechanistically distinct REE biosensors, which have potential application in mining and medicine. Notably, the role of REEs in biology has only been known for a decade, suggesting their considerable scope for developing new understanding and novel applications.

Lanmodulin's EF 2-3 Domain: Insights from Infrared Spectroscopy and Simulations

Lanmodulins are small, ∼110-residue proteins with four EF-hand motifs that demonstrate a picomolar affinity for lanthanide ions, making them efficient in the recovery and separation of these technologically important metals. In this study, we examine the thermodynamic and structural complexities of lanthanide ion binding to a 41-residue domain, EF 2-3, that constitutes the two highest-affinity metal-binding sites in the lanmodulin protein from Methylorubrum extorquens. Using a combination of circular dichroism (CD) spectroscopy, isothermal titration calorimetry (ITC), two-dimensional infrared (2D IR) spectroscopy, and molecular dynamics (MD) simulations, we characterize the metal binding capabilities of EF 2-3. ITC demonstrates that binding occurs between peptide and lanthanides with conditional dissociation constants (Kd) in the range 20-30 μM, with no significant differences in the Kd values for La3+, Eu3+, and Tb3+ at pH 7.4. In addition, CD spectroscopy suggests that only one binding site of EF 2-3 undergoes a significant conformational change in the presence of lanthanides. 2D IR spectroscopy demonstrates the presence of both mono- and bidentate binding configurations in EF 2-3 with all three lanthanides. MD simulations, supported by Eu3+ luminescence measurements, explore these results, suggesting a competition between water-lanthanide and carboxylate-lanthanide interactions in the EF 2-3 domain. These results underscore the role of the core helical bundle of the protein architecture in influencing binding affinities and communication between the metal-binding sites in the full-length protein.

Recovery of rare earth elements from low-grade coal fly ash using a recyclable protein biosorbent

Rare earth elements (REEs), including those in the lanthanide series, are crucial components essential for clean energy transitions, but they originate from geographically limited regions. Exploiting new and diverse supply sources is vital to facilitating a clean energy future. Hence, we explored the recovery of REEs from coal fly ash (FA), a complex, low-grade industrial feedstock that is currently underutilized (leachate concentrations of REEs in FA are < 0.003 mol%). Herein, we demonstrated the thermo-responsive genetically encoded REE-selective elastin-like polypeptides (RELPs) as a recyclable bioengineered protein adsorbent for the selective retrieval of REEs from coal fly ash over multiple cycles. The results showed that RELPs could be efficiently separated using temperature cycling and reused with high stability, as they retained ∼95% of their initial REE binding capacity even after four cycles. Moreover, RELPs selectively recovered high-purity REEs from the simulated solution containing one representative REE in the range of 0.0001-0.005 mol%, resulting in up to a 100,000-fold increase in REE purity. This study offers a sustainable approach to diversifying REE supplies by recovering REEs from low-grade coal fly ash in industrial wastes and provides a scientific basis for the extraction of high-purity REEs for industrial purposes.

Engineering biomaterials for the recovery of rare earth elements

The escalating global demand for rare earth elements (REEs) and the overabundance of REE-containing waste require innovative technologies for REE recovery from waste to achieve a sustainable supply of REEs while reducing the environmental burden. Biosorption mediated by peptides or proteins has emerged as a promising approach for selective REE recovery. To date, multiple peptides and proteins with high REE-binding affinity and selectivity have been discovered, and various strategies are being exploited to engineer robust and reusable biosorptive materials for selective REE recovery. This review highlights recent advances in discovering and engineering peptides and proteins for REE recovery. Future research prospects and challenges are also discussed.

Zeta potential of Z-DNA: A new signature to study B-Z transition in linear and branched DNA

Zeta potential is commonly referred as surface charge density and is a key factor in modulating the structural and functional properties of nucleic acids. Although the negative charge density of B-DNA is well understood, there is no prior description of the zeta potential measurement of Z-DNA. In this study, for the first time we discover the zeta potential difference between B-DNA and lanthanum chloride-induced Z-DNA. A series of linear repeat i.e. (CG)n and (GC)n DNA as well as branched DNA (bDNA) structures was used for the B-to-Z DNA transition. Herein, the positive zeta potential of Z-DNA has been demonstrated as a powerful tool to discriminate between B-form and Z-form of DNA. The generality of the approach has been validated both in linear and bDNA nanostructures. Thus, we suggest zeta potential can be used as an ideal signature for the left-handed Z-DNA.

Spectroscopic characterization of europium binding to a calmodulin-EF4 hand peptide-polymer conjugate

The emergence of biological ligand as an alternative to chemical ligands enables a sustainable lanthanide extraction route. In this study, a peptide originating from the loop of domain 4 calmodulin (EF4) was synthesized and the interaction with europium ions was monitored using time resolved laser fluorescence spectroscopy (TRLFS). Despite being retracted from its full protein structure, the twelve amino acids of calmodulin-EF4 showed binding to europium. Europium-peptide complex formation was evident by an increase in decay time from 110 to 187 μs. The spectra of europium bound to peptide can be easily distinguished from the free europium ion as the 5D0 → 7F2 peak intensifies. When europium bound to the peptide-polymer conjugate, the decay time was further increased to 259 μs. This suggests that lanthanide binding can be enhanced by immobilizing the short peptide into a polymer matrix. The europium-peptide/conjugate bond was reversible, triggered by pH, promoting peptide reusability. Due to the fact that the study was conducted exclusively in water, it suggests minimal use of chemicals is possible while maintaining peptide affinity. This makes the calmodulin-EF4 peptide an ideal candidate as biological ligand. This study lays the groundwork for developing a peptide-based filter material for lanthanide separation.

Investigation of Rare Earth Element Binding to a Surface-Bound Affinity Peptide Derived from EF-Hand Loop I of Lanmodulin

Bioinspired strategies have been given extensive attention for the recovery of rare earth elements (REEs) from waste streams because of their high selectivity, regeneration potential, and sustainability as well as low cost. Lanmodulin protein is an emerging biotechnology that is highly selective for REE binding. Mimicking lanmodulin with shorter peptides is advantageous because they are simpler and potentially easier to manipulate and optimize. Lanmodulin-derived peptides have been found to bind REEs, but their properties have not been explored when immobilized on solid substrates, which is required for many advanced separation technologies. Here, two peptides, LanM1 and scrambled LanM1, are designed from the EF-hand loop 1 of lanmodulin and investigated for their binding affinity toward different REEs when surface-bound. First, the ability of LanM1 to bind REEs was confirmed and characterized in solution using circular dichroism (CD), nuclear magnetic resonance (NMR), and molecular dynamics (MD) simulations for Ce(III) ions. Isothermal titration calorimetry (ITC) was used to further analyze the binding of the LanM1 to Ce(III), Nd(III), Eu(III), and Y(III) ions and in low-pH conditions. The performance of the immobilized peptides on a model gold surface was examined using a quartz crystal microbalance with dissipation (QCM-D). The studies show that the LanM1 peptide has a stronger REE binding affinity than that of scrambled LanM1 when in solution and when immobilized on a gold surface. QCM-D data were fit to the Langmuir adsorption model to estimate the surface-bound dissociation constant (Kd) of LanM1 with Ce(III) and Nd(III). The results indicate that LanM1 peptides maintain a high affinity for REEs when immobilized, and surface-bound LanM1 has no affinity for potential competitor calcium and copper ions. The utility of surface-bound LanM1 peptides was further demonstrated by immobilizing them to gold nanoparticles (GNPs) and capturing REEs from solution in experiments utilizing an Arsenazo III-based colorimetric dye displacement assay and ultraviolet-visible (UV-vis) spectrophotometry. The saturated adsorption capacity of GNPs was estimated to be around 3.5 μmol REE/g for Ce(III), Nd(III), Eu(III), and Y(III) ions, with no binding of non-REE Ca(II) ions observed.

Mononuclear binding and catalytic activity of europium(III) and gadolinium(III) at the active site of the model metalloenzyme phosphotriesterase

Lanthanide ions have ideal chemical properties for catalysis, such as hard Lewis acidity, fast ligand-exchange kinetics, high coordination-number preferences and low geometric requirements for coordination. As a result, many small-molecule lanthanide catalysts have been described in the literature. Yet, despite the ability of enzymes to catalyse highly stereoselective reactions under gentle conditions, very few lanthanoenzymes have been investigated. In this work, the mononuclear binding of europium(III) and gadolinium(III) to the active site of a mutant of the model enzyme phosphotriesterase are described using X-ray crystallography at 1.78 and 1.61 Å resolution, respectively. It is also shown that despite coordinating a single non-natural metal cation, the PTE-R18 mutant is still able to maintain esterase activity.

Mechanistic analysis of the sub chronic toxicity of La and Gd in Daphnia magna based on TKTD modelling and synchrotron X-ray fluorescence imaging

The release of lanthanides (Ln) into the environment has increased in recent decades due to their expanding applications in society. Studying their toxicity in aquatic ecosystems is urgent and challenging, with contradictory evidence presented in the literature. This study compared the biodistribution of La and Gd in Daphnia magna exposed to sub-chronic conditions and developed the first Toxicokinetic-Toxicodynamic (TKTD) model for these lanthanides with this model crustacean. D. magna were initially exposed for 7 days to concentrations close to the LC50 of La (2.10 mg L-1) and Gd (1.70 mg L-1). After exposure, half of the live daphnids were introduced in a clean media to allow depuration over 24 h, while the other organisms were directly prepared for synchrotron imaging measurements. Synchrotron X-ray fluorescence analysis revealed that metal distribution in the organisms was similar for both La and Gd, predominantly localized in the intestinal tract, even after the depuration process. These results indicate that ingested metal can adversely affect organisms under sub-chronic exposure conditions, highlighting the importance of using nominal concentrations as a more suitable indicator of metal bioavailability for risk assessment. The General Unified Threshold Model of Survival (GUTS) TKTD framework, in its reduced form (GUTS-RED), was developed for La and Gd using dissolved and nominal concentrations. D. magna were exposed for 7 days to concentrations from 0.5 to 5 mg L-1 of La or Gd and mortality monitored daily. The mechanistic model revealed a faster toxicokinetics for La than Gd and a higher toxicity for Gd than La in the organism. This study confirmed, despite similar chemical properties, the variation in both toxicity and toxicokinetics between these two metals.