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Gonzalez WG, Sakhdari S, Alam MS, Dhulipala G, Kavallieratos K, Miksovska J. DMNP as an Effective Cage for Ln 3+: A Spectroscopic and Thermodynamic Study. Inorg Chem 2024; 63:14366-14374. [PMID: 39041599 DOI: 10.1021/acs.inorgchem.4c00815] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/24/2024]
Abstract
Dimethoxynitrophenyl-EDTA (DMNP) is a popular calcium cage that is frequently used to investigate the role of Ca2+ in signaling processes in vivo. Lanthanides have been used in Ca2+ biomimetics due to similarities in coordination properties of Ln3+ and Ca2+ that may enable fluorescence and NMR studies of functional and structural properties of Ca2+ binding proteins. In this study, we show that Tb3+, Eu3+, and Nd3+ bind strongly to DMNP in a 1:1 ratio. Isothermal titration calorimetric measurements of Ca2+ displacement by Ln3+ in DMNP provide the equilibrium binding constants for Ln3+DMNP complexation with association constants, K11 = (1.2 ± 0.7) × 1012 M-1 for Eu3+, (2.5 ± 1.7) × 1012 M-1 for Nd3+, and (2.8 ± 0.8) × 1012 M-1 for Tb3+. The kinetics and thermodynamics of Ca2+, Mg2+, and Tb3+ release from DMNP were characterized using photothermal beam deflection (PBD). Ligand release from the DMNP cage was rapid and occurred within 10 μs upon cage photofragmentation and was associated with similar reaction volume and enthalpy changes that can be attributed to the photoreleased ion solvation. In the case of Ca2+DMNP photodissociation at subsaturating Ca2+ concentrations, we observed a slower phase with a lifetime of 300 μs that we attribute to Ca2+ rebinding to unphotolyzed DMNP. These results demonstrate that DMNP can serve as an effective photolabile cage for oxophilic Ln3+ that has similar coordination properties to Ca2+ and Mg2+.
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Affiliation(s)
- Walter G Gonzalez
- Department of Chemistry and Biochemistry and Biomolecular Sciences Institute, Florida International University, Miami, Florida 33199, United States
| | - Setareh Sakhdari
- Department of Chemistry and Biochemistry and Biomolecular Sciences Institute, Florida International University, Miami, Florida 33199, United States
| | - Md Shofiul Alam
- Department of Chemistry and Biochemistry and Biomolecular Sciences Institute, Florida International University, Miami, Florida 33199, United States
| | - Gangadhar Dhulipala
- Department of Chemistry and Biochemistry and Biomolecular Sciences Institute, Florida International University, Miami, Florida 33199, United States
| | - Konstantinos Kavallieratos
- Department of Chemistry and Biochemistry and Biomolecular Sciences Institute, Florida International University, Miami, Florida 33199, United States
| | - Jaroslava Miksovska
- Department of Chemistry and Biochemistry and Biomolecular Sciences Institute, Florida International University, Miami, Florida 33199, United States
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2
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Khoury F, Su Z, Banta S. Rare Earth Element Binding and Recovery by a Beta Roll-Forming RTX Domain. Inorg Chem 2024; 63:13223-13230. [PMID: 38986039 DOI: 10.1021/acs.inorgchem.4c00420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/12/2024]
Abstract
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).
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Affiliation(s)
- Farid Khoury
- Department of Chemical Engineering, Columbia University, New York, New York 10027, United States
| | - Zihang Su
- Department of Chemical Engineering, Columbia University, New York, New York 10027, United States
| | - Scott Banta
- Department of Chemical Engineering, Columbia University, New York, New York 10027, United States
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3
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Verma G, Hostert J, Summerville AA, Robang AS, Garcia Carcamo R, Paravastu AK, Getman RB, Duval CE, Renner J. Investigation of Rare Earth Element Binding to a Surface-Bound Affinity Peptide Derived from EF-Hand Loop I of Lanmodulin. ACS APPLIED MATERIALS & INTERFACES 2024; 16:16912-16926. [PMID: 38527460 PMCID: PMC10995902 DOI: 10.1021/acsami.3c17565] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Revised: 01/17/2024] [Accepted: 02/27/2024] [Indexed: 03/27/2024]
Abstract
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.
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Affiliation(s)
- Geeta Verma
- Department
of Chemical and Biomolecular Engineering, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Jacob Hostert
- Department
of Chemical and Biomolecular Engineering, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Alex A. Summerville
- Department
of Chemical and Biomolecular Engineering, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Alicia S. Robang
- School
of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Ricardo Garcia Carcamo
- Department
of Chemical and Biomolecular Engineering, Ohio State University, Columbus, Ohio 43210, United States
| | - Anant K. Paravastu
- School
of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
- Parker
H. Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, 315 Ferst Drive, Atlanta, Georgia 30332, United States
| | - Rachel B. Getman
- Department
of Chemical and Biomolecular Engineering, Ohio State University, Columbus, Ohio 43210, United States
| | - Christine E. Duval
- Department
of Chemical and Biomolecular Engineering, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Julie Renner
- Department
of Chemical and Biomolecular Engineering, Case Western Reserve University, Cleveland, Ohio 44106, United States
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Wang M, Xiong Q, Wang M, Lewis NHC, Ying D, Yan G, Hoenig E, Han Y, Lee OS, Peng G, Zhou H, Schatz GC, Liu C. Lanthanide transport in angstrom-scale MoS 2-based two-dimensional channels. SCIENCE ADVANCES 2024; 10:eadh1330. [PMID: 38489373 PMCID: PMC10942105 DOI: 10.1126/sciadv.adh1330] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Accepted: 02/09/2024] [Indexed: 03/17/2024]
Abstract
Rare earth elements (REEs), critical to modern industry, are difficult to separate and purify, given their similar physicochemical properties originating from the lanthanide contraction. Here, we systematically study the transport of lanthanide ions (Ln3+) in artificially confined angstrom-scale two-dimensional channels using MoS2-based building blocks in an aqueous environment. The results show that the uptake and permeability of Ln3+ assume a well-defined volcano shape peaked at Sm3+. This transport behavior is rooted from the tradeoff between the barrier for dehydration and the strength of interactions of lanthanide ions in the confinement channels, reminiscent of the Sabatier principle. Molecular dynamics simulations reveal that Sm3+, with moderate hydration free energy and intermediate affinity for channel interaction, exhibit the smallest dehydration degree, consequently resulting in the highest permeability. Our work not only highlights the distinct mass transport properties under extreme confinement but also demonstrates the potential of dialing confinement dimension and chemistry for greener REEs separation.
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Affiliation(s)
- Mingzhan Wang
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
| | - Qinsi Xiong
- Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
| | - Maoyu Wang
- X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Nicholas H. C. Lewis
- Department of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, University of Chicago, Chicago, IL 60637, USA
| | - Dongchen Ying
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
| | - Gangbin Yan
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
| | - Eli Hoenig
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
| | - Yu Han
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
| | - One-Sun Lee
- Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
| | - Guiming Peng
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
| | - Hua Zhou
- X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, IL 60439, USA
| | - George C. Schatz
- Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
| | - Chong Liu
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
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5
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Smerigan A, Biswas S, Vila FD, Hong J, Perez-Aguilar J, Hoffman AS, Greenlee L, Getman RB, Bare SR. Aqueous Structure of Lanthanide-EDTA Coordination Complexes Determined by a Combined DFT/EXAFS Approach. Inorg Chem 2023; 62:14523-14532. [PMID: 37624729 DOI: 10.1021/acs.inorgchem.3c01334] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/27/2023]
Abstract
Sustainable production of rare earth elements (REEs) is critical for technologies needed for climate change mitigation, including wind turbines and electric vehicles. However, separation technologies currently used in REE production have large environmental footprints, necessitating more sustainable strategies. Aqueous, affinity-based separations are examples of such strategies. To make these technologies feasible, it is imperative to connect aqueous ligand structure to ligand selectivity for individual REEs. As a step toward this goal, we analyzed the extended X-ray absorption fine structure (EXAFS) of four lanthanides (La, Ce, Pr, and Nd) complexed by a common REE chelator, ethylenediaminetetraacetic acid (EDTA) to determine the aqueous-phase structure. Reference structures from density functional theory (DFT) were used to help fit the EXAFS spectra. We found that all four Ln-EDTA coordination complexes formed 9-coordinate structures with 6 coordinating atoms from EDTA (4 carboxyl oxygen atoms and 2 nitrogen atoms) and 3 oxygen atoms from water molecules. All EXAFS fits were of high quality (R-factor < 0.02) and showed decreasing average first-shell coordination distance across the series (2.62-2.57 Å from La-Nd), in agreement with DFT (2.65-2.56 Å from La-Nd). The insights determined herein will be useful in the development of ligands for sustainable rare earth elements (REE) separation technologies.
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Affiliation(s)
- Adam Smerigan
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Sayani Biswas
- Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina 29634, United States
| | - Fernando D Vila
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Jiyun Hong
- SSRL, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Jorge Perez-Aguilar
- SSRL, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Adam S Hoffman
- SSRL, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Lauren Greenlee
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Rachel B Getman
- Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina 29634, United States
| | - Simon R Bare
- SSRL, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
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6
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Coherent spin transport in a lanthanide-binding protein. Theor Chem Acc 2022. [DOI: 10.1007/s00214-022-02924-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/10/2022]
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7
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Improved Recovery and Selectivity of Lanthanide-Ion-Binding Cyclic Peptide Hosts by Changing the Position of Acidic Amino Acids. MINERALS 2022. [DOI: 10.3390/min12020148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The development of an effective host molecule to separate lanthanide (Ln) ions and a method for predicting its guest recognition/self-assembly behavior based on primary chemical structures are highly sought after in both academia and industry. Herein, we report the improvement of one-pot Ln ion recovery and a performance prediction method for four new cyclic peptide hosts that differ in the position of acidic amino acids. These cyclic peptide hosts could recognize Ln3+ directly through a 1:1 complexation–precipitation process and exhibited high Lu3+ selectivity in spite of similar ion size and electronegativity when the positions of the acidic amino acids were changed. This unpredictable selectivity was explained by considering the dipole moment, lowest unoccupied molecular orbital, and cohesion energy. In addition, a semi-empirical function using these parameters was proposed for screening the sequence and estimating the isolated yields without long-time molecular dynamics calculations. The insights obtained from this study can be employed for the development of high-performance peptides for the selective recovery of Ln and other metal ions, as well as for the construction of diverse supramolecular recognition systems.
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Gutenthaler SM, Tsushima S, Steudtner R, Gailer M, Hoffmann-Röder A, Drobot B, Daumann LJ. Lanmodulin peptides – unravelling the binding of the EF-Hand loop sequences stripped from the structural corset. Inorg Chem Front 2022; 9:4009-4021. [PMID: 36091973 PMCID: PMC9362731 DOI: 10.1039/d2qi00933a] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Accepted: 05/23/2022] [Indexed: 12/25/2022]
Abstract
Lanmodulin (LanM), a naturally lanthanide (Ln)-binding protein with a remarkable selectivity for Lns over Ca(ii) and affinities in the picomolar range, is an attractive target to address challenges in Ln separation. Why LanM has such a high selectivity is currently not entirely understood; both specific amino acid sequences of the EF-Hand loops and cooperativity effects have been suggested. Here, we removed the effect of cooperativity and synthesised all four 12-amino acid EF-Hand loop peptides, and investigated their affinity for two Lns (Eu(iii) and Tb(iii)), the actinide Cm(iii) and Ca(ii). Using isothermal titration calorimetry and time-resolved laser fluorescence spectroscopy (TRLFS) combined with parallel factor analysis, we show that the four short peptides behave very similarly, having affinities in the micromolar range for Eu(iii) and Tb(iii). Ca(ii) was shown not to bind to the peptides, which was verified with circular dichroism spectroscopy. This technique also revealed an increase in structural organisation upon Eu(iii) addition, which was supported by molecular dynamics simulations. Lastly, we put Eu(iii) and Cm(iii) in direct competition using TRLFS. Remarkably, a slightly higher affinity for Cm(iii) was found. Our results demonstrate that the picomolar affinities in LanM are largely an effect of pre-structuring and therefore a reduction of flexibility in combination with cooperative effects, and that all EF-Hand loops possess similar affinities when detached from the protein backbone, albeit still retaining the high selectivity for lanthanides and actinides over calcium. Taking a closer look at Lanmodulin’s remarkable selectivity for lanthanides (Ln) over Ca(ii) and high Ln/actinide affinities on the amino acid level by investigating the four binding-loops as peptides with Ca(ii), Eu(iii), Tb(iii) and Cm(iii).![]()
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Affiliation(s)
- Sophie M. Gutenthaler
- Department of Chemistry Ludwig-Maximilians-University Munich Butenandtstraße 5-13, 81377 München, Germany
| | - Satoru Tsushima
- Institute of Resource Ecology Helmholtz-Zentrum Dresden-Rossendorf e.V. Bautzner Landstraße 400, 01328 Dresden, Germany
- International Research Frontiers Initiative, Institute of Innovative Research, Tokyo Institute of Technology, Meguro 152-8550, Tokyo, Japan
| | - Robin Steudtner
- Institute of Resource Ecology Helmholtz-Zentrum Dresden-Rossendorf e.V. Bautzner Landstraße 400, 01328 Dresden, Germany
| | - Manuel Gailer
- Department of Chemistry Ludwig-Maximilians-University Munich Butenandtstraße 5-13, 81377 München, Germany
| | - Anja Hoffmann-Röder
- Department of Chemistry Ludwig-Maximilians-University Munich Butenandtstraße 5-13, 81377 München, Germany
| | - Björn Drobot
- Institute of Resource Ecology Helmholtz-Zentrum Dresden-Rossendorf e.V. Bautzner Landstraße 400, 01328 Dresden, Germany
| | - Lena J. Daumann
- Department of Chemistry Ludwig-Maximilians-University Munich Butenandtstraße 5-13, 81377 München, Germany
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Singer H, Drobot B, Zeymer C, Steudtner R, Daumann LJ. Americium preferred: lanmodulin, a natural lanthanide-binding protein favors an actinide over lanthanides. Chem Sci 2021; 12:15581-15587. [PMID: 35003587 PMCID: PMC8654097 DOI: 10.1039/d1sc04827a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Accepted: 10/25/2021] [Indexed: 11/21/2022] Open
Abstract
The separation and recycling of lanthanides is an active area of research with a growing demand that calls for more environmentally friendly lanthanide sources. Likewise, the efficient and industrial separation of lanthanides from the minor actinides (Np, Am–Fm) is one of the key questions for closing the nuclear fuel cycle; reducing costs and increasing safety. With the advent of the field of lanthanide-dependent bacterial metabolism, bio-inspired applications are in reach. Here, we utilize the natural lanthanide chelator lanmodulin and the luminescent probes Eu3+ and Cm3+ to investigate the inter-metal competition behavior of all lanthanides (except Pm) and the major actinide plutonium as well as three minor actinides neptunium, americium and curium to lanmodulin. Using time-resolved laser-induced fluorescence spectroscopy we show that lanmodulin has the highest relative binding affinity to Nd3+ and Eu3+ among the lanthanide series. When equimolar mixtures of Cm3+ and Am3+ are added to lanmodulin, lanmodulin preferentially binds to Am3+ over Cm3+ whilst Nd3+ and Cm3+ bind with similar relative affinity. The results presented show that a natural lanthanide-binding protein can bind a major and various minor actinides with high relative affinity, paving the way to bio-inspired separation applications. In addition, an easy and versatile method was developed, using the fluorescence properties of only two elements, Eu and Cm, for inter-metal competition studies regarding lanthanides and selected actinides and their binding to biological molecules. In need of environmentally friendly methods for the separation and recycling of lanthanides and actinides, the binding of the protein lanmodulin to lanthanides and actinides was studied using time resolved laser induced fluorescence spectroscopy.![]()
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Affiliation(s)
- Helena Singer
- Department of Chemistry, Ludwig-Maximilians-University Munich Butenandtstraße 5 - 13 81377 München Germany
| | - Björn Drobot
- Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf e.V. Bautzner Landstraße 400 01328 Dresden Germany
| | - Cathleen Zeymer
- Department of Chemistry, Technische Universität München Lichtenbergstraße 4 85748 Garching Germany
| | - Robin Steudtner
- Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf e.V. Bautzner Landstraße 400 01328 Dresden Germany
| | - Lena J Daumann
- Department of Chemistry, Ludwig-Maximilians-University Munich Butenandtstraße 5 - 13 81377 München Germany
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10
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Liu S, Featherston ER, Cotruvo JA, Baiz CR. Lanthanide-dependent coordination interactions in lanmodulin: a 2D IR and molecular dynamics simulations study. Phys Chem Chem Phys 2021; 23:21690-21700. [PMID: 34581354 DOI: 10.1039/d1cp03628a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The biological importance of lanthanides, and the early lanthanides (La3+-Nd3+) in particular, has only recently been recognized, and the structural principles underlying selective binding of lanthanide ions in biology are not yet well established. Lanmodulin (LanM) is a novel protein that displays unprecedented affinity and selectivity for lanthanides over most other metal ions, with an uncommon preference for the early lanthanides. Its utilization of EF-hand motifs to bind lanthanides, rather than the Ca2+ typically recognized by these motifs in other proteins, has led it to be used as a model system to understand selective lanthanide recognition. Two-dimensional infrared (2D IR) spectroscopy combined with molecular dynamics simulations were used to investigate LanM's selectivity mechanisms by characterizing local binding site geometries upon coordination of early and late lanthanides as well as calcium. These studies focused on the protein's uniquely conserved proline residues in the second position of each EF-hand binding loop. We found that these prolines constrain the EF-hands for strong coordination of early lanthanides. Substitution of this proline results in a more flexible binding site to accommodate a larger range of ions but also results in less compact coordination geometries and greater disorder within the binding site. Finally, we identify the conserved glycine in the sixth position of each EF-hand as a mediator of local binding site conformation and global secondary structure. Uncovering fundamental structure-function relationships in LanM informs the development of synthetic biology technologies targeting lanthanides in industrial applications.
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Affiliation(s)
- Stephanie Liu
- Department of Chemistry, University of Texas at Austin, Austin, TX 78712, USA.
| | - Emily R Featherston
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA.
| | - Joseph A Cotruvo
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA.
| | - Carlos R Baiz
- Department of Chemistry, University of Texas at Austin, Austin, TX 78712, USA.
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