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Konieczna W, Mierek-Adamska A, Chojnacka N, Antoszewski M, Szydłowska-Czerniak A, Dąbrowska GB. Characterization of the Metallothionein Gene Family in Avena sativa L. and the Gene Expression during Seed Germination and Heavy Metal Stress. Antioxidants (Basel) 2023; 12:1865. [PMID: 37891944 PMCID: PMC10603854 DOI: 10.3390/antiox12101865] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 10/10/2023] [Accepted: 10/11/2023] [Indexed: 10/29/2023] Open
Abstract
Metallothioneins (MTs) are a family of small proteins rich in cysteine residues. The sulfhydryl group of metallothioneins can bind to metal ions, maintaining metal homeostasis and protecting the cells from damage caused by toxic heavy metals. Moreover, MTs can function as reactive oxygen species scavengers since cysteine thiols undergo reversible and irreversible oxidation. Here, we identified 21 metallothionein genes (AsMTs) in the oat (Avena sativa L.) genome, which were divided into four types depending on the amino acid sequences of putative proteins encoded by identified genes. Analysis of promoter sequences showed that MTs might respond to a variety of stimuli, including biotic and abiotic stresses and phytohormones. The results of qRT-PCR showed that all four types of AsMTs are differentially expressed during the first 48 hours of seed germination. Moreover, stress induced by the application of zinc, cadmium, and a mixture of zinc and cadmium affects the expression of oat MTs variously depending on the MT type, indicating that AsMT1-4 fulfil different roles in plant cells.
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Affiliation(s)
- Wiktoria Konieczna
- Department of Genetics, Faculty of Biological and Veterinary Sciences, Nicolaus Copernicus University in Toruń, Lwowska 1, 87-100 Toruń, Poland; (W.K.); (M.A.)
- Centre for Modern Interdisciplinary Technologies, Nicolaus Copernicus University in Toruń, Wileńska 4, 87-100 Toruń, Poland
| | - Agnieszka Mierek-Adamska
- Department of Genetics, Faculty of Biological and Veterinary Sciences, Nicolaus Copernicus University in Toruń, Lwowska 1, 87-100 Toruń, Poland; (W.K.); (M.A.)
- Centre for Modern Interdisciplinary Technologies, Nicolaus Copernicus University in Toruń, Wileńska 4, 87-100 Toruń, Poland
| | - Natalia Chojnacka
- Department of Genetics, Faculty of Biological and Veterinary Sciences, Nicolaus Copernicus University in Toruń, Lwowska 1, 87-100 Toruń, Poland; (W.K.); (M.A.)
- Centre for Modern Interdisciplinary Technologies, Nicolaus Copernicus University in Toruń, Wileńska 4, 87-100 Toruń, Poland
| | - Marcel Antoszewski
- Department of Genetics, Faculty of Biological and Veterinary Sciences, Nicolaus Copernicus University in Toruń, Lwowska 1, 87-100 Toruń, Poland; (W.K.); (M.A.)
- Centre for Modern Interdisciplinary Technologies, Nicolaus Copernicus University in Toruń, Wileńska 4, 87-100 Toruń, Poland
| | - Aleksandra Szydłowska-Czerniak
- Department of Analytical Chemistry and Applied Spectroscopy, Faculty of Chemistry, Nicolaus Copernicus University in Toruń, Gagarina 7, 87-100 Toruń, Poland;
| | - Grażyna B. Dąbrowska
- Department of Genetics, Faculty of Biological and Veterinary Sciences, Nicolaus Copernicus University in Toruń, Lwowska 1, 87-100 Toruń, Poland; (W.K.); (M.A.)
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Mosna K, Jurczak K, Krężel A. Differentiated Zn(II) binding affinities in animal, plant, and bacterial metallothioneins define their zinc buffering capacity at physiological pZn. Metallomics 2023; 15:mfad061. [PMID: 37804185 PMCID: PMC10612145 DOI: 10.1093/mtomcs/mfad061] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Accepted: 10/05/2023] [Indexed: 10/09/2023]
Abstract
Metallothioneins (MTs) are small, Cys-rich proteins present in various but not all organisms, from bacteria to humans. They participate in zinc and copper metabolism, toxic metals detoxification, and protection against reactive species. Structurally, they contain one or multiple domains, capable of binding a variable number of metal ions. For experimental convenience, biochemical characterization of MTs is mainly performed on Cd(II)-loaded proteins, frequently omitting or limiting Zn(II) binding features and related functions. Here, by choosing 10 MTs with relatively well-characterized structures from animals, plants, and bacteria, we focused on poorly investigated Zn(II)-to-protein affinities, stability-structure relations, and the speciation of individual complexes. For that purpose, MTs were characterized in terms of stoichiometry, pH-dependent Zn(II) binding, and competition with chromogenic and fluorescent probes. To shed more light on protein folding and its relation with Zn(II) affinity, reactivity of variously Zn(II)-loaded MTs was studied by (5,5'-dithiobis(2-nitrobenzoic acid) oxidation in the presence of mild chelators. The results show that animal and plant MTs, despite their architectural differences, demonstrate the same affinities to Zn(II), varying from nano- to low picomolar range. Bacterial MTs bind Zn(II) more tightly but, importantly, with different affinities from low picomolar to low femtomolar range. The presence of weak, moderate, and tight zinc sites is related to the folding mechanisms and internal electrostatic interactions. Differentiated affinities of all MTs define their zinc buffering capacity required for Zn(II) donation and acceptance at various free Zn(II) concentrations (pZn levels). The data demonstrate critical roles of individual Zn(II)-depleted MT species in zinc buffering processes.
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Affiliation(s)
- Karolina Mosna
- Department of Chemical Biology, Faculty of Biotechnology, University of Wrocław, Joliot-Curie 14a, 50-383 Wrocław, Poland
| | - Kinga Jurczak
- Department of Chemical Biology, Faculty of Biotechnology, University of Wrocław, Joliot-Curie 14a, 50-383 Wrocław, Poland
| | - Artur Krężel
- Department of Chemical Biology, Faculty of Biotechnology, University of Wrocław, Joliot-Curie 14a, 50-383 Wrocław, Poland
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Valsecchi R, Baumann C, Lila A, Zerbe O. Evolution of Cd2+ and Cu+ binding in Helix pomatia metallothioneins. Metallomics 2023; 15:mfad057. [PMID: 37738453 PMCID: PMC10548783 DOI: 10.1093/mtomcs/mfad057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Accepted: 09/14/2023] [Indexed: 09/24/2023]
Abstract
Metallothioneins (MTs) are small proteins present in all kingdoms of life. Their high cysteine content enables them to bind metal ions, such as Zn2+, Cd2+, and Cu+, providing means for detoxification and metal homeostasis. Three MT isoforms with distinct metal binding preferences are present in the Roman Snail Helix pomatia. Here, we use nuclear magnetic resonance (NMR) to follow the evolution of Cd2+ and Cu+ binding from the reconstructed ancestral Stylommatophora MT to the three H. pomatia MT (HpMT) isoforms. Information obtained from [15N,1H]-HSQC spectra and T2 relaxation times are combined to describe the conformational stability of the MT-metal complexes. A well-behaved MT-metal complex adopts a unique structure and does not undergo additional conformational exchange. The ancestor to all three HpMTs forms conformationally stable Cd2+ complexes and closely resembles the Cd2+-specific HpCdMT isoform, suggesting a role in Cd2+ detoxification for the ancestral protein. All Cu+-MT complexes, including the Cu+-specific HpCuMT isoform, undergo a considerable amount of conformational exchange. The unspecific HpCd/CuMT and the Cu+-specific HpCuMT isoforms form Cu+ complexes with comparable characteristics. It is possible to follow how Cd2+ and Cu+ binding changed throughout evolution. Interestingly, Cu+ binding improved independently in the lineages leading to the unspecific and the Cu+-specific HpMT isoforms. C-terminal domains are generally less capable of coordinating the non-cognate metal ion than N-terminal domains, indicating a higher level of specialization of the C-domain. Our findings provide new insights into snail MT evolution, helping to understand the interplay between biological function and structural features toward a comprehensive understanding of metal preference.
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Affiliation(s)
- Renato Valsecchi
- Department of Chemistry, University of Zurich, 8057 Zurich, Winterthurerstrasse 190, Switzerland
| | - Christian Baumann
- Department of Chemistry, University of Zurich, 8057 Zurich, Winterthurerstrasse 190, Switzerland
| | - Ardit Lila
- Department of Chemistry, University of Zurich, 8057 Zurich, Winterthurerstrasse 190, Switzerland
| | - Oliver Zerbe
- Department of Chemistry, University of Zurich, 8057 Zurich, Winterthurerstrasse 190, Switzerland
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Zhou Z, Dong Y, Zhu L, Xia X, Li S, Wang G, Shi K. Effective and stable adsorptive removal of Cadmium(II) and Lead(II) using selenium nanoparticles modified by microbial SmtA metallothionein. CHEMOSPHERE 2022; 307:135818. [PMID: 35944684 DOI: 10.1016/j.chemosphere.2022.135818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Revised: 07/19/2022] [Accepted: 07/20/2022] [Indexed: 06/15/2023]
Abstract
Metallothionein SmtA-modified selenium nanoparticles (SmtA-SeNPs), efficient adsorbents for Cd(II) and Pb(II), were synthesized in the present work. The ligand, microbial SmtA protein, was synthesized using an engineered strain Escherichia coli, posing the benefits of simplicity, safety, and high production. SmtA-SeNPs were spheres with diameters between 68.1 and 122.4 nm, containing amino, hydroxyl, and sulfhydryl functional groups with negatively charged (pH > 5). SmtA-SeNPs displayed better adsorption performance than dissociative SmtA and SeNPs. The adsorption of Cd(II) and Pb(II) mainly depends on the electrostatic attractions and the metal chelation of abundant functional groups. The maximum adsorption capacity was 506.3 mg/g for Cd(II) and 346.7 mg/g for Pb(II), which were higher than the values of most nanoparticles. In addition, SmtA-SeNPs were immobilized with a membrane filter to produce a SmtA-SeNPs filter, and the percentage removal of Cd(II) and Pb(II) increased from 26.75% to 98.13% for Cd(II) and from 9.95% to 99.20% compared with the blank filter. Moreover, the SmtA-SeNPs filter was regenerated using subacid deionized water, and the filter exhibited a stable removal ratio of Cd(II) and Pb(II) in ten continuous cycles of Cd(II)- or Pb(II)-containing wastewater treatment. The residual amounts of Cd and Pb met national standard levels of wastewater discharge.
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Affiliation(s)
- Zijie Zhou
- State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, PR China
| | - Yixuan Dong
- State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, PR China
| | - Lin Zhu
- State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, PR China
| | - Xian Xia
- Hubei Key Laboratory of Edible Wild Plants Conservation and Utilization, College of Life Sciences, Hubei Normal University, Huangshi, 435002, PR China
| | - Sikui Li
- State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, PR China
| | - Gejiao Wang
- State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, PR China.
| | - Kaixiang Shi
- State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, PR China.
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Mikhaylina A, Scott L, Scanlan DJ, Blindauer CA. A metallothionein from an open ocean cyanobacterium removes zinc from the sensor protein controlling its transcription. J Inorg Biochem 2022; 230:111755. [DOI: 10.1016/j.jinorgbio.2022.111755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 02/05/2022] [Accepted: 02/06/2022] [Indexed: 10/19/2022]
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García-Risco M, Calatayud S, Niederwanger M, Albalat R, Palacios Ò, Capdevila M, Dallinger R. Two Unconventional Metallothioneins in the Apple Snail Pomacea bridgesii Have Lost Their Metal Specificity during Adaptation to Freshwater Habitats. Int J Mol Sci 2020; 22:ijms22010095. [PMID: 33374169 PMCID: PMC7796288 DOI: 10.3390/ijms22010095] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Revised: 12/17/2020] [Accepted: 12/18/2020] [Indexed: 01/08/2023] Open
Abstract
Metallothioneins (MTs) are a diverse group of proteins responsible for the control of metal homeostasis and detoxification. To investigate the impact that environmental conditions might have had on the metal-binding abilities of these proteins, we have characterized the MTs from the apple snail Pomacea bridgesii, a gastropod species belonging to the class of Caenogastropoda with an amphibious lifestyle facing diverse situations of metal bioavailability. P. bridgesii has two structurally divergent MTs, named PbrMT1 and PbrMT2, that are longer than other gastropod MTs due to the presence of extra sequence motifs and metal-binding domains. We have characterized the Zn(II), Cd(II), and Cu(I) binding abilities of these two MTs after their heterologous expression in E. coli. Our results have revealed that despite their structural differences, both MTs share an unspecific metal-binding character, and a great ability to cope with elevated amounts of different metal ions. Our analyses have also revealed slight divergences in their metal-binding features: PbrMT1 shows a more pronounced Zn(II)-thionein character than PbrMT2, while the latter has a stronger Cu(I)-thionein character. The characterization of these two unconventional PbrMTs supports the loss of the metal-binding specificity during the evolution of the MTs of the Ampullariid family, and further suggests an evolutionary link of this loss with the adaptation of these gastropod lineages to metal-poor freshwater habitats.
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Affiliation(s)
- Mario García-Risco
- Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Cerdanyola del Vallès, Spain; (M.G.-R.); (Ò.P.); (M.C.)
| | - Sara Calatayud
- Departament de Genètica, Microbiologia i Estadística and Institut de Recerca de la Biodiversitat (IRBio), Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 643, E-08028 Barcelona, Spain; (S.C.); (R.A.)
| | - Michael Niederwanger
- Institute of Zoology, Center of Molecular Biosciences, University of Innsbruck, Technikerstraße 25, A-6020 Innsbruck, Austria;
| | - Ricard Albalat
- Departament de Genètica, Microbiologia i Estadística and Institut de Recerca de la Biodiversitat (IRBio), Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 643, E-08028 Barcelona, Spain; (S.C.); (R.A.)
| | - Òscar Palacios
- Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Cerdanyola del Vallès, Spain; (M.G.-R.); (Ò.P.); (M.C.)
| | - Mercè Capdevila
- Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Cerdanyola del Vallès, Spain; (M.G.-R.); (Ò.P.); (M.C.)
| | - Reinhard Dallinger
- Institute of Zoology, Center of Molecular Biosciences, University of Innsbruck, Technikerstraße 25, A-6020 Innsbruck, Austria;
- Correspondence:
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Perinelli M, Tegoni M, Freisinger E. Different Behavior of the Histidine Residue toward Cadmium and Zinc in a Cadmium-Specific Metallothionein from an Aquatic Fungus. Inorg Chem 2020; 59:16988-16997. [DOI: 10.1021/acs.inorgchem.0c02171] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Monica Perinelli
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Matteo Tegoni
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17A, 43124 Parma, Italy
| | - Eva Freisinger
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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Chatterjee S, Kumari S, Rath S, Priyadarshanee M, Das S. Diversity, structure and regulation of microbial metallothionein: metal resistance and possible applications in sequestration of toxic metals. Metallomics 2020; 12:1637-1655. [PMID: 32996528 DOI: 10.1039/d0mt00140f] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Metallothioneins (MTs) are a group of cysteine-rich, universal, low molecular weight proteins distributed widely in almost all major taxonomic groups ranging from tiny microbes to highly organized vertebrates. The primary function of this protein is storage, transportation and binding of metals, which enable microorganisms to detoxify heavy metals. In the microbial world, these peptides were first identified in a cyanobacterium Synechococcus as the SmtA protein which exhibits high affinity towards rising level of zinc and cadmium to preserve metal homeostasis in a cell. In yeast, MTs aid in reserving copper and confer protection against copper toxicity by chelating excess copper ions in a cell. Two MTs, CUP1 and Crs5, originating from Saccharomyces cerevisiae predominantly bind to copper though are capable of binding with zinc and cadmium ions. MT superfamily 7 is found in ciliated protozoa which show high affinity towards copper and cadmium. Several tools and techniques, such as western blot, capillary electrophoresis, inductively coupled plasma, atomic emission spectroscopy and high performance liquid chromatography, have been extensively utilized for the detection and quantification of microbial MTs which are utilized for the efficient remediation and sequestration of heavy metals from a contaminated environment.
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Affiliation(s)
- Shreosi Chatterjee
- Laboratory of Environmental Microbiology and Ecology (LEnME), Department of Life Science, National Institute of Technology, Rourkela 769 008, Odisha, India.
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Metagenomics-Guided Discovery of Potential Bacterial Metallothionein Genes from the Soil Microbiome That Confer Cu and/or Cd Resistance. Appl Environ Microbiol 2020; 86:AEM.02907-19. [PMID: 32111593 DOI: 10.1128/aem.02907-19] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Accepted: 02/15/2020] [Indexed: 12/18/2022] Open
Abstract
Metallothionein (MT) genes are valuable genetic materials for developing metal bioremediation tools. Currently, a limited number of prokaryotic MTs have been experimentally identified, which necessitates the expansion of bacterial MT diversity. In this study, we conducted a metagenomics-guided analysis for the discovery of potential bacterial MT genes from the soil microbiome. More specifically, we combined resistance gene enrichment through diversity loss, metagenomic mining with a dedicated MT database, evolutionary trace analysis, DNA chemical synthesis, and functional genomic validation to identify novel MTs. Results showed that Cu stress induced a compositional change in the soil microbiome, with an enrichment of metal-resistant bacteria in soils with higher Cu concentrations. Shotgun metagenomic sequencing was performed to obtain the gene pool of environmental DNA (eDNA), which was subjected to a local BLAST search against an MT database for detecting putative MT genes. Evolutional trace analysis led to the identification of 27 potential MTs with conserved cysteine/histidine motifs different from those of known prokaryotic MTs. Following chemical synthesis of these 27 potential MT genes and heterologous expression in Escherichia coli, six of them were found to improve the hosts' growth substantially and enhanced the hosts' sorption of Cu, Cd, and Zn, among which MT5 led to a 13.7-fold increase in Cd accumulation. Furthermore, four of them restored Cu and/or Cd resistance in two metal-sensitive E. coli strains.IMPORTANCE The metagenomics-guided procedure developed here bypasses the difficulties encountered in classic PCR-based approaches and led to the discovery of novel MT genes, which may be useful in developing bioremediation tools. The procedure used here expands our knowledge on the diversity of bacterial MTs in the environment and may also be applicable to identify other functional genes from eDNA.
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Scheller JS, Irvine GW, Stillman MJ. Unravelling the mechanistic details of metal binding to mammalian metallothioneins from stoichiometric, kinetic, and binding affinity data. Dalton Trans 2018; 47:3613-3637. [PMID: 29431781 DOI: 10.1039/c7dt03319b] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Metallothioneins (MTs) are small, cysteine-rich proteins, found throughout Nature. Their ability to bind a number of different metals with a range of stoichiometric ratios means that this protein family is critically important for essential metal (Zn2+ and Cu+) homeostasis, metal storage, metal donation to nascent metalloenzymes as well as heavy metal detoxification. With its 20 cysteines, metallothionein is also considered to protect cells against oxidative stress. MT has been studied by a large number of researchers over the last 6 decades using a variety of spectroscopic techniques. The lack of distinguishing chromophores for the multitude of binding sites has made the evaluation of stoichiometric properties for different metals challenging. Initially, only 113Cd-NMR spectroscopy could provide strong evidence for the proposed cluster formation of Cd-MT. The extraordinary development of electrospray ionization mass spectrometry (ESI-MS), where all coexisting species in solution are observed, revolutionized MT research. Prior to the use of ESI-MS data, a range of "magic numbers" representing metal-to-MT molar ratios were reported from optical spectroscopic studies. The availability of ESI mass spectral data led to (i) the confirmation of cluster formation, (ii) a conceptual understanding of the cooperativity involved in multiple metal binding events, (iii) the presence of domain specificity between regions of the protein and (iv) mechanistic details involving both binding affinities and rate constants. The kinetic experiments identified the presence of multiple individual binding sites, each with a unique rate constant and an analogous binding affinity. The almost linear trend in rate constants as a function of bound As3+ provided a unique insight that became a critical step in the complete understanding of the mechanistic details of the metalation of MT. To fully define the biological function of this sulfur-rich protein it is necessary to determine kinetic rate constants and binding affinities for the essential metals. Recently, Zn2+ competition experiments between both of the isolated fragments (α and β) and the full-length protein (βα-MT 1a) as well as Zn2+ competition between βα-MT 1a and carbonic anhydrase were reported. From these data, the trend in binding affinities and the values of the Kf of the 7 bimolecular reactions involved in metalation were determined. From the analysis of ESI-MS data for Cu+ binding to βα-MT 1a at different pH-values, a trend in the 20 binding affinities for the complete metalation mechanism was reported. This review details a personal view of the historical development of the determination of stoichiometry for metal binding, the structure of the binding sites, the rates of the metalation reactions and the underlying binding affinities for each metalation step. We have attempted to summarize the experimental developments that led to the publication in May 2017 of the experimental determination of the 20 binding constants for the 20 sequential bimolecular reactions for Cu+ binding to the 20 Cys of apoMT as a function of pH that show the appearance and disappearance of clusters. We report both published data and in a series of tables an assembly of stoichiometries, and equilibrium constants for Zn2+ and Cu+ for many different metallothioneins.
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Affiliation(s)
- Judith S Scheller
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada.
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Tarasava K, Freisinger E. Investigating the influence of histidine residues on the metal ion binding ability of the wheat metallothionein γ-Ec-1 domain. J Inorg Biochem 2015; 153:197-203. [DOI: 10.1016/j.jinorgbio.2015.08.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2015] [Revised: 07/15/2015] [Accepted: 08/05/2015] [Indexed: 10/23/2022]
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Saffar B, Mehri Ghahfarrokhi A, Mahnam K, Mobini-Dehkordi M. Improvement of Cd(2+) uptake ability of SmtA protein by Lys/Cys mutation; experimental and theoretical studies. J Biomol Struct Dyn 2015; 33:2347-59. [PMID: 26006175 DOI: 10.1080/07391102.2015.1054431] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The improved Cd(2+) surface affinity characteristics of a mutated cyanobacterial metallothionein SmtA (K45C) were investigated via experimental and theoretical methods. Molecular dynamics simulations were carried out using a model of Cd(2+) and other ions enclosed in a fully hydrated simulation box with the wild-type or mutated SmtA protein. The theoretical results suggested that mutated SmtA was more powerful in absorption of Cd(2+) than the wild-type protein. Then, the mutated smtA gene (from Synechococcus PCC 7942) was synthesized by simplified gene synthesis method and expressed on isopropyl-beta-d-thiogalactopyranoside induction. The protein expression was investigated by SDS-PAGE and verified by Western blotting. Finally, cadmium uptake ratio of mutant protein toward wild type was analyzed by atomic absorption. This study is the first example of cytoplasmic expression of a mutant protein. Experimental results also verified that the mutation intensifies uptake of Cd(2+) ions.
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Affiliation(s)
- B Saffar
- a Faculty of Science, Department of Genetics , Shahrekord University , Shahrekord , Iran.,b Biotechnology Research Institute , Shahrekord University , Shahrekord , Iran
| | - A Mehri Ghahfarrokhi
- c Master of Science, Department of Genetics , Shahrekord University , Shahrekord , Iran
| | - K Mahnam
- d Faculty of Science, Department of Biology , Shahrekord University , Shahrekord , Iran
| | - M Mobini-Dehkordi
- a Faculty of Science, Department of Genetics , Shahrekord University , Shahrekord , Iran
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13
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Blindauer CA. Advances in the molecular understanding of biological zinc transport. Chem Commun (Camb) 2015; 51:4544-63. [DOI: 10.1039/c4cc10174j] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Recognition of the importance of zinc homeostasis for health has driven a surge in structural data on major zinc-transporting proteins.
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14
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Tomas M, Pagani MA, Andreo CS, Capdevila M, Bofill R, Atrian S. His-containing plant metallothioneins: comparative study of divalent metal-ion binding by plant MT3 and MT4 isoforms. J Biol Inorg Chem 2014; 19:1149-64. [PMID: 24951240 DOI: 10.1007/s00775-014-1170-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Accepted: 05/31/2014] [Indexed: 11/30/2022]
Abstract
Metallothioneins (MTs) are a superfamily of Cys-rich, low-molecular weight metalloproteins that bind heavy metal ions. These cytosolic metallopeptides, which exist in most living organisms, are thought to be involved in metal homeostasis, metal detoxification, and oxidative stress protection. In this work, we characterise the Zn(II)- and Cd(II)-binding abilities of plant type 3 and type 4 MTs identified in soybean and sunflower, both of them being His-containing peptides. The recombinant metal-MT complexes synthesised in Zn(II) or Cd(II)-enriched Escherichia coli cultures have been analysed by ESI-MS, and CD, ICP-AES, and UV spectroscopies. His-to-Ala type 3 MT mutants have also been constructed and synthesised for the study of the role of His in divalent metal ion coordination. The results show comparable divalent metal-binding capacities for the MTs of type 3, and suggest, for the first time, the participation of their conserved C-term His residues in metal binding. Interesting features for the Zn(II)-binding abilities of type 4 MTs are also reported, as their variable His content may be considered crucial for their biological performance.
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Affiliation(s)
- Mireia Tomas
- Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, 08093, Barcelona, Spain
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Sutherland DEK, Stillman MJ. Challenging conventional wisdom: single domain metallothioneins. Metallomics 2014; 6:702-28. [DOI: 10.1039/c3mt00216k] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Metallation studies of human metallothioneins support the role of single metal-binding-domains as commonplace with the typical two-domain-cluster structure as exceptional.
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16
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Leonhardt T, Sácký J, Šimek P, Šantrůček J, Kotrba P. Metallothionein-like peptides involved in sequestration of Zn in the Zn-accumulating ectomycorrhizal fungus Russula atropurpurea. Metallomics 2014; 6:1693-701. [DOI: 10.1039/c4mt00141a] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The first evidence of the existence of gene-encoded Zn-binding peptides that sequester a substantial portion of intracellular Zn in ectomycorrhizal fungi under natural conditions.
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Affiliation(s)
- Tereza Leonhardt
- Institute of Chemical Technology, Prague
- Department of Biochemistry and Microbiology
- 166 28 Prague, Czech Republic
| | - Jan Sácký
- Institute of Chemical Technology, Prague
- Department of Biochemistry and Microbiology
- 166 28 Prague, Czech Republic
| | - Pavel Šimek
- Institute of Chemical Technology, Prague
- Department of Biochemistry and Microbiology
- 166 28 Prague, Czech Republic
| | - Jiří Šantrůček
- Institute of Chemical Technology, Prague
- Department of Biochemistry and Microbiology
- 166 28 Prague, Czech Republic
| | - Pavel Kotrba
- Institute of Chemical Technology, Prague
- Department of Biochemistry and Microbiology
- 166 28 Prague, Czech Republic
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Loebus J, Leitenmaier B, Meissner D, Braha B, Krauss GJ, Dobritzsch D, Freisinger E. The major function of a metallothionein from the aquatic fungus Heliscus lugdunensis is cadmium detoxification. J Inorg Biochem 2013; 127:253-60. [DOI: 10.1016/j.jinorgbio.2013.06.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2013] [Revised: 05/31/2013] [Accepted: 06/02/2013] [Indexed: 10/26/2022]
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18
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Pérez-Rafael S, Pagani A, Palacios Ò, Dallinger R, Capdevila M, Atrian S. The Role of Histidine in a Copper-Specific Metallothionein. Z Anorg Allg Chem 2013. [DOI: 10.1002/zaac.201300053] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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19
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Chen YH, Lin TT, Chen HY, Kao CL, Chen HY, Hsu SC, Carey JR, Chiang MY. A simple competition assay to probe pentacopper(I)-thiolato cluster ligand exchange. J Inorg Biochem 2013; 120:24-31. [DOI: 10.1016/j.jinorgbio.2012.11.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2012] [Revised: 09/28/2012] [Accepted: 11/26/2012] [Indexed: 10/27/2022]
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20
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Blindauer CA. Lessons on the critical interplay between zinc binding and protein structure and dynamics. J Inorg Biochem 2013; 121:145-55. [PMID: 23376625 DOI: 10.1016/j.jinorgbio.2013.01.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2012] [Revised: 01/08/2013] [Accepted: 01/08/2013] [Indexed: 02/05/2023]
Abstract
Zinc is one of the most important micronutrients for virtually all living organisms, and hence, it is important to understand the molecular mechanisms for its homeostasis. Besides proteins involved in transmembrane transport, both extra- and intracellular zinc-binding proteins play important roles in the respective metabolic networks. Important examples for extracellular zinc transporters are mammalian serum albumins, and for intracellular zinc handling, certain metallothioneins are of relevance. The availability of protein structures including relevant metal binding sites is a fundamental prerequisite to decipher the mechanisms that govern zinc binding dynamics in these proteins, but their determination can prove to be surprisingly challenging. Due to the spectroscopic silence of Zn(2+), combinations of biophysical techniques including electrospray ionisation mass spectrometry (ESI-MS) and multinuclear NMR, isothermal titration calorimetry (ITC) and extended X-ray absorption fine structure (EXAFS) spectroscopy, coupled with site-directed mutagenesis and molecular modelling have proven to be valuable approaches to understand not only the zinc-binding properties of metallothioneins and albumins, but also the influence of other physiologically relevant competing agents. These studies have demonstrated why the bacterial metallothionein SmtA contains a site inert towards exchange with Cd(2+), why the plant metallothionein EC from wheat is partially unfolded in the presence of Cd(2+), and how fatty acids impact on the zinc-binding ability of mammalian serum albumins.
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21
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Leszczyszyn OI, Imam HT, Blindauer CA. Diversity and distribution of plant metallothioneins: a review of structure, properties and functions. Metallomics 2013; 5:1146-69. [DOI: 10.1039/c3mt00072a] [Citation(s) in RCA: 133] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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22
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Barnett JP, Millard A, Ksibe AZ, Scanlan DJ, Schmid R, Blindauer CA. Mining genomes of marine cyanobacteria for elements of zinc homeostasis. Front Microbiol 2012; 3:142. [PMID: 22514551 PMCID: PMC3323870 DOI: 10.3389/fmicb.2012.00142] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 03/25/2012] [Indexed: 12/13/2022] Open
Abstract
Zinc is a recognized essential element for the majority of organisms, and is indispensable for the correct function of hundreds of enzymes and thousands of regulatory proteins. In aquatic photoautotrophs including cyanobacteria, zinc is thought to be required for carbonic anhydrase and alkaline phosphatase, although there is evidence that at least some carbonic anhydrases can be cambialistic, i.e., are able to acquire in vivo and function with different metal cofactors such as Co2+ and Cd2+. Given the global importance of marine phytoplankton, zinc availability in the oceans is likely to have an impact on both carbon and phosphorus cycles. Zinc concentrations in seawater vary over several orders of magnitude, and in the open oceans adopt a nutrient-like profile. Most studies on zinc handling by cyanobacteria have focused on freshwater strains and zinc toxicity; much less information is available on marine strains and zinc limitation. Several systems for zinc homeostasis have been characterized in the freshwater species Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803, but little is known about zinc requirements or zinc handling by marine species. Comparative metallo-genomics has begun to explore not only the putative zinc proteome, but also specific protein families predicted to have an involvement in zinc homeostasis, including sensors for excess and limitation (SmtB and its homologs as well as Zur), uptake systems (ZnuABC), putative intracellular zinc chaperones (COG0523) and metallothioneins (BmtA), and efflux pumps (ZiaA and its homologs).
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23
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Capdevila M, Bofill R, Palacios Ò, Atrian S. State-of-the-art of metallothioneins at the beginning of the 21st century. Coord Chem Rev 2012. [DOI: 10.1016/j.ccr.2011.07.006] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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24
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Nagy KL, Manceau A, Gasper JD, Ryan JN, Aiken GR. Metallothionein-like multinuclear clusters of mercury(II) and sulfur in peat. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2011; 45:7298-306. [PMID: 21809860 DOI: 10.1021/es201025v] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Strong mercury(II)-sulfur (Hg-SR) bonds in natural organic matter, which influence mercury bioavailability, are difficult to characterize. We report evidence for two new Hg-SR structures using X-ray absorption spectroscopy in peats from the Florida Everglades with added Hg. The first, observed at a mole ratio of organic reduced S to Hg (S(red)/Hg) between 220 and 1140, is a Hg(4)S(x) type of cluster with each Hg atom bonded to two S atoms at 2.34 Å and one S at 2.53 Å, and all Hg atoms 4.12 Å apart. This model structure matches those of metal-thiolate clusters in metallothioneins, but not those of HgS minerals. The second, with one S atom at 2.34 Å and about six C atoms at 2.97 to 3.28 Å, occurred at S(red)/Hg between 0.80 and 4.3 and suggests Hg binding to a thiolated aromatic unit. The multinuclear Hg cluster indicates a strong binding environment to cysteinyl sulfur that might impede methylation. Along with a linear Hg(SR)(2) unit with Hg-S bond lengths of 2.34 Å at S(red)/Hg of about 10 to 20, the new structures support a continuum in Hg-SR binding strength in natural organic matter.
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Affiliation(s)
- Kathryn L Nagy
- Department of Earth and Environmental Sciences, MC-186, 845 West Taylor Street, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
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25
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Bacterial metallothioneins: past, present, and questions for the future. J Biol Inorg Chem 2011; 16:1011-24. [DOI: 10.1007/s00775-011-0790-y] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Accepted: 05/04/2011] [Indexed: 10/18/2022]
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26
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Schmidt A, Hagen M, Schütze E, Schmidt A, Kothe E. In silico prediction of potential metallothioneins and metallohistins in actinobacteria. J Basic Microbiol 2011; 50:562-9. [PMID: 21077111 DOI: 10.1002/jobm.201000055] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Metallothioneins and metallohistins are short peptides with a high cysteine and/or histidine content able to coordinate metals intracellularly, thereby increasing the tolerance against elevated concentrations of metals. Because of their features, they can be detected by in silico prediction from proteomes annotated from sequenced genomes. Here, we analyzed 73 sequenced actinobacterial genomes for peptides (≤ 100 amino acids) with a high content of cysteine and histidine (≥ 15%) and identified 103 putative metallothioneins and metallohistins. For 45 of these peptides, we found similarities to metal binding protein domains, including zinc fingers, heavy metal transporters or eukaryotic metallothioneins, which can serve as proof-of-principle in underscoring a potential function as metal binding peptides. An evolutionary origin from metal containing domains of enzymes is discussed and metallohistins not containing cysteine are described for the first time for bacteria.
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Affiliation(s)
- Andre Schmidt
- Microbial Phytopathology, Institute of Microbiology, Faculty of Biology and Pharmacy, Friedrich-Schiller-University, Jena, Germany
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27
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Abstract
Metallothioneins (MT) are a family of small cysteine rich proteins, which since their discovery in 1957, have been implicated in a range of roles including toxic metal detoxification, protection against oxidative stress, and as a metallochaperone involved in the homeostasis of both zinc and copper. The most well studied member of the family is the mammalian metallothionein, which consists of two domains: a β-domain with 9 cysteine residues, which sequesters 3 Cd(2+) or Zn(2+) or 6 Cu(+) ions, and an α-domain with 11 cysteine residues and, which sequesters 4 Cd(2+) or Zn(2+) or 6 Cu(+) ions. Despite over half a century of research, the exact functions of MT are still unknown. Much of current research aims to elucidate the mechanism of metal binding, as well as to isolate intermediates in metal exchange reactions; reactions necessary to maintain homeostatic equilibrium. These studies further our understanding of the role(s) of this remarkable and ubiquitous protein. Recently, supermetallated forms of the protein, where supermetallation describes metallation in excess of traditional levels, have been reported. These species may potentially be the metal exchange intermediates necessary to maintain homeostatic equilibrium. This review focuses on recent advances in the understanding of the mechanistic properties of metal binding, the implications for the metal induced protein folding reactions proposed for metallothionein metallation, the value of "magic numbers", which we informally define as the commonly determined metal-to-protein stoichiometric ratios and the significance of the new supermetallated states of the protein and the possible interpretation of the structural properties of this new metallation status. Together we provide a commentary on current experimental and theoretical advances and frame our consideration in terms of the possible functions of MT.
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Leszczyszyn OI, White CRJ, Blindauer CA. The isolated Cys2His2 site in EC metallothionein mediates metal-specific protein folding. MOLECULAR BIOSYSTEMS 2010; 6:1592-603. [PMID: 20467686 DOI: 10.1039/c002348e] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The selectivity of proteins involved in metal ion homeostasis is an important part of the puzzle to understand how cells allocate the correct metal ions to the correct proteins. Due to their similar ligand-binding properties, and their frequent co-existence in soils, essential zinc and toxic cadmium are a particularly challenging couple. Thus, minimisation of competition of Cd(2+) for Zn(2+) sites is of crucial importance for organisms that are in direct contact with soil. Amongst these, plants have an especially critical role, due to their importance for nutrition and energy. We have studied an embryo-specific, zinc-binding metallothionein (E(C)) from wheat by nuclear magnetic resonance, electrospray mass spectrometry, site-directed mutagenesis, and molecular modelling. Wheat E(C) exploits differences in affinities of Cys(4) and Cys(2)His(2) sites for Cd(2+) and Zn(2+) to achieve metal-selective protein folding. We propose that this may constitute a novel mechanism to discriminate between essential Zn(2+) and toxic Cd(2+).
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29
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Zeitoun-Ghandour S, Charnock JM, Hodson ME, Leszczyszyn OI, Blindauer CA, Stürzenbaum SR. The two Caenorhabditis elegans metallothioneins (CeMT-1 and CeMT-2) discriminate between essential zinc and toxic cadmium. FEBS J 2010; 277:2531-42. [PMID: 20553489 DOI: 10.1111/j.1742-4658.2010.07667.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The nematode Caenorhabditis elegans expresses two metallothioneins (MTs), CeMT-1 and CeMT-2, that are believed to be key players in the protection against metal toxicity. In this study, both isoforms were expressed in vitro in the presence of either Zn(II) or Cd(II). Metal binding stoichiometries and affinities were determined by ESI-MS and NMR, respectively. Both isoforms had equal zinc binding ability, but differed in their cadmium binding behaviour, with higher affinity found for CeMT-2. In addition, wild-type C. elegans, single MT knockouts and a double MT knockout allele were exposed to zinc (340 microm) or cadmium (25 microm) to investigate effects in vivo. Zinc levels were significantly increased in all knockout strains, but were most pronounced in the CeMT-1 knockout, mtl-1 (tm1770), while cadmium accumulation was highest in the CeMT-2 knockout, mtl-2 (gk125) and the double knockout mtl-1;mtl-2 (zs1). In addition, metal speciation was assessed by X-ray absorption fine-structure spectroscopy. This showed that O-donating, probably phosphate-rich, ligands play a dominant role in maintaining the physiological concentration of zinc, independently of metallothionein status. In contrast, cadmium was shown to coordinate with thiol groups, and the cadmium speciation of the wild-type and the CeMT-2 knockout strain was distinctly different to the CeMT-1 and double knockouts. Taken together, and supported by a simple model calculation, these findings show for the first time that the two MT isoforms have differential affinities towards Cd(II) and Zn(II) at a cellular level, and this is reflected at the protein level. This suggests that the two MT isoforms have distinct in vivo roles.
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30
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Blindauer CA, Leszczyszyn OI. Metallothioneins: unparalleled diversity in structures and functions for metal ion homeostasis and more. Nat Prod Rep 2010; 27:720-41. [PMID: 20442962 DOI: 10.1039/b906685n] [Citation(s) in RCA: 144] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Metallothioneins have been the subject of intense study for five decades, and have greatly inspired the development of bio-analytical methodologies including multi-dimensional and multi-nuclear NMR.With further advancements in molecular biology, protein science, and instrumental techniques, recent years have seen a renaissance of research into metallothioneins. The current report focuses on in vitro studies of so-called class II metallothioneins from a variety of phyla, highlighting the diversity of metallothioneins in terms of structure, biological functions, and molecular functions such as metal ion specificity, thermodynamic stabilities, and kinetic reactivity. We are still far from being able to predict any of these properties, and further efforts will be required to generate the knowledge that will enable a better understanding of what governs the biological and chemical properties of these unusual and intriguing small proteins.
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31
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Peroza EA, Schmucki R, Güntert P, Freisinger E, Zerbe O. The βE-Domain of Wheat Ec-1 Metallothionein: A Metal-Binding Domain with a Distinctive Structure. J Mol Biol 2009; 387:207-18. [DOI: 10.1016/j.jmb.2009.01.035] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2008] [Revised: 01/19/2009] [Accepted: 01/20/2009] [Indexed: 10/21/2022]
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Abstract
Zinc is a constituent of all six classes of enzymes, plays important roles in gene regulation, and is thought to be essential for most organisms. Despite initial discoveries of cyanobacterial metallothioneins, zinc efflux pumps and uptake systems, and zinc sensors, our knowledge of the zinc requirements, uptake, and detoxification mechanisms of cyanobacteria is still limited. Although cyanobacteria occupy extremely diverse habitats, most available data pertains to freshwater species, and almost no studies of zinc-handling mechanisms have been conducted in marine species. The current report highlights what is known about zinc homeostasis in cyanobacteria, and presents an analysis of the 40 sequenced cyanobacterial genomes.
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Gold B, Deng H, Bryk R, Vargas D, Eliezer D, Roberts J, Jiang X, Nathan C. Identification of a copper-binding metallothionein in pathogenic mycobacteria. Nat Chem Biol 2008; 4:609-16. [PMID: 18724363 DOI: 10.1038/nchembio.109] [Citation(s) in RCA: 157] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2007] [Accepted: 08/01/2008] [Indexed: 11/09/2022]
Abstract
A screen of a genomic library from Mycobacterium tuberculosis (Mtb) identified a small, unannotated open reading frame (MT0196) that encodes a 4.9-kDa, cysteine-rich protein. Despite extensive nucleotide divergence, the amino acid sequence is highly conserved among mycobacteria that are pathogenic in vertebrate hosts. We synthesized the protein and found that it preferentially binds up to six Cu(I) ions in a solvent-shielded core. Copper, cadmium and compounds that generate nitric oxide or superoxide induced the gene's expression in Mtb up to 1,000-fold above normal expression. The native protein bound copper within Mtb and partially protected Mtb from copper toxicity. We propose that the product of the MT0196 gene be named mycobacterial metallothionein (MymT). To our knowledge, MymT is the first metallothionein of a Gram-positive bacterium with a demonstrated function.
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Affiliation(s)
- Ben Gold
- Department of Microbiology and Immunology, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, USA
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Bonomi F, Iametti S, Ferranti P, Kurtz DM, Morleo A, Ragg EM. "Iron priming" guides folding of denatured aporubredoxins. J Biol Inorg Chem 2008; 13:981-91. [PMID: 18446387 DOI: 10.1007/s00775-008-0385-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Accepted: 04/09/2008] [Indexed: 11/25/2022]
Abstract
The relationship between iron uptake by aporubredoxins (apoRds) and formation of native holorubredoxins (holoRd), including their Fe(SCys)(4) sites, was studied. In the absence of denaturants, apoRds exhibited spectroscopic features consistent with structures very similar to those of the folded holoRds. However, additions of either ferric or ferrous salts to the apoRds in the absence of denaturants gave less than 40% recovery of the native holoRd circular dichroism and UV-vis spectroscopic features. In the presence of either 6 M urea or 6 M guanidine hydrochloride, the nativelike structural features of the apoRds were absent. Nevertheless, nearly quantitative recoveries of the native holoRd spectroscopic features were achieved by addition of either ferric or ferrous salts to the denatured apoRds without diluting the denaturant. Consistent with this observation, the native spectroscopic features were unaffected by addition of the same denaturant concentrations to the as-isolated holoRds. Denaturing concentrations of urea or guanidine hydrochloride also increased the rates of holoRd recoveries from apoRds and ferrous salts. Mass spectrometry confirmed that ferric iron binding to the denatured apoRds precedes the recoveries of protein secondary structures and Fe(SCys)(4) sites. Thus, iron binding to the apoRds guides, both kinetically and thermodynamically, refolding to the native holoRd structures. Our results imply that the ferrous oxidation state would more efficiently drive formation of the native holoRd structure from the nascent apoprotein in vivo, but that the Fe(SCys)(4) site must attain the ferric state in order to achieve its native structure.
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Affiliation(s)
- Francesco Bonomi
- DISMA, University of Milan, Via G. Celoria 2, 20133 Milan, Italy.
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35
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Blindauer CA. Metallothioneins with unusual residues: histidines as modulators of zinc affinity and reactivity. J Inorg Biochem 2007; 102:507-21. [PMID: 18171588 DOI: 10.1016/j.jinorgbio.2007.10.032] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2007] [Revised: 10/19/2007] [Accepted: 10/29/2007] [Indexed: 02/09/2023]
Abstract
For many years, paradigms regarding metallothioneins comprised the exclusive metal coordination by thiolates from cysteine residues and the absence of aromatic residues. As more sequence and in vitro data on metallothioneins, in particular from non-vertebrate organisms, has become available, both the occurrence of and metal coordination by histidine residues in metallothioneins is emerging as a more frequent feature than expected. We discuss the general implications of histidines versus cysteines in zinc binding sites, and review some recent results from literature and our own lab. We conclude that histidines can stabilise metallothionein clusters by reducing the overall charge, offering the ability to help with structural organisation by supplying H-bond donor and acceptor properties, reducing the likelihood for disulfide bond formation, whilst maintaining a high affinity towards metal ions, in particular the borderline zinc ion.
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36
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Leszczyszyn OI, Schmid R, Blindauer CA. Toward a property/function relationship for metallothioneins: Histidine coordination and unusual cluster composition in a zinc-metallothionein from plants. Proteins 2007; 68:922-35. [PMID: 17563107 DOI: 10.1002/prot.21463] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Early cysteine labeled (E(C)) proteins are plant metallothioneins, which were first identified in wheat embryos and are thought to be seed-specific. An exhaustive analysis of expressed sequence tag (EST) entries reveals that homologs are expressed in embryos of both classes of flowering plants (monocotyledons and dicotyledons), but also occur in conifers (gymnosperms) and seed-free spike moss (lycophyta). Mass spectrometric and elemental analysis results indicate that, contrary to the widely propagated number of five, E(C) binds predominantly six zinc ions in at least two zinc-thiolate clusters. 1H and 111Cd NMR experiments suggest that, in contrast to the majority of previously characterized metallothioneins, two conserved histidine residues participate in metal binding. The collected data is consistent with the presence of clusters unprecedented in metallothioneins so far. This novel cluster composition is accompanied by metal-binding properties that are substantially different from other metallothioneins; thus wheat E(C) binds zinc less strongly than either mammalian or cyanobacterial MTs. The unique biochemical properties of wheat E(C) render it ideally suited for a role in zinc donation to nascent proteins during seed development, a role that has been suggested based on the fact that E(C) is induced by the plant hormone abscisic acid, but not by heavy metals. Our results provide a step further toward developing a property/function relationship for metallothioneins.
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Affiliation(s)
- Oksana I Leszczyszyn
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, United Kingdom
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