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Abstract
Metallothioneins (MTs) are low molecular weight ubiquitous metalloproteins with high cysteine (thiol) content. The intracellular concentration of zinc (Zn) is tightly regulated and MT plays a crucial role in it. The present study investigates the relationship between the Zn status (as a function of Zn concentration and time) in the rat liver and the occurrence of hepatic MT. For dose dependent study, four experimental groups, one control and three receiving different levels of metal supplementation, were chosen [Group 1 control and Group 2, Group 3, Group 4 receiving subcutaneous dose of 10, 50 and 100 mg of Zn/kg body weight (in the form of ZnSO4·7H2O), respectively]. For the time dependent expression of MT, again four experimental groups, i.e. Group 5 control and Group 6, Group 7, Group 8 receiving 50 mg of Zn/kg body weight (in the form of ZnSO4·7H2O) subcutaneously and sacrificed at different time intervals after last injection i.e. 6, 18, 48 h, respectively were chosen. Isolation of MT was done by using combination of gel filtration and ion exchange chromatography while characterization of MT fraction was carried in the wavelength range 200-400 nm. Expression of MT was studied by using Western blot analysis. The results revealed that the MT expression increases with increasing the dose of Zn administered and maximum at 18 h after last Zn injection. Accumulation of MT with increase dose would help in maintaining the intracellular Zn concentration by its sequestration which further reduces the possibility of undesirable binding of Zn to other proteins significantly and maintains Zn homeostasis. The maximum expression of MT at 18 h is indicative of its half life.
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2
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Hallinger M, Gerhard AC, Ritz MD, Sacks JS, Poutsma JC, Pike RD, Wojtas L, Bebout DC. Metal Substitution and Solvomorphism in Alkylthiolate-Bridged Zn 3 and HgZn 2 Metal Clusters. ACS OMEGA 2017; 2:6391-6404. [PMID: 31457242 PMCID: PMC6645076 DOI: 10.1021/acsomega.7b01087] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Accepted: 09/21/2017] [Indexed: 06/10/2023]
Abstract
The impact of substituting Hg(II) for Zn(II) in a thiolate-bridged trinuclear cluster with parallels to a metallothionein metal cluster was investigated. A new solvomorph of [Zn(ZnL)2](ClO4)2 (1) (L = N-(2-pyridylmethyl)-N-(2-(ethylthiolato)-amine) and five solvomorphs of a new compound [Hg(ZnL)2](ClO4)2 (2) were characterized by single-crystal X-ray crystallography. The interplay of hydrogen bonding and aromatic-packing interactions in producing lamellar, 2D lamellar, and columnar arrangements of complex cations in the crystalline state is discussed. Both variable temperature proton nuclear magnetic resonance and electrospray ion-mass spectrometry (ESI-MS) suggest that the complex ions of 1 and 2 are the predominant solution species at moderate concentrations. ESI-MS was also used to monitor differences in metal ion redistribution as 1 was titrated with Hg(ClO4)2 and [HgL(ClO4)]. These studies document the facile replacement of Zn(II) by Hg(II) with the preservation of the overall structure in thiolate-rich clusters.
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Affiliation(s)
- Madeline
R. Hallinger
- Department
of Chemistry, College of William & Mary, P.O. Box 8795, Williamsburg, Virginia 23188, United
States
| | - Alison C. Gerhard
- Department
of Chemistry, College of William & Mary, P.O. Box 8795, Williamsburg, Virginia 23188, United
States
| | - Mikhaila D. Ritz
- Department
of Chemistry, College of William & Mary, P.O. Box 8795, Williamsburg, Virginia 23188, United
States
| | - Joshua S. Sacks
- Department
of Chemistry, College of William & Mary, P.O. Box 8795, Williamsburg, Virginia 23188, United
States
| | - John C. Poutsma
- Department
of Chemistry, College of William & Mary, P.O. Box 8795, Williamsburg, Virginia 23188, United
States
| | - Robert D. Pike
- Department
of Chemistry, College of William & Mary, P.O. Box 8795, Williamsburg, Virginia 23188, United
States
| | - Lukasz Wojtas
- Department
of Chemistry, University of South Florida, 4202 E. Fowler Avenue, CHE 205, Tampa, Florida 33620, United States
| | - Deborah C. Bebout
- Department
of Chemistry, College of William & Mary, P.O. Box 8795, Williamsburg, Virginia 23188, United
States
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3
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Irvine GW, Stillman MJ. Cadmium binding mechanisms of isolated domains of human MT isoform 1a: Non-cooperative terminal sites and cooperative cluster sites. J Inorg Biochem 2016; 158:115-121. [DOI: 10.1016/j.jinorgbio.2016.03.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 03/05/2016] [Accepted: 03/10/2016] [Indexed: 10/22/2022]
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4
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Gil-Moreno S, Jiménez-Martí E, Palacios Ò, Zerbe O, Dallinger R, Capdevila M, Atrian S. Does Variation of the Inter-Domain Linker Sequence Modulate the Metal Binding Behaviour of Helix pomatia Cd-Metallothionein? Int J Mol Sci 2015; 17:E6. [PMID: 26703589 PMCID: PMC4730253 DOI: 10.3390/ijms17010006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 12/11/2015] [Accepted: 12/14/2015] [Indexed: 11/16/2022] Open
Abstract
Snail metallothioneins (MTs) constitute an ideal model to study structure/function relationships in these metal-binding polypeptides. Helix pomatia harbours three MT isoforms: the highly specific CdMT and CuMT, and an unspecific Cd/CuMT, which represent paralogous proteins with extremely different metal binding preferences while sharing high sequence similarity. Preceding work allowed assessing that, although, the Cys residues are responsible for metal ion coordination, metal specificity or preference is achieved by diversification of the amino acids interspersed between them. The metal-specific MT polypeptides fold into unique, energetically-optimized complexes of defined metal content, when binding their cognate metal ions, while they produce a mixture of complexes, none of them representing a clear energy minimum, with non-cognate metal ions. Another critical, and so far mostly unexplored, region is the stretch linking the individual MT domains, each of which represents an independent metal cluster. In this work, we have designed and analyzed two HpCdMT constructs with substituted linker segments, and determined their coordination behavior when exposed to both cognate and non-cognate metal ions. Results unequivocally show that neither length nor composition of the inter-domain linker alter the features of the Zn(II)- and Cd(II)-complexes, but surprisingly that they influence their ability to bind Cu(I), the non-cognate metal ion.
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Affiliation(s)
- Selene Gil-Moreno
- Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Cerdanyola del Vallès, Spain.
| | - Elena Jiménez-Martí
- Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 643, E-08028 Barcelona, Spain.
| | - Òscar Palacios
- Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Cerdanyola del Vallès, Spain.
| | - Oliver Zerbe
- Institute of Organic Chemistry, University of Zurich, 8057 Zurich, Switzerland.
| | - Reinhard Dallinger
- Institute of Zoology, University of Innsbruck, Technikerstraße 25, A-6020 Innsbruck, Austria.
| | - Mercè Capdevila
- Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Cerdanyola del Vallès, Spain.
| | - Sílvia Atrian
- Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 643, E-08028 Barcelona, Spain.
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5
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Putting the pieces into place: Properties of intact zinc metallothionein 1A determined from interaction of its isolated domains with carbonic anhydrase. Biochem J 2015; 471:347-56. [DOI: 10.1042/bj20150676] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 08/20/2015] [Indexed: 12/25/2022]
Abstract
Competitive metallation reactions between the isolated domain fragments and apo-carbonic anhydrase [CA; metal-free CA (apo-CA)] provided the binding affinities for each of the eight sites and showed that CA competed more efficiently for added zinc with the β-domain fragment. The combined effects of the number of sites, chain length and cysteine accessibility modulate the zinc-binding properties of mammalian metallothionein (MT).
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6
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Cronin M, Coolbaugh MJ, Nellis D, Zhu J, Wood DW, Nussinov R, Ma B. Dynamics differentiate between active and inactive inteins. Eur J Med Chem 2015; 91:51-62. [PMID: 25087201 PMCID: PMC4308580 DOI: 10.1016/j.ejmech.2014.07.094] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Revised: 07/21/2014] [Accepted: 07/25/2014] [Indexed: 11/29/2022]
Abstract
The balance between stability and dynamics for active enzymes can be somewhat quantified by studies of intein splicing and cleaving reactions. Inteins catalyze the ligation of flanking host exteins while excising themselves. The potential for applications led to engineering of a mini-intein splicing domain, where the homing endonuclease domain of the Mycobacterium tuberculosis RecA (Mtu recA) intein was removed. The remaining domains were linked by several short peptides, but splicing activity in all was substantially lower than the full-length intein. Native splicing activity was restored in some cases by a V67L mutation. Using computations and experiments, we examine the impact of this mutation on the stability and conformational dynamics of the mini-intein splicing domain. Molecular dynamics simulations were used to delineate the factors that determine the active state, including the V67L mini-intein mutant, and peptide linker. We found that (1) the V67L mutation lowers the global fluctuations in all modeled mini-inteins, stabilizing the mini-intein constructs; (2) the connecting linker length affects intein dynamics; and (3) the flexibilities of the linker and intein core are higher in the active structure. We have observed that the interaction of the linker region and a turn region around residues 35-41 provides the pathway for the allostery interaction. Our experiments reveal that intein catalysis is characterized by non-linear Arrhenius plot, confirming the significant contribution of protein conformational dynamics to intein function. We conclude that while the V67L mutation stabilizes the global structure, cooperative dynamics of all intein regions appear more important for intein function than high stability. Our studies suggest that effectively quenching the conformational dynamics of an intein through engineered allosteric interactions could deactivate intein splicing or cleaving.
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Affiliation(s)
- Melissa Cronin
- Basic Science Program, Leidos Biomedical Research, Inc., Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, USA
| | - Michael J Coolbaugh
- Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, OH 43210, USA
| | - David Nellis
- Biopharmaceutical Development Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA
| | - Jianwei Zhu
- School of Pharmacy, Shanghai Jiao Tong University, 800 DongChuan Road, Shanghai 200240, China
| | - David W Wood
- Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, OH 43210, USA
| | - Ruth Nussinov
- Basic Science Program, Leidos Biomedical Research, Inc., Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, USA; Sackler Inst. of Molecular Medicine, Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
| | - Buyong Ma
- Basic Science Program, Leidos Biomedical Research, Inc., Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, USA.
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7
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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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8
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Affiliation(s)
- Shengwen Shen
- Department
of Laboratory Medicine
and Pathology, 10-102 Clinical Sciences Building, University
of Alberta, Edmonton, Alberta, Canada, T6G 2G3
| | - Xing-Fang Li
- Department
of Laboratory Medicine
and Pathology, 10-102 Clinical Sciences Building, University
of Alberta, Edmonton, Alberta, Canada, T6G 2G3
| | - William R. Cullen
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver,
British Columbia, Canada, V6T 1Z1
| | - Michael Weinfeld
- Department of Oncology, Cross
Cancer Institute, University of Alberta, 11560 University Avenue, Edmonton, Alberta, Canada, T6G 1Z2
| | - X. Chris Le
- Department
of Laboratory Medicine
and Pathology, 10-102 Clinical Sciences Building, University
of Alberta, Edmonton, Alberta, Canada, T6G 2G3
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9
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Sargent F, Davidson FA, Kelly CL, Binny R, Christodoulides N, Gibson D, Johansson E, Kozyrska K, Lado LL, MacCallum J, Montague R, Ortmann B, Owen R, Coulthurst SJ, Dupuy L, Prescott AR, Palmer T. A synthetic system for expression of components of a bacterial microcompartment. MICROBIOLOGY-SGM 2013; 159:2427-2436. [PMID: 24014666 PMCID: PMC3836489 DOI: 10.1099/mic.0.069922-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In general, prokaryotes are considered to be single-celled organisms that lack internal membrane-bound organelles. However, many bacteria produce proteinaceous microcompartments that serve a similar purpose, i.e. to concentrate specific enzymic reactions together or to shield the wider cytoplasm from toxic metabolic intermediates. In this paper, a synthetic operon encoding the key structural components of a microcompartment was designed based on the genes for the Salmonella propanediol utilization (Pdu) microcompartment. The genes chosen included pduA, -B, -J, -K, -N, -T and -U, and each was shown to produce protein in an Escherichia coli chassis. In parallel, a set of compatible vectors designed to express non-native cargo proteins was also designed and tested. Engineered hexa-His tags allowed isolation of the components of the microcompartments together with co-expressed, untagged, cargo proteins. Finally, an in vivo protease accessibility assay suggested that a PduD–GFP fusion could be protected from proteolysis when co-expressed with the synthetic microcompartment operon. This work gives encouragement that it may be possible to harness the genes encoding a non-native microcompartment for future biotechnological applications.
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Affiliation(s)
- Frank Sargent
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Fordyce A Davidson
- Division of Mathematics, College of Art, Science & Engineering, University of Dundee, Dundee DD1 4HN, Scotland, UK
| | - Ciarán L Kelly
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Rachelle Binny
- Division of Mathematics, College of Art, Science & Engineering, University of Dundee, Dundee DD1 4HN, Scotland, UK.,College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | | | - David Gibson
- School of Computing, College of Art, Science & Engineering, University of Dundee, Dundee DD1 4HN, Scotland, UK
| | - Emelie Johansson
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Katarzyna Kozyrska
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Lucia Licandro Lado
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Jane MacCallum
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Rachel Montague
- School of Computing, College of Art, Science & Engineering, University of Dundee, Dundee DD1 4HN, Scotland, UK
| | - Brian Ortmann
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Richard Owen
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Sarah J Coulthurst
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Lionel Dupuy
- Ecological Sciences, The James Hutton Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK
| | - Alan R Prescott
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Tracy Palmer
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
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10
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Summers KL, Sutherland DEK, Stillman MJ. Single-domain metallothioneins: evidence of the onset of clustered metal binding domains in Zn-rhMT 1a. Biochemistry 2013; 52:2461-71. [PMID: 23506369 DOI: 10.1021/bi400021b] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Mammalian metallothioneins bind up to seven Zn(2+) ions in two distinct domains: an N-terminal β-domain that binds three Zn(2+) ions and a C-terminal α-domain that binds four Zn(2+) ions. Domain specificity has been invoked in the metalation mechanism with cluster formation and bridging of the 20 Cys residues taking place prior to saturation with seven Zn(2+) ions. We report a novel experiment that examines Zn(2+) metalation by exploiting the expected decrease in K(F) at the onset of clustering using electrospray ionization mass spectrometry (ESI-MS). During the titration with Zn(2+), the ESI-MS data show that several metalated species coexist until the fully saturated proteins are formed. The relative Zn binding affinities of the seven total sites in the α- and β-fragments were determined through direct competition for added Zn(2+). The K(F) values for each Zn(2+) are expected to decrease as a function of the remaining available sites and the onset of clustering. Analysis shows that Zn(2+) binds to β-rhMT with a greater affinity than α-rhMT. The incremental distribution of Zn(2+) between the competing fragments and apo-βα-rhMT (essentially three and four sites competing with seven sites) identifies the exact point at which clustering begins in the full protein. Analysis of the speciation data shows that Zn(5)-MT forms before clustering begins. This means that all 20 Cys residues of apo-βα-rhMT are bound terminally to Zn(2+) as [Zn(Cys)(4)](2-) units before clustering begins; there is no domain preference in this first metalation stage. Preferential binding of Zn(2+) to β- and α-rhMT at the point where βα-rhMT must form clusters is caused by a significant decrease in the affinity of βα-rhMT for further Zn(2+). The single-domain Zn(5)-rhMT, in which there are no exposed cysteine sulfurs, is a key component of the metalation pathway because the lower affinities of the two clustered Zn(2+) ions allow donation to apoenzymes.
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Affiliation(s)
- Kelly L Summers
- Department of Chemistry, The University of Western Ontario, London, Canada N6A 5B7
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11
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Irvine GW, Summers KL, Stillman MJ. Cysteine accessibility during As3+ metalation of the α- and β-domains of recombinant human MT1a. Biochem Biophys Res Commun 2013; 433:477-83. [PMID: 23523794 DOI: 10.1016/j.bbrc.2013.03.026] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Accepted: 03/02/2013] [Indexed: 10/27/2022]
Abstract
Metallothionein is a ubiquitous metal binding protein that plays an important role in metal ion homeostasis and redox chemistry within cells. Mammalian metallothioneins bind a wide variety of metals including the metalloid As3+ in two domains (β and α) connected by a short linker sequence. Three As3+ bind in each domain for a total of 6 As3+ per protein. In recombinant human metallothionein (rh-MT1a) each As3+ binds three cysteine residues to form As3Cys9(CysSH)2-α-rhMT1a in the 11 Cys α-domain and As3Cys9-β-rhMT1a in the 9 Cys β-domain. This means that there should be 2 free cysteines in the α-domain but no free cysteines in the β-domain. By using benzoquinone, the number and relative accessibility of the free cysteinyl thiols during the metalation reactions were determined. The electrospray ionization mass spectrometry (ESI-MS) data confirmed that each As3+ binds using exactly 3 cysteine thiols and showed that there was a significant difference in the reactivity of the free cysteines during the metalation reaction. After a reaction with two molar equivalents of As3+ to form As2Cys6(CysSH)3-αβ-rhMT1a, the remaining 3 Cys in the 9 Cys β-domain were far less reactive than those in the α-domain. Molecular dynamics calculations for the metalation reactions with As3+ measured by ESI-MS allowed an interpretation of the mass spectral data in terms of the relative location of the cysteine thiols that were not involved in As3+ coordination. Together, these data provide insight into the selection of a specific cysteinyl thiol by the incoming metals during the stepwise metalation of metallothioneins.
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Affiliation(s)
- Gordon W Irvine
- Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
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12
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Sutherland DE, Summers KL, Stillman MJ. Modeling the Zn2+ and Cd2+ metalation mechanism in mammalian metallothionein 1a. Biochem Biophys Res Commun 2012; 426:601-7. [DOI: 10.1016/j.bbrc.2012.08.136] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Accepted: 08/28/2012] [Indexed: 10/27/2022]
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13
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Tiedemann MT, Heinrichs DE, Stillman MJ. Multiprotein Heme Shuttle Pathway in Staphylococcus aureus: Iron-Regulated Surface Determinant Cog-Wheel Kinetics. J Am Chem Soc 2012; 134:16578-85. [DOI: 10.1021/ja305115y] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Michael T. Tiedemann
- Department of Chemistry, The University of Western Ontario, London, Ontario,
Canada, N6A 5B7
| | - David E. Heinrichs
- Department
of Microbiology and
Immunology, The University of Western Ontario, London, Ontario, Canada, N6A 5C1
| | - Martin J. Stillman
- Department of Chemistry, The University of Western Ontario, London, Ontario,
Canada, N6A 5B7
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14
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Sutherland DEK, Summers KL, Stillman MJ. Noncooperative Metalation of Metallothionein 1a and Its Isolated Domains with Zinc. Biochemistry 2012; 51:6690-700. [DOI: 10.1021/bi3004523] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
| | - Kelly L. Summers
- Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Martin J. Stillman
- Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
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15
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Whaley-Martin KJ, Koch I, Moriarty M, Reimer KJ. Arsenic speciation in blue mussels (Mytilus edulis) along a highly contaminated arsenic gradient. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2012; 46:3110-8. [PMID: 22329691 DOI: 10.1021/es203812u] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Arsenic is naturally present in marine ecosystems, and these can become contaminated from mining activities, which may be of toxicological concern to organisms that bioaccumulate the metalloid into their tissues. The toxic properties of arsenic are dependent on the chemical form in which it is found (e.g., toxic inorganic arsenicals vs nontoxic arsenobetaine), and two analytical techniques, high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) and X-ray absorption spectroscopy (XAS), were used in the present study to examine the arsenic species distribution in blue mussels (Mytilus edulis) obtained from an area where there is a strong arsenic concentration gradient as a consequence of mining impacted sediments. A strong positive correlation was observed between the concentration of inorganic arsenic species (arsenic compounds with no As-C bonds) and total arsenic concentrations present in M. edulis tissues (R(2) = 0.983), which could result in significant toxicological consequences to the mussels and higher trophic consumers. However, concentrations of organoarsenicals, dominated by arsenobetaine, remained relatively constant regardless of the increasing As concentration in M. edulis tissue (R(2) = 0.307). XANES bulk analysis and XAS two-dimensional mapping of wet M. edulis tissue revealed the presence of predominantly arsenic-sulfur compounds. The XAS mapping revealed that the As(III)-S and/or As(III) compounds were concentrated in the digestive gland. However, arsenobetaine was found in small and similar concentrations in the digestive gland as well as the surrounding tissue suggesting arsenobetaine may being used in all of the mussel's cells in a physiological function such as an intracellular osmolyte.
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Affiliation(s)
- K J Whaley-Martin
- Environmental Sciences Group, Royal Military College of Canada, PO Box 17000 Station Forces, Kingston, Ontario K7K 7B4, Canada
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16
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Ma B, Tsai CJ, Haliloğlu T, Nussinov R. Dynamic allostery: linkers are not merely flexible. Structure 2011; 19:907-17. [PMID: 21742258 PMCID: PMC6361528 DOI: 10.1016/j.str.2011.06.002] [Citation(s) in RCA: 179] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Revised: 06/05/2011] [Accepted: 06/07/2011] [Indexed: 12/19/2022]
Abstract
Most proteins consist of multiple domains. How do linkers efficiently transfer information between sites that are on different domains to activate the protein? Mere flexibility only implies that the conformations would be sampled. For fast timescales between triggering events and cellular response, which often involves large conformational change, flexibility on its own may not constitute a good solution. We posit that successive conformational states along major allosteric propagation pathways are pre-encoded in linker sequences where each state is encoded by the previous one. The barriers between these states that are hierarchically populated are lower, achieving faster timescales even for large conformational changes. We further propose that evolution has optimized the linker sequences and lengths for efficiency, which explains why mutations in linkers may affect protein function and review the literature in this light.
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Affiliation(s)
- Buyong Ma
- Basic Science Program, SAIC-Frederick, Inc., Center for Cancer Research Nanobiology Program, NCI-Frederick, Frederick, MD 21702, USA
| | - Chung-Jung Tsai
- Basic Science Program, SAIC-Frederick, Inc., Center for Cancer Research Nanobiology Program, NCI-Frederick, Frederick, MD 21702, USA
| | - Türkan Haliloğlu
- Polymer Research Center and Chemical Engineering Department, Bogazici University, Bebek-Istanbul 34342, Turkey
| | - Ruth Nussinov
- Basic Science Program, SAIC-Frederick, Inc., Center for Cancer Research Nanobiology Program, NCI-Frederick, Frederick, MD 21702, USA
- Sackler Institute of Molecular Medicine, Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
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17
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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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Ngu TT, Dryden MD, Stillman MJ. Arsenic transfer between metallothionein proteins at physiological pH. Biochem Biophys Res Commun 2010; 401:69-74. [DOI: 10.1016/j.bbrc.2010.09.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2010] [Accepted: 09/04/2010] [Indexed: 10/19/2022]
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19
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Sutherland DEK, Willans MJ, Stillman MJ. Supermetalation of the β Domain of Human Metallothionein 1a. Biochemistry 2010; 49:3593-601. [DOI: 10.1021/bi1003537] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Mathew J. Willans
- Department of Chemistry, The University of Western Ontario, London, ON, Canada N6A 5B7
| | - Martin J. Stillman
- Department of Chemistry, The University of Western Ontario, London, ON, Canada N6A 5B7
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