1
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Young TR, Deery E, Foster AW, Martini MA, Osman D, Warren MJ, Robinson NJ. Two Distinct Thermodynamic Gradients for Cellular Metalation of Vitamin B 12. JACS Au 2023; 3:1472-1483. [PMID: 37234125 PMCID: PMC10206600 DOI: 10.1021/jacsau.3c00119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Revised: 04/13/2023] [Accepted: 04/25/2023] [Indexed: 05/27/2023]
Abstract
The acquisition of CoII by the corrin component of vitamin B12 follows one of two distinct pathways, referred to as early or late CoII insertion. The late insertion pathway exploits a CoII metallochaperone (CobW) from the COG0523 family of G3E GTPases, while the early insertion pathway does not. This provides an opportunity to contrast the thermodynamics of metalation in a metallochaperone-requiring and a metallochaperone-independent pathway. In the metallochaperone-independent route, sirohydrochlorin (SHC) associates with the CbiK chelatase to form CoII-SHC. CoII-buffered enzymatic assays indicate that SHC binding enhances the thermodynamic gradient for CoII transfer from the cytosol to CbiK. In the metallochaperone-dependent pathway, hydrogenobyrinic acid a,c-diamide (HBAD) associates with the CobNST chelatase to form CoII-HBAD. Here, CoII-buffered enzymatic assays indicate that CoII transfer from the cytosol to HBAD-CobNST must somehow traverse a highly unfavorable thermodynamic gradient for CoII binding. Notably, there is a favorable gradient for CoII transfer from the cytosol to the MgIIGTP-CobW metallochaperone, but further transfer of CoII from the GTP-bound metallochaperone to the HBAD-CobNST chelatase complex is thermodynamically unfavorable. However, after nucleotide hydrolysis, CoII transfer from the chaperone to the chelatase complex is calculated to become favorable. These data reveal that the CobW metallochaperone can overcome an unfavorable thermodynamic gradient for CoII transfer from the cytosol to the chelatase by coupling this process to GTP hydrolysis.
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Affiliation(s)
- Tessa R. Young
- Department
of Biosciences, Durham University, Durham DH1 3LE, U.K.
- Department
of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Evelyne Deery
- School
of Biosciences, University of Kent, Canterbury CT2 7NJ, U.K.
| | - Andrew W. Foster
- Department
of Biosciences, Durham University, Durham DH1 3LE, U.K.
- Department
of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Maria Alessandra Martini
- Department
of Biosciences, Durham University, Durham DH1 3LE, U.K.
- Department
of Inorganic Spectroscopy, Max Planck Institute
for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany
| | - Deenah Osman
- Department
of Biosciences, Durham University, Durham DH1 3LE, U.K.
- Department
of Chemistry, Durham University, Durham DH1 3LE, U.K.
| | - Martin J. Warren
- School
of Biosciences, University of Kent, Canterbury CT2 7NJ, U.K.
- Quadram
Institute Bioscience, Norwich Research Park, Norwich NR4 7UQ, U.K.
| | - Nigel J. Robinson
- Department
of Biosciences, Durham University, Durham DH1 3LE, U.K.
- Department
of Chemistry, Durham University, Durham DH1 3LE, U.K.
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2
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Foster AW, Clough SE, Aki Z, Young TR, Clarke AR, Robinson NJ. Metalation calculators for E. coli strain JM109 (DE3): Aerobic, anaerobic and hydrogen peroxide exposed cells cultured in LB media. Metallomics 2022; 14:6657815. [PMID: 35933161 PMCID: PMC9434800 DOI: 10.1093/mtomcs/mfac058] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Accepted: 07/24/2022] [Indexed: 11/14/2022]
Abstract
Three web-based calculators, and three analogous spreadsheets, have been generated that predict in vivo metal occupancies of proteins based on known metal affinities. The calculations exploit estimates of the availabilities of the labile buffered pools of different metals inside a cell. Here, metal availabilities have been estimated for a strain of E. coli that is commonly used in molecular biology and biochemistry research, for example in the production of recombinant proteins. Metal availabilities have been examined for cells grown in LB medium aerobically, anaerobically and in response to H2O2 by monitoring the abundance of a selected set of metal-responsive transcripts by qPCR. The selected genes are regulated by DNA-binding metal sensors that have been thermodynamically characterised in related bacterial cells enabling gene expression to be read-out as a function of intracellular metal availabilities expressed as free energies for forming metal complexes. The calculators compare these values with the free energies for forming complexes with the protein of interest, derived from metal affinities, to estimate how effectively the protein can compete with exchangeable binding sites in the intracellular milieu. The calculators then inter-compete the different metals, limiting total occupancy of the site to a maximum stoichiometry of 1, to output percentage occupancies with each metal. In addition to making these new and conditional calculators available, an original purpose of this article was to provide a tutorial which discusses constraints of this approach and presents ways in which such calculators might be exploited in basic and applied research, and in next-generation manufacturing.
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Affiliation(s)
- Andrew W Foster
- Department of Biosciences, Durham University, Durham, UK.,Department of Chemistry, Durham University, Durham, UK
| | - Sophie E Clough
- Department of Biosciences, Durham University, Durham, UK.,Department of Chemistry, Durham University, Durham, UK
| | - Zeynep Aki
- Advanced Research Computing, Durham University, Durham, UK
| | - Tessa R Young
- Department of Biosciences, Durham University, Durham, UK.,Department of Chemistry, Durham University, Durham, UK
| | | | - Nigel J Robinson
- Department of Biosciences, Durham University, Durham, UK.,Department of Chemistry, Durham University, Durham, UK
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3
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Abstract
Inorganic metals supplement the chemical repertoire of organic molecules, especially proteins. This requires the correct metals to associate with proteins at metalation. Protein mismetalation typically occurs when excesses of unbound metals compete for a binding site ex vivo. However, in biology, excesses of metal-binding sites typically compete for limiting amounts of exchangeable metals. Here, we summarise mechanisms of metal homeostasis that sustain optimal metal availabilities in biology. We describe recent progress to understand metalation by comparing the strength of metal binding to a protein versus the strength of binding to competing sites inside cells.
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Affiliation(s)
- Andrew W Foster
- Department of Biosciences, Durham University, Durham, DH1 3LE, UK; Department of Chemistry, Durham University, Durham, DH1 3LE, UK
| | - Tessa R Young
- Department of Biosciences, Durham University, Durham, DH1 3LE, UK; Department of Chemistry, Durham University, Durham, DH1 3LE, UK
| | - Peter T Chivers
- Department of Biosciences, Durham University, Durham, DH1 3LE, UK; Department of Chemistry, Durham University, Durham, DH1 3LE, UK
| | - Nigel J Robinson
- Department of Biosciences, Durham University, Durham, DH1 3LE, UK; Department of Chemistry, Durham University, Durham, DH1 3LE, UK.
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4
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Osman D, Martini MA, Foster AW, Chen J, Scott AJP, Morton RJ, Steed JW, Lurie-Luke E, Huggins TG, Lawrence AD, Deery E, Warren MJ, Chivers PT, Robinson NJ. Bacterial sensors define intracellular free energies for correct enzyme metalation. Nat Chem Biol 2019; 15:241-249. [PMID: 30692683 PMCID: PMC6420079 DOI: 10.1038/s41589-018-0211-4] [Citation(s) in RCA: 94] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Accepted: 12/04/2018] [Indexed: 01/06/2023]
Abstract
There is a challenge for metalloenzymes to acquire their correct metals because some inorganic elements form more stable complexes with proteins than do others. These preferences can be overcome provided some metals are more available than others. However, while the total amount of cellular metal can be readily measured, the available levels of each metal have been more difficult to define. Metal-sensing transcriptional regulators are tuned to the intracellular availabilities of their cognate ions. Here we have determined the standard free energy for metal complex formation to which each sensor, in a set of bacterial metal sensors, is attuned: The less competitive the metal, the less favorable the free energy and hence greater availability to which the cognate allosteric mechanism is tuned. Comparing these free energies with values derived from the metal affinities of a metalloprotein reveals the mechanism of correct metalation exemplified here by a cobalt-chelatase for vitamin B12.
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Affiliation(s)
- Deenah Osman
- Department of Biosciences, Durham University, Durham, UK.,Department of Chemistry, Durham University, Durham, UK
| | | | - Andrew W Foster
- Department of Biosciences, Durham University, Durham, UK.,Department of Chemistry, Durham University, Durham, UK
| | - Junjun Chen
- Procter and Gamble, Mason Business Center, Cincinnati, OH, USA
| | | | - Richard J Morton
- Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle-upon-Tyne, UK
| | | | | | | | | | - Evelyne Deery
- School of Biosciences, University of Kent, Canterbury, Kent, UK
| | - Martin J Warren
- School of Biosciences, University of Kent, Canterbury, Kent, UK
| | - Peter T Chivers
- Department of Biosciences, Durham University, Durham, UK. .,Department of Chemistry, Durham University, Durham, UK.
| | - Nigel J Robinson
- Department of Biosciences, Durham University, Durham, UK. .,Department of Chemistry, Durham University, Durham, UK.
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5
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Osman D, Foster AW, Chen J, Svedaite K, Steed JW, Lurie-Luke E, Huggins TG, Robinson NJ. Fine control of metal concentrations is necessary for cells to discern zinc from cobalt. Nat Commun 2017; 8:1884. [PMID: 29192165 PMCID: PMC5709419 DOI: 10.1038/s41467-017-02085-z] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Accepted: 11/06/2017] [Indexed: 12/31/2022] Open
Abstract
Bacteria possess transcription factors whose DNA-binding activity is altered upon binding to specific metals, but metal binding is not specific in vitro. Here we show that tight regulation of buffered intracellular metal concentrations is a prerequisite for metal specificity of Zur, ZntR, RcnR and FrmR in Salmonella Typhimurium. In cells, at non-inhibitory elevated concentrations, Zur and ZntR, only respond to Zn(II), RcnR to cobalt and FrmR to formaldehyde. However, in vitro all these sensors bind non-cognate metals, which alters DNA binding. We model the responses of these sensors to intracellular-buffered concentrations of Co(II) and Zn(II) based upon determined abundances, metal affinities and DNA affinities of each apo- and metalated sensor. The cognate sensors are modelled to respond at the lowest concentrations of their cognate metal, explaining specificity. However, other sensors are modelled to respond at concentrations only slightly higher, and cobalt or Zn(II) shock triggers mal-responses that match these predictions. Thus, perfect metal specificity is fine-tuned to a narrow range of buffered intracellular metal concentrations.
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Affiliation(s)
- Deenah Osman
- Department of Biosciences, Durham University, Durham, DH1 3LE, UK.,Department of Chemistry, Durham University, Durham, DH1 3LE, UK
| | - Andrew W Foster
- Department of Biosciences, Durham University, Durham, DH1 3LE, UK.,Department of Chemistry, Durham University, Durham, DH1 3LE, UK
| | - Junjun Chen
- Procter and Gamble, Mason Business Center, Cincinnati, OH, 45040, USA
| | - Kotryna Svedaite
- Department of Biosciences, Durham University, Durham, DH1 3LE, UK.,Department of Chemistry, Durham University, Durham, DH1 3LE, UK
| | | | - Elena Lurie-Luke
- Procter and Gamble, Singapore Innovation Center, Singapore, 138589, Singapore
| | - Thomas G Huggins
- Procter and Gamble, Mason Business Center, Cincinnati, OH, 45040, USA
| | - Nigel J Robinson
- Department of Biosciences, Durham University, Durham, DH1 3LE, UK. .,Department of Chemistry, Durham University, Durham, DH1 3LE, UK.
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6
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Carr CE, Foster AW, Maroney MJ. An XAS investigation of the nickel site structure in the transcriptional regulator InrS. J Inorg Biochem 2017; 177:352-358. [PMID: 28844329 PMCID: PMC5741488 DOI: 10.1016/j.jinorgbio.2017.08.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 07/10/2017] [Accepted: 08/05/2017] [Indexed: 12/29/2022]
Abstract
InrS (Internal nickel-responsive Sensor) is a transcriptional repressor of the nickel exporter NrsD and de-represses expression of the exporter upon binding Ni(II) ions. Although a crystal structure of apo-InrS has been reported, no structure of the protein with metal ions bound is available. Herein we report the results of metal site structural investigations of Ni(II) and Cu(II) complexes of InrS using X-ray absorption spectroscopy (XAS) that are complementary to data available from the apo-InrS crystal structure, and are consistent with a planar four-coordinate [Ni(His)2(Cys)2] structure, where the ligands are derived from the side chains of His21, Cys53, His78, and Cys82. Coordination of Cu(II) to InrS forms a nearly identical planar four-coordinate complex that is consistent with a simple replacement of the Ni(II) center by Cu(II).
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Affiliation(s)
- Carolyn E Carr
- Chemistry Department, University of Massachusetts Amherst, MA 01003, USA
| | - Andrew W Foster
- Department of Biosciences, Durham University, Durham, UK; Department of Chemistry, Durham University, Durham, UK
| | - Michael J Maroney
- Chemistry Department, University of Massachusetts Amherst, MA 01003, USA; Program in Molecular and Cellular Biology, University of Massachusetts Amherst, MA 01003, USA.
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7
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Foster AW, Pernil R, Patterson CJ, Scott AJP, Pålsson LO, Pal R, Cummins I, Chivers PT, Pohl E, Robinson NJ. A tight tunable range for Ni(II) sensing and buffering in cells. Nat Chem Biol 2017; 13:409-414. [PMID: 28166209 PMCID: PMC5365139 DOI: 10.1038/nchembio.2310] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 12/01/2016] [Indexed: 11/08/2022]
Abstract
The metal affinities of metal-sensing transcriptional regulators co-vary with cellular metal concentrations over more than 12 orders of magnitude. To understand the cause of this relationship, we determined the structure of the Ni(II) sensor InrS and then created cyanobacteria (Synechocystis PCC 6803) in which transcription of genes encoding a Ni(II) exporter and a Ni(II) importer were controlled by InrS variants with weaker Ni(II) affinities. Variant strains were sensitive to elevated nickel and contained more nickel, but the increase was small compared with the change in Ni(II) affinity. All of the variant sensors retained the allosteric mechanism that inhibits DNA binding following metal binding, but a response to nickel in vivo was observed only when the sensitivity was set to respond in a relatively narrow (less than two orders of magnitude) range of nickel concentrations. Thus, the Ni(II) affinity of InrS is attuned to cellular metal concentrations rather than the converse.
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Affiliation(s)
- Andrew W. Foster
- Department of Biosciences, Durham University, DH1 3LE, UK
- Department of Chemistry, Durham University, DH1 3LE, UK
| | - Rafael Pernil
- Department of Biosciences, Durham University, DH1 3LE, UK
- Department of Chemistry, Durham University, DH1 3LE, UK
| | - Carl J. Patterson
- Department of Biosciences, Durham University, DH1 3LE, UK
- Department of Chemistry, Durham University, DH1 3LE, UK
| | | | | | - Robert Pal
- Department of Chemistry, Durham University, DH1 3LE, UK
| | - Ian Cummins
- Department of Biosciences, Durham University, DH1 3LE, UK
| | - Peter T. Chivers
- Department of Biosciences, Durham University, DH1 3LE, UK
- Department of Chemistry, Durham University, DH1 3LE, UK
| | - Ehmke Pohl
- Department of Biosciences, Durham University, DH1 3LE, UK
- Department of Chemistry, Durham University, DH1 3LE, UK
| | - Nigel J. Robinson
- Department of Biosciences, Durham University, DH1 3LE, UK
- Department of Chemistry, Durham University, DH1 3LE, UK
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8
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Rubio MÁ, Napolitano M, Ochoa de Alda JAG, Santamaría-Gómez J, Patterson CJ, Foster AW, Bru-Martínez R, Robinson NJ, Luque I. Trans-oligomerization of duplicated aminoacyl-tRNA synthetases maintains genetic code fidelity under stress. Nucleic Acids Res 2015; 43:9905-17. [PMID: 26464444 PMCID: PMC4787780 DOI: 10.1093/nar/gkv1020] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 09/28/2015] [Indexed: 12/23/2022] Open
Abstract
Aminoacyl-tRNA synthetases (aaRSs) play a key role in deciphering the genetic message by producing charged tRNAs and are equipped with proofreading mechanisms to ensure correct pairing of tRNAs with their cognate amino acid. Duplicated aaRSs are very frequent in Nature, with 25,913 cases observed in 26,837 genomes. The oligomeric nature of many aaRSs raises the question of how the functioning and oligomerization of duplicated enzymes is organized. We characterized this issue in a model prokaryotic organism that expresses two different threonyl-tRNA synthetases, responsible for Thr-tRNA(Thr) synthesis: one accurate and constitutively expressed (T1) and another (T2) with impaired proofreading activity that also generates mischarged Ser-tRNA(Thr). Low zinc promotes dissociation of dimeric T1 into monomers deprived of aminoacylation activity and simultaneous induction of T2, which is active for aminoacylation under low zinc. T2 either forms homodimers or heterodimerizes with T1 subunits that provide essential proofreading activity in trans. These findings evidence that in organisms with duplicated genes, cells can orchestrate the assemblage of aaRSs oligomers that meet the necessities of the cell in each situation. We propose that controlled oligomerization of duplicated aaRSs is an adaptive mechanism that can potentially be expanded to the plethora of organisms with duplicated oligomeric aaRSs.
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Affiliation(s)
- Miguel Ángel Rubio
- Instituto de Bioquímica Vegetal y Fotosíntesis, C.S.I.C. and Universidad de Sevilla, Avda Américo Vespucio 49, E-41092 Seville, Spain
| | - Mauro Napolitano
- Instituto de Bioquímica Vegetal y Fotosíntesis, C.S.I.C. and Universidad de Sevilla, Avda Américo Vespucio 49, E-41092 Seville, Spain
| | - Jesús A G Ochoa de Alda
- Facultad de Formación del Profesorado. Universidad de Extremadura, Avda de la Universidad s/n. E-10003, Cáceres, Spain
| | - Javier Santamaría-Gómez
- Instituto de Bioquímica Vegetal y Fotosíntesis, C.S.I.C. and Universidad de Sevilla, Avda Américo Vespucio 49, E-41092 Seville, Spain
| | | | | | - Roque Bru-Martínez
- Department of Agrochemistry and Biochemistry, Faculty of Science, University of Alicante, E-03080, Spain
| | | | - Ignacio Luque
- Instituto de Bioquímica Vegetal y Fotosíntesis, C.S.I.C. and Universidad de Sevilla, Avda Américo Vespucio 49, E-41092 Seville, Spain
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9
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Osman D, Piergentili C, Chen J, Chakrabarti B, Foster AW, Lurie-Luke E, Huggins TG, Robinson NJ. Generating a Metal-responsive Transcriptional Regulator to Test What Confers Metal Sensing in Cells. J Biol Chem 2015; 290:19806-22. [PMID: 26109070 PMCID: PMC4528141 DOI: 10.1074/jbc.m115.663427] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2015] [Indexed: 11/06/2022] Open
Abstract
FrmR from Salmonella enterica serovar typhimurium (a CsoR/RcnR-like transcriptional de-repressor) is shown to repress the frmRA operator-promoter, and repression is alleviated by formaldehyde but not manganese, iron, cobalt, nickel, copper, or Zn(II) within cells. In contrast, repression by a mutant FrmRE64H (which gains an RcnR metal ligand) is alleviated by cobalt and Zn(II). Unexpectedly, FrmR was found to already bind Co(II), Zn(II), and Cu(I), and moreover metals, as well as formaldehyde, trigger an allosteric response that weakens DNA affinity. However, the sensory metal sites of the cells' endogenous metal sensors (RcnR, ZntR, Zur, and CueR) are all tighter than FrmR for their cognate metals. Furthermore, the endogenous metal sensors are shown to out-compete FrmR. The metal-sensing FrmRE64H mutant has tighter metal affinities than FrmR by approximately 1 order of magnitude. Gain of cobalt sensing by FrmRE64H remains enigmatic because the cobalt affinity of FrmRE64H is substantially weaker than that of the endogenous cobalt sensor. Cobalt sensing requires glutathione, which may assist cobalt access, conferring a kinetic advantage. For Zn(II), the metal affinity of FrmRE64H approaches the metal affinities of cognate Zn(II) sensors. Counter-intuitively, the allosteric coupling free energy for Zn(II) is smaller in metal-sensing FrmRE64H compared with nonsensing FrmR. By determining the copies of FrmR and FrmRE64H tetramers per cell, then estimating promoter occupancy as a function of intracellular Zn(II) concentration, we show how a modest tightening of Zn(II) affinity, plus weakened DNA affinity of the apoprotein, conspires to make the relative properties of FrmRE64H (compared with ZntR and Zur) sufficient to sense Zn(II) inside cells.
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Affiliation(s)
- Deenah Osman
- From the School of Biological and Biomedical Sciences and Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Cecilia Piergentili
- From the School of Biological and Biomedical Sciences and Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Junjun Chen
- Procter and Gamble, Mason Business Centre, Cincinnati, Ohio 45040, and
| | - Buddhapriya Chakrabarti
- From the School of Biological and Biomedical Sciences and Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Andrew W Foster
- From the School of Biological and Biomedical Sciences and Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Elena Lurie-Luke
- Life Sciences Open Innovation, London Innovation Centre, Procter and Gamble Technical Centres, Ltd., Egham TW20 9NW, United Kingdom
| | - Thomas G Huggins
- Procter and Gamble, Mason Business Centre, Cincinnati, Ohio 45040, and
| | - Nigel J Robinson
- From the School of Biological and Biomedical Sciences and Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom,
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10
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Abstract
The metal binding preferences of most metalloproteins do not match their metal requirements. Thus, metallation of an estimated 30% of metalloenzymes is aided by metal delivery systems, with ∼ 25% acquiring preassembled metal cofactors. The remaining ∼ 70% are presumed to compete for metals from buffered metal pools. Metallation is further aided by maintaining the relative concentrations of these pools as an inverse function of the stabilities of the respective metal complexes. For example, magnesium enzymes always prefer to bind zinc, and these metals dominate the metalloenzymes without metal delivery systems. Therefore, the buffered concentration of zinc is held at least a million-fold below magnesium inside most cells.
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Affiliation(s)
- Andrew W Foster
- From the Department of Chemistry and School of Biological and Biomedical Sciences, Durham University, Durham DH1 3LE, United Kingdom
| | - Deenah Osman
- From the Department of Chemistry and School of Biological and Biomedical Sciences, Durham University, Durham DH1 3LE, United Kingdom
| | - Nigel J Robinson
- From the Department of Chemistry and School of Biological and Biomedical Sciences, Durham University, Durham DH1 3LE, United Kingdom
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11
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Foster AW, Dainty SJ, Patterson CJ, Pohl E, Blackburn H, Wilson C, Hess CR, Rutherford JC, Quaranta L, Corran A, Robinson NJ. A chemical potentiator of copper-accumulation used to investigate the iron-regulons of Saccharomyces cerevisiae. Mol Microbiol 2014; 93:317-30. [PMID: 24895027 PMCID: PMC4149784 DOI: 10.1111/mmi.12661] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/29/2014] [Indexed: 12/29/2022]
Abstract
The extreme resistance of Saccharomyces cerevisiae to copper is overcome by 2-(6-benzyl-2-pyridyl)quinazoline (BPQ), providing a chemical-biology tool which has been exploited in two lines of discovery. First, BPQ is shown to form a red (BPQ)2Cu(I) complex and promote Ctr1-independent copper-accumulation in whole cells and in mitochondria isolated from treated cells. Multiple phenotypes, including loss of aconitase activity, are consistent with copper-BPQ mediated damage to mitochondrial iron–sulphur clusters. Thus, a biochemical basis of copper-toxicity in S. cerevisiae is analogous to other organisms. Second, iron regulons controlled by Aft1/2, Cth2 and Yap5 that respond to mitochondrial iron–sulphur cluster status are modulated by copper-BPQ causing iron hyper-accumulation via upregulated iron-import. Comparison of copper-BPQ treated, untreated and copper-only treated wild-type and fra2Δ by RNA-seq has uncovered a new candidate Aft1 target-gene (LSO1) and paralogous non-target (LSO2), plus nine putative Cth2 target-transcripts. Two lines of evidence confirm that Fra2 dominates basal repression of the Aft1/2 regulons in iron-replete cultures. Fra2-independent control of these regulons is also observed but CTH2 itself appears to be atypically Fra2-dependent. However, control of Cth2-target transcripts which is independent of CTH2 transcript abundance or of Fra2, is also quantified. Use of copper-BPQ supports a substantial contribution of metabolite repression to iron-regulation.
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Affiliation(s)
- Andrew W Foster
- Department of Chemistry, School of Biological and Biomedical Sciences, Durham University, Durham, DH1 3LE, UK
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12
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Foster AW, Pernil R, Patterson CJ, Robinson NJ. Metal specificity of cyanobacterial nickel-responsive repressor InrS: cells maintain zinc and copper below the detection threshold for InrS. Mol Microbiol 2014; 92:797-812. [PMID: 24666373 PMCID: PMC4235346 DOI: 10.1111/mmi.12594] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/24/2014] [Indexed: 12/25/2022]
Abstract
InrS is a Ni(II)-responsive, CsoR/RcnR-like, DNA-binding transcriptional repressor of the nrsD gene, but the Ni(II) co-ordination sphere of InrS is unlike Ni(II)-RcnR. We show that copper and Zn(II) also bind tightly to InrS and in vitro these ions also impair InrS binding to the nrsD operator-promoter. InrS does not respond to Zn(II) (or copper) in vivo after 48 h, when Zn(II) sensor ZiaR responds, but InrS transiently responds (1 h) to both metals. InrS conserves only one (of two) second co-ordination shell residues of CsoR (Glu98 in InrS). The allosteric mechanism of InrS is distinct from Cu(I)-CsoR and conservation of deduced second shell residues better predicts metal specificity than do the metal ligands. The allosteric mechanism of InrS permits greater promiscuity in vitro than CsoR. The factors dictating metal-selectivity in vivo are that KNi(II) and ΔGCNi(II)-InrS·DNA are sufficiently high, relative to other metal sensors, for InrS to detect Ni(II), while the equivalent parameters for copper may be insufficient for copper-sensing in S ynechocystis (at 48 h). InrS KZn(II) (5.6 × 10−13 M) is comparable to the sensory sites of ZiaR (and Zur), but ΔGCZn(II)-InrS·DNA is less than ΔGCZn(II)-ZiaR·DNA implying that relative to other sensors, ΔGCZn(II)-Sensor·DNA rather than KZn(II) determines the final detection threshold for Zn(II).
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Affiliation(s)
- Andrew W Foster
- Department of Chemistry, School of Biological and Biomedical Sciences, Durham University, Durham, DH1 3LE, UK
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Patterson CJ, Pernil R, Dainty SJ, Chakrabarti B, Henry CE, Money VA, Foster AW, Robinson NJ. Co(ll)-detection does not follow Kco(ll) gradient: channelling in Co(ll)-sensing. Metallomics 2013; 5:352-62. [PMID: 23420021 DOI: 10.1039/c3mt20241k] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The MerR-like transcriptional activator CoaR detects surplus Co(ll) to regulate Co(ll) efflux in a cyanobacterium. This organism also has cytosolic metal-sensors from three further families represented by Zn(ll)-sensors ZiaR and Zur plus Ni(ll)-sensor InrS. Here we discover by competition with Fura-2 that CoaR has KCo(ll) weaker than 7 × 10(-8) M, which is weaker than ZiaR, Zur and InrS (KCo(ll) = 6.94 ± 1.3 × 10(-10) M; 4.56 ± 0.16 × 10(-10) M; and 7.69 ± 1.1 × 10(-9) M respectively). KCo(ll) for CoaR is also weak in the CoaR-DNA adduct. Further, Co(ll) promotes DNA-dissociation by ZiaR and DNA-association by Zur in vitro in a manner analogous to Zn(ll), as monitored by fluorescence anisotropy. After 48 h exposure to maximum non-inhibitory [Co(ll)], CoaR responds in vivo yet the two Zn(ll)-sensors do not, despite their tighter KCo(ll) and despite Co(ll) triggering allostery in ZiaR and Zur in vitro. These data imply that the two Zn(ll) sensors fail to respond because they fail to gain access to Co(ll) under these conditions in vivo. Several lines of evidence suggest that CoaR is membrane associated via a domain with sequence similarity to precorrin isomerase, an enzyme of vitamin B12 biosynthesis. Moreover, site directed mutagenesis reveals that transcriptional activation requires CoaR residues that are predicted to form hydrogen bonds to a tetrapyrrole. The Co(ll)-requiring vitamin B12 biosynthetic pathway is also membrane associated suggesting putative mechanisms by which Co(ll)-containing tetrapyrroles and/or Co(ll) ions are channelled to CoaR.
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Affiliation(s)
- Carl J Patterson
- School/Department of Biological and Biomedical Sciences, Biophysical Sciences Institute, Durham University, DH1 3LE, UK
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Foster AW, Patterson CJ, Pernil R, Hess CR, Robinson NJ. Cytosolic Ni(II) sensor in cyanobacterium: nickel detection follows nickel affinity across four families of metal sensors. J Biol Chem 2012; 287:12142-51. [PMID: 22356910 PMCID: PMC3320959 DOI: 10.1074/jbc.m111.338301] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Efflux of surplus Ni(II) across the outer and inner membranes of Synechocystis PCC 6803 is mediated by the Nrs system under the control of a sensor of periplasmic Ni(II), NrsS. Here, we show that the product of ORF sll0176, which encodes a CsoR/RcnR-like protein now designated InrS (for internal nickel-responsive sensor), represses nrsD (NrsD is deduced to efflux Ni(II) across the inner membrane) from a cryptic promoter between the final two ORFs in the nrs operon. Transcripts initiated from the newly identified nrsD promoter accumulate in response to nickel or cobalt but not copper, and recombinant InrS forms specific, Ni(II)-inhibited complexes with the nrsD promoter region. Metal-dependent difference spectra of Ni(II)- and Cu(I)-InrS are similar to Cu(I)-sensing CsoR and dissimilar to Ni(II)/Co(II)-sensing RcnR, consistent with factors beyond the primary coordination sphere switching metal selectivity. Competition with chelators mag-fura-2, nitrilotriacetic acid, EDTA, and EGTA estimate KD Ni(II) for the tightest site of InrS as 2.05 (±1.5) × 10−14m, and weaker KD Ni(II) for the cells' metal sensors of other types: Zn(II) co-repressor Zur, Co(II) activator CoaR, and Zn(II) derepressor ZiaR. Ni(II) transfer to InrS occurs upon addition to Ni(II) forms of each other sensor. InrS binds Ni(II) sufficiently tightly to derepress Ni(II) export at concentrations below KD Ni(II) of the other sensors.
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Affiliation(s)
- Andrew W Foster
- Biophysical Sciences Institute, Department of Chemistry, School of Biological and Biomedical Sciences, University of Durham, Durham DH1 3LE, United Kingdom
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Abstract
Metalloproteins are essential for many cellular functions, but it has not been clear how they distinguish between the different metals to bind the correct ones. A report in BMC Biology finds that preferences of two metallothionein isoforms for two different cations are due to inherent properties of these usually less discriminating proteins. Here these observations are discussed in the context of the cellular mechanisms that regulate metal binding to proteins. See research article: http://www.biomedcentral.com/1741-7007/9/4
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Affiliation(s)
- Andrew W Foster
- Biophysical Sciences Institute, Department of Chemistry, School of Biological and Biomedical Sciences, Durham University, DH1 3LE, UK.
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Branzetti JB, Aldeen AZ, Foster AW, Courtney DM. A novel online didactic curriculum helps improve knowledge acquisition among non-emergency medicine rotating residents. Acad Emerg Med 2011; 18:53-9. [PMID: 21175925 DOI: 10.1111/j.1553-2712.2010.00951.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVES Rotating residents represent a significant proportion of housestaff in academic emergency departments (EDs), yet they rarely receive targeted didactic education during their emergency medicine (EM) rotations. The goals of this study were: 1) to determine the effectiveness of an online didactic curriculum in improving EM knowledge among rotating residents and 2) to assess rotating resident satisfaction with this curriculum. METHODS The authors created an online lecture series of six EM subject areas targeted to rotating residents called the Northwestern University Rotating Resident Curriculum (NURRC). All rotating residents at the study site were eligible, written consent was obtained, and the study was approved by the institutional review board. Consenting participants were pretested with a 42-question multiple-choice examination and then randomized to two groups: one with access to the NURRC during the first 2 weeks of the rotation (experimental) and one without (control). Halfway through the rotation, all participants were post-tested with a different multiple-choice examination, and the controls were then granted NURRC access. The primary outcome was the difference between pretest and posttest scores (score delta). The t-test was used to compare mean scores, and a linear regression model was used to determine the association of NURRC access on score delta after adjustment for pretest type and resident type. A postintervention survey was administered at the end of the rotation to assess satisfaction with the NURRC and collect suggestions for improvement. RESULTS Fifty-four rotating residents were enrolled: 29 in the experimental group and 25 in the control group. There was no significant difference in pretest scores between the two groups. Mean score delta was 17.3% in the experimental group and 1.6% in the control group, an absolute difference of 15.7% (95% confidence interval [CI]=10% to 22%). After adjustment for resident type and pretest type, the only variable positively associated with the primary outcome was NURRC access. Third-year and preliminary-year internal medicine (IM) residents demonstrated the greatest absolute improvement in score delta when granted NURRC access. Eighty percent of the participants responded to the satisfaction survey. Over 80% of the survey respondents approved of each component lecture and of the NURRC overall. CONCLUSIONS After exposure to an online didactic curriculum, rotating residents demonstrated a significant increase in EM knowledge and reported a high level of satisfaction with the didactic program.
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Affiliation(s)
- Jeremy B Branzetti
- Department of Emergency Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
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