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Choi WW, Jeong H, Kim Y, Lee HS. Gene nceA encodes a Ni/Co-sensing transcription factor to regulate metal efflux in Corynebacterium glutamicum. METALLOMICS : INTEGRATED BIOMETAL SCIENCE 2022; 14:6865361. [PMID: 36460048 DOI: 10.1093/mtomcs/mfac094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Accepted: 11/23/2022] [Indexed: 12/04/2022]
Abstract
The function of Corynebacterium glutamicum open reading frame (ORF) NCgl2684 (named nceA in this study), which was annotated to encode a metalloregulator, was assessed using physiological, genetic, and biochemical approaches. Cells with deleted-nceA (ΔnceA) showed a resistant phenotype to NiSO4 and CoSO4 and showed faster growth in minimal medium containing 20 μM NiSO4 or 10 μM CoSO4 than both the wild-type and nceA-overexpressing (P180-nceA) cells. In the ΔnceA strain, the transcription of the downstream-located ORF NCgl2685 (nceB), annotated to encode efflux protein, was increased approximately 4-fold, whereas gene transcription decreased down to 30% level in the P180-nceA strain. The transcriptions of the nceA and nceB genes were stimulated, even when as little as 5 nM NiSO4 was added to the growth medium. Protein NceA was able to bind DNA comprising the promoter region (from -14 to + 18) of the nceA--nceB operon. The protein-DNA interaction was abolished in the presence of 20 μM NiSO4, 50 μM CoSO4, or 50 μM CdSO4. Although manganese induced the transcription of the nceA and nceB genes, it failed to interrupt protein-DNA interaction. Simultaneously, the P180-nceA cells showed increased sensitivity to oxidants such as menadione, hydrogen peroxide, and cumene hydroperoxide, but not diamide. Collectively, our data show that NceA is a nickel- and cobalt-sensing transcriptional regulator that controls the transcription of the probable efflux protein-encoding nceB. The genes are able to suppress intracellular levels of nickel to prevent reactions, which can cause oxidative damage to cellular components.
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Affiliation(s)
- Won-Woo Choi
- Department of Biotechnology and Bioinformatics, Korea University, Sejong 30019, Republic of Korea.,Interdisciplinary Graduate Program for Artificial Intelligence Smart Convergence Technology, Korea University, Sejong 30019, Republic of Korea
| | - Haeri Jeong
- Department of Biotechnology and Bioinformatics, Korea University, Sejong 30019, Republic of Korea
| | - Younhee Kim
- Department of Korean Medicine, Semyung University, Jecheon, Chungbuk 27136, Republic of Korea
| | - Heung-Shick Lee
- Department of Biotechnology and Bioinformatics, Korea University, Sejong 30019, Republic of Korea.,Interdisciplinary Graduate Program for Artificial Intelligence Smart Convergence Technology, Korea University, Sejong 30019, Republic of Korea
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Adhikary A, Biswal S, Chatterjee D, Ghosh AS. A NiCoT family metal transporter of Mycobacterium tuberculosis (Rv2856/NicT) behaves as a drug efflux pump that facilitates cross-resistance to antibiotics. MICROBIOLOGY (READING, ENGLAND) 2022; 168. [PMID: 36282241 DOI: 10.1099/mic.0.001260] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Metals often act as a facilitator in the proliferation and persistence of antibiotic resistance. Efflux pumps play key roles in the co-selection of metal and antibiotic resistance. Here, we report the ability of a putative nickel/cobalt transporter (NiCoT family), Rv2856 or NicT of Mycobacterium tuberculosis (Mtb), to transport metal and antibiotics and identified some key amino acid residues that are important for its function. Ectopic expression of NicT in Escherichia coli CS109 resulted in the increase of intracellular nickel uptake. Additionally, enhanced tolerance towards several antibiotics (norfloxacin, sparfloxacin, ofloxacin, gentamicin, nalidixic acid and isoniazid) was observed with NicT overexpression in E. coli and Mycobacterium smegmatis. A comparatively lower intracellular accumulation of norfloxacin upon NicT overexpression than that of the cells without NicT indicated the involvement of NicT in an active efflux process. Although expression of NicT did not alter the sensitivity towards kanamycin, doxycycline, tetracycline, apramycin, neomycin and ethambutol, the presence of a sub-inhibitory dose of Ni2+ resulted in the manifestation of low-level tolerance towards these drugs. Further, substitution of four residues (H77I, D82I, H83L and D227I) in the conserved regions of NicT by isoleucine and leucine resulted in reduced to nearly complete loss of the transport function for both metals and antimicrobials. Therefore, the study suggests that nickel transporter Rv2856/NicT may actively export different drugs and the presence of nickel might drive the cross-resistance to some of the antibiotics.
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Affiliation(s)
- Anwesha Adhikary
- Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal-721302, India
| | - Sarmistha Biswal
- Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal-721302, India
| | - Debasmita Chatterjee
- Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal-721302, India
| | - Anindya S Ghosh
- Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal-721302, India
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3
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Mazzei L, Musiani F, Żerko S, Koźminski W, Cianci M, Beniamino Y, Ciurli S, Zambelli B. Structure, dynamics, and function of SrnR, a transcription factor for nickel-dependent gene expression. Metallomics 2021; 13:6445039. [PMID: 34850061 DOI: 10.1093/mtomcs/mfab069] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Accepted: 11/18/2021] [Indexed: 11/14/2022]
Abstract
Streptomyces griseus, a bacterium producing antibacterial drugs and featuring possible application in phytoremediation, expresses two metal-dependent superoxide dismutase (SOD) enzymes, containing either Fe(II) or Ni(II) in their active site. In particular, the alternative expression of the two proteins occurs in a metal-dependent mode, with the Fe(II)-enzyme gene (sodF) repressed at high intracellular Ni(II) concentrations by a two-component system (TCS). This complex involves two proteins, namely SgSrnR and SgSrnQ, which represent the transcriptional regulator and the Ni(II) sensor of the system, respectively. SgSrnR belongs to the ArsR/SmtB family of metal-dependent transcription factors; in the apo-form and in the absence of SgSrnQ, it can bind the DNA operator of sodF, upregulating gene transcription. According to a recently proposed hypothesis, Ni(II) binding to SgSrnQ would promote its interaction with SgSrnR, causing the release of the complex from DNA and the consequent downregulation of the sodF expression. SgSrnQ is predicted to be highly disordered, thus the understanding, at the molecular level, of how the SgSrnR/SgSrnQ TCS specifically responds to Ni(II) requires the knowledge of the structural, dynamic, and functional features of SgSrnR. These were investigated synergistically in this work using X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy, atomistic molecular dynamics calculations, isothermal titration calorimetry, and in silico molecular docking. The results reveal that the homodimeric apo-SgSrnR binds to its operator in a two-step process that involves the more rigid globular portion of the protein and leaves its largely disordered regions available to possibly interact with the disordered SgSrnQ in a Ni-dependent process.
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Affiliation(s)
- Luca Mazzei
- Laboratory of Bioinorganic Chemistry, Department of Pharmacy and Biotechnology (FaBiT), University of Bologna, Via Giuseppe Fanin 40, I-40127 Bologna. Italy
| | - Francesco Musiani
- Laboratory of Bioinorganic Chemistry, Department of Pharmacy and Biotechnology (FaBiT), University of Bologna, Via Giuseppe Fanin 40, I-40127 Bologna. Italy
| | - Szymon Żerko
- Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Żwirki i Wigury 101, 02-089, Warsaw, Poland
| | - Wiktor Koźminski
- Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Żwirki i Wigury 101, 02-089, Warsaw, Poland
| | - Michele Cianci
- Department of Agricultural, Food and Environmental Sciences, Polytechnic University of Marche, Via Brecce Bianche, I-60131 Ancona, Italy
| | - Ylenia Beniamino
- Laboratory of Bioinorganic Chemistry, Department of Pharmacy and Biotechnology (FaBiT), University of Bologna, Via Giuseppe Fanin 40, I-40127 Bologna. Italy
| | - Stefano Ciurli
- Laboratory of Bioinorganic Chemistry, Department of Pharmacy and Biotechnology (FaBiT), University of Bologna, Via Giuseppe Fanin 40, I-40127 Bologna. Italy
| | - Barbara Zambelli
- Laboratory of Bioinorganic Chemistry, Department of Pharmacy and Biotechnology (FaBiT), University of Bologna, Via Giuseppe Fanin 40, I-40127 Bologna. Italy
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4
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Principles and practice of determining metal-protein affinities. Biochem J 2021; 478:1085-1116. [PMID: 33710331 PMCID: PMC7959690 DOI: 10.1042/bcj20200838] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 02/05/2021] [Accepted: 02/11/2021] [Indexed: 01/02/2023]
Abstract
Metal ions play many critical roles in biology, as structural and catalytic cofactors, and as cell regulatory and signalling elements. The metal–protein affinity, expressed conveniently by the metal dissociation constant, KD, describes the thermodynamic strength of a metal–protein interaction and is a key parameter that can be used, for example, to understand how proteins may acquire metals in a cell and to identify dynamic elements (e.g. cofactor binding, changing metal availabilities) which regulate protein metalation in vivo. Here, we outline the fundamental principles and practical considerations that are key to the reliable quantification of metal–protein affinities. We review a selection of spectroscopic probes which can be used to determine protein affinities for essential biological transition metals (including Mn(II), Fe(II), Co(II), Ni(II), Cu(I), Cu(II) and Zn(II)) and, using selected examples, demonstrate how rational probe selection combined with prudent experimental design can be applied to determine accurate KD values.
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Calculating metalation in cells reveals CobW acquires Co II for vitamin B 12 biosynthesis while related proteins prefer Zn II. Nat Commun 2021; 12:1195. [PMID: 33608553 PMCID: PMC7895991 DOI: 10.1038/s41467-021-21479-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 01/25/2021] [Indexed: 02/01/2023] Open
Abstract
Protein metal-occupancy (metalation) in vivo has been elusive. To address this challenge, the available free energies of metals have recently been determined from the responses of metal sensors. Here, we use these free energy values to develop a metalation-calculator which accounts for inter-metal competition and changing metal-availabilities inside cells. We use the calculator to understand the function and mechanism of GTPase CobW, a predicted CoII-chaperone for vitamin B12. Upon binding nucleotide (GTP) and MgII, CobW assembles a high-affinity site that can obtain CoII or ZnII from the intracellular milieu. In idealised cells with sensors at the mid-points of their responses, competition within the cytosol enables CoII to outcompete ZnII for binding CobW. Thus, CoII is the cognate metal. However, after growth in different [CoII], CoII-occupancy ranges from 10 to 97% which matches CobW-dependent B12 synthesis. The calculator also reveals that related GTPases with comparable ZnII affinities to CobW, preferentially acquire ZnII due to their relatively weaker CoII affinities. The calculator is made available here for use with other proteins.
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Abstract
Nickel is essential for the survival of many pathogenic bacteria. E. coli and H. pylori require nickel for [NiFe]-hydrogenases. H. pylori also requires nickel for urease. At high concentrations nickel can be toxic to the cell, therefore, nickel concentrations are tightly regulated. Metalloregulators help to maintain nickel concentration in the cell by regulating the expression of the genes associated with nickel import and export. Nickel import into the cell, delivery of nickel to target proteins, and export of nickel from the cell is a very intricate and well-choreographed process. The delivery of nickel to [NiFe]-hydrogenase and urease is complex and involves several chaperones and accessory proteins. A combination of biochemical, crystallographic, and spectroscopic techniques has been utilized to study the structures of these proteins, as well as protein-protein interactions resulting in an expansion of our knowledge regarding how these proteins sense and bind nickel. In this review, recent advances in the field will be discussed, focusing on the metal site structures of nickel bound to metalloregulators and chaperones.
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7
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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: 105] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [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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8
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Roy R, Samanta S, Patra S, Mahato NK, Saha RP. In silico identification and characterization of sensory motifs in the transcriptional regulators of the ArsR-SmtB family. Metallomics 2018; 10:1476-1500. [PMID: 30191942 DOI: 10.1039/c8mt00082d] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The ArsR-SmtB family of proteins displays the greatest diversity among the bacterial metal-binding transcriptional regulators with regard to the variety of metal ions that they can sense. In the presence of increased levels of toxic heavy metals, these proteins dissociate from their cognate DNA upon the direct binding of metal ions to the appropriate sites, designated motifs on the proteins, either at the interface of the dimers or at the intra-subunit locations. In addition to the metal-mediated regulation, some proteins were also found to control transcription via redox reactions. In the present work, we have identified several new sequence motifs and expanded the knowledge base of metal binding sites in the ArsR-SmtB family of transcriptional repressors, and characterized them in terms of the ligands to the metal, distribution among different phyla of bacteria and archaea, amino acid propensities, protein length distributions and evolutionary interrelationships. We built structural models of the motifs to show the importance of specific residues in an individual motif. The wide abundance of these motifs in sequences of bacteria and archaea indicates the importance of these regulators in combating metal-toxicity within and outside of the hosts. We also show that by using residue composition, one can distinguish the ArsR-SmtB proteins from other metalloregulatory families. In addition, we show the importance of horizontal gene transfer in microorganisms, residing in similar habitats, on the evolution of the structural motifs in the family. Knowledge of the diverse metalloregulatory systems in microorganisms could enable us to manipulate specific genes that may result in a toxic metal-free environment.
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Affiliation(s)
- Rima Roy
- Department of Biotechnology, School of Biotechnology, Adamas University, Kolkata 700 126, India.
| | - Saikat Samanta
- Department of Biotechnology, School of Biotechnology, Adamas University, Kolkata 700 126, India.
| | - Surajit Patra
- Department of Biotechnology, School of Biotechnology, Adamas University, Kolkata 700 126, India.
| | - Nav Kumar Mahato
- Department of Mathematics, School of Science, Adamas University, Kolkata 700 126, India
| | - Rudra P Saha
- Department of Biotechnology, School of Biotechnology, Adamas University, Kolkata 700 126, India.
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Saha RP, Samanta S, Patra S, Sarkar D, Saha A, Singh MK. Metal homeostasis in bacteria: the role of ArsR-SmtB family of transcriptional repressors in combating varying metal concentrations in the environment. Biometals 2017; 30:459-503. [PMID: 28512703 DOI: 10.1007/s10534-017-0020-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Accepted: 05/09/2017] [Indexed: 02/02/2023]
Abstract
Bacterial infections cause severe medical problems worldwide, resulting in considerable death and loss of capital. With the ever-increasing rise of antibiotic-resistant bacteria and the lack of development of new antibiotics, research on metal-based antimicrobial therapy has now gained pace. Metal ions are essential for survival, but can be highly toxic to organisms if their concentrations are not strictly controlled. Through evolution, bacteria have acquired complex metal-management systems that allow them to acquire metals that they need for survival in different challenging environments while evading metal toxicity. Metalloproteins that controls these elaborate systems in the cell, and linked to key virulence factors, are promising targets for the anti-bacterial drug development. Among several metal-sensory transcriptional regulators, the ArsR-SmtB family displays greatest diversity with several distinct metal-binding and nonmetal-binding motifs that have been characterized. These prokaryotic metolloregulatory transcriptional repressors represses the expression of operons linked to stress-inducing concentrations of metal ions by directly binding to the regulatory regions of DNA, while derepression results from direct binding of metal ions by these homodimeric proteins. Many bacteria, e.g., Mycobacterium tuberculosis, Bacillus anthracis, etc., have evolved to acquire multiple metal-sensory motifs which clearly demonstrate the importance of regulating concentrations of multiple metal ions. Here, we discussed the mechanisms of how ArsR-SmtB family regulates the intracellular bioavailability of metal ions both inside and outside of the host. Knowledge of the metal-challenges faced by bacterial pathogens and their survival strategies will enable us to develop the next generation drugs.
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Affiliation(s)
- Rudra P Saha
- Department of Biotechnology, School of Biotechnology, Adamas University, Kolkata, 700126, India.
| | - Saikat Samanta
- Department of Microbiology, School of Science, Adamas University, Kolkata, 700126, India
| | - Surajit Patra
- Department of Biotechnology, School of Biotechnology, Adamas University, Kolkata, 700126, India
| | - Diganta Sarkar
- Department of Biotechnology, Techno India University, Kolkata, 700091, India
| | - Abinit Saha
- Department of Biotechnology, School of Biotechnology, Adamas University, Kolkata, 700126, India
| | - Manoj Kumar Singh
- Department of Biotechnology, School of Biotechnology, Adamas University, Kolkata, 700126, India
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Abstract
Nickel supports the growth of microbes from a variety of very different growth environments that affect nickel speciation. The mechanisms of nickel uptake and the molecular bases for the selectivity of this process are emerging. The recent surge of Ni-importer protein structures provides an understanding of Ni-recognition in the initial binding step of the import process. This review compares the structural basis for Ni-recognition in the complexes (ABC and ECF-type) that dominate primary (ATP-dependent) transport, with a focus on how the structures suggest mechanisms for Ni selectivity. The structures raise key questions about the mechanisms of nickel-transfer reactions involved in import. There is also a discussion of key experimental approaches necessary to help establish the physiological importance of these structures.
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Affiliation(s)
- Peter T Chivers
- Department of Chemistry and School of Biological and Biomedical Sciences, Durham University, Durham, UK.
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Campeciño JO, Dudycz LW, Tumelty D, Berg V, Cabelli DE, Maroney MJ. A Semisynthetic Strategy Leads to Alteration of the Backbone Amidate Ligand in the NiSOD Active Site. J Am Chem Soc 2015; 137:9044-52. [PMID: 26135142 DOI: 10.1021/jacs.5b03629] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Computational investigations have implicated the amidate ligand in nickel superoxide dismutase (NiSOD) in stabilizing Ni-centered redox catalysis and in preventing cysteine thiolate ligand oxidation. To test these predictions, we have used an experimental approach utilizing a semisynthetic scheme that employs native chemical ligation of a pentapeptide (HCDLP) to recombinant S. coelicolor NiSOD lacking these N-terminal residues, NΔ5-NiSOD. Wild-type enzyme produced in this manner exhibits the characteristic spectral properties of recombinant WT-NiSOD and is as catalytically active. The semisynthetic scheme was also employed to construct a variant where the amidate ligand was converted to a secondary amine, H1*-NiSOD, a novel strategy that retains a backbone N-donor atom. The H1*-NiSOD variant was found to have only ∼1% of the catalytic activity of the recombinant wild-type enzyme, and had altered spectroscopic properties. X-ray absorption spectroscopy reveals a four-coordinate planar site with N2S2-donor ligands, consistent with electronic absorption spectroscopic results indicating that the Ni center in H1*-NiSOD is mostly reduced in the as-isolated sample, as opposed to 50:50 Ni(II)/Ni(III) mixture that is typical for the recombinant wild-type enzyme. The EPR spectrum of as-isolated H1*-NiSOD accounts for ∼11% of the Ni in the sample and is similar to WT-NiSOD, but more axial, with gz < gx,y. (14)N-hyperfine is observed on gz, confirming the addition of the apical histidine ligand in the Ni(III) complex. The altered electronic properties and implications for redox catalysis are discussed in light of predictions based on synthetic and computational models.
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Affiliation(s)
- Julius O Campeciño
- †Department of Chemistry University of Massachusetts, Amherst, Massachusetts 01003, United States
| | - Lech W Dudycz
- ‡Lex Company Research Lab, Phoenix Park, 2 Shaker Road, Suite D 106, Shirley, Massachusetts 01464, United States
| | - David Tumelty
- §New England Peptide, 65 Zub Lane, Gardner, Massachusetts 01440, United States
| | - Volker Berg
- †Department of Chemistry University of Massachusetts, Amherst, Massachusetts 01003, United States
| | - Diane E Cabelli
- ∥Department of Chemistry, Brookhaven National Laboratory, Building 555A, P.O. Box 5000 Upton, New York 11973, United States
| | - Michael J Maroney
- †Department of Chemistry University of Massachusetts, Amherst, Massachusetts 01003, United States
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Kim HM, Ahn BE, Lee JH, Roe JH. Regulation of a nickel–cobalt efflux system and nickel homeostasis in a soil actinobacterium Streptomyces coelicolor. Metallomics 2015; 7:702-9. [DOI: 10.1039/c4mt00318g] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
In nickel-tolerantStreptomyces coelicolor, a highly nickel-sensitive regulator (Nur) for nickel uptake systems and an extremely insensitive regulator (NmtR) for a nickel efflux pump constitute the nickel homeostasis system.
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Affiliation(s)
- Hae Mi Kim
- School of Biological Sciences, and Institute of Microbiology
- Seoul National University
- Seoul 151-742, Korea
| | - Bo-Eun Ahn
- School of Biological Sciences, and Institute of Microbiology
- Seoul National University
- Seoul 151-742, Korea
| | - Ju-Hyung Lee
- School of Biological Sciences, and Institute of Microbiology
- Seoul National University
- Seoul 151-742, Korea
| | - Jung-Hye Roe
- School of Biological Sciences, and Institute of Microbiology
- Seoul National University
- Seoul 151-742, Korea
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Furnholm TR, Tisa LS. The ins and outs of metal homeostasis by the root nodule actinobacterium Frankia. BMC Genomics 2014; 15:1092. [PMID: 25495525 PMCID: PMC4531530 DOI: 10.1186/1471-2164-15-1092] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 11/19/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Frankia are actinobacteria that form a symbiotic nitrogen-fixing association with actinorhizal plants, and play a significant role in actinorhizal plant colonization of metal contaminated areas. Many Frankia strains are known to be resistant to several toxic metals and metalloids including Pb(2+), Al(+3), SeO2, Cu(2+), AsO4, and Zn(2+). With the availability of eight Frankia genome databases, comparative genomics approaches employing phylogeny, amino acid composition analysis, and synteny were used to identify metal homeostasis mechanisms in eight Frankia strains. Characterized genes from the literature and a meta-analysis of 18 heavy metal gene microarray studies were used for comparison. RESULTS Unlike most bacteria, Frankia utilize all of the essential trace elements (Ni, Co, Cu, Se, Mo, B, Zn, Fe, and Mn) and have a comparatively high percentage of metalloproteins, particularly in the more metal resistant strains. Cation diffusion facilitators, being one of the few known metal resistance mechanisms found in the Frankia genomes, were strong candidates for general divalent metal resistance in all of the Frankia strains. Gene duplication and amino acid substitutions that enhanced the metal affinity of CopA and CopCD proteins may be responsible for the copper resistance found in some Frankia strains. CopA and a new potential metal transporter, DUF347, may be involved in the particularly high lead tolerance in Frankia. Selenite resistance involved an alternate sulfur importer (CysPUWA) that prevents sulfur starvation, and reductases to produce elemental selenium. The pattern of arsenate, but not arsenite, resistance was achieved by Frankia using the novel arsenite exporter (AqpS) previously identified in the nitrogen-fixing plant symbiont Sinorhizobium meliloti. Based on the presence of multiple tellurite resistance factors, a new metal resistance (tellurite) was identified and confirmed in Frankia. CONCLUSIONS Each strain had a unique combination of metal import, binding, modification, and export genes that explain differences in patterns of metal resistance between strains. Frankia has achieved similar levels of metal and metalloid resistance as bacteria from highly metal-contaminated sites. From a bioremediation standpoint, it is important to understand mechanisms that allow the endosymbiont to survive and infect actinorhizal plants in metal contaminated soils.
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Affiliation(s)
- Teal R Furnholm
- Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, Durham, NH, USA.
| | - Louis S Tisa
- Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, Durham, NH, USA.
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14
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Chivers PT. Cobalt and Nickel. BINDING, TRANSPORT AND STORAGE OF METAL IONS IN BIOLOGICAL CELLS 2014. [DOI: 10.1039/9781849739979-00381] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Cobalt and nickel play key roles in biological systems as cofactors in a small number of important enzymes. The majority of these are found in microbes. Evidence for direct roles for Ni(II) and Co(II) enzymes in higher organisms is limited, with the exception of the well-known requirement for the cobalt-containing vitamin B12 cofactor and the Ni-dependent urease in plants. Nonetheless, nickel in particular plays a key role in human health because of its essential role in microbes that inhabit various growth niches within the body. These roles can be beneficial, as can be seen with the anaerobic production and consumption of H2 in the digestive tract by bacteria and archaea that results in increased yields of short-chain fatty acids. In other cases, nickel has an established role in the establishment of pathogenic infection (Helicobacter pylori urease and colonization of the stomach). The synthesis of Co- and Ni-containing enzymes requires metal import from the extracellular milieu followed by the targeting of these metals to the appropriate protein and enzymes involved in metallocluster or cofactor biosynthesis. These metals are toxic in excess so their levels must be regulated carefully. This complex pathway of metalloenzyme synthesis and intracellular homeostasis requires proteins that can specifically recognize these metals in a hierarchical manner. This chapter focuses on quantitative and structural details of the cobalt and nickel binding sites in transport, trafficking and regulatory proteins involved in cobalt and nickel metabolism in microbes.
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Affiliation(s)
- Peter T. Chivers
- Department of Chemistry, School of Biological and Biomedical Sciences, and Biophysical Sciences Institute, Durham University Durham UK
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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] [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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16
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Higgins KA, Giedroc D. Insights into Protein Allostery in the CsoR/RcnR Family of Transcriptional Repressors. CHEM LETT 2014; 43:20-25. [PMID: 24695963 DOI: 10.1246/cl.130965] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
CsoR/RcnR transcriptional repressors adopt a disc-shaped, all α-helical dimer of dimers tetrameric architecture, with a four-helix bundle the key structural feature of the dimer. Individual members of this large family of repressors coordinate Cu(I) or Ni(II)/Co(II) or perform cysteine sulfur chemistry in mitigating the effects of metal or metabolite toxicity, respectively. Here we highlight recent insights into the functional diversity of this fascinating family of repressors.
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Affiliation(s)
- Khadine A Higgins
- Department of Chemistry, Indiana University, 212 S. Hawthorne Drive, Bloomington, IN 47405, USA
| | - David Giedroc
- Department of Chemistry, Indiana University, 212 S. Hawthorne Drive, Bloomington, IN 47405, USA
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17
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Lee CW, Giedroc DP. ¹H, ¹³C, and ¹⁵N resonance assignments of NmtR, a Ni(II)/Co(II) metalloregulatory protein of Mycobacterium tuberculosis. BIOMOLECULAR NMR ASSIGNMENTS 2013; 7:145-148. [PMID: 22618866 DOI: 10.1007/s12104-012-9397-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Accepted: 05/02/2012] [Indexed: 06/01/2023]
Abstract
NmtR is a Ni(II)/Co(II)-specific repressor expressed in Mycobacterium tuberculosis, which regulates the transcription of a membrane transporter proposed to mediate cytoplasmic Ni(II)/Co(II) efflux. Here we report the backbone and side chain resonance assignments of the apo-NmtR and the backbone assignments of Ni(II)-bound form of NmtR.
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Affiliation(s)
- Chul Won Lee
- Department of Chemistry, Indiana University, 212 S. Hawthorne Drive, Bloomington, IN 47405-7102, USA
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18
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Stapleton B, Walker LR, Logan TM. Zn(II) stimulation of Fe(II)-activated repression in the iron-dependent repressor from Mycobacterium tuberculosis. Biochemistry 2013; 52:1927-38. [PMID: 23432191 DOI: 10.1021/bi301608p] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Thermodynamic measurements of Fe(II) binding and activation of repressor function in the iron-dependent repressor from Mycobacterium tuberculosis (IdeR) are reported. IdeR, a member of the diphtheria toxin repressor family of proteins, regulates iron homeostasis and contributes to the virulence response in M. tuberculosis. Although iron is the physiological ligand, this is the first detailed analysis of iron binding and activation in this protein. The results showed that IdeR binds 2 equiv of Fe(II) with dissociation constants that differ by a factor of 25. The high- and low-affinity iron binding sites were assigned to physical binding sites I and II, respectively, using metal binding site mutants. IdeR was also found to contain a high-affinity Zn(II) binding site that was assigned to physical metal binding site II through the use of binding site mutants and metal competition assays. Fe(II) binding was modestly weaker in the presence of Zn(II), but the coupled metal binding-DNA binding affinity was significantly stronger, requiring 30-fold less Fe(II) to activate DNA binding compared to Fe(II) alone. Together, these results suggest that IdeR is a mixed-metal repressor, where Zn(II) acts as a structural metal and Fe(II) acts to trigger the physiologically relevant promoter binding. This new model for IdeR activation provides a better understanding of IdeR and the biology of iron homeostasis in M. tuberculosis.
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Affiliation(s)
- Brian Stapleton
- Department of Chemistry and Biochemistry, 102 Varsity Way, Florida State University, Tallahassee, Florida 32306-4390, United States
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19
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20
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Chakravorty DK, Parker TM, Guerra AJ, Sherrill CD, Giedroc DP, Merz KM. Energetics of zinc-mediated interactions in the allosteric pathways of metal sensor proteins. J Am Chem Soc 2012; 135:30-3. [PMID: 23214972 DOI: 10.1021/ja309170g] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
A metal-mediated interprotomer hydrogen bond has been implicated in the allosteric mechanism of DNA operator binding in several metal-sensing proteins. Using computational methods, we investigate the energetics of such zinc-mediated interactions in members of the ArsR/SmtB family of proteins (CzrA, SmtB, CadC, and NmtR) and the MarR family zinc-uptake repressor AdcR, which feature similar interactions, but in sites that differ widely in their allosteric responsiveness. We provide novel structural insight into previously uncharacterized allosteric forms of these proteins using computational methodologies. We find this metal-mediated interaction to be significantly stronger (∼8 kcal/mol) at functional allosteric metal binding sites compared to a nonresponsive site (CadC) and the apo-proteins. Simulations of the apo-proteins further reveal that the high interaction energy works to overcome the considerable disorder at these hydrogen-bonding sites and functions as a "switch" to lock in a weak DNA-binding conformation once metal is bound. These findings suggest a conserved functional role of metal-mediated second coordination shell hydrogen bonds at allosterically responsive sites in zinc-sensing transcription regulators.
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Affiliation(s)
- Dhruva K Chakravorty
- Department of Chemistry and Quantum Theory Project, University of Florida, Gainesville, Florida 32611-8435, United States
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21
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Higgins KA, Carr CE, Maroney MJ. Specific metal recognition in nickel trafficking. Biochemistry 2012; 51:7816-32. [PMID: 22970729 DOI: 10.1021/bi300981m] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Nickel is an essential metal for a number of bacterial species that have developed systems for acquiring, delivering, and incorporating the metal into target enzymes and controlling the levels of nickel in cells to prevent toxic effects. As with other transition metals, these trafficking systems must be able to distinguish between the desired metal and other transition metal ions with similar physical and chemical properties. Because there are few enzymes (targets) that require nickel for activity (e.g., Escherichia coli transports nickel for hydrogenases made under anaerobic conditions, and Helicobacter pylori requires nickel for hydrogenase and urease that are essential for acid viability), the "traffic pattern" for nickel is relatively simple, and nickel trafficking therefore presents an opportunity to examine a system for the mechanisms that are used to distinguish nickel from other metals. In this review, we describe the details known for examples of uptake permeases, metallochaperones and proteins involved in metallocenter assembly, and nickel metalloregulators. We also illustrate a variety of mechanisms, including molecular recognition in the case of NikA protein and examples of allosteric regulation for HypA, NikR, and RcnR, employed to generate specific biological responses to nickel ions.
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Affiliation(s)
- Khadine A Higgins
- Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA
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22
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Higgins KA, Chivers PT, Maroney MJ. Role of the N-terminus in determining metal-specific responses in the E. coli Ni- and Co-responsive metalloregulator, RcnR. J Am Chem Soc 2012; 134:7081-93. [PMID: 22471551 PMCID: PMC3375346 DOI: 10.1021/ja300834b] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
RcnR (resistance to cobalt and nickel regulator) is a 40-kDa homotetrameric protein and metalloregulator that controls the transcription of the Co(II) and Ni(II) exporter, RcnAB, by binding to DNA as an apoprotein and releasing DNA in response to specifically binding Co(II) and Ni(II) ions. Using X-ray absorption spectroscopy (XAS) to examine the structure of metals bound and lacZ reporter assays of the transcription of RcnA in response to metal binding, in WT and mutant proteins, the roles of coordination number, ligand selection, and residues in the N-terminus of the protein were examined as determinants in metal ion recognition. The studies show that the cognate metal ions, Co(II) and Ni(II), which bind in (N/O)(5)S six-coordinate sites, are distinguished from non-cognate metal ions (Cu(I) and Zn(II)), which bind only three protein ligands and one anion from the buffer, by coordination number and ligand selection. Using mutations of residues near the N-terminus, the N-terminal amine is shown to be a ligand of the cognate metal ions that is missing in the complexes with non-cognate metal ions. The side chain of His3 is also shown to play an important role in distinguishing metal ions. The imidazole group is shown to be a ligand in the Co(II) RcnR complex, but not in the Zn(II) complex. Further, His3 does not appear to bind to Ni(II), providing a structural basis for the differential regulation of RcnAB by the two cognate ions. The Zn(II) complexes change coordination number in response to the residue in position three. In H3C-RcnR, the Zn(II) complex is five-coordinate, and in H3E-RcnR the Zn(II) ion is bound to six protein ligands. The metric parameters of this unusual Zn(II) structure resemble those of the WT-Ni(II) complex, and the mutant protein is able to regulate expression of RcnAB in response to binding the non-cognate ion. The results are discussed within a protein allosteric model for gene regulation by metalloregulators.
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Affiliation(s)
- Khadine A. Higgins
- Department of Chemistry , University of Massachusetts, Amherst, Massachusetts 01003
| | - Peter T. Chivers
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis MO 63110
| | - Michael J. Maroney
- Department of Chemistry , University of Massachusetts, Amherst, Massachusetts 01003
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Guerra AJ, Giedroc DP. Metal site occupancy and allosteric switching in bacterial metal sensor proteins. Arch Biochem Biophys 2012; 519:210-22. [PMID: 22178748 PMCID: PMC3312040 DOI: 10.1016/j.abb.2011.11.021] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2011] [Revised: 11/23/2011] [Accepted: 11/29/2011] [Indexed: 12/22/2022]
Abstract
All prokaryotes encode a panel of metal sensor or metalloregulatory proteins that govern the expression of genes that allows an organism to quickly adapt to toxicity or deprivation of both biologically essential transition metal ions, e.g., Zn, Cu, Fe, and heavy metal pollutants. As such, metal sensor proteins can be considered arbiters of intracellular transition metal bioavailability and thus potentially control the metallation state of the metalloproteins in the cell. Metal sensor proteins are specialized allosteric proteins that regulate transcription as a result direct binding of one or two cognate metal ions, to the exclusion of all others. In most cases, the binding of the cognate metal ion induces a structural change in a protein oligomer that either activates or inhibits operator DNA binding. A quantitative measure of the degree to which a particular metal drives metalloregulation of operator DNA-binding is the allosteric coupling free energy, ΔGc. In this review, we summarize recent work directed toward understanding metal occupancy and metal selectivity of these allosteric switches in selected families of metal sensor proteins and examine the structural origins of ΔGc in the functional context a thermodynamic "set-point" model of intracellular metal homeostasis.
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Affiliation(s)
- Alfredo J. Guerra
- Department of Chemistry, Indiana University, 212 S. Hawthorne Drive, Bloomington, IN USA 47405-7102
| | - David P. Giedroc
- Department of Chemistry, Indiana University, 212 S. Hawthorne Drive, Bloomington, IN USA 47405-7102
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Lee CW, Chakravorty DK, Chang FMJ, Reyes-Caballero H, Ye Y, Merz KM, Giedroc DP. Solution structure of Mycobacterium tuberculosis NmtR in the apo state: insights into Ni(II)-mediated allostery. Biochemistry 2012; 51:2619-29. [PMID: 22394357 DOI: 10.1021/bi3001402] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Mycobacterium tuberculosis is an obligate human respiratory pathogen that encodes approximately 10 arsenic repressor (ArsR) family regulatory proteins that allow the organism to respond to a wide range of changes in its immediate microenvironment. How individual ArsR repressors have evolved to respond to selective stimuli is of intrinsic interest. The Ni(II)/Co(II)-specific repressor NmtR and related actinomycete nickel sensors harbor a conserved N-terminal α-NH(2)-Gly2-His3-Gly4 sequence. Here, we present the solution structure of homodimeric apo-NmtR and show that the core of the molecule adopts a typical winged-helix ArsR repressor (α1-α2-α3-αR-β1-β2-α5) "open conformation" that is similar to that of the related zinc sensor Staphylococcus aureus CzrA, but harboring long, flexible N-terminal (residues 2-16) and C-terminal (residues 109-120) extensions. Binding of Ni(II) to the regulatory sites induces strong paramagnetic broadening of the α5 helical region and the extreme N-terminal tail to residue 10. Ratiometric pulse chase amidination mass spectrometry reveals that the rate of amidination of the α-amino group of Gly2 is strongly attenuated in the Ni(II) complex relative to the apo state and noncognate Zn(II) complex. Ni(II) binding also induces dynamic disorder on the microsecond to millisecond time scale of key DNA interacting regions that likely contributes to the negative regulation of DNA binding by Ni(II). Molecular dynamics simulations and quantum chemical calculations reveal that NmtR readily accommodates a distal Ni(II) hexacoordination model involving the α-amine and His3 of the N-terminal region and α5 residues Asp91', His93', His104, and His107, which collectively define a new metal sensing site configuration in ArsR family regulators.
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Affiliation(s)
- Chul Won Lee
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, United States
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25
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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] [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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