1
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Nissan N, Hooker J, Pattang A, Charette M, Morrison M, Yu K, Hou A, Golshani A, Molnar SJ, Cober ER, Samanfar B. Novel QTL for Low Seed Cadmium Accumulation in Soybean. PLANTS (BASEL, SWITZERLAND) 2022; 11:1146. [PMID: 35567147 PMCID: PMC9102923 DOI: 10.3390/plants11091146] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/09/2022] [Revised: 04/20/2022] [Accepted: 04/22/2022] [Indexed: 11/24/2022]
Abstract
Soybean is a valuable crop, used in animal feed and for human consumption. Selecting soybean cultivars with low seed cadmium (Cd) concentration is important for the purpose of minimizing the transfer of Cd into the human body. To ensure international trade, farmers need to produce soybean that meets the European Union (EU) Cd limit of 0.2 mg kg-1. In this study, we evaluated two populations of recombinant inbred lines (RILs), X5154 and X4050, for seed Cd accumulation. Linkage maps were constructed with 325 and 280 polymorphic simple sequence repeat (SSR) markers, respectively, and used to identify a novel minor quantitative trait locus (QTL) on chromosome 13 in the X4050 population between SSR markers Satt522 and Satt218. Based on a gene ontology search within the QTL region, seven genes were identified as candidates responsible for low seed Cd accumulation, including Glyma.13G308700 and Glyma.13G309100. In addition, we confirmed the known major gene, Cda1, in the X5154 population and developed KASP and CAPS/dCAPS allele-specific markers for efficient marker-assisted breeding for Cda1.
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Affiliation(s)
- Nour Nissan
- Agriculture and Agri-Food Canada, Ottawa Research and Development Centre, Ottawa, ON K1A 0C6, Canada; (N.N.); (J.H.); (A.P.); (M.C.); (M.M.); (S.J.M.); (E.R.C.)
- Department of Biology, Ottawa Institute of Systems Biology, Carleton University, Ottawa, ON K1S 5B6, Canada;
| | - Julia Hooker
- Agriculture and Agri-Food Canada, Ottawa Research and Development Centre, Ottawa, ON K1A 0C6, Canada; (N.N.); (J.H.); (A.P.); (M.C.); (M.M.); (S.J.M.); (E.R.C.)
- Department of Biology, Ottawa Institute of Systems Biology, Carleton University, Ottawa, ON K1S 5B6, Canada;
| | - Arezo Pattang
- Agriculture and Agri-Food Canada, Ottawa Research and Development Centre, Ottawa, ON K1A 0C6, Canada; (N.N.); (J.H.); (A.P.); (M.C.); (M.M.); (S.J.M.); (E.R.C.)
- Department of Biology, Ottawa Institute of Systems Biology, Carleton University, Ottawa, ON K1S 5B6, Canada;
| | - Martin Charette
- Agriculture and Agri-Food Canada, Ottawa Research and Development Centre, Ottawa, ON K1A 0C6, Canada; (N.N.); (J.H.); (A.P.); (M.C.); (M.M.); (S.J.M.); (E.R.C.)
| | - Malcolm Morrison
- Agriculture and Agri-Food Canada, Ottawa Research and Development Centre, Ottawa, ON K1A 0C6, Canada; (N.N.); (J.H.); (A.P.); (M.C.); (M.M.); (S.J.M.); (E.R.C.)
| | - Kangfu Yu
- Agriculture and Agri-Food Canada, Harrow Research and Development Centre, Harrow, ON N0R 1G0, Canada;
| | - Anfu Hou
- Agriculture and Agri-Food Canada, Morden Research and Development Centre, Morden, MB R6M 1Y5, Canada;
| | - Ashkan Golshani
- Department of Biology, Ottawa Institute of Systems Biology, Carleton University, Ottawa, ON K1S 5B6, Canada;
| | - Stephen J. Molnar
- Agriculture and Agri-Food Canada, Ottawa Research and Development Centre, Ottawa, ON K1A 0C6, Canada; (N.N.); (J.H.); (A.P.); (M.C.); (M.M.); (S.J.M.); (E.R.C.)
| | - Elroy R. Cober
- Agriculture and Agri-Food Canada, Ottawa Research and Development Centre, Ottawa, ON K1A 0C6, Canada; (N.N.); (J.H.); (A.P.); (M.C.); (M.M.); (S.J.M.); (E.R.C.)
| | - Bahram Samanfar
- Agriculture and Agri-Food Canada, Ottawa Research and Development Centre, Ottawa, ON K1A 0C6, Canada; (N.N.); (J.H.); (A.P.); (M.C.); (M.M.); (S.J.M.); (E.R.C.)
- Department of Biology, Ottawa Institute of Systems Biology, Carleton University, Ottawa, ON K1S 5B6, Canada;
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2
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Kowatz T, Maguire ME. Loss of cytosolic Mg 2+ binding sites in the Thermotoga maritima CorA Mg 2+ channel is not sufficient for channel opening. Biochim Biophys Acta Gen Subj 2018; 1863:25-30. [PMID: 30293964 DOI: 10.1016/j.bbagen.2018.09.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Revised: 08/29/2018] [Accepted: 09/03/2018] [Indexed: 10/28/2022]
Abstract
The CorA Mg2+ channel is a homopentamer with five-fold symmetry. Each monomer consists of a large cytoplasmic domain and two transmembrane helices connected via a short periplasmic loop. In the Thermotoga maritima CorA crystal structure, a Mg2+ is bound between D89 of one monomer and D253 of the adjacent monomer (M1 binding site). Release of Mg2+ from these sites has been hypothesized to cause opening of the channel. We generated mutants to disrupt Mg2+ interaction with the M1 site. Crystal structures of the D89K/D253K and D89R/D253R mutants, determined to 3.05 and 3.3 Å, respectively, showed no significant structural differences with the wild type structure despite absence of Mg2+ at the M1 sites. Both mutants still appear to be in the closed state. All three mutant CorA proteins exhibited transport of 63Ni2+, indicating functionality. Thus, absence of Mg2+ from the M1 sites neither causes channel opening nor prevents function. We also provide evidence that the T. maritima CorA is a Mg2+ channel and not a Co2+ channel.
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Affiliation(s)
- Thomas Kowatz
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4965, USA
| | - Michael E Maguire
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4965, USA.
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3
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Hong X, Chen HD, Groisman EA. Gene expression kinetics governs stimulus-specific decoration of the Salmonella outer membrane. Sci Signal 2018; 11:11/529/eaar7921. [PMID: 29739882 DOI: 10.1126/scisignal.aar7921] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Lipid A is the innermost component of the lipopolysaccharide (LPS) molecules that occupy the outer leaflet of the outer membrane in Gram-negative bacteria. Lipid A is recognized by the host immune system and targeted by cationic antimicrobial compounds. In Salmonella enterica serovar Typhimurium, the phosphates of lipid A are chemically modified by enzymes encoded by targets of the transcriptional regulator PmrA. These modifications increase resistance to the cationic peptide antibiotic polymyxin B by reducing the negative charge of the LPS. We report the mechanism by which Salmonella produces different lipid A profiles when PmrA is activated by low Mg2+ versus a mildly acidic pH. Low Mg2+ favored modification of the lipid A phosphates with 4-amino-4-deoxy-l-aminoarabinose (l-Ara4N) by activating the regulatory protein PhoP, which initially increased the LPS negative charge by promoting transcription of lpxT, encoding an enzyme that adds an additional phosphate group to lipid A. Later, PhoP activated PmrA posttranslationally, resulting in expression of PmrA-activated genes, including those encoding the LpxT inhibitor PmrR and enzymes responsible for the incorporation of l-Ara4N. By contrast, a mildly acidic pH favored modification of the lipid A phosphates with a mixture of l-Ara4N and phosphoethanolamine (pEtN) by simultaneously inducing the PhoP-activated lpxT and PmrA-activated pmrR genes. Although l-Ara4N reduces the LPS negative charge more than does pEtN, modification of lipid A phosphates solely with l-Ara4N required a prior transient increase in lipid A negative charge. Our findings demonstrate how bacteria tailor their cell surface to different stresses, such as those faced inside phagocytes.
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Affiliation(s)
- Xinyu Hong
- Department of Cell Biology, Yale School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA.,Department of Microbial Pathogenesis, Yale School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA.,Yale Microbial Sciences Institute, P.O. Box 27389, West Haven, CT 06516, USA.,Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, CT 06536, USA
| | - H Deborah Chen
- Department of Microbial Pathogenesis, Yale School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA
| | - Eduardo A Groisman
- Department of Microbial Pathogenesis, Yale School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA. .,Yale Microbial Sciences Institute, P.O. Box 27389, West Haven, CT 06516, USA
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4
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Pontes MH, Groisman EA. Protein synthesis controls phosphate homeostasis. Genes Dev 2018; 32:79-92. [PMID: 29437726 PMCID: PMC5828397 DOI: 10.1101/gad.309245.117] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Accepted: 12/27/2017] [Indexed: 12/22/2022]
Abstract
In this study, Pontes et al. show that impaired protein synthesis alone triggers a Pi starvation response even when Pi is plentiful in the extracellular milieu in yeast and bacteria. Their findings identify a regulatory connection between protein synthesis and Pi homeostasis that is widespread in nature. Phosphorus is an essential element assimilated largely as orthophosphate (Pi). Cells respond to Pi starvation by importing Pi from their surroundings. We now report that impaired protein synthesis alone triggers a Pi starvation response even when Pi is plentiful in the extracellular milieu. In the bacterium Salmonella enterica serovar Typhimurium, this response entails phosphorylation of the regulatory protein PhoB and transcription of PhoB-dependent Pi transporter genes and is eliminated upon stimulation of adenosine triphosphate (ATP) hydrolysis. When protein synthesis is impaired due to low cytoplasmic magnesium (Mg2+), Salmonella triggers the Pi starvation response because ribosomes are destabilized, which reduces ATP consumption and thus free cytoplasmic Pi. This response is transient because low cytoplasmic Mg2+ promotes an uptake in Mg2+ and a decrease in ATP levels, which stabilizes ribosomes, resulting in ATP consumption and Pi increase, thus ending the response. Notably, pharmacological inhibition of protein synthesis also elicited a Pi starvation response in the bacterium Escherichia coli and the yeast Saccharomyces cerevisiae. Our findings identify a regulatory connection between protein synthesis and Pi homeostasis that is widespread in nature.
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Affiliation(s)
- Mauricio H Pontes
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut 06536, USA.,Yale Microbial Sciences Institute, West Haven, Connecticut 06516, USA
| | - Eduardo A Groisman
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut 06536, USA.,Yale Microbial Sciences Institute, West Haven, Connecticut 06516, USA
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5
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Choi E, Choi S, Nam D, Park S, Han Y, Lee JS, Lee EJ. Elongation factor P restricts Salmonella's growth by controlling translation of a Mg 2+ transporter gene during infection. Sci Rep 2017; 7:42098. [PMID: 28181542 PMCID: PMC5299641 DOI: 10.1038/srep42098] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Accepted: 01/06/2017] [Indexed: 12/31/2022] Open
Abstract
When a ribosome translates mRNA sequences, the ribosome often stalls at certain codons because it is hard to translate. Consecutive proline codons are such examples that induce ribosome stalling and elongation factor P (EF-P) is required for the stalled ribosome to continue translation at those consecutive proline codons. We found that EF-P is required for translation of the mgtB gene encoding a Mg2+ transporter in the mgtCBR virulence operon from the intracellular pathogen Salmonella enterica serovar Typhimurium. Salmonella lacking EF-P decreases MgtB protein levels in a manner dependent on consecutive proline codons located in the mgtB coding region despite increasing transcription of the mgtCBR operon via the mgtP open reading frame in the leader RNA, resulting in an altered ratio between MgtC and MgtB proteins within the operon. Substitution of the consecutive proline codons to alanine codons eliminates EF-P-mediated control of the mgtB gene during infection and thus contributes to Salmonella's survival inside macrophages where Salmonella experiences low levels of EF-P. This suggests that this pathogen utilizes a strategy to coordinate expression of virulence genes by an evolutionarily conserved translation factor.
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Affiliation(s)
- Eunna Choi
- Department of Genetic Engineering and Graduate School of Biotechnology, College of Life Sciences, Kyung Hee University, Yongin 17104, South Korea
| | - Soomin Choi
- Department of Genetic Engineering and Graduate School of Biotechnology, College of Life Sciences, Kyung Hee University, Yongin 17104, South Korea
| | - Daesil Nam
- Division of Microbiology, Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 16419, South Korea
| | - Shinae Park
- Department of Molecular Bioscience, College of Biomedical Science, Kangwon National University, Chuncheon 24341, South Korea
| | - Yoontak Han
- Department of Genetic Engineering and Graduate School of Biotechnology, College of Life Sciences, Kyung Hee University, Yongin 17104, South Korea
| | - Jung-Shin Lee
- Department of Molecular Bioscience, College of Biomedical Science, Kangwon National University, Chuncheon 24341, South Korea
| | - Eun-Jin Lee
- Department of Genetic Engineering and Graduate School of Biotechnology, College of Life Sciences, Kyung Hee University, Yongin 17104, South Korea
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6
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Genetic Determinants of Salmonella enterica Serovar Typhimurium Proliferation in the Cytosol of Epithelial Cells. Infect Immun 2016; 84:3517-3526. [PMID: 27698022 DOI: 10.1128/iai.00734-16] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Accepted: 09/26/2016] [Indexed: 11/20/2022] Open
Abstract
Intestinal epithelial cells provide an important colonization niche for Salmonella enterica serovar Typhimurium during gastrointestinal infections. In infected epithelial cells, a subpopulation of S Typhimurium bacteria damage their internalization vacuole, leading to escape from the Salmonella-containing vacuole (SCV) and extensive proliferation in the cytosol. Little is known about the bacterial determinants of nascent SCV lysis and subsequent survival and replication of Salmonella in the cytosol. To pinpoint S Typhimurium virulence factors responsible for these steps in the intracellular infectious cycle, we screened a S Typhimurium multigene deletion library in Caco-2 C2Bbe1 and HeLa epithelial cells for mutants that had an altered proportion of cytosolic bacteria compared to the wild type. We used a gentamicin protection assay in combination with a chloroquine resistance assay to quantify total and cytosolic bacteria, respectively, for each strain. Mutants of three S Typhimurium genes, STM1461 (ydgT), STM2829 (recA), and STM3952 (corA), had reduced cytosolic proliferation compared to wild-type bacteria, and one gene, STM2120 (asmA), displayed increased cytosolic replication. None of the mutants were affected for lysis of the nascent SCV or vacuolar replication in epithelial cells, indicating that these genes are specifically required for survival and proliferation of S Typhimurium in the epithelial cell cytosol. These are the first genes identified to contribute to this step of the S Typhimurium infectious cycle.
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7
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Pontes MH, Yeom J, Groisman EA. Reducing Ribosome Biosynthesis Promotes Translation during Low Mg 2+ Stress. Mol Cell 2016; 64:480-492. [PMID: 27746019 DOI: 10.1016/j.molcel.2016.05.008] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 03/31/2016] [Accepted: 05/05/2016] [Indexed: 12/30/2022]
Abstract
The synthesis of ribosomes is regulated by both amino acid abundance and the availability of ATP, which regenerates guanosine triphosphate (GTP), powers ribosomes, and promotes transcription of rRNA genes. We now report that bacteria supersede both of these controls when experiencing low cytosolic magnesium (Mg2+), a divalent cation essential for ribosome stabilization and for neutralization of ATP's negative charge. We uncover a regulatory circuit that responds to low cytosolic Mg2+ by promoting expression of proteins that import Mg2+ and lower ATP amounts. This response reduces the levels of ATP and ribosomes, making Mg2+ ions available for translation. Mutants defective in Mg2+ uptake and unable to reduce ATP levels accumulate non-functional ribosomal components and undergo translational arrest. Our findings establish a paradigm whereby cells reduce the amounts of translating ribosomes to carry out protein synthesis.
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Affiliation(s)
- Mauricio H Pontes
- Department of Microbial Pathogenesis, Yale School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA; Yale Microbial Sciences Institute, PO Box 27389, West Haven, CT 06516, USA
| | - Jinki Yeom
- Department of Microbial Pathogenesis, Yale School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA
| | - Eduardo A Groisman
- Department of Microbial Pathogenesis, Yale School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA; Yale Microbial Sciences Institute, PO Box 27389, West Haven, CT 06516, USA.
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8
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Jia S, Liu Y, Shi Y, Ma Y, Hu Y, Wang M, Li X. Elevation of Brain Magnesium Potentiates Neural Stem Cell Proliferation in the Hippocampus of Young and Aged Mice. J Cell Physiol 2016; 231:1903-12. [PMID: 26754806 DOI: 10.1002/jcp.25306] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 01/06/2016] [Indexed: 12/22/2022]
Abstract
In the adult brain, neural stem cells (NSCs) can self-renew and generate all neural lineage types, and they persist in the sub-granular zone (SGZ) of the hippocampus and the sub-ventricular zone (SVZ) of the cortex. Here, we show that dietary-supplemented - magnesium-L-threonate (MgT), a novel magnesium compound designed to elevate brain magnesium regulates the NSC pool in the adult hippocampus. We found that administration of both short- and long-term regimens of MgT, increased the number of hippocampal NSCs. We demonstrated that in young mice, dietary supplementation with MgT significantly enhanced NSC proliferation in the SGZ. Importantly, in aged mice that underwent long-term (12-month) supplementation with MgT, MgT did not deplete the hippocampal NSC reservoir but rather curtailed the age-associated decline in NSC proliferation. We further established an association between extracellular magnesium concentrations and NSC self-renewal in vitro by demonstrating that elevated Mg(2+) concentrations can maintain or increase the number of cultured hippocampal NSCs. Our study also suggests that key signaling pathways for cell growth and proliferation may be candidate targets for Mg(2+) 's effects on NSC self-renewal. J. Cell. Physiol. 231: 1903-1912, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Shanshan Jia
- Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
| | - Yunpeng Liu
- Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
| | - Yang Shi
- Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
| | - Yihe Ma
- Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
| | - Yixin Hu
- Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
| | - Meiyan Wang
- Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
| | - Xue Li
- Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
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9
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Kobayashi NI, Tanoi K. Critical Issues in the Study of Magnesium Transport Systems and Magnesium Deficiency Symptoms in Plants. Int J Mol Sci 2015; 16:23076-93. [PMID: 26404266 PMCID: PMC4613352 DOI: 10.3390/ijms160923076] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 08/27/2015] [Accepted: 09/06/2015] [Indexed: 12/16/2022] Open
Abstract
Magnesium (Mg) is the second most abundant cation in living cells. Over 300 enzymes are known to be Mg-dependent, and changes in the Mg concentration significantly affects the membrane potential. As Mg becomes deficient, starch accumulation and chlorosis, bridged by the generation of reactive oxygen species, are commonly found in Mg-deficient young mature leaves. These defects further cause the inhibition of photosynthesis and finally decrease the biomass. Recently, transcriptome analysis has indicated the transcriptinal downregulation of chlorophyll apparatus at the earlier stages of Mg deficiency, and also the potential involvement of complicated networks relating to hormonal signaling and circadian oscillation. However, the processes of the common symptoms as well as the networks between Mg deficiency and signaling are not yet fully understood. Here, for the purpose of defining the missing pieces, several problems are considered and explained by providing an introduction to recent reports on physiological and transcriptional responses to Mg deficiency. In addition, it has long been unclear whether the Mg deficiency response involves the modulation of Mg2+ transport system. In this review, the current status of research on Mg2+ transport and the relating transporters are also summarized. Especially, the rapid progress in physiological characterization of the plant MRS2 gene family as well as the fundamental investigation about the molecular mechanism of the action of bacterial CorA proteins are described.
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Affiliation(s)
- Natsuko I Kobayashi
- Graduate School of Agricultural and Life Sciences, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
| | - Keitaro Tanoi
- Graduate School of Agricultural and Life Sciences, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
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10
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Mao D, Chen J, Tian L, Liu Z, Yang L, Tang R, Li J, Lu C, Yang Y, Shi J, Chen L, Li D, Luan S. Arabidopsis Transporter MGT6 Mediates Magnesium Uptake and Is Required for Growth under Magnesium Limitation. THE PLANT CELL 2014; 26:2234-2248. [PMID: 24794135 PMCID: PMC4079380 DOI: 10.1105/tpc.114.124628] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Although magnesium (Mg2+) is the most abundant divalent cation in plant cells, little is known about the mechanism of Mg2+ uptake by plant roots. Here, we report a key function of Magnesium Transport6 (MGT6)/Mitochondrial RNA Splicing2-4 in Mg2+ uptake and low-Mg2+ tolerance in Arabidopsis thaliana. MGT6 is expressed mainly in plant aerial tissues when Mg2+ levels are high in the soil or growth medium. Its expression is highly induced in the roots during Mg2+ deficiency, suggesting a role for MGT6 in response to the low-Mg2+ status in roots. Silencing of MGT6 in transgenic plants by RNA interference (RNAi) resulted in growth retardation under the low-Mg2+ condition, and the phenotype was restored to normal growth after RNAi plants were transferred to Mg2+-sufficient medium. RNAi plants contained lower levels of Mg2+ compared with wild-type plants under low Mg2+ but not under Mg2+-sufficient conditions. Further analysis indicated that MGT6 was localized in the plasma membrane and played a key role in Mg2+ uptake by roots under Mg2+ limitation. We conclude that MGT6 mediates Mg2+ uptake in roots and is required for plant adaptation to a low-Mg2+ environment.
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Affiliation(s)
- Dandan Mao
- College of Life Sciences, Hunan Normal University, Changsha 410081, China Nanjing University-Nanjing Forestry University Joint Institute for Plant Molecular Biology, State Key Laboratory for Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Jian Chen
- College of Life Sciences, Hunan Normal University, Changsha 410081, China
| | - Lianfu Tian
- College of Life Sciences, Hunan Normal University, Changsha 410081, China
| | - Zhenhua Liu
- College of Life Sciences, Hunan Normal University, Changsha 410081, China
| | - Lei Yang
- Nanjing University-Nanjing Forestry University Joint Institute for Plant Molecular Biology, State Key Laboratory for Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Renjie Tang
- Department of Plant and Microbial Biology, University of California, Berkeley, California 94720
| | - Jian Li
- College of Life Sciences, Hunan Normal University, Changsha 410081, China
| | - Changqing Lu
- College of Life Sciences, Hunan Normal University, Changsha 410081, China
| | - Yonghua Yang
- Nanjing University-Nanjing Forestry University Joint Institute for Plant Molecular Biology, State Key Laboratory for Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Jisen Shi
- Nanjing University-Nanjing Forestry University Joint Institute for Plant Molecular Biology, MOF Key Laboratory of Forest Genetics and Biotechnology, Nanjing Forestry University, Nanjing 210037, China
| | - Liangbi Chen
- College of Life Sciences, Hunan Normal University, Changsha 410081, China
| | - Dongping Li
- College of Life Sciences, Hunan Normal University, Changsha 410081, China
| | - Sheng Luan
- Nanjing University-Nanjing Forestry University Joint Institute for Plant Molecular Biology, State Key Laboratory for Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China Department of Plant and Microbial Biology, University of California, Berkeley, California 94720
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11
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Dalmas O, Sompornpisut P, Bezanilla F, Perozo E. Molecular mechanism of Mg2+-dependent gating in CorA. Nat Commun 2014; 5:3590. [PMID: 24694723 PMCID: PMC4066822 DOI: 10.1038/ncomms4590] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Accepted: 03/07/2014] [Indexed: 11/09/2022] Open
Abstract
CorA is the major transport system responsible for Mg2+ uptake in bacteria and can functionally substitute for its homologue Mrs2p in the yeast inner mitochondrial membrane. Although several CorA crystal structures are available, the molecular mechanism of Mg2+ uptake remains to be established. Here we use EPR spectroscopy, electrophysiology and molecular dynamic simulations to show that CorA is regulated by cytoplasmic Mg2+ acting as a ligand and elucidate the basic conformational rearrangements responsible for Mg2+-dependent gating. Mg2+ unbinding at the divalent cation sensor triggers a conformational change that leads to the inward motion of the stalk helix, which propagates to the pore forming transmembrane helix TM1. Helical tilting and rotation in TM1 generates an iris-like motion that increases the diameter of the permeation pathway, triggering ion conduction. This work establishes the molecular basis of a Mg2+-driven negative feedback loop in CorA as the key physiological event controlling Mg2+ uptake and homeostasis in prokaryotes.
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Affiliation(s)
- Olivier Dalmas
- Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, The University of Chicago, 929 E. 57th Street, Chicago, Illinois 60637, USA
| | - Pornthep Sompornpisut
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
| | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, The University of Chicago, 929 E. 57th Street, Chicago, Illinois 60637, USA
| | - Eduardo Perozo
- Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, The University of Chicago, 929 E. 57th Street, Chicago, Illinois 60637, USA
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12
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Kato A, Chen HD, Latifi T, Groisman EA. Reciprocal control between a bacterium's regulatory system and the modification status of its lipopolysaccharide. Mol Cell 2012; 47:897-908. [PMID: 22921935 DOI: 10.1016/j.molcel.2012.07.017] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2011] [Revised: 06/18/2012] [Accepted: 07/14/2012] [Indexed: 01/29/2023]
Abstract
Gram-negative bacteria often modify their lipopolysaccharide (LPS), thereby increasing resistance to antimicrobial agents and avoidance of the host immune system. However, it is unclear how bacteria adjust the levels and activities of LPS-modifying enzymes in response to the modification status of their LPS. We now address this question by investigating the major regulator of LPS modifications in Salmonella enterica. We report that the PmrA/PmrB system controls expression of a membrane peptide that inhibits the activity of LpxT, an enzyme responsible for increasing the LPS negative charge. LpxT's inhibition and the PmrA-dependent incorporation of positively charged L-4-aminoarabinose into the LPS decrease Fe(3+) binding to the bacterial cell. Because Fe(3+) is an activating ligand for the sensor PmrB, transcription of PmrA-dependent LPS-modifying genes is reduced. This mechanism enables bacteria to sense their cell surface by its effect on the availability of an inducing signal for the system regulating cell-surface modifications.
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Affiliation(s)
- Akinori Kato
- Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, MO 63110, USA
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13
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Rinnenthal J, Klinkert B, Narberhaus F, Schwalbe H. Modulation of the stability of the Salmonella fourU-type RNA thermometer. Nucleic Acids Res 2011; 39:8258-70. [PMID: 21727085 PMCID: PMC3185406 DOI: 10.1093/nar/gkr314] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2011] [Revised: 04/19/2011] [Accepted: 04/19/2011] [Indexed: 11/15/2022] Open
Abstract
RNA thermometers are translational control elements that regulate the expression of bacterial heat shock and virulence genes. They fold into complex secondary structures that block translation at low temperatures. A temperature increase releases the ribosome binding site and thus permits translation initiation. In fourU-type RNA thermometers, the AGGA sequence of the SD region is paired with four consecutive uridines. We investigated the melting points of the wild-type and mutant sequences. It was decreased by 5°C when a stabilizing GC basepair was exchanged by an AU pair or increased by 11°C when an internal AG mismatch was converted to a GC pair, respectively. Stabilized or destabilized RNA structures are directly correlated with decreased or increased in vivo gene expression, respectively. Mg(2+) also affected the melting point of the fourU thermometer. Variations of the Mg(2+) concentration in the physiological range between 1 and 2 mM translated into a 2.8°C shift of the melting point. Thus, Mg(2+) binding to the hairpin RNA is regulatory relevant. Applying three different NMR techniques, two Mg(2+) binding sites were found in the hairpin structure. One of these binding sites could be identified as outer sphere binding site that is located within the fourU motif. Binding of the two Mg(2+) ions exhibits a positive cooperativity with a Hill coefficient of 1.47. Free energy values ΔG for Mg(2+) binding determined by NMR are in agreement with data determined from CD measurements.
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Affiliation(s)
- Jörg Rinnenthal
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance, Johann Wolfgang Goethe-University, Max-von-Laue-Strasse 7, D-60438 Frankfurt/Main and Microbial Biology, Ruhr-Universität Bochum, Universitätsstrasse 150, NDEF06/783, 44780 Bochum, Germany
| | - Birgit Klinkert
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance, Johann Wolfgang Goethe-University, Max-von-Laue-Strasse 7, D-60438 Frankfurt/Main and Microbial Biology, Ruhr-Universität Bochum, Universitätsstrasse 150, NDEF06/783, 44780 Bochum, Germany
| | - Franz Narberhaus
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance, Johann Wolfgang Goethe-University, Max-von-Laue-Strasse 7, D-60438 Frankfurt/Main and Microbial Biology, Ruhr-Universität Bochum, Universitätsstrasse 150, NDEF06/783, 44780 Bochum, Germany
| | - Harald Schwalbe
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance, Johann Wolfgang Goethe-University, Max-von-Laue-Strasse 7, D-60438 Frankfurt/Main and Microbial Biology, Ruhr-Universität Bochum, Universitätsstrasse 150, NDEF06/783, 44780 Bochum, Germany
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14
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Gan SW, Vararattanavech A, Nordin N, Eshaghi S, Torres J. A cost-effective method for simultaneous homo-oligomeric size determination and monodispersity conditions for membrane proteins. Anal Biochem 2011; 416:100-6. [PMID: 21624344 DOI: 10.1016/j.ab.2011.05.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Revised: 04/29/2011] [Accepted: 05/04/2011] [Indexed: 10/18/2022]
Abstract
The use of blue native polyacrylamide gel electrophoresis (BN-PAGE) has been reported in the literature to retain both water-soluble and membrane protein complexes in their native hetero-oligomeric state and to determine the molecular weight of membrane proteins. However, membrane proteins show abnormal mobility when compared with water-soluble markers. Although one could use membrane proteins as markers or apply a conversion factor to the observed molecular weight to account for the bound Coomassie blue dye, when one just wants to assess homo-oligomeric size, these methods appear to be too time-consuming or might not be generally applicable. Here, during detergent screening studies to identify the best detergent for achieving a monodisperse sample, we observed that under certain conditions membrane proteins tend to form ladders of increasing oligomeric size. Although the ladders themselves contain no indication of which band represents the correct oligomeric size, they provide a scale that can be compared with a single band, representing the native homo-oligomeric size, obtained in other conditions of the screen. We show that this approach works for three membrane proteins: CorA (42 kDa), aquaporin Z (25 kDa), and small hydrophobic (SH) protein from respiratory syncytial virus (8 kDa). In addition, polydispersity results and identification of the most suitable detergent correlate optimally not only with size exclusion chromatography (SEC) but also with results from sedimentation velocity and equilibrium experiments. Because it involves minute quantities of sample and detergent, this method can be used in high-throughput approaches as a low-cost technique.
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Affiliation(s)
- Siok Wan Gan
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
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15
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Chen J, Li LG, Liu ZH, Yuan YJ, Guo LL, Mao DD, Tian LF, Chen LB, Luan S, Li DP. Magnesium transporter AtMGT9 is essential for pollen development in Arabidopsis. Cell Res 2009; 19:887-98. [PMID: 19436262 DOI: 10.1038/cr.2009.58] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Magnesium (Mg(2+)) is abundant in plant cells and plays a critical role in many physiological processes. A 10-member gene family AtMGT (also known as AtMRS2) was identified in Arabidopsis, which belongs to a eukaryote subset of the CorA superfamily, functioning as Mg(2+) transporters. Some family members (AtMGT1 and AtMGT10) function as high-affinity Mg(2+) transporter and could complement bacterial mutant or yeast mutant lacking Mg(2+) transport capability. Here we report an AtMGT family member, AtMGT9, that functions as a low-affinity Mg(2+) transporter, and is essential for pollen development. The functional complementation assay in Salmonella mutant strain MM281 showed that AtMGT9 is capable of mediating Mg(2+) uptake in the sub-millimolar range of Mg(2+). The AtMGT9 gene was expressed most strongly in mature anthers and was also detectable in vascular tissues of the leaves, and in young roots. Disruption of AtMGT9 gene expression resulted in abortion of half of the mature pollen grains in heterozygous mutant +/mgt9, and no homozygous mutant plant was obtained in the progeny of selfed +/mgt9 plants. Transgenic plants expressing AtMGT9 in these heterozygous plants can recover the pollen phenotype to the wild type. In addition, AtMGT9 RNAi transgenic plants also showed similar abortive pollen phenotype to mutant +/mgt9. Together, our results demonstrate that AtMGT9 functions as a low-affinity Mg(2+) transporter that plays a crucial role in male gametophyte development and male fertility.
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Affiliation(s)
- Jian Chen
- College of Life Science, Hunan Normal University, Changsha, China
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16
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Abstract
Considering the biological abundance and importance of Mg2+, there is a surprising lack of information regarding the proteins that transport Mg2+, the mechanisms by which they do so, and their physiological roles within the cell. The best characterized Mg2+ channel to date is the bacterial protein CorA, present in a wide range of bacterial species. The CorA homolog Mrs2 forms the mitochondrial Mg2+ channel in all eukaryotes. Physiologically, CorA is involved in bacterial pathogenesis, and the Mrs2 eukaryotic homolog is essential for cell survival. A second Mg2+ channel widespread in bacteria is MgtE. Its eukaryotic homologs are the SLC41 family of carriers. Physiological roles for MgtE and its homologs have not been established. Recently, the crystal structures for the bacterial CorA and MgtE Mg2+ channels were solved, the first structures of any divalent cation channel. As befits the unique biological chemistry of Mg2+, both structures are unique, unlike that of any other channel or transporter. Although structurally quite different, both CorA and MgtE appear to be gated in a similar manner through multiple Mg2+ binding sites in the cytosolic domain of the channels. These sites essentially serve as Mg2+ "sensors" of cytosolic Mg2+ concentration. Many questions about these channels remain, however, including the molecular basis of Mg2+ selectivity and the physiological role(s) of their eukaryotic homologs.
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Affiliation(s)
- Andrea S Moomaw
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
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17
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The CorA Mg2+ channel is required for the virulence of Salmonella enterica serovar typhimurium. J Bacteriol 2008; 190:6517-23. [PMID: 18676664 DOI: 10.1128/jb.00772-08] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
CorA is the primary Mg(2+) channel in Salmonella enterica serovar Typhimurium. A corA mutant is attenuated in mice and defective for invasion of and replication within epithelial cells. Microarray studies show that several virulence effectors are repressed in a corA mutant strain, which ultimately manifests itself as a decrease in virulence.
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18
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Günzel D, Kucharski LM, Kehres DG, Romero MF, Maguire ME. The MgtC virulence factor of Salmonella enterica serovar Typhimurium activates Na(+),K(+)-ATPase. J Bacteriol 2006; 188:5586-94. [PMID: 16855249 PMCID: PMC1540036 DOI: 10.1128/jb.00296-06] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mgtC gene of Salmonella enterica serovar Typhimurium encodes a membrane protein of unknown function that is important for full virulence in the mouse. Since mgtC is part of an operon with mgtB which encodes a Mg(2+)-transporting P-type ATPase, MgtC was hypothesized to function in ion transport, possibly in Mg(2+) transport. Consequently, MgtC was expressed in Xenopus laevis oocytes, and its effect on ion transport was evaluated using ion selective electrodes. Oocytes expressing MgtC did not exhibit altered currents or membrane potentials in response to changes in extracellular H(+), Mg(2+), or Ca(2+), thus ruling out a previously postulated function as a Mg(2+)/H(+) antiporter. However, addition of extracellular K(+) markedly hyperpolarized membrane potential instead of the expected depolarization. Addition of ouabain to block the oocyte Na(+),K(+)-ATPase completely prevented hyperpolarization and restored the normal K(+)-induced depolarization response. These results suggested that the Na(+),K(+)-ATPase was constitutively activated in the presence of MgtC resulting in a membrane potential largely dependent on Na(+),K(+)-ATPase. Consistent with the involvement of Na(+),K(+)-ATPase, oocytes expressing MgtC exhibited an increased rate of (86)Rb(+) uptake and had increased intracellular free [K(+)] and decreased free [Na(+)] and ATP. The free concentrations of Mg(2+) and Ca(2+) and cytosolic pH were unchanged, although the total intracellular Ca(2+) content was slightly elevated. These results suggest that the serovar Typhimurium MgtC protein may be involved in regulating membrane potential but does not directly transport Mg(2+) or another ion.
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Affiliation(s)
- Dorothee Günzel
- Institut für klinische Physiologie, Charité-Universitätsmedizin Berlin, D-12200 Berlin, Germany
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19
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The MgtC virulence factor of Salmonella enterica serovar Typhimurium activates Na(+),K(+)-ATPase. J Bacteriol 2006. [PMID: 16855249 DOI: 10.1128/jb.00296-06/format/epub] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The mgtC gene of Salmonella enterica serovar Typhimurium encodes a membrane protein of unknown function that is important for full virulence in the mouse. Since mgtC is part of an operon with mgtB which encodes a Mg(2+)-transporting P-type ATPase, MgtC was hypothesized to function in ion transport, possibly in Mg(2+) transport. Consequently, MgtC was expressed in Xenopus laevis oocytes, and its effect on ion transport was evaluated using ion selective electrodes. Oocytes expressing MgtC did not exhibit altered currents or membrane potentials in response to changes in extracellular H(+), Mg(2+), or Ca(2+), thus ruling out a previously postulated function as a Mg(2+)/H(+) antiporter. However, addition of extracellular K(+) markedly hyperpolarized membrane potential instead of the expected depolarization. Addition of ouabain to block the oocyte Na(+),K(+)-ATPase completely prevented hyperpolarization and restored the normal K(+)-induced depolarization response. These results suggested that the Na(+),K(+)-ATPase was constitutively activated in the presence of MgtC resulting in a membrane potential largely dependent on Na(+),K(+)-ATPase. Consistent with the involvement of Na(+),K(+)-ATPase, oocytes expressing MgtC exhibited an increased rate of (86)Rb(+) uptake and had increased intracellular free [K(+)] and decreased free [Na(+)] and ATP. The free concentrations of Mg(2+) and Ca(2+) and cytosolic pH were unchanged, although the total intracellular Ca(2+) content was slightly elevated. These results suggest that the serovar Typhimurium MgtC protein may be involved in regulating membrane potential but does not directly transport Mg(2+) or another ion.
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20
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Papp KM, Maguire ME. The CorA Mg2+ transporter does not transport Fe2+. J Bacteriol 2004; 186:7653-8. [PMID: 15516579 PMCID: PMC524906 DOI: 10.1128/jb.186.22.7653-7658.2004] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2004] [Accepted: 08/13/2004] [Indexed: 11/20/2022] Open
Abstract
corA encodes the constitutively expressed primary Mg2+ uptake system of most eubacteria and many archaea. Recently, a mutation in corA was reported to make Salmonella enterica serovar Typhimurium markedly resistant to Fe2+-mediated toxicity. Mechanistically, this was hypothesized to be from an ability of CorA to mediate the influx of Fe2+. Consequently, we directly examined Fe2+ transport and toxicity in wild-type versus corA cells. As determined by direct transport assay, CorA cannot transport Fe2+ and Fe2+ does not potently inhibit CorA transport of 63Ni2+. Mg2+ can, relatively weakly, inhibit Fe2+ uptake, but inhibition is not dependent on the presence of a functional corA allele. Although excess Fe2+ was slightly toxic to S. enterica serovar Typhimurium, we were unable to elicit a significant differential sensitivity in a wild-type versus a corA strain. We conclude that CorA does not transport Fe2+ and that the relationship, if any, between iron toxicity and corA is indirect.
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Affiliation(s)
- Krisztina M Papp
- Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4965, USA
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21
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Abstract
It is difficult to over-state the importance of Zn(II) in biology. It is a ubiquitous essential metal ion and plays a role in catalysis, protein structure and perhaps as a signal molecule, in organisms from all three kingdoms. Of necessity, organisms have evolved to optimise the intracellular availability of Zn(II) despite the extracellular milieu. To this end, prokaryotes contain a range of Zn(II) import, Zn(II) export and/or binding proteins, some of which utilise either ATP or the chemiosmotic potential to drive the movement of Zn(II) across the cytosolic membrane, together with proteins that facilitate the diffusion of this ion across either the outer or inner membranes of prokaryotes. This review seeks to give an overview of the systems currently classified as altering Zn(II) availability in prokaryotes.
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Affiliation(s)
- Dayle K Blencowe
- Cardiff School of Biosciences (2), Cardiff University, Museum Avenue, P.O. Box 911, Cardiff CF10 3US, Wales, UK
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22
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Affiliation(s)
- Huguette C Politi
- Department of Pharmacology and Physiology, Drexel University College of Medicine, 245 N 15th Street, Philadelphia, PA 19102, USA
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23
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Szegedy MA, Maguire ME. The CorA Mg(2+) transport protein of Salmonella typhimurium. Mutagenesis of conserved residues in the second membrane domain. J Biol Chem 1999; 274:36973-9. [PMID: 10601252 DOI: 10.1074/jbc.274.52.36973] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Salmonella typhimurium CorA is the archetypal member of the largest family of Mg(2+) transporters of the Bacteria and Archaea. It contains three transmembrane segments. There are no conserved charged residues within these segments indicating electrostatic interactions are not used in Mg(2+) transport through CorA. Previous mutagenesis studies of CorA revealed a single face of the third transmembrane segment that is important for Mg(2+) transport. In this study, we mutated hydroxyl-bearing and other conserved residues in the second transmembrane segment to identify residues involved in transport. Residues Ser(260), Thr(270), and Ser(274) appear to be important for transport and are oriented such that they would also line a face of an alpha-helix. In addition, the sequence (276)YGMNF(280), found in virtually all CorA homologues, is critical for CorA function because even conservative mutations are not tolerated at these residues. Finally, mutations of residues in the second transmembrane segment, unlike those in the third transmembrane segment, revealed cooperative behavior for the influx of Mg(2+). We conclude that the second transmembrane segment forms a major part of the Mg(2+) pore with the third transmembrane segment of CorA.
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Affiliation(s)
- M A Szegedy
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106-4965, USA.
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24
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Zemsky J, Rusinova E, Nemerson Y, Luck LA, Ross JA. Probing local environments of tryptophan residues in proteins: Comparison of19F nuclear magnetic resonance results with the intrinsic fluorescence of soluble human tissue factor. Proteins 1999. [DOI: 10.1002/(sici)1097-0134(19991201)37:4<709::aid-prot19>3.0.co;2-v] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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25
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Abstract
The cooCTJ gene products are coexpressed with CO-dehydrogenase (CODH) and facilitate in vivo nickel insertion into CODH. A Ni(2+) transport assay was used to monitor uptake and accumulation of (63)Ni(2+) into R. rubrum and to observe the effect of mutations in the cooC, cooT, and cooJ genes on (63)Ni(2+) transport and accumulation. Cells grown either in the presence or absence of CO transported Ni(2+) with a K(m) of 19 +/- 4 microM and a V(max) of 310 +/- 22 pmol of Ni/min/mg of total protein. Insertional mutations disrupting the reading frame of the cooCTJ genes, either individually or all three genes simultaneously, transported Ni(2+) the same as wild-type cells. The nickel specificity for transport was tested by conducting the transport assay in the presence of other divalent metal ions. At a 17-fold excess Mn(2+), Mg(2+), Ca(2+), and Zn(2+) showed no inhibition of (63)Ni(2+) transport but Co(2+), Cd(2+), and Cu(2+) inhibited transport 35, 58, and 66%, respectively. Nickel transport was inhibited by cold (50% at 4 degrees C), by protonophores (carbonyl cyanide m-chlorophenylhydrazone, 44%, and 2,4-dinitrophenol, 26%), by sodium azide (25%), and hydroxyl amine (33%). Inhibitors of ATP synthase (N, N'-dicyclohexylcarbodiimide and oligomycin) and incubation of cells in the dark stimulated Ni(2+) transport. (63)Ni accumulation after 2 h was four times greater in CO-induced cells than in cells not exposed to CO. The CO-stimulated (63)Ni(2+) accumulation coincided with the appearance of CODH activity in the culture, suggesting that the (63)Ni(2+) was accumulating in CODH. The cooC, cooT, and cooJ genes are required for the increased (63)Ni(2+) accumulation observed upon CO exposure because cells containing mutations disrupting any or all of these genes accumulated (63)Ni(2+) like cells unexposed to CO.
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Affiliation(s)
- R K Watt
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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26
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The magnesium transport ATPases of Salmonella typhimurium. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s1874-5342(06)80011-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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27
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Abstract
We present edition VIII of the genetic map of Salmonella typhimurium LT2. We list a total of 1,159 genes, 1,080 of which have been located on the circular chromosome and 29 of which are on pSLT, the 90-kb plasmid usually found in LT2 lines. The remaining 50 genes are not yet mapped. The coordinate system used in this edition is neither minutes of transfer time in conjugation crosses nor units representing "phage lengths" of DNA of the transducing phage P22, as used in earlier editions, but centisomes and kilobases based on physical analysis of the lengths of DNA segments between genes. Some of these lengths have been determined by digestion of DNA by rare-cutting endonucleases and separation of fragments by pulsed-field gel electrophoresis. Other lengths have been determined by analysis of DNA sequences in GenBank. We have constructed StySeq1, which incorporates all Salmonella DNA sequence data known to us. StySeq1 comprises over 548 kb of nonredundant chromosomal genomic sequences, representing 11.4% of the chromosome, which is estimated to be just over 4,800 kb in length. Most of these sequences were assigned locations on the chromosome, in some cases by analogy with mapped Escherichia coli sequences.
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Affiliation(s)
- K E Sanderson
- Department of Biological Sciences, University of Calgary, Alberta, Canada
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28
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Tao T, Snavely MD, Farr SG, Maguire ME. Magnesium transport in Salmonella typhimurium: mgtA encodes a P-type ATPase and is regulated by Mg2+ in a manner similar to that of the mgtB P-type ATPase. J Bacteriol 1995; 177:2654-62. [PMID: 7751273 PMCID: PMC176934 DOI: 10.1128/jb.177.10.2654-2662.1995] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Salmonella typhimurium has three distinct Mg2+ transport systems: CorA, MgtA, and MgtB, each encoded by its respective gene. corA and mgtB have been previously sequenced and characterized. This report details the sequence and properties of mgtA. Like mgtB, mgtA encodes a P-type ATPase. The mgtA gene encodes a slightly smaller protein than does mgtB, with a predicted molecular mass of about 95 kDa, running at 91 kDa on protein gels, which compares with values of 101 and 102 kDa, respectively, for the MgtB protein. The deduced amino acid sequence of MgtA is only 50% identical to that of MgtB, with a further 25% conservative amino acid substitutions, surprisingly low for such otherwise functionally similar proteins from the same organism. Codon usage for each gene is normal for S. typhimurium, however, indicating that neither gene is the result of a recent acquisition from another organism. A single open reading frame at mgtA encodes MgtA, in contrast to mgtB, which is shown to be an operon encoding (5' to 3') the 22.5-kDa MgtC and the MgtB proteins. Genetic constructs were used to show that deletion of MgtC does not alter the expression or transport properties of MgtB, making the role of the companion MgtC protein unclear. (The S. typhimurium homolog of treR, which encodes a putative repressor for trehalose uptake, is encoded by a gene adjacent to mgtA, and its sequence is also reported. Finally, exteremely strong Mg(2+) regulation of the mgtA and mgtB promoters but not of the corA or treR promoters was demonstrated by cloning the appropriate DNA sequences with luxAB and measuring enhancement of light production as a function of extracellular Mg(2+) concentration. Lowering the extracellular Mg(2+) concentration from 10 mM to 1 or 10 microM elicited a transcriptional response of several thousandfold from both the mgtA and mgtB promoters.
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Affiliation(s)
- T Tao
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, USA
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29
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Abstract
Magnesium is unique among biological cations. Its volume change from hydrated cation to atomic ion is over an order of magnitude larger than that of any other biological cation. This volume change presents particular problems for a magnesium transport system and suggests that these systems may be significantly different from other classes of ion transport systems. Detailed study of Mg2+ transport in complex organisms is limited by severe technical problems. However, molecular genetic techniques have enabled the isolation of three Mg2+ transport systems from the Gram-negative bacterium Salmonella typhimurium. The MgtA and MgtB transport systems are members of the P-type ATPase superfamily of transporters but possess unique characteristics among members of this family. The CorA transport protein is the first member of an entirely new class of transport proteins. In addition, another completely new family of Mg2+ transport proteins have been identified that is present in both Gram-negative and Gram-positive bacteria. Characterization of these transporters should provide substantial insight into Mg2+ transport and cellular Mg2+ homeostasis.
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Affiliation(s)
- S K Roof
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4965
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30
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Maruyama T, Masuda N, Kakinuma Y, Igarashi K. Polyamine-sensitive magnesium transport in Saccharomyces cerevisiae. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1194:289-95. [PMID: 7918542 DOI: 10.1016/0005-2736(94)90311-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
In Saccharomyces cerevisiae we found a toxic effect of polyamines, well-known metabolites important for cell proliferation; in magnesium-limited (50 microM Mg2+) synthetic medium, cell growth was severely inhibited by spermine, spermidine and putrescine in descending order. In conjunction with a decrease in the growth rate by the addition of 0.5 mM spermine, the internal Mg2+ content decreased and the spermine content increased. When cell growth ceased, the Mg2+ content had finally decreased to about 40% of the value before the addition of spermine (120-130 nmol/mg dry weight), and the spermine content concomitantly increased 30-fold (from 1 to 30 nmol/mg dry weight); spermine4+ apparently took the internal place of Mg2+ with a probable stoichiometry of 1:2. However, the total amount of Mg2+ retained in the cells remained constant even with the addition of spermine, suggesting that spermine blocks Mg2+ accumulation. In high (2 mM) Mg2+ medium, cell growth was hardly affected by polyamines, and an exchange of spermine and Mg2+ was minimal. Energy-dependent Mg2+ uptake by whole cells was inhibited by spermine, spermidine and putrescine in a similar manner as the growth rates. On the other hand, Mg2+ inhibited spermine uptake. These results suggest that competition takes place between extracellular spermine and Mg2+ for their accumulations. It is thus clear that polyamine-sensitive Mg2+ transport system is indispensable for the physiology of this organism.
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Affiliation(s)
- T Maruyama
- Faculty of Pharmaceutical Sciences, Chiba University, Japan
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31
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Abstract
This review highlights the important roles played by magnesium in the growth and metabolic functions of microbial and animal cells, and therefore assigns a key role for magnesium ions in biotechnology. The fundamental biochemical and physiological actions of magnesium as a regulatory cation are outlined. Such actions are deemed to be relevant in an applied sense, because Mg2+ availability in cell culture and fermentation media can dramatically influence growth and metabolism of cells. Manipulation of extracellular and intracellular magnesium ions can thus be envisaged as a relatively simplistic, but nevertheless versatile, means of physiological cell engineering. In addition, biological antagonism between calcium and magnesium at the molecular level may have profound consequences for the optimization of biotechnological processes that exploit cells. In fermentation, for example, it is argued that the efficiency of microbial conversion of substrate to product may be improved by altering Mg:Ca concentration ratios in industrial feedstocks in a way that makes more magnesium available to the cells. With particular respect to yeast-based biotechnologies, magnesium availability is seen as being crucially important in governing central pathways of carbohydrate catabolism, especially ethanolic fermentation. It is proposed that such influences of magnesium ions are expressed at the combined levels of key enzyme activation and cell membrane stabilization. The former ensures optimum flow of substrate to ethanol and the latter acts to protect yeasts from physical and chemical stress.
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Affiliation(s)
- G M Walker
- Department of Molecular and Life Sciences, University of Abertay Dundee, Scotland
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32
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Maguire ME, Snavely MD, Leizman JB, Gura S, Bagga D, Tao T, Smith DL. Mg2+ transporting P-type ATPases of Salmonella typhimurium. Wrong way, wrong place enzymes. Ann N Y Acad Sci 1992; 671:244-55; discussion 255-6. [PMID: 1288323 DOI: 10.1111/j.1749-6632.1992.tb43800.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- M E Maguire
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
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Abstract
The gram-negative bacterium Salmonella typhimurium possesses three distinct Mg2+ transport systems, encoded by the corA, mgtA, and mgtB loci. The CorA transport system is the constitutive Mg2+ influx system. It can also mediate Mg2+ efflux at very high extracellular Mg2+ concentrations. In contrast, the MgtA and MgtB Mg2+ transport systems are normally expressed only at low extracellular Mg2+ concentrations. A strain of S. typhimurium was constructed by mutagenesis which lacks Mg2+ transport and requires 100 mM Mg2+ for growth. Using this strain, both the MgtA and MgtB transport systems were cloned by complementation of the strains inability to grow without Mg2+ supplementation. After sequencing and further genetic analysis, the MgtB system appears to be an operon composed of the mgtC and mgtB genes (5' to 3'). The downstream mgtB gene encodes the 102 kDa MgtB protein which by sequence analysis is clearly a P-type ATPase. Interestingly, while MgtB has relatively poor homology to other known prokaryotic P-type ATPases, it is highly homologous to mammalian reticular Ca(2+)-ATPases. MgtC is a 22.5 kDa hydrophobic membrane protein that lacks homology to any known protein. Transposon insertions in this gene abolish uptake by the MgtB transport system. We hypothesize that MgtC is a subunit of the MgtB ATPase involved either in proper insertion of MgtB into the membrane or possibly in binding of extracellular Mg2+ for delivery to the ATPase subunit. The sequence of the MgtA gene has recently been completed, and it too is a P-type ATPase more similar to eukaryotic than prokaryotic P-type ATPases. Expression of both MgtA and MgtB are highly regulated by the concentration of extracellular Mg2+. Transcription of mgtB can be increased about 1000 fold by lowering Mg2+ from 1 mM to 1 microM. Likewise, when mgtB is expressed from a multicopy plasmid, a similar decrease in extracellular Mg2+ greatly increases transport. Under growth conditions of limiting Mg2+, MgtB becomes the dominant Mg2+ influx system in S. typhimurium. Even so, since MgtB (and MgtA) mediate only influx of Mg2+, it is unclear why the cell requires energy from ATP to mediate Mg2+ entry into the cell down a large electrochemical gradient. Further studies of the structure-function and energetics of these novel Mg2+ influx P-type ATPases should yield insights into the function of P-type ATPases in general as well as information about the regulation of cellular Mg2+ fluxes.
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Affiliation(s)
- M E Maguire
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
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Silver S, Walderhaug M. Gene regulation of plasmid- and chromosome-determined inorganic ion transport in bacteria. Microbiol Rev 1992; 56:195-228. [PMID: 1579110 PMCID: PMC372861 DOI: 10.1128/mr.56.1.195-228.1992] [Citation(s) in RCA: 165] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Regulation of chromosomally determined nutrient cation and anion uptake systems shows important similarities to regulation of plasmid-determined toxic ion resistance systems that mediate the outward transport of deleterious ions. Chromosomally determined transport systems result in accumulation of K+, Mg2+, Fe3+, Mn2+, PO4(3-), SO4(2-), and additional trace nutrients, while bacterial plasmids harbor highly specific resistance systems for AsO2-, AsO4(3-), CrO4(2-), Cd2+, Co2+, Cu2+, Hg2+, Ni2+, SbO2-, TeO3(2-), Zn2+, and other toxic ions. To study the regulation of these systems, we need to define both the trans-acting regulatory proteins and the cis-acting target operator DNA regions for the proteins. The regulation of gene expression for K+ and PO4(3-) transport systems involves two-component sensor-effector pairs of proteins. The first protein responds to an extracellular ionic (or related) signal and then transmits the signal to an intracellular DNA-binding protein. Regulation of Fe3+ transport utilizes the single iron-binding and DNA-binding protein Fur. The MerR regulatory protein for mercury resistance both represses and activates transcription. The ArsR regulatory protein functions as a repressor for the arsenic and antimony(III) efflux system. Although the predicted cadR regulatory gene has not been identified, cadmium, lead, bismuth, zinc, and cobalt induce this system in a carefully regulated manner from a single mRNA start site. The cadA Cd2+ resistance determinant encodes an E1(1)-1E2-class efflux ATPase (consisting of two polypeptides, rather than the one earlier identified). Cadmium resistance is also conferred by the czc system (which confers resistances to zinc and cobalt in Alcaligenes species) via a complex efflux pump consisting of four polypeptides. These two cadmium efflux systems are not otherwise related. For chromate resistance, reduced cellular accumulation is again the resistance mechanism, but the regulatory components are not identified. For other toxic heavy metals (with few exceptions), there exist specific plasmid resistances that remain relatively terra incognita for future exploration of bioinorganic molecular genetics and gene regulation.
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Affiliation(s)
- S Silver
- Department of Microbiology and Immunology, University of Illinois College of Medicine, Chicago 60680
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Conlin CA, Miller CG. Cloning and nucleotide sequence of opdA, the gene encoding oligopeptidase A in Salmonella typhimurium. J Bacteriol 1992; 174:1631-40. [PMID: 1537805 PMCID: PMC206560 DOI: 10.1128/jb.174.5.1631-1640.1992] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The opdA gene (formerly called optA) of Salmonella typhimurium encodes a metallopeptidase, oligopeptidase A (OpdA), first recognized by its ability to cleave and allow utilization of N-acetyl-L-Ala4 (E. R. Vimr, L. Green, and C. G. Miller, J. Bacteriol. 153:1259-1265, 1983). Derivatives of pBR328 carrying the opdA gene were isolated and shown to express oligopeptidase activity at levels approximately 100-fold higher than that of the wild type. These plasmids complemented all of the phenotypes associated with opdA mutations (failure to use N-acetyl-L-Ala4, defective phage P22 development, and diminished endopeptidase activity). The opdA region of one of these plasmids (pCM127) was defined by insertions of Tn1000 (gamma delta), and these insertions were used as priming sites to determine the nucleotide sequence of a 2,843-bp segment of the insert DNA. This region contained an open reading frame coding for a 680-amino-acid protein, the N terminus of which agreed with that determined for purified OpdA. This open reading frame contained both a sequence motif typical of Zn2+ metalloproteases and a putative sigma 32 promoter. However, no induction was detected upon temperature shift by using a beta-galactosidase operon fusion. The predicted OpdA sequence showed similarity to dipeptidyl carboxypeptidase, the product of the S. typhimurium gene dcp, and to rat metallopeptidase EC 3.4.24.15., which is involved in peptide hormone processing.
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Affiliation(s)
- C A Conlin
- Department of Molecular Biology and Microbiology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
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Abstract
The divalent cations of cobalt, zinc, and nickel are essential nutrients for bacteria, required as trace elements at nanomolar concentrations. However, at micro- or millimolar concentrations, Co2+, Zn2+, and Ni2+ (and "bad ions" without nutritional roles such as Cd2+) are toxic. These cations are transported into the cell by constitutively expressed divalent cation uptake systems of broad specificity, i.e., basically Mg2+ transport systems. Therefore, in case of a heavy metal stress, uptake of the toxic ions cannot be reduced by a simple down-regulation of the transport activity. As a response to the resulting metal toxicity, metal resistance determinants evolved which are mostly plasmid-encoded in bacteria. In contrast to that of the cation Hg2+, chemical reduction of Co2+, Zn2+, Ni2+, and Cd2+ by the cell is not possible or sensible. Therefore, other than mutations limiting the ion range of the uptake system, only two basic mechanisms of resistance to these ions are possible (and were developed by evolution): intracellular complexation of the toxic metal ion is mainly used in eucaryotes; the cadmium-binding components are phytochelatins in plant and yeast cells and metallothioneins in animals, plants, and yeasts. In contrast, reduced accumulation based on an active efflux of the cation is the primary mechanism developed in procaryotes and perhaps in Saccharomyces cerevisiae. All bacterial cation efflux systems characterized to date are plasmid-encoded and inducible but differ in energy-coupling and in the number and types of proteins involved in metal transport and in regulation. In the gram-positive multiple-metal-resistant bacterium Staphylococcus aureus, Cd2+ (and probably Zn2+) efflux is catalyzed by the membrane-bound CadA protein, a P-type ATPase. However, a second protein (CadC) is required for full resistance and a third one (CadR) is hypothesized for regulation of the resistance determinant. The czc determinant from the gram-negative multiple-metal-resistant bacterium Alcaligenes eutrophus encodes proteins required for Co2+, Zn2+, and Cd2+ efflux (CzcA, CzcB, and CzcC) and regulation of the czc determinant (CzcD). In the current working model CzcA works as a cation-proton antiporter, CzcB as a cation-binding subunit, and CzcC as a modifier protein required to change the substrate specificity of the system from Zn2+ only to Co2+, Zn2+, and Cd2+.
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Affiliation(s)
- D H Nies
- Institut für Pflanzenphysiologie und Mikrobiologie, Freie Universität Berlin, Germany
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Ivey D, Guffanti A, Bossewitch J, Padan E, Krulwich T. Molecular cloning and sequencing of a gene from alkaliphilic Bacillus firmus OF4 that functionally complements an Escherichia coli strain carrying a deletion in the nhaA Na+/H+ antiporter gene. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54523-3] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Gibson MM, Bagga DA, Miller CG, Maguire ME. Magnesium transport in Salmonella typhimurium: the influence of new mutations conferring Co2+ resistance on the CorA Mg2+ transport system. Mol Microbiol 1991; 5:2753-62. [PMID: 1779764 DOI: 10.1111/j.1365-2958.1991.tb01984.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The CorA Mg2+ transport system of Salmonella typhimurium mediates both influx and efflux of Mg2+. Mutations at the corA locus (83.5 min) confer resistance to Co2+. Using transposon mutagenesis, three additional Co2+ resistance loci (corB, corC, and corD) were found and mapped to 55, 15, and 3min, respectively, on the S. typhimurium chromosome. No mutations corresponding to the reported corB locus at 95 min in Escherichia coli were obtained. The corB, corC, and corD mutations confer levels of Co2+ resistance intermediate between those of the wild-type and corA mutations. Isogenic strains were constructed containing combinations of transposon insertion mutations in each of the three Co(2+)-resistance loci to assess their influence on the CorA Mg2+ transport system. The Vmax and Km values for 28Mg2+ or for 57Co2+ and 63Ni2+ influx, analogues of Mg2+ transported by the CorA system, were changed less than twofold compared with the wild-type values, regardless of the mutation(s) present. However, while efflux of 28Mg2+ through the CorA system was decreased threefold in strains carrying one or two mutant alleles among corB, corC, or corD, efflux was completely abolished in either a corA or a corBCD strain. Thus, although the corA gene product is necessary and sufficient to mediate Mg2+ influx, Mg2+ efflux requires the presence of a wild-type allele of at least one of the corB, corC or corD loci.
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Affiliation(s)
- M M Gibson
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
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Snavely MD, Gravina SA, Cheung TT, Miller CG, Maguire ME. Magnesium transport in Salmonella typhimurium. Regulation of mgtA and mgtB expression. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(17)35247-x] [Citation(s) in RCA: 133] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Hmiel SP, Snavely MD, Florer JB, Maguire ME, Miller CG. Magnesium transport in Salmonella typhimurium: genetic characterization and cloning of three magnesium transport loci. J Bacteriol 1989; 171:4742-51. [PMID: 2548998 PMCID: PMC210275 DOI: 10.1128/jb.171.9.4742-4751.1989] [Citation(s) in RCA: 116] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Salmonella typhimurium strains lacking the CorA Mg2+ transport system retain Mg2+ transport and the ability to grow in medium containing a low concentration of Mg2+. Mutagenesis of a corA strain followed by ampicillin selection allowed isolation of a strain that required Mg2+-supplemented media for growth. This strain contained mutations in at least two loci in addition to corA, designated mgtA and mgtB (for magnesium transport). Strains with mutations at all three loci (corA, mgtA, and mgtB) exhibited no detectable Mg2+ uptake and required 10 mM Mg2+ in the medium for growth at the wild-type rate. A wild-type allele at any one of the three loci was sufficient to restore both Mg2+ transport and growth on 50 microM Mg2+. P22 transduction was used to map the mgt loci. The mgtA mutation was located to approximately 98 map units (cotransducible with pyrB), and mgtB mapped at about 80.5 map units (near gltC). A chromosomal library from S. typhimurium was screened for clones that complemented the Mg2+ requirement of a corA mgtA mgtB mutant. The three classes of plasmids obtained could each independently restore Mg2+ transport to this strain and corresponded to the corA, mgtA, and mgtB loci. Whereas the corA locus of S. typhimurium is analogous to the corA locus previously described for Escherichia coli, neither of the mgt loci described in this report appears analogous to the single mgt locus described in E. coli. Our data in this and the accompanying papers (M. D. Snavely, J. B. Florer, C. G. Miller, and M. E. Maguire, J. Bacteriol. 171:4752-4760, 4761-4766, 1989) indicate that the corA, mgtA, and mgtB loci of S. typhimurium represent three distinct systems that transport Mg2+.
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Affiliation(s)
- S P Hmiel
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
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Snavely MD, Florer JB, Miller CG, Maguire ME. Magnesium transport in Salmonella typhimurium: 28Mg2+ transport by the CorA, MgtA, and MgtB systems. J Bacteriol 1989; 171:4761-6. [PMID: 2670893 PMCID: PMC210277 DOI: 10.1128/jb.171.9.4761-4766.1989] [Citation(s) in RCA: 149] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Three loci in Salmonella typhimurium (corA, mgtA, and mgtB) code for components of distinct Mg2+ transport systems (S. P. Hmiel, M. D. Snavely, J. B. Florer, M. E. Maguire, and C. G. Miller, J. Bacteriol. 171:4742-4751, 1989). Strains carrying one wild-type and two mutant alleles of the three loci were constructed to study the kinetics and specificity of ion transport of each system in isolation. The transport systems had different Km and Vmax values for Mg2+ uptake, and each was inhibited by other divalent cations in a distinct rank order of potency: for CorA, Mg2+ greater than Mn2+ greater than Co2+ greater than Ni2+ greater than Ca2+; for MgtA, Zn2+ greater than or equal to Mg2+ greater than Ni2+ approximately Co2+ greater than Ca2+; and for MgtB, Mg2+ approximately Ni2+ approximately Ni2+ greater than Mn2+ much greater than Ca2+. Other differences among the three systems were apparent. The CorA transport system functioned as a Mg2+-Mg2+ exchange system, mediating both efflux and influx of Mg2+. Neither the MgtA nor the MgtB system could mediate Mg2+ efflux. Transport via the MgtB system was very temperature sensitive; Mg2+ was transported at 37 degrees C but not at 20 degrees C. The MgtA and the MgtB transport systems were found to be regulated by the extracellular concentration of Mg2+.
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Affiliation(s)
- M D Snavely
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44120
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