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Peng M, Mathew ND, Anderson VE, Falk MJ, Nakamaru-Ogiso E. N -Glycosylation of MRS2 balances aerobic and anaerobic energy production by reducing rapid mitochondrial Mg 2+ influx in conditions of high glucose or impaired respiratory chain function. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.09.602756. [PMID: 39026824 PMCID: PMC11257584 DOI: 10.1101/2024.07.09.602756] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2024]
Abstract
N- linked glycoproteins function in numerous biological processes, modulating enzyme activities as well as protein folding, stability, oligomerization, and trafficking. While N- glycosylation of mitochondrial proteins has been detected by untargeted MS-analyses, the physiological existence and roles of mitochondrial protein N- linked glycosylation remain under debate. Here, we report that MRS2, a mitochondrial inner membrane protein that functions as the high flux magnesium transporter, is N- glycosylated to various extents depending on cellular bioenergetic status. Both N -glycosylated and unglycosylated isoforms were consistently detected in mitochondria isolated from mouse liver, rat and mouse liver fibroblast cells (BRL 3A and AFT024, respectively) as well as human skin fibroblast cells. Immunoblotting of MRS2 showed it was bound to, and required stringent elution conditions to remove from, lectin affinity columns with covalently bound concanavalin A or Lens culinaris agglutinin. Following peptide: N- glycosidase F (PNGase F) digestion of the stringently eluted proteins, the higher M r MRS2 bands gel-shifted to lower M r and loss of lectin affinity was seen. BRL 3A cells treated with two different N- linked glycosylation inhibitors, tunicamycin or 6-diazo-5-oxo-L-norleucine, resulted in decreased intensity or loss of the higher M r MRS2 isoform. To investigate the possible functional role of MRS2 N- glycosylation, we measured rapid Mg 2+ influx capacity in intact mitochondria isolated from BRL 3A cells in control media or following treatment with tunicamycin or 6-diazo-5-oxo-L-norleucine. Interestingly, rapid Mg 2+ influx capacity increased in mitochondria isolated from BRL 3A cells treated with either N- glycosylation inhibitor. Forcing reliance on mitochondrial respiration by treatment with either galactose media or the glycolytic inhibitor 2-deoxyglucose or by minimizing glucose concentration similarly reduced the N- glycosylated isoform of MRS2, with a correlated concomitant increase in rapid Mg 2+ influx capacity. Conversely, inhibiting mitochondrial energy production in BRL 3A cells with either rotenone or oligomycin resulted in an increased fraction of N- glycosylated MRS2, with decreased rapid Mg 2+ influx capacity. Collectively, these data provide strong evidence that MRS2 N -glycosylation is directly involved in the regulation of mitochondrial matrix Mg 2+ , dynamically communicating relative cellular nutrient status and bioenergetic capacity by serving as a physiologic brake on the influx of mitochondrial matrix Mg 2+ under conditions of glucose excess or mitochondrial bioenergetic impairment.
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Chaudhry AH, Nayab S, Hussain SB, Ali M, Pan Z. Current Understandings on Magnesium Deficiency and Future Outlooks for Sustainable Agriculture. Int J Mol Sci 2021; 22:1819. [PMID: 33673043 PMCID: PMC7917752 DOI: 10.3390/ijms22041819] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Revised: 01/27/2021] [Accepted: 01/28/2021] [Indexed: 11/24/2022] Open
Abstract
The productivity of agricultural produce is fairly dependent on the availability of nutrients and efficient use. Magnesium (Mg2+) is an essential macronutrient of living cells and is the second most prevalent free divalent cation in plants. Mg2+ plays a role in several physiological processes that support plant growth and development. However, it has been largely forgotten in fertilization management strategies to increase crop production, which leads to severe reductions in plant growth and yield. In this review, we discuss how the Mg2+ shortage induces several responses in plants at different levels: morphological, physiological, biochemical and molecular. Additionally, the Mg2+ uptake and transport mechanisms in different cellular organelles and the role of Mg2+ transporters in regulating Mg2+ homeostasis are also discussed. Overall, in this review, we critically summarize the available information about the responses of Mg deficiency on plant growth and development, which would facilitate plant scientists to create Mg2+-deficiency-resilient crops through agronomic and genetic biofortification.
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Affiliation(s)
- Ahmad Hassan Chaudhry
- College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan 430070, China;
| | - Shafa Nayab
- Department of Horticulture, Muhammad Nawaz Shareef University of Agriculture, Multan 60000, Pakistan; (S.N.); (S.B.H.)
| | - Syed Bilal Hussain
- Department of Horticulture, Muhammad Nawaz Shareef University of Agriculture, Multan 60000, Pakistan; (S.N.); (S.B.H.)
| | - Muqarrab Ali
- Department of Agronomy, Muhammad Nawaz Shareef University of Agriculture, Multan 60000, Pakistan;
| | - Zhiyong Pan
- College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan 430070, China;
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Functional analysis of whether the glycine residue of the GMN motif of the Arabidopsis MRS2/MGT/CorA-type Mg 2+ channel protein AtMRS2-11 is critical for Mg 2+ transport activity. Arch Biochem Biophys 2020; 697:108673. [PMID: 33217378 DOI: 10.1016/j.abb.2020.108673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Revised: 10/09/2020] [Accepted: 11/08/2020] [Indexed: 11/21/2022]
Abstract
Magnesium (Mg2+) plays a critical role in many physiological processes. The AtMRS2/MGT family, which contains nine Arabidopsis genes (and two pseudogenes), belongs to a eukaryotic subset of the CorA superfamily of divalent cation transporters. AtMRS2-11/MGT10 possesses the signature GlyMetAsn sequence (the GMN motif) conserved in the CorA superfamily; however, little is known about the role of the GMN motif in AtMRS2. Direct measurement using the fluorescent dye mag-fura-2 revealed that reconstituted AtMRS2-11 mediated rapid Mg2+ uptake into proteoliposomes at extraliposomal Mg2+ concentrations of 10 and 20 mM. Mutations in the GMN motif, G417 to A, S or V, did not show a significant change in Mg2+ uptake relative to the wild-type protein. The G417W mutant exhibited a significant increase in Mg2+ uptake. The functional complementation assay in Escherichia coli strain TM2 showed that E. coli cells expressing AtMRS2-11 with mutations in G of the GMN motif did not grow in LB medium without Mg2+ supplementation, while growth was observed in LB medium supplemented with 0.5 mM Mg2+; no difference was observed between the growth of TM2 cells expressing the AtMRS2-11 G417W mutant and that of cells expressing wild-type AtMRS2-11. These results suggested that the Mg2+ transport activity of the AtMRS2-11 GMN-motif mutants was low at low physiological Mg2+ concentrations; thus, the Gly residue is critical for Mg2+ transport, and the Mg2+ transport activity of the GMN-motif mutants was increased at high Mg2+ concentrations.
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Merolle L, Sponder G, Sargenti A, Mastrototaro L, Cappadone C, Farruggia G, Procopio A, Malucelli E, Parisse P, Gianoncelli A, Aschenbach JR, Kolisek M, Iotti S. Overexpression of the mitochondrial Mg channel MRS2 increases total cellular Mg concentration and influences sensitivity to apoptosis. Metallomics 2019; 10:917-928. [PMID: 29952392 DOI: 10.1039/c8mt00050f] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The mechanism of action of the mitochondrial Mg channel MRS2 and its involvement in cell viability remain unclear. Deletion of MRS2 has been reported to abolish Mg influx into mitochondria, to induce functional defects in mitochondrial organelles, and to result in cell death. We evaluated whether MRS2 expression had an impact on total Mg cellular content by inducing the overexpression of MRS2 in HEK-293 cells. We observed a remarkable increase of total intracellular Mg concentration in cells overexpressing MRS2 compared with control cells. In order to investigate whether and in what manner the detected Mg increment was involved in the MRS2 influence on cell viability, we treated MRS2-overexpressing cells with two known apoptotic inducers. We found that cells overexpressing the MRS2 channel became less responsive to these pharmacological insults. Our experimental evidence indicates that the MRS2 channel controls overall intracellular Mg levels, the alteration of which might have a role in the molecular signaling leading to apoptotic cell death.
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Affiliation(s)
- Lucia Merolle
- Transfusion Medicine Unit, Azienda Unità Sanitaria Locale-IRCCS di Reggio Emilia, 42123, Italy.
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Trachsel E, Redder P, Linder P, Armitano J. Genetic screens reveal novel major and minor players in magnesium homeostasis of Staphylococcus aureus. PLoS Genet 2019; 15:e1008336. [PMID: 31415562 PMCID: PMC6711546 DOI: 10.1371/journal.pgen.1008336] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 08/27/2019] [Accepted: 07/29/2019] [Indexed: 12/19/2022] Open
Abstract
Magnesium is one of the most abundant metal ions in living cells. Very specific and devoted transporters have evolved for transporting Mg2+ ions across the membrane and maintain magnesium homeostasis. Using genetic screens, we were able to identify the main players in magnesium homeostasis in the opportunistic pathogen Staphylococcus aureus. Here, we show that import of magnesium relies on the redundant activity of either CorA2 or MgtE since in absence of these two importers, bacteria require increased amounts of magnesium in the medium. A third CorA-like importer seems to play a minor role, at least under laboratory conditions. For export of magnesium, we identified two proteins, MpfA and MpfB. MpfA, is the main actor since it is essential for growth in high magnesium concentrations. We show that gain of function mutations or overexpression of the minor factor, MpfB, which is part of a sigmaB controlled stress response regulon, can compensate for the absence of MpfA.
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Affiliation(s)
- Emilie Trachsel
- Department of Microbiology and Molecular Medicine, CMU, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Peter Redder
- Department of Microbiology and Molecular Medicine, CMU, Faculty of Medicine, University of Geneva, Geneva, Switzerland
- LMGM UMR5100, Centre de Biologie Integrative, Paul Sabatier University, Toulouse, France
| | - Patrick Linder
- Department of Microbiology and Molecular Medicine, CMU, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Joshua Armitano
- Department of Microbiology and Molecular Medicine, CMU, Faculty of Medicine, University of Geneva, Geneva, Switzerland
- * E-mail:
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Zhang L, Wen A, Wu X, Pan X, Wu N, Chen X, Chen Y, Mao D, Chen L, Luan S. Molecular identification of the magnesium transport gene family in Brassica napus. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2019; 136:204-214. [PMID: 30690277 DOI: 10.1016/j.plaphy.2019.01.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2018] [Revised: 01/14/2019] [Accepted: 01/14/2019] [Indexed: 05/24/2023]
Abstract
Magnesium (Mg2+) is an essential element for plant growth. Its transport and homeostasis in plants is mainly maintained by the MRS2/MGT of Mg2+ transporters. Little is known about the MRS2/MGT gene family in Brassica napus L. (B. napus), one of the most important oil grains. In our present study, we identified 36 putative MRS2/MGT genes (BnMGTs) from B. napus and investigated their phylogeny, expression pattern and function. These BnMGT genes were sorted into five distinguished groups by the phylogenetic analysis, and they were clearly homologous with the MRS2/MGT genes in Arabidopsis and rice. Complementation assays using the Salmonella typhimurium mutant MM281 demonstrated that the BnMGT genes were capable of mediating Mg2+ uptake and transport, with varied affinities to Mg2+. The expression pattern analysis showed that the expression of BnMGTs were tissue-specific and varied in different tissues. This work provides the molecular basis to discover the function of BnMGT gene family in plant growth and development.
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Affiliation(s)
- Lin Zhang
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China
| | - Anning Wen
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China
| | - Xiaoqi Wu
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China
| | - Xiaoling Pan
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China
| | - Nan Wu
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China
| | - Xuan Chen
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China
| | - Yan Chen
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China
| | - Dandan Mao
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China.
| | - Liangbi Chen
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China.
| | - Sheng Luan
- College of Life Sciences, Hunan Normal University, Changsha, 410081, China; Department of Plant and Microbial Biology, University of California, Berkeley, 94720, California, USA.
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Ishijima S, Manabe Y, Shinkawa Y, Hotta A, Tokumasu A, Ida M, Sagami I. The homologous Arabidopsis MRS2/MGT/CorA-type Mg2+ channels, AtMRS2-10 and AtMRS2-1 exhibit different aluminum transport activity. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:2184-2191. [DOI: 10.1016/j.bbamem.2018.08.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Revised: 08/24/2018] [Accepted: 08/29/2018] [Indexed: 11/30/2022]
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Magnesium Extravaganza: A Critical Compendium of Current Research into Cellular Mg 2+ Transporters Other than TRPM6/7. Rev Physiol Biochem Pharmacol 2018; 176:65-105. [PMID: 30406297 DOI: 10.1007/112_2018_15] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Magnesium research has boomed within the last 20 years. The real breakthrough came at the start of the new millennium with the discovery of a plethora of possible Mg homeostatic factors that, in particular, included putative Mg2+ transporters. Until that point, Mg research was limited to biochemical and physiological work, as no target molecular entities were known that could be used to explore the molecular biology of Mg homeostasis at the level of the cell, tissue, organ, or organism and to translate such knowledge into the field of clinical medicine and pharmacology. Because of the aforementioned, Mg2+ and Mg homeostasis, both of which had been heavily marginalized within the biomedical field in the twentieth century, have become overnight a focal point of many studies ranging from primary biomedical research to translational medicine.The amount of literature concerning cellular Mg2+ transport and cellular Mg homeostasis is increasing, together with a certain amount of confusion, especially about the function(s) of the newly discovered and, in the majority of instances, still only putative Mg2+ transporters/Mg2+ homeostatic factors. Newcomers to the field of Mg research will thus find it particularly difficult to orient themselves.Here, we briefly but critically summarize the status quo of the current understanding of the molecular entities behind cellular Mg2+ homeostasis in mammalian/human cells other than TRPM6/7 chanzymes, which have been universally accepted as being unspecific cation channel kinases allowing the flux of Mg2+ while constituting the major gateway for Mg2+ to enter the cell.
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Li H, Du H, Huang K, Chen X, Liu T, Gao S, Liu H, Tang Q, Rong T, Zhang S. Identification, and Functional and Expression Analyses of the CorA/MRS2/MGT-Type Magnesium Transporter Family in Maize. PLANT & CELL PHYSIOLOGY 2016; 57:1153-68. [PMID: 27084594 DOI: 10.1093/pcp/pcw064] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 03/22/2016] [Indexed: 05/24/2023]
Abstract
Magnesium (Mg(2+)) is an essential macronutrient for plant growth and development, and the CorA/MRS2/MGT-type Mg(2+) transporters play important roles in maintaining Mg(2+) homeostasis in plants. Although the MRS2/MGT genes have been identified in two model plant species, Arabidopsis and rice, a comprehensive analysis of the MRS2/MGT gene family in other plants is lacking. In this work, 12 putative MRS2/MGT genes (ZmMGT1- ZmMGT12) were identified in maize and all of them were classified into five distinct subfamilies by phylogenetic analysis. A complementation assay in the Salmonella typhimurium MM281 strain showed that five representatives of the 12 members possess Mg(2+) transport abilities. Inhibition of ZmMGT protein activity using the hexaamminecobalt (III) (Co-Hex) inhibitor indicated that the ZmMGT protein mediated both low-affinity and high-affinity Mg(2+) transport in maize. A semi-quantitative reverse transcription-PCR (RT-PCR) analysis revealed that eight genes were constitutively expressed in all of the detected tissues, with one being specifically expressed in roots and three having no detectable expression signals. A quantitative RT-PCR analysis showed that some ZmMGT members displayed differential responses to Mg(2+) deficiency and aluminum (Al) stress. Furthermore, root growth inhibition and Mg(2+) accumulation analyses in two maize inbred lines, which conferred different levels of Al tolerance, revealed that ZmMGT proteins contributed to the Al resistance of the Al tolerance genotype. We hypothesize that ZmMGT family members function as Mg(2+) transporters and may play a role in linking Mg(2+) deficiency and Al stress responses. Our results will be valuable in a further analysis of the important biological functions of ZmMGT members in maize.
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Affiliation(s)
- Hongyou Li
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
| | - Hanmei Du
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
| | - Kaifeng Huang
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
| | - Xin Chen
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
| | - Tianyu Liu
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
| | - Shibin Gao
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
| | - Hailan Liu
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
| | - Qilin Tang
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
| | - Tingzhao Rong
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
| | - Suzhi Zhang
- Key Laboratory of Biology and Genetic Improvement of Maize in Southwest China of Agricultural Department, Ministry of Agriculture, Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China
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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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Rengel Z, Bose J, Chen Q, Tripathi BN. Magnesium alleviates plant toxicity of aluminium and heavy metals. CROP AND PASTURE SCIENCE 2015; 66:1298. [PMID: 0 DOI: 10.1071/cp15284] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Magnesium (Mg) is an essential nutrient that can alleviate soilborne toxicity of many ions. This review paper critically assesses the literature on interactions and mechanisms influencing Mg alleviation of aluminium (Al) and heavy metal toxicity. Hydrated radii of Mg2+ and Al3+ are similar; therefore, these two ions compete for binding to ion transporters and other important biological molecules. In monocotyledonous species such as rice and wheat, millimolar concentrations of Mg alleviate Al toxicity, mainly by decreasing Al saturation and activity at cell wall and plasma membrane binding sites. In dicotyledonous legume species such as soybean (Glycine max), rice bean (Vigna umbellata) and broad bean (Vicia faba), micromolar concentrations of Mg may enhance biosynthesis of organic ligands and thus underpin alleviation of Al toxicity. Resistance to Al may be enhanced by increased expression of the genes coding for Mg transporters, as well as by upregulation of activity of Mg-transport proteins; intracellular Mg2+ activity may thus be increased under Al stress, which may increase the activity of H+-ATPases. In Vicia faba, Mg-related enhancement in the activity of plasma membrane H+-ATPase under Al stress was found to be due to post-translational modification (increased phosphorylation of the penultimate threonine as well as association with regulatory 14-3-3 proteins), resulting in increased resistance to Al stress. Magnesium can alleviate heavy metal stress by decreasing negative electrical potential and thus metal ion activities at the plasma membrane surface (physico-chemical competition), by enhancing activities of enzymes involved in biosynthesis of organic ligands, and by increasing vacuolar sequestration of heavy metals via increasing H+-pumping activity at the tonoplast. Future work should concentrate on characterising the role of intracellular Mg2+ homeostasis and Mg transporters in alleviating metal stress as well as in transcriptional, translational and post-translational regulation of H+-pumps and enzymes involved in biosynthesis and exudation of organic ligands.
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A repulsion mechanism explains magnesium permeation and selectivity in CorA. Proc Natl Acad Sci U S A 2014; 111:3002-7. [PMID: 24516146 DOI: 10.1073/pnas.1319054111] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Magnesium (Mg(2+)) plays a central role in biology, regulating the activity of many enzymes and stabilizing the structure of key macromolecules. In bacteria, CorA is the primary source of Mg(2+) uptake and is self-regulated by intracellular Mg(2+). Using a gating mutant at the divalent ion binding site, we were able to characterize CorA selectivity and permeation properties to both monovalent and divalent cations under perfused two-electrode voltage clamp. The present data demonstrate that under physiological conditions, CorA is a multioccupancy Mg(2+)-selective channel, fully excluding monovalent cations, and Ca(2+), whereas in absence of Mg(2+), CorA is essentially nonselective, displaying only mild preference against other divalents (Ca(2+) > Mn(2+) > Co(2+) > Mg(2+) > Ni(2)(+)). Selectivity against monovalent cations takes place via Mg(2+) binding at a high-affinity site, formed by the Gly-Met-Asn signature sequence (Gly312 and Asn314) at the extracellular side of the pore. This mechanism is reminiscent of repulsion models proposed for Ca(2+) channel selectivity despite differences in sequence and overall structure.
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Payandeh J, Pfoh R, Pai EF. The structure and regulation of magnesium selective ion channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2778-92. [PMID: 23954807 DOI: 10.1016/j.bbamem.2013.08.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 07/30/2013] [Accepted: 08/02/2013] [Indexed: 10/26/2022]
Abstract
The magnesium ion (Mg(2+)) is the most abundant divalent cation within cells. In man, Mg(2+)-deficiency is associated with diseases affecting the heart, muscle, bone, immune, and nervous systems. Despite its impact on human health, little is known about the molecular mechanisms that regulate magnesium transport and storage. Complete structural information on eukaryotic Mg(2+)-transport proteins is currently lacking due to associated technical challenges. The prokaryotic MgtE and CorA magnesium transport systems have recently succumbed to structure determination by X-ray crystallography, providing first views of these ubiquitous and essential Mg(2+)-channels. MgtE and CorA are unique among known membrane protein structures, each revealing a novel protein fold containing distinct arrangements of ten transmembrane-spanning α-helices. Structural and functional analyses have established that Mg(2+)-selectivity in MgtE and CorA occurs through distinct mechanisms. Conserved acidic side-chains appear to form the selectivity filter in MgtE, whereas conserved asparagines coordinate hydrated Mg(2+)-ions within the selectivity filter of CorA. Common structural themes have also emerged whereby MgtE and CorA sense and respond to physiologically relevant, intracellular Mg(2+)-levels through dedicated regulatory domains. Within these domains, multiple primary and secondary Mg(2+)-binding sites serve to staple these ion channels into their respective closed conformations, implying that Mg(2+)-transport is well guarded and very tightly regulated. The MgtE and CorA proteins represent valuable structural templates to better understand the related eukaryotic SLC41 and Mrs2-Alr1 magnesium channels. Herein, we review the structure, function and regulation of MgtE and CorA and consider these unique proteins within the expanding universe of ion channel and transporter structural biology.
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Affiliation(s)
- Jian Payandeh
- Department of Structural Biology, Genentech Inc., 1 DNA Way, South San Francisco, CA 94080, USA.
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