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Pflüger T, Gschell M, Zhang L, Shnitsar V, Zabadné AJ, Zierep P, Günther S, Einsle O, Andrade SLA. How sensor Amt-like proteins integrate ammonium signals. SCIENCE ADVANCES 2024; 10:eadm9441. [PMID: 38838143 DOI: 10.1126/sciadv.adm9441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 04/30/2024] [Indexed: 06/07/2024]
Abstract
Unlike aquaporins or potassium channels, ammonium transporters (Amts) uniquely discriminate ammonium from potassium and water. This feature has certainly contributed to their repurposing as ammonium receptors during evolution. Here, we describe the ammonium receptor Sd-Amt1, where an Amt module connects to a cytoplasmic diguanylate cyclase transducer module via an HAMP domain. Structures of the protein with and without bound ammonium were determined to 1.7- and 1.9-Ångstrom resolution, depicting the ON and OFF states of the receptor and confirming the presence of a binding site for two ammonium cations that is pivotal for signal perception and receptor activation. The transducer domain was disordered in the crystals, and an AlphaFold2 prediction suggests that the helices linking both domains are flexible. While the sensor domain retains the trimeric fold formed by all Amt family members, the HAMP domains interact as pairs and serve to dimerize the transducer domain upon activation.
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Affiliation(s)
- Tobias Pflüger
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Mathias Gschell
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Lin Zhang
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Volodymyr Shnitsar
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Annas J Zabadné
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Paul Zierep
- Faculty of Chemistry and Pharmacy, Institute for Pharmaceutical Sciences, University Freiburg, Hermann-Herder-Str. 9, 79104 Freiburg, Germany
| | - Stefan Günther
- Faculty of Chemistry and Pharmacy, Institute for Pharmaceutical Sciences, University Freiburg, Hermann-Herder-Str. 9, 79104 Freiburg, Germany
| | - Oliver Einsle
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
- BIOSS Centre for Biological Signaling Studies, University Freiburg, Schänzlerstr. 1, 79104 Freiburg, Germany
| | - Susana L A Andrade
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
- BIOSS Centre for Biological Signaling Studies, University Freiburg, Schänzlerstr. 1, 79104 Freiburg, Germany
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Chen YN, Ho CH. CIPK15-mediated inhibition of NH 4+ transport protects Arabidopsis from submergence. Heliyon 2023; 9:e20235. [PMID: 37810036 PMCID: PMC10560025 DOI: 10.1016/j.heliyon.2023.e20235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2023] [Revised: 07/18/2023] [Accepted: 09/14/2023] [Indexed: 10/10/2023] Open
Abstract
Ammonium (NH4+) serves as a vital nitrogen source for plants, but it can turn toxic when it accumulates in excessive amounts. Toxicity is aggravated under hypoxic/anaerobic conditions, e.g., during flooding or submergence, due to a lower assimilation capacity. AMT1; 1 mediates NH4+ uptake into roots. Under conditions of oxygen-deficiency, i.e., submergence, the CBL-interacting protein kinase OsCIPK15 has been shown to trigger SnRK1A signaling, promoting starch mobilization, thereby the increasing availability of ATP, reduction equivalents and acceptors for NH4+ assimilation in rice. Our previous study in Arabidopsis demonstrates that AtCIPK15 phosphorylates AMT1; 1 whose activity is under allosteric feedback control by phosphorylation of T460 in the cytosolic C-terminus. Here we show that submergence cause higher NH4+ accumulation in wild-type, plant but not of nitrate, nor in a quadruple amt knock-out mutant. In addition, submergence triggers rapid accumulation of AtAMT1;1 and AtCIPK15 transcripts as well as AMT1 phosphorylation. Significantly, cipk15 knock-out mutants do not exhibit an increase in AMT1 phosphorylation; however, they do display heightened sensitivity to submergence. These findings suggest that CIPK15 suppresses AMT activity, resulting in decreased NH4+ accumulation during submergence, a period when NH4+ assimilation capacity may be impaired.
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Affiliation(s)
- Yen-Ning Chen
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Cheng-Hsun Ho
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
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3
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Bizior A, Williamson G, Harris T, Hoskisson PA, Javelle A. Prokaryotic ammonium transporters: what has three decades of research revealed? MICROBIOLOGY (READING, ENGLAND) 2023; 169:001360. [PMID: 37450375 PMCID: PMC10433425 DOI: 10.1099/mic.0.001360] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Accepted: 06/24/2023] [Indexed: 07/18/2023]
Abstract
The exchange of ammonium across cellular membranes is a fundamental process in all domains of life. In plants, bacteria and fungi, ammonium represents a vital source of nitrogen, which is scavenged from the external environment. In contrast, in animal cells ammonium is a cytotoxic metabolic waste product and must be excreted to prevent cell death. Transport of ammonium is facilitated by the ubiquitous Amt/Mep/Rh transporter superfamily. In addition to their function as transporters, Amt/Mep/Rh proteins play roles in a diverse array of biological processes and human physiopathology. Despite this clear physiological importance and medical relevance, the molecular mechanism of Amt/Mep/Rh proteins has remained elusive. Crystal structures of bacterial Amt/Rh proteins suggest electroneutral transport, whilst functional evidence supports an electrogenic mechanism. Here, focusing on bacterial members of the family, we summarize the structure of Amt/Rh proteins and what three decades of research tells us concerning the general mechanisms of ammonium translocation, in particular the possibility that the transport mechanism might differ in various members of the Amt/Mep/Rh superfamily.
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Affiliation(s)
- Adriana Bizior
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
| | - Gordon Williamson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
| | - Thomas Harris
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
| | - Paul A. Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
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4
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Bao YQ, Zhang MT, Feng BY, Jieensi W, Xu Y, Xu LR, Han YY, Chen YP. Construction, Characterization, and Application of an Ammonium Transporter (AmtB) Deletion Mutant of the Nitrogen-Fixing Bacterium Kosakonia radicincitans GXGL-4A in Cucumis sativus L. Seedlings. Curr Microbiol 2023; 80:58. [PMID: 36588112 DOI: 10.1007/s00284-022-03160-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2022] [Accepted: 12/19/2022] [Indexed: 01/03/2023]
Abstract
Nitrogen is an important factor affecting crop yield, but excessive use of chemical nitrogen fertilizer has caused decline in nitrogen utilization and soil and water pollution. Reducing the utilization of chemical nitrogen fertilizers by biological nitrogen fixation (BNF) is feasible for green production of crops. However, there are few reports on how to have more ammonium produced by nitrogen-fixing bacteria (NFB) flow outside the cell. In the present study, the amtB gene encoding an ammonium transporter (AmtB) in the genome of NFB strain Kosakonia radicincitans GXGL-4A was deleted and the △amtB mutant was characterized. The results showed that deletion of the amtB gene had no influence on the growth of bacterial cells. The extracellular ammonium nitrogen (NH4+) content of the △amtB mutant under nitrogen-free culture conditions was significantly higher than that of the wild-type strain GXGL-4A (WT-GXGL-4A), suggesting disruption of NH4+ transport. Meanwhile, the plant growth-promoting effect in cucumber seedlings was visualized after fertilization using cells of the △amtB mutant. NFB fertilization continuously increased the cucumber rhizosphere soil pH. The nitrate nitrogen (NO3-) content in soil in the △amtB treatment group was significantly higher than that in the WT-GXGL-4A treatment group in the short term but there was no difference in soil NH4+ contents between groups. Soil enzymatic activities varied during a 45-day assessment period, indicating that △amtB fertilization influenced soil nitrogen cycling in the cucumber rhizosphere. The results will provide a solid foundation for developing the NFB GXGL-4A into an efficient biofertilizer agent.
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Affiliation(s)
- Yu-Qing Bao
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, 200093, China
| | - Meng-Ting Zhang
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Bao-Yun Feng
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Wulale Jieensi
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Yu Xu
- College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua, 321004, China
| | - Lu-Rong Xu
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Ying-Ying Han
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, 200093, China
| | - Yun-Peng Chen
- Department of Resources and Environment, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China.
- Ministry of Science and Technology, Shanghai Yangtze River Delta Eco-Environmental Change and Research Station, Shanghai, 200240, China.
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Ye Z, Liu F, Ferguson ST, Baker A, Pitts RJ, Zwiebel LJ. Ammonium transporter AcAmt mutagenesis uncovers reproductive and physiological defects without impacting olfactory responses to ammonia in the malaria vector mosquito Anopheles coluzzii. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2021; 134:103578. [PMID: 33933561 PMCID: PMC8187335 DOI: 10.1016/j.ibmb.2021.103578] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2021] [Revised: 03/30/2021] [Accepted: 04/07/2021] [Indexed: 05/25/2023]
Abstract
Anopheline mosquitoes are the sole vectors of malaria and rely on olfactory cues for host seeking in which ammonia derived from human sweat plays an essential role. To investigate the function of the Anopheles coluzzii ammonium transporter (AcAmt) in the mosquito olfactory system, we generated an AcAmt null mutant line using CRISPR/Cas9. AcAmt-/- mutants displayed a series of novel phenotypes compared with wild-type mosquitoes including significantly lower insemination rates during mating and increased mortality during eclosion. Furthermore, AcAmt-/- males showed significantly lower sugar consumption while AcAmt-/- females and pupae displayed significantly higher ammonia levels than their wild-type counterparts. Surprisingly, in contrast to previous studies in Drosophila that revealed that the mutation of the ammonium transporter (DmAmt) induces a dramatic reduction of ammonia responses in antennal coeloconic sensilla, no significant differences were observed across a range of peripheral sensory neuron responses to ammonia and other odorants between wild-type and AcAmt-/- females. These data support the existence in mosquitoes of novel compensatory ammonia-sensing mechanisms that are likely to have evolved as a result of the importance of ammonia in host-seeking and other behaviors.
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Affiliation(s)
- Zi Ye
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA
| | - Feng Liu
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA
| | - Stephen T Ferguson
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA
| | - Adam Baker
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA
| | - R Jason Pitts
- Department of Biology, Baylor University, Waco, TX, 76706, USA
| | - Laurence J Zwiebel
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA.
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6
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Chen HY, Chen YN, Wang HY, Liu ZT, Frommer WB, Ho CH. Feedback inhibition of AMT1 NH 4+-transporters mediated by CIPK15 kinase. BMC Biol 2020; 18:196. [PMID: 33317525 PMCID: PMC7737296 DOI: 10.1186/s12915-020-00934-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 11/24/2020] [Indexed: 11/24/2022] Open
Abstract
Background Ammonium (NH4+), a key nitrogen form, becomes toxic when it accumulates to high levels. Ammonium transporters (AMTs) are the key transporters responsible for NH4+ uptake. AMT activity is under allosteric feedback control, mediated by phosphorylation of a threonine in the cytosolic C-terminus (CCT). However, the kinases responsible for the NH4+-triggered phosphorylation remain unknown. Results In this study, a functional screen identified protein kinase CBL-Interacting Protein Kinase15 (CIPK15) as a negative regulator of AMT1;1 activity. CIPK15 was able to interact with several AMT1 paralogs at the plasma membrane. Analysis of AmTryoshka, an NH4+ transporter activity sensor for AMT1;3 in yeast, and a two-electrode-voltage-clamp (TEVC) of AMT1;1 in Xenopus oocytes showed that CIPK15 inhibits AMT activity. CIPK15 transcript levels increased when seedlings were exposed to elevated NH4+ levels. Notably, cipk15 knockout mutants showed higher 15NH4+ uptake and accumulated higher amounts of NH4+ compared to the wild-type. Consistently, cipk15 was hypersensitive to both NH4+ and methylammonium but not nitrate (NO3−). Conclusion Taken together, our data indicate that feedback inhibition of AMT1 activity is mediated by the protein kinase CIPK15 via phosphorylation of residues in the CCT to reduce NH4+-accumulation. Supplementary information The online version contains supplementary material available at 10.1186/s12915-020-00934-w.
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Affiliation(s)
- Hui-Yu Chen
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Yen-Ning Chen
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Hung-Yu Wang
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Zong-Ta Liu
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan
| | - Wolf B Frommer
- Institute for Molecular Physiology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.,Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya, 464-8601, Japan
| | - Cheng-Hsun Ho
- Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan.
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7
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Complete Genome Sequence of Lactobacillus hilgardii LMG 7934, Carrying the Gene Encoding for the Novel PII-Like Protein PotN. Curr Microbiol 2020; 77:3538-3545. [PMID: 32803419 DOI: 10.1007/s00284-020-02161-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Accepted: 08/07/2020] [Indexed: 02/02/2023]
Abstract
Lactic acid bacteria are widespread in various ecological niches with the excess of nutrients and have reduced capabilities to adapt to starvation. Among more than 280 Lactobacillus species known to the date, only five, including Lactobacillus hilgardii, carry in their genome the gene encoding for PII-like protein, one of the central regulators of cellular metabolism generally responding to energy- and carbon-nitrogen status in many free-living Bacteria, Archaea and in plant chloroplasts. In contrast to the classical PII encoding genes, in L. hilgardii genome the gene for PII homologue is located within the potABCD operon, encoding the ABC transporter for polyamines. Based on the unique genetic context and low sequence identity with genes of any other so-far characterized PII subfamilies, we termed this gene potN (Pot-protein, Nucleotide-binding). The second specific feature of L. hilgardii genome is that many genes encoding the proteins with similar function are present in two copies, while with low mutual identity. Thus, L. hilgardii LMG 7934 genome carries two genes of glutamine synthetase with 55% identity. One gene is located within classical glnRA operon with the gene of GlnR-like transcriptional regulator, while the second is monocistronic. Together with the relative large genome of L. hilgardii as compared to other Lactobacilli (2.771.862 bp vs ~ 2.2 Mbp in median), these data suggest significant re-arrangements of the genome and a wider range of adaptive capabilities of L. hilgardii in comparison to other bacteria of the genus Lactobacillus.
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8
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Smeulders MJ, Peeters SH, van Alen T, de Bruijckere D, Nuijten GHL, op den Camp HJM, Jetten MSM, van Niftrik L. Nutrient Limitation Causes Differential Expression of Transport- and Metabolism Genes in the Compartmentalized Anammox Bacterium Kuenenia stuttgartiensis. Front Microbiol 2020; 11:1959. [PMID: 32903544 PMCID: PMC7438415 DOI: 10.3389/fmicb.2020.01959] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 07/24/2020] [Indexed: 12/11/2022] Open
Abstract
Anaerobic ammonium-oxidizing (anammox) bacteria, members of the "Candidatus Brocadiaceae" family, play an important role in the nitrogen cycle and are estimated to be responsible for about half of the oceanic nitrogen loss to the atmosphere. Anammox bacteria combine ammonium with nitrite and produce dinitrogen gas via the intermediates nitric oxide and hydrazine (anammox reaction) while nitrate is formed as a by-product. These reactions take place in a specialized, membrane-enclosed compartment called the anammoxosome. Therefore, the substrates ammonium, nitrite and product nitrate have to cross the outer-, cytoplasmic-, and anammoxosome membranes to enter or exit the anammoxosome. The genomes of all anammox species harbor multiple copies of ammonium-, nitrite-, and nitrate transporter genes. Here we investigated how the distinct genes for ammonium-, nitrite-, and nitrate- transport were expressed during substrate limitation in membrane bioreactors. Transcriptome analysis of Kuenenia stuttgartiensis planktonic cells showed that four of the seven ammonium transporter homologs and two of the nine nitrite transporter homologs were significantly upregulated during ammonium-limited growth, while another ammonium transporter- and four nitrite transporter homologs were upregulated in nitrite limited growth conditions. The two nitrate transporters were expressed to similar levels in both conditions. In addition, genes encoding enzymes involved in the anammox reaction were differentially expressed, with those using nitrite as a substrate being upregulated under nitrite limited growth and those using ammonium as a substrate being upregulated during ammonium limitation. Taken together, these results give a first insight in the potential role of the multiple nutrient transporters in regulating transport of substrates and products in and out of the compartmentalized anammox cell.
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Affiliation(s)
| | | | | | | | | | | | | | - Laura van Niftrik
- Department of Microbiology, Institute for Water and Wetland Research, Faculty of Science, Radboud University Nijmegen, Nijmegen, Netherlands
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Pflüger T, Hernández CF, Lewe P, Frank F, Mertens H, Svergun D, Baumstark MW, Lunin VY, Jetten MSM, Andrade SLA. Signaling ammonium across membranes through an ammonium sensor histidine kinase. Nat Commun 2018; 9:164. [PMID: 29323112 PMCID: PMC5764959 DOI: 10.1038/s41467-017-02637-3] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Accepted: 12/15/2017] [Indexed: 01/07/2023] Open
Abstract
Sensing and uptake of external ammonium is essential for anaerobic ammonium-oxidizing (anammox) bacteria, and is typically the domain of the ubiquitous Amt/Rh ammonium transporters. Here, we report on the structure and function of an ammonium sensor/transducer from the anammox bacterium "Candidatus Kuenenia stuttgartiensis" that combines a membrane-integral ammonium transporter domain with a fused histidine kinase. It contains a high-affinity ammonium binding site not present in assimilatory Amt proteins. The levels of phosphorylated histidine in the kinase are coupled to the presence of ammonium, as conformational changes during signal recognition by the Amt module are transduced internally to modulate the kinase activity. The structural analysis of this ammonium sensor by X-ray crystallography and small-angle X-ray-scattering reveals a flexible, bipartite system that recruits a large uptake transporter as a sensory module and modulates its functionality to achieve a mechanistic coupling to a kinase domain in order to trigger downstream signaling events.
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Affiliation(s)
- Tobias Pflüger
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany
| | - Camila F Hernández
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany
| | - Philipp Lewe
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany
| | - Fabian Frank
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany
| | - Haydyn Mertens
- European Molecular Biology Laboratory, Hamburg Unit, EMBL c/o DESY, Notkestr. 85, Hamburg, D-22603, Germany
| | - Dmitri Svergun
- European Molecular Biology Laboratory, Hamburg Unit, EMBL c/o DESY, Notkestr. 85, Hamburg, D-22603, Germany
| | - Manfred W Baumstark
- Center for Medicine, Institute for Exercise and Occupational Medicine, Medical Center, University of Freiburg, Hugstetterstr. 55, Freiburg, 79106, Germany.,Faculty of Medicine, University of Freiburg, Freiburg, 79106, Germany
| | - Vladimir Y Lunin
- Institute of Mathematical Problems of Biology RAS, Keldysh Institute of Applied Mathematics of Russian Academy of Sciences, Vitkevicha str. 1, Pushchino, 142290, Russia
| | - Mike S M Jetten
- Department of Microbiology, Radboud University, Institute for Water and Wetland Research, Heyendaalseweg 135, Nijmegen, NL-6525 AJ, The Netherlands
| | - Susana L A Andrade
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany. .,BIOSS Centre for Biological Signalling Studies, University of Freiburg, Schänzlestr. 1, Freiburg, 79104, Germany.
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10
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Bao A, Liang Z, Zhao Z, Cai H. Overexpressing of OsAMT1-3, a High Affinity Ammonium Transporter Gene, Modifies Rice Growth and Carbon-Nitrogen Metabolic Status. Int J Mol Sci 2015; 16:9037-63. [PMID: 25915023 PMCID: PMC4463577 DOI: 10.3390/ijms16059037] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2015] [Revised: 04/11/2015] [Accepted: 04/13/2015] [Indexed: 11/16/2022] Open
Abstract
AMT1-3 encodes the high affinity NH₄⁺ transporter in rice roots and is predominantly expressed under nitrogen starvation. In order to evaluate the effect of AMT1-3 gene on rice growth, nitrogen absorption and metabolism, we generated AMT1-3-overexpressing plants and analyzed the growth phenotype, yield, carbon and nitrogen metabolic status, and gene expression profiles. Although AMT1-3 mRNA accumulated in transgenic plants, these plants displayed significant decreases in growth when compared to the wild-type plants. The nitrogen uptake assay using a 15N tracer revealed poor nitrogen uptake ability in AMT1-3-overexpressing plants. We found significant decreases in AMT1-3-overexpressing plant leaf carbon and nitrogen content accompanied with a higher leaf C/N ratio. Significant changes in soluble proteins and carbohydrates were also observed in AMT1-3-overexpressing plants. In addition, metabolite profile analysis demonstrated significant changes in individual sugars, organic acids and free amino acids. Gene expression analysis revealed distinct expression patterns of genes that participate in carbon and nitrogen metabolism. Additionally, the correlation between the metabolites and gene expression patterns was consistent in AMT1-3-overexpressing plants under both low and high nitrogen growth conditions. Therefore, we hypothesized that the carbon and nitrogen metabolic imbalance caused by AMT1-3 overexpressing attributed to the poor growth and yield of transgenic plants.
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Affiliation(s)
- Aili Bao
- Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Microelement Research Center, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China.
| | - Zhijun Liang
- Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Microelement Research Center, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China.
| | - Zhuqing Zhao
- Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Microelement Research Center, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China.
| | - Hongmei Cai
- Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Microelement Research Center, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China.
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11
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Pitts RJ, Derryberry SL, Pulous FE, Zwiebel LJ. Antennal-expressed ammonium transporters in the malaria vector mosquito Anopheles gambiae. PLoS One 2014; 9:e111858. [PMID: 25360676 PMCID: PMC4216128 DOI: 10.1371/journal.pone.0111858] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Accepted: 10/07/2014] [Indexed: 01/13/2023] Open
Abstract
The principal Afrotropical malaria vector mosquito, Anopheles gambiae remains a significant threat to human health. In this anthropophagic species, females detect and respond to a range of human-derived volatile kairomones such as ammonia, lactic acid, and other carboxylic acids in their quest for blood meals. While the molecular underpinnings of mosquito olfaction and host seeking are becoming better understood, many questions remain unanswered. In this study, we have identified and characterized two candidate ammonium transporter genes, AgAmt and AgRh50 that are expressed in the mosquito antenna and may contribute to physiological and behavioral responses to ammonia, which is an important host kairomone for vector mosquitoes. AgAmt transcripts are highly enhanced in female antennae while a splice variant of AgRh50 appears to be antennal-specific. Functional expression of AgAmt in Xenopus laevis oocytes facilitates inward currents in response to both ammonium and methylammonium, while AgRh50 is able to partially complement a yeast ammonium transporter mutant strain, validating their conserved roles as ammonium transporters. We present evidence to suggest that both AgAmt and AgRh50 are in vivo ammonium transporters that are important for ammonia sensitivity in An. gambiae antennae, either by clearing ammonia from the sensillar lymph or by facilitating sensory neuron responses to environmental exposure. Accordingly, AgAmt and AgRh50 represent new and potentially important targets for the development of novel vector control strategies.
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Affiliation(s)
- R. Jason Pitts
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, United States of America
- Vanderbilt Institute for Global Health, Nashville, Tennessee, United States of America
| | - Stephen L. Derryberry
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Fadi E. Pulous
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Laurence J. Zwiebel
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, United States of America
- Vanderbilt Institute for Global Health, Nashville, Tennessee, United States of America
- Department of Pharmacology, Vanderbilt Brain Institute, Program in Developmental Biology and Institute of Chemical Biology, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America
- * E-mail:
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12
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Ardin AC, Fujita K, Nagayama K, Takashima Y, Nomura R, Nakano K, Ooshima T, Matsumoto-Nakano M. Identification and functional analysis of an ammonium transporter in Streptococcus mutans. PLoS One 2014; 9:e107569. [PMID: 25229891 PMCID: PMC4167856 DOI: 10.1371/journal.pone.0107569] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Accepted: 08/13/2014] [Indexed: 12/26/2022] Open
Abstract
Streptococcus mutans, a Gram-positive bacterium, is considered to be a major etiologic agent of human dental caries and reported to form biofilms known as dental plaque on tooth surfaces. This organism is also known to possess a large number of transport proteins in the cell membrane for export and import of molecules. Nitrogen is an essential nutrient for Gram-positive bacteria, though alternative sources such as ammonium can also be utilized. In order to obtain nitrogen for macromolecular synthesis, nitrogen-containing compounds must be transported into the cell. However, the ammonium transporter in S. mutans remains to be characterized. The present study focused on characterizing the ammonium transporter gene of S. mutans and its operon, while related regulatory genes were also analyzed. The SMU.1658 gene corresponding to nrgA in S. mutans is homologous to the ammonium transporter gene in Bacillus subtilis and SMU.1657, located upstream of the nrgA gene and predicted to be glnB, is a member of the PII protein family. Using a nrgA-deficient mutant strain (NRGD), we examined bacterial growth in the presence of ammonium, calcium chloride, and manganese sulfate. Fluorescent efflux assays were also performed to reveal export molecules associated with the ammonium transporter. The growth rate of NRGD was lower, while its fluorescent intensity was much higher as compared to the parental strain. In addition, confocal laser scanning microscopy revealed that the structure of biofilms formed by NRGD was drastically different than that of the parental strain. Furthermore, transcriptional analysis showed that the nrgA gene was co-transcribed with the glnB gene. These results suggest that the nrgA gene in S. mutans is essential for export of molecules and biofilm formation.
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Affiliation(s)
- Arifah Chieko Ardin
- Department of Pediatric Dentistry, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan
| | - Kazuyo Fujita
- Department of Pediatric Dentistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan
| | - Kayoko Nagayama
- Department of Pediatric Dentistry, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan
| | - Yukiko Takashima
- Department of Pediatric Dentistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan
| | - Ryota Nomura
- Department of Pediatric Dentistry, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan
| | - Kazuhiko Nakano
- Department of Pediatric Dentistry, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan
| | - Takashi Ooshima
- Department of Pediatric Dentistry, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan
| | - Michiyo Matsumoto-Nakano
- Department of Pediatric Dentistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan
- * E-mail:
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13
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Offre P, Kerou M, Spang A, Schleper C. Variability of the transporter gene complement in ammonia-oxidizing archaea. Trends Microbiol 2014; 22:665-75. [PMID: 25169021 DOI: 10.1016/j.tim.2014.07.007] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2014] [Revised: 07/17/2014] [Accepted: 07/30/2014] [Indexed: 12/19/2022]
Abstract
Ammonia-oxidizing archaea (AOA) are a widespread and abundant component of microbial communities in many different ecosystems. The extent of physiological differences between individual AOA is, however, unknown. Here, we compare the transporter gene complements of six AOA, from four different environments and two major clades, to assess their potential for substrate uptake and efflux. Each of the corresponding AOA genomes encode a unique set of transporters and although the composition of AOA transporter complements follows a phylogenetic pattern, few transporter families are conserved in all investigated genomes. A comparison of ammonia transporters encoded by archaeal and bacterial ammonia oxidizers highlights the variance among AOA lineages as well as their distinction from the ammonia-oxidizing bacteria, and suggests differential ecological adaptations.
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Affiliation(s)
- Pierre Offre
- University of Vienna, Department of Ecogenomics and Systems Biology, Archaea Biology and Ecogenomics Division, Althanstrasse 14, A-1090 Wien, Austria.
| | - Melina Kerou
- University of Vienna, Department of Ecogenomics and Systems Biology, Archaea Biology and Ecogenomics Division, Althanstrasse 14, A-1090 Wien, Austria
| | - Anja Spang
- Uppsala University, Department of Cell and Molecular Biology, Science for Life Laboratory, Box 596, SE-75123, Uppsala, Sweden
| | - Christa Schleper
- University of Vienna, Department of Ecogenomics and Systems Biology, Archaea Biology and Ecogenomics Division, Althanstrasse 14, A-1090 Wien, Austria.
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14
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Direct observation of electrogenic NH4(+) transport in ammonium transport (Amt) proteins. Proc Natl Acad Sci U S A 2014; 111:9995-10000. [PMID: 24958855 DOI: 10.1073/pnas.1406409111] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Ammonium transport (Amt) proteins form a ubiquitous family of integral membrane proteins that specifically shuttle ammonium across membranes. In prokaryotes, archaea, and plants, Amts are used as environmental NH4(+) scavengers for uptake and assimilation of nitrogen. In the eukaryotic homologs, the Rhesus proteins, NH4(+)/NH3 transport is used instead in acid-base and pH homeostasis in kidney or NH4(+)/NH3 (and eventually CO2) detoxification in erythrocytes. Crystal structures and variant proteins are available, but the inherent challenges associated with the unambiguous identification of substrate and monitoring of transport events severely inhibit further progress in the field. Here we report a reliable in vitro assay that allows us to quantify the electrogenic capacity of Amt proteins. Using solid-supported membrane (SSM)-based electrophysiology, we have investigated the three Amt orthologs from the euryarchaeon Archaeoglobus fulgidus. Af-Amt1 and Af-Amt3 are electrogenic and transport the ammonium and methylammonium cation with high specificity. Transport is pH-dependent, with a steep decline at pH values of ∼5.0. Despite significant sequence homologies, functional differences between the three proteins became apparent. SSM electrophysiology provides a long-sought-after functional assay for the ubiquitous ammonium transporters.
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15
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De Michele R, Ast C, Loqué D, Ho CH, Andrade SLA, Lanquar V, Grossmann G, Gehne S, Kumke MU, Frommer WB. Fluorescent sensors reporting the activity of ammonium transceptors in live cells. eLife 2013; 2:e00800. [PMID: 23840931 PMCID: PMC3699834 DOI: 10.7554/elife.00800] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Accepted: 05/18/2013] [Indexed: 01/14/2023] Open
Abstract
Ammonium serves as key nitrogen source and metabolic intermediate, yet excess causes toxicity. Ammonium uptake is mediated by ammonium transporters, whose regulation is poorly understood. While transport can easily be characterized in heterologous systems, measuring transporter activity in vivo remains challenging. Here we developed a simple assay for monitoring activity in vivo by inserting circularly-permutated GFP into conformation-sensitive positions of two plant and one yeast ammonium transceptors (‘AmTrac’ and ‘MepTrac’). Addition of ammonium to yeast cells expressing the sensors triggered concentration-dependent fluorescence intensity (FI) changes that strictly correlated with the activity of the transporter. Fluorescence-based activity sensors present a novel technology for monitoring the interaction of the transporters with their substrates, the activity of transporters and their regulation in vivo, which is particularly valuable in the context of analytes for which no radiotracers exist, as well as for cell-specific and subcellular transport processes that are otherwise difficult to track. DOI:http://dx.doi.org/10.7554/eLife.00800.001 Ammonium provides a vital source of nitrogen for bacteria, fungi and plants, and is produced by animals as a waste product of metabolism. High levels of ammonium can be toxic, so all organisms need to control their uptake or excretion of this substance. Ammonium transporters, which are highly conserved from bacteria to plants to humans, are essential for this process but, along with transporters in general, they are hard to study. Their activity can be examined in vitro by expressing them in heterologous systems—that is, in cells other than those in which they are naturally found. But in vivo studies must rely on indirect techniques such as monitoring radioactive isotopes or membrane potentials, and these cannot distinguish between the activity of ammonium transporters and uptake of ammonium through other routes. One approach that has been successful in other fields is the use of fluorescent proteins that can signal conformational changes—such as those that occur when a transporter is activated—by a shift in fluorescence. Green fluorescent protein (GFP) is a commonly used fluorescent indicator, and a particularly useful variant is ‘circularly permutated GFP’. This is GFP in which parts of the amino acid sequence have been rearranged without fundamentally changing the overall structure or function of the protein. Circularly permutated GFP can be fused to another protein in such a way that a conformational change in the second protein triggers a change in fluorescence that can be detected by fluorescence spectroscopy or microscopy. Now, De Michele et al. have applied this approach to the study of both plant and yeast ammonium transporters. They constructed a library of fusion proteins made up of circularly permutated GFP and an ammonium transporter from the plant Arabidopsis thaliana—and found one version that functioned normally as a transporter but also produced a detectable change in fluorescence that correlated precisely with transporter activity. De Michele et al. then used the same method to produce fluorescent indicator fusion proteins of two more ammonium transporters—a second isoform from Arabidopsis and one from yeast. These fluorescent sensors should be a great boon to researchers studying the ammonium transport system. Moreover, this approach could in theory be applied to other transporter proteins that are currently difficult to study, and so could help to open up research into a variety of transport processes. DOI:http://dx.doi.org/10.7554/eLife.00800.002
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Affiliation(s)
- Roberto De Michele
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.,Institute of Plant Genetics, Italian National Research Council (CNR-IGV), Palermo, Italy
| | - Cindy Ast
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.,NanoPolyPhotonik, Fraunhofer Institute for Applied Polymer Research, Potsdam-Golm, Germany
| | - Dominique Loqué
- Feedstocks Division, Joint BioEnergy Institute, Emeryville, United States
| | - Cheng-Hsun Ho
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Susana LA Andrade
- Department of Biochemistry, Institute for Organic Chemistry and Biochemistry, and BIOSS Center for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
| | - Viviane Lanquar
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Guido Grossmann
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Sören Gehne
- Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany
| | - Michael U Kumke
- Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany
| | - Wolf B Frommer
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
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16
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De Michele R, Ast C, Loqué D, Ho CH, Andrade SLA, Lanquar V, Grossmann G, Gehne S, Kumke MU, Frommer WB. Fluorescent sensors reporting the activity of ammonium transceptors in live cells. eLife 2013; 2:e00800. [PMID: 23840931 DOI: 10.7554/elife.00800.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Accepted: 05/18/2013] [Indexed: 05/26/2023] Open
Abstract
Ammonium serves as key nitrogen source and metabolic intermediate, yet excess causes toxicity. Ammonium uptake is mediated by ammonium transporters, whose regulation is poorly understood. While transport can easily be characterized in heterologous systems, measuring transporter activity in vivo remains challenging. Here we developed a simple assay for monitoring activity in vivo by inserting circularly-permutated GFP into conformation-sensitive positions of two plant and one yeast ammonium transceptors ('AmTrac' and 'MepTrac'). Addition of ammonium to yeast cells expressing the sensors triggered concentration-dependent fluorescence intensity (FI) changes that strictly correlated with the activity of the transporter. Fluorescence-based activity sensors present a novel technology for monitoring the interaction of the transporters with their substrates, the activity of transporters and their regulation in vivo, which is particularly valuable in the context of analytes for which no radiotracers exist, as well as for cell-specific and subcellular transport processes that are otherwise difficult to track. DOI:http://dx.doi.org/10.7554/eLife.00800.001.
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Affiliation(s)
- Roberto De Michele
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
- Institute of Plant Genetics, Italian National Research Council (CNR-IGV), Palermo, Italy
| | - Cindy Ast
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
- NanoPolyPhotonik, Fraunhofer Institute for Applied Polymer Research, Potsdam-Golm, Germany
| | - Dominique Loqué
- Feedstocks Division, Joint BioEnergy Institute, Emeryville, United States
| | - Cheng-Hsun Ho
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Susana LA Andrade
- Department of Biochemistry, Institute for Organic Chemistry and Biochemistry, and BIOSS Center for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
| | - Viviane Lanquar
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Guido Grossmann
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
| | - Sören Gehne
- Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany
| | - Michael U Kumke
- Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany
| | - Wolf B Frommer
- Department of Plant Biology, Carnegie Institution for Science, Stanford, United States
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17
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Yuan L, Gu R, Xuan Y, Smith-Valle E, Loqué D, Frommer WB, von Wirén N. Allosteric regulation of transport activity by heterotrimerization of Arabidopsis ammonium transporter complexes in vivo. THE PLANT CELL 2013; 25:974-84. [PMID: 23463773 PMCID: PMC3634700 DOI: 10.1105/tpc.112.108027] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Ammonium acquisition by plant roots is mediated by AMMONIUM TRANSPORTERs (AMTs), ubiquitous membrane proteins with essential roles in nitrogen nutrition in all organisms. In microbial and plant cells, ammonium transport activity is controlled by ammonium-triggered feedback inhibition to prevent cellular ammonium toxicity. Data from heterologous expression in yeast indicate that oligomerization of plant AMTs is critical for allosteric regulation of transport activity, in which the conserved cytosolic C terminus functions as a trans-activator. Employing the coexpressed transporters AMT1;1 and AMT1;3 from Arabidopsis thaliana as a model, we show here that these two isoforms form functional homo- and heterotrimers in yeast and plant roots and that AMT1;3 carrying a phosphomimic residue in its C terminus regulates both homo- and heterotrimers in a dominant-negative fashion in vivo. (15)NH4(+) influx studies further indicate that allosteric inhibition represses ammonium transport activity in roots of transgenic Arabidopsis expressing a phosphomimic mutant together with functional AMT1;3 or AMT1;1. Our study demonstrates in planta a regulatory role in transport activity of heterooligomerization of transporter isoforms, which may enhance their versatility for signal exchange in response to environmental triggers.
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Affiliation(s)
- Lixing Yuan
- Department of Plant Nutrition, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China
| | - Riliang Gu
- Department of Plant Nutrition, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China
| | - Yuanhu Xuan
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Erika Smith-Valle
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Dominique Loqué
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
- Joint Bioenergy Institute, Emeryville, California 94608
| | - Wolf B. Frommer
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Nicolaus von Wirén
- Molecular Plant Nutrition, Leibniz Institute for Plant Genetics and Crop Plant Research, 06466 Gatersleben, Germany
- Address correspondence to
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18
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Ullmann RT, Andrade SLA, Ullmann GM. Thermodynamics of transport through the ammonium transporter Amt-1 investigated with free energy calculations. J Phys Chem B 2012; 116:9690-703. [PMID: 22804733 DOI: 10.1021/jp305440f] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Amt-1 from Archaeoglobus fulgidus (AfAmt-1) belongs to the Amt/Rh family of ammonium/ammonia transporting membrane proteins. The transport mode and the precise microscopic permeation mechanism utilized by these proteins are intensely debated. Open questions concern the identity of the transported substrate (ammonia and/or ammonium) and whether the transport is passive or active. To address these questions, we studied the overall thermodynamics of the different transport modes as a function of the environmental conditions. Then, we investigated the thermodynamics of the underlying microscopic transport mechanisms with free energy calculations within a continuum electrostatics model. The formalism developed for this purpose is of general utility in the calculation of binding free energies for ligands with multiple protonation forms or other binding forms. The results of our calculations are compared to the available experimental and theoretical data on Amt/Rh proteins and discussed in light of the current knowledge on the physiological conditions experienced by microorganisms and plants. We found that microscopic models of electroneutral and electrogenic transport modes are in principle thermodynamically viable. However, only the electrogenic variants have a net thermodynamic driving force under the physiological conditions experienced by microorganisms and plants. Thus, the transport mechanism of AfAmt-1 is most likely electrogenic.
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Affiliation(s)
- R Thomas Ullmann
- Structural Biology/Bioinformatics, University of Bayreuth, Universitätsstrasse 30, BGI, 95447 Bayreuth, Germany.
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19
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Involvement of the ammonium transporter AmtB in nitrogenase regulation and ammonium excretion in Pseudomonas stutzeri A1501. Res Microbiol 2012; 163:332-9. [PMID: 22659337 DOI: 10.1016/j.resmic.2012.05.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Accepted: 04/19/2012] [Indexed: 01/16/2023]
Abstract
The nitrogen-fixing Pseudomonas stutzeri strain A1501 contains two ammonium transporter genes, amtB1 and amtB2, linked to glnK. Growth of an amtB1-amtB2 double deletion mutant strain was not impaired compared to that of the wild type under any conditions tested, and it was still capable of taking up ammonium ions at nearly wild-type rates. Nitrogenase activity was repressed in wild-type strain A1501 in response to the addition of ammonium, but nitrogenase activity was only partially impaired in the amtB1 and amtB2 double mutant, suggesting that the two AmtB proteins are involved in regulating expression of nitrogenase or its activity in response to ammonium. An interaction between GlnK and AmtB1 or AmtB2 was observed in a yeast two-hybrid assay. Ammonium was excreted by the amtB double mutant strain under nitrogen fixation conditions, particularly when nifA was expressed constitutively. This suggests that AmtB proteins play a role in controlling the internal pool of ammonia within the cell.
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20
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Huergo LF, Pedrosa FO, Muller-Santos M, Chubatsu LS, Monteiro RA, Merrick M, Souza EM. PII signal transduction proteins: pivotal players in post-translational control of nitrogenase activity. MICROBIOLOGY-SGM 2012; 158:176-190. [PMID: 22210804 DOI: 10.1099/mic.0.049783-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The fixation of atmospheric nitrogen by the prokaryotic enzyme nitrogenase is an energy- expensive process and consequently it is tightly regulated at a variety of levels. In many diazotrophs this includes post-translational regulation of the enzyme's activity, which has been reported in both bacteria and archaea. The best understood response is the short-term inactivation of nitrogenase in response to a transient rise in ammonium levels in the environment. A number of proteobacteria species effect this regulation through reversible ADP-ribosylation of the enzyme, but other prokaryotes have evolved different mechanisms. Here we review current knowledge of post-translational control of nitrogenase and show that, for the response to ammonium, the P(II) signal transduction proteins act as key players.
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Affiliation(s)
- Luciano F Huergo
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Fábio O Pedrosa
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Marcelo Muller-Santos
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Leda S Chubatsu
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Rose A Monteiro
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Mike Merrick
- Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, UK
| | - Emanuel M Souza
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
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De Michele R, Loqué D, Lalonde S, Frommer WB. Ammonium and urea transporter inventory of the selaginella and physcomitrella genomes. FRONTIERS IN PLANT SCIENCE 2012; 3:62. [PMID: 22639655 PMCID: PMC3355718 DOI: 10.3389/fpls.2012.00062] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Accepted: 03/14/2012] [Indexed: 05/05/2023]
Abstract
Ammonium and urea are important nitrogen sources for autotrophic organisms. Plant genomes encode several families of specific transporters for these molecules, plus other uptake mechanisms such as aquaporins and ABC transporters. Selaginella and Physcomitrella are representatives of lycophytes and bryophytes, respectively, and the recent completion of their genome sequences provided us with an opportunity for comparative genome studies, with special emphasis on the adaptive processes that accompanied the conquest of dry land and the evolution of a vascular system. Our phylogenetic analysis revealed that the number of genes encoding urea transporters underwent a progressive reduction during evolution, eventually down to a single copy in vascular plants. Conversely, no clear evolutionary pattern was found for ammonium transporters, and their number and distribution in families varies between species. In particular Selaginella, similar to rice, favors the AMT2/MEP family of ammonium transporters over the plant-specific AMT1 type. In comparison, Physcomitrella presents several members belonging to both families.
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Affiliation(s)
- Roberto De Michele
- Department of Plant Biology, Carnegie Institution for ScienceStanford, CA, USA
- Plant Genetics Institute, National Research Council of ItalyPalermo, Italy
| | | | - Sylvie Lalonde
- Department of Plant Biology, Carnegie Institution for ScienceStanford, CA, USA
| | - Wolf B. Frommer
- Department of Plant Biology, Carnegie Institution for ScienceStanford, CA, USA
- *Correspondence: Wolf B. Frommer, Department of Plant Biology, Carnegie Institution for Science, 260 Panama Street, Stanford, CA 94305, USA. e-mail:
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22
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Umair S, Knight JS, Patchett ML, Bland RJ, Simpson HV. Molecular and biochemical characterisation of a Teladorsagia circumcincta glutamate dehydrogenase. Exp Parasitol 2011; 129:240-6. [PMID: 21864529 DOI: 10.1016/j.exppara.2011.08.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Revised: 08/05/2011] [Accepted: 08/08/2011] [Indexed: 01/15/2023]
Abstract
A full length cDNA encoding glutamate dehydrogenase was cloned from Teladorsagia circumcincta (TcGDH). The TcGDH cDNA (1614 bp) encoded a 538 amino acid protein. The predicted amino acid sequence showed 96% and 93% similarity with Haemonchus contortus and Caenorhabditis elegans GDH, respectively. A soluble N-terminal 6xHis-tagged GDH protein was expressed in the recombinant Escherichia coli strain BL21 (DE3) pGroESL, purified and characterised. The recombinant TcGDH had similar kinetic properties to those of the enzyme in homogenates of T. circumcincta, including greater activity in the aminating than deaminating reaction. Addition of 1mM ADP and ATP increased activity about 3-fold in the deaminating reaction, but had no effect in the reverse direction. TcGDH was a dual co-factor enzyme that operated both with NAD(+) and NADP(+), GDH activity was greater in the deaminating reaction with NADP(+) as co-factor and more with NADH in the aminating reaction.
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Affiliation(s)
- S Umair
- Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11-222, Palmerston North, New Zealand
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23
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Bernier SP, Létoffé S, Delepierre M, Ghigo JM. Biogenic ammonia modifies antibiotic resistance at a distance in physically separated bacteria. Mol Microbiol 2011; 81:705-16. [PMID: 21651627 DOI: 10.1111/j.1365-2958.2011.07724.x] [Citation(s) in RCA: 120] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Bacteria release low-molecular-weight by-products called secondary metabolites, which contribute to bacterial ecology and biology. Whereas volatile compounds constitute a large class of potential infochemicals, their role in bacteria-bacteria interactions remains vastly unexplored. Here we report that exposure to gaseous ammonia released from stationary-phase bacterial cultures modifies the antibiotic resistance spectrum of all tested Gram-negative and Gram-positive bacteria. Using Escherichia coli K12 as a model organism, and increased resistance to tetracycline as the phenotypic read-out, we demonstrate that exposure to ammonia generated by the catabolism of l-aspartate increases the level of intracellular polyamines, in turn leading to modifications in membrane permeability to different antibiotics as well as increased resistance to oxidative stress. We show that the inability to import ammonia via the Amt gas channel or to synthesize polyamines prevent modification in the resistance profile of aerially exposed bacteria. We therefore provide here the first detailed molecular characterization of widespread, long-range chemical interference between physically separated bacteria.
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Affiliation(s)
- Steve P Bernier
- Institut Pasteur, Unité de Génétique des Biofilms, CNRS URA 2172, 25 rue du Dr. Roux, 75724 Paris CEDEX 15, France
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24
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Rodrigues TE, Souza VEP, Monteiro RA, Gerhardt ECM, Araújo LM, Chubatsu LS, Souza EM, Pedrosa FO, Huergo LF. In vitro interaction between the ammonium transport protein AmtB and partially uridylylated forms of the P(II) protein GlnZ. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:1203-9. [PMID: 21645649 DOI: 10.1016/j.bbapap.2011.05.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Revised: 04/28/2011] [Accepted: 05/13/2011] [Indexed: 12/18/2022]
Abstract
The ammonium transport family Amt/Rh comprises ubiquitous integral membrane proteins that facilitate ammonium movement across biological membranes. Besides their role in transport, Amt proteins also play a role in sensing the levels of ammonium in the environment, a process that depends on complex formation with cytosolic proteins of the P(II) family. Trimeric P(II) proteins from a variety of organisms undergo a cycle of reversible posttranslational modification according to the prevailing nitrogen supply. In proteobacteria, P(II) proteins are subjected to reversible uridylylation of each monomer. In this study we used the purified proteins from Azospirillum brasilense to analyze the effect of P(II) uridylylation on the protein's ability to engage complex formation with AmtB in vitro. Our results show that partially uridylylated P(II) trimers can interact with AmtB in vitro, the implication of this finding in the regulation of nitrogen metabolism is discussed. We also report an improved expression and purification protocol for the A. brasilense AmtB protein that might be applicable to AmtB proteins from other organisms.
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Affiliation(s)
- Thiago E Rodrigues
- Department of Biochemistry and Molecular Biology, Universidade Federal do Parana, Curitiba, Brazil
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Kayumov A, Heinrich A, Fedorova K, Ilinskaya O, Forchhammer K. Interaction of the general transcription factor TnrA with the PII-like protein GlnK and glutamine synthetase in Bacillus subtilis. FEBS J 2011; 278:1779-89. [DOI: 10.1111/j.1742-4658.2011.08102.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Frank CS, Langhammer P, Fuchs BM, Harder J. Ammonium and attachment of Rhodopirellula baltica. Arch Microbiol 2011; 193:365-72. [PMID: 21340506 DOI: 10.1007/s00203-011-0681-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2010] [Revised: 01/12/2011] [Accepted: 01/25/2011] [Indexed: 12/17/2022]
Abstract
A dimorphic life cycle has been described for the planctomycete Rhodopirellula baltica SH1(T), with juvenile motile, free-swimming cells and adult sessile, attached-living cells. However, attachment as a response to environmental factors was not investigated. We studied the response of R. baltica to nitrogen limitation. In batch cultures, ammonium limitation coincided with a dominance of free-swimming cells and a low number of aggregates. Flow cytometry revealed a quantitative shift with increasing ammonium availability, from single cells towards attached cells in large aggregates. During growth of R. baltica on glucose and ammonium in chemostats, an ammonium addition caused a macroscopic change of the growth behaviour, from homogeneous growth in the liquid phase to a biofilm on the borosilicate glass wall of the chemostat vessel. Thus, an ammonium limitation-a carbon to nitrogen supply ratio of 30:1-sustained free-living growth without aggregate formation. A sudden increase in ammonium supply induced sessile growth of R. baltica. These observations reveal a response of Rhodopirellula baltica cells to ammonium: they abandon the free-swimming life, attach to particles and form biofilms.
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Affiliation(s)
- Carsten S Frank
- Department of Microbiology, Max Planck Institute for Marine Microbiology, Bremen, Germany
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Wang J, Yang H, Zuo Z, Yan X, Wang Y, Luo X, Jiang H, Chen K, Zhu W. Molecular Dynamics Simulations on the Mechanism of Transporting Methylamine and Ammonia by Ammonium Transporter AmtB. J Phys Chem B 2010; 114:15172-9. [DOI: 10.1021/jp104508k] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Jinan Wang
- Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China, School of Biomedical Sciences, Curtin University of Technology, Perth WA 6485, Australia, and School of Science, East China University of Science and Technology, Shanghai, 200237, China
| | - Huaiyu Yang
- Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China, School of Biomedical Sciences, Curtin University of Technology, Perth WA 6485, Australia, and School of Science, East China University of Science and Technology, Shanghai, 200237, China
| | - Zhili Zuo
- Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China, School of Biomedical Sciences, Curtin University of Technology, Perth WA 6485, Australia, and School of Science, East China University of Science and Technology, Shanghai, 200237, China
| | - Xiuhua Yan
- Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China, School of Biomedical Sciences, Curtin University of Technology, Perth WA 6485, Australia, and School of Science, East China University of Science and Technology, Shanghai, 200237, China
| | - Yong Wang
- Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China, School of Biomedical Sciences, Curtin University of Technology, Perth WA 6485, Australia, and School of Science, East China University of Science and Technology, Shanghai, 200237, China
| | - Xiaomin Luo
- Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China, School of Biomedical Sciences, Curtin University of Technology, Perth WA 6485, Australia, and School of Science, East China University of Science and Technology, Shanghai, 200237, China
| | - Hualiang Jiang
- Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China, School of Biomedical Sciences, Curtin University of Technology, Perth WA 6485, Australia, and School of Science, East China University of Science and Technology, Shanghai, 200237, China
| | - Kaixian Chen
- Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China, School of Biomedical Sciences, Curtin University of Technology, Perth WA 6485, Australia, and School of Science, East China University of Science and Technology, Shanghai, 200237, China
| | - Weiliang Zhu
- Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China, School of Biomedical Sciences, Curtin University of Technology, Perth WA 6485, Australia, and School of Science, East China University of Science and Technology, Shanghai, 200237, China
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Teixeira PF, Selao TT, Henriksson V, Wang H, Norén A, Nordlund S. Diazotrophic growth of Rhodospirillum rubrum with 2-oxoglutarate as sole carbon source affects regulation of nitrogen metabolism as well as the soluble proteome. Res Microbiol 2010; 161:651-9. [PMID: 20600859 DOI: 10.1016/j.resmic.2010.06.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2010] [Revised: 06/02/2010] [Accepted: 06/08/2010] [Indexed: 10/19/2022]
Abstract
2-Oxoglutarate plays a central role as a signal in the regulation of nitrogen metabolism in the phototrophic diazotroph Rhodospirillum rubrum. In order to further study the role of this metabolite, we have constructed an R. rubrum strain that has the capacity to grow on 2-oxoglutarate as sole carbon source, in contrast to wild-type R. rubrum. This strain has the same growth characteristics as wild-type with malate as carbon source, but showed clear metabolic differences when 2-oxoglutarate was used. Among other things, the regulation of nitrogen metabolism is altered, which can be related to different modification profiles of the regulatory PII proteins.
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Affiliation(s)
- Pedro Filipe Teixeira
- Department of Biochemistry and Biophysics, Stockholm University, 10691 Stockholm, Sweden
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Amon J, Titgemeyer F, Burkovski A. Common patterns - unique features: nitrogen metabolism and regulation in Gram-positive bacteria. FEMS Microbiol Rev 2010; 34:588-605. [PMID: 20337720 DOI: 10.1111/j.1574-6976.2010.00216.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Gram-positive bacteria have developed elaborate mechanisms to control ammonium assimilation, at the levels of both transcription and enzyme activity. In this review, the common and specific mechanisms of nitrogen assimilation and regulation in Gram-positive bacteria are summarized and compared for the genera Bacillus, Clostridium, Streptomyces, Mycobacterium and Corynebacterium, with emphasis on the high G+C genera. Furthermore, the importance of nitrogen metabolism and control for the pathogenic lifestyle and virulence is discussed. In summary, the regulation of nitrogen metabolism in prokaryotes shows an impressive diversity. Virtually every phylum of bacteria evolved its own strategy to react to the changing conditions of nitrogen supply. Not only do the transcription factors differ between the phyla and sometimes even between families, but the genetic targets of a given regulon can also differ between closely related species.
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Affiliation(s)
- Johannes Amon
- Lehrstuhl für Mikrobiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
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Nitrogen and Molybdenum Control of Nitrogen Fixation in the Phototrophic Bacterium Rhodobacter capsulatus. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 675:49-70. [DOI: 10.1007/978-1-4419-1528-3_4] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Lanquar V, Loqué D, Hörmann F, Yuan L, Bohner A, Engelsberger WR, Lalonde S, Schulze WX, von Wirén N, Frommer WB. Feedback inhibition of ammonium uptake by a phospho-dependent allosteric mechanism in Arabidopsis. THE PLANT CELL 2009; 21:3610-22. [PMID: 19948793 PMCID: PMC2798313 DOI: 10.1105/tpc.109.068593] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Revised: 09/23/2009] [Accepted: 11/06/2009] [Indexed: 05/18/2023]
Abstract
The acquisition of nutrients requires tight regulation to ensure optimal supply while preventing accumulation to toxic levels. Ammonium transporter/methylamine permease/rhesus (AMT/Mep/Rh) transporters are responsible for ammonium acquisition in bacteria, fungi, and plants. The ammonium transporter AMT1;1 from Arabidopsis thaliana uses a novel regulatory mechanism requiring the productive interaction between a trimer of subunits for function. Allosteric regulation is mediated by a cytosolic C-terminal trans-activation domain, which carries a conserved Thr (T460) in a critical position in the hinge region of the C terminus. When expressed in yeast, mutation of T460 leads to inactivation of the trimeric complex. This study shows that phosphorylation of T460 is triggered by ammonium in a time- and concentration-dependent manner. Neither Gln nor l-methionine sulfoximine-induced ammonium accumulation were effective in inducing phosphorylation, suggesting that roots use either the ammonium transporter itself or another extracellular sensor to measure ammonium concentrations in the rhizosphere. Phosphorylation of T460 in response to an increase in external ammonium correlates with inhibition of ammonium uptake into Arabidopsis roots. Thus, phosphorylation appears to function in a feedback loop restricting ammonium uptake. This novel autoregulatory mechanism is capable of tuning uptake capacity over a wide range of supply levels using an extracellular sensory system, potentially mediated by a transceptor (i.e., transporter and receptor).
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Affiliation(s)
- Viviane Lanquar
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Dominique Loqué
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Friederike Hörmann
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | - Lixing Yuan
- Key Lab of Plant Nutrition, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China
| | - Anne Bohner
- Molecular Plant Nutrition, Leibniz-Institute for Plant Genetics and Crop Plant Research, 06466 Gatersleben, Germany
| | | | - Sylvie Lalonde
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
| | | | - Nicolaus von Wirén
- Molecular Plant Nutrition, Leibniz-Institute for Plant Genetics and Crop Plant Research, 06466 Gatersleben, Germany
| | - Wolf B. Frommer
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305
- Address correspondence to
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Loqué D, Mora SI, Andrade SLA, Pantoja O, Frommer WB. Pore mutations in ammonium transporter AMT1 with increased electrogenic ammonium transport activity. J Biol Chem 2009; 284:24988-95. [PMID: 19581303 DOI: 10.1074/jbc.m109.020842] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
AMT/Mep ammonium transporters mediate high affinity ammonium/ammonia uptake in bacteria, fungi, and plants. The Arabidopsis AMT1 proteins mediate uptake of the ionic form of ammonium. AMT transport activity is controlled allosterically via a highly conserved cytosolic C terminus that interacts with neighboring subunits in a trimer. The C terminus is thus capable of modulating the conductivity of the pore. To gain insight into the underlying mechanism, pore mutants suppressing the inhibitory effect of mutations in the C-terminal trans-activation domain were characterized. AMT1;1 carrying the mutation Q57H in transmembrane helix I (TMH I) showed increased ammonium uptake but reduced capacity to take up methylammonium. To explore whether the transport mechanism was altered, the AMT1;1-Q57H mutant was expressed in Xenopus oocytes and analyzed electrophysiologically. AMT1;1-Q57H was characterized by increased ammonium-induced and reduced methylammonium-induced currents. AMT1;1-Q57H possesses a 100x lower affinity for ammonium (K(m)) and a 10-fold higher V(max) as compared with the wild type form. To test whether the trans-regulatory mechanism is conserved in archaeal homologs, AfAmt-2 from Archaeoglobus fulgidus was expressed in yeast. The transport function of AfAmt-2 also depends on trans-activation by the C terminus, and mutations in pore-residues corresponding to Q57H of AMT1;1 suppress nonfunctional AfAmt-2 mutants lacking the activating C terminus. Altogether, our data suggest that bacterial and plant AMTs use a conserved allosteric mechanism to control ammonium flux, potentially using a gating mechanism that limits flux to protect against ammonium toxicity.
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Affiliation(s)
- Dominique Loqué
- Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305, USA
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Specific interactions between four molybdenum-binding proteins contribute to Mo-dependent gene regulation in Rhodobacter capsulatus. J Bacteriol 2009; 191:5205-15. [PMID: 19502397 DOI: 10.1128/jb.00526-09] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The phototrophic purple bacterium Rhodobacter capsulatus encodes two transcriptional regulators, MopA and MopB, with partially overlapping and specific functions in molybdate-dependent gene regulation. Both MopA and MopB consist of an N-terminal DNA-binding helix-turn-helix domain and a C-terminal molybdate-binding di-MOP domain. They formed homodimers as apo-proteins and in the molybdate-bound state as shown by yeast two-hybrid (Y2H) studies, glutaraldehyde cross-linking, gel filtration chromatography, and copurification experiments. Y2H studies suggested that both the DNA-binding and the molybdate-binding domains contribute to dimer formation. Analysis of molybdate binding to MopA and MopB revealed a binding stoichiometry of four molybdate oxyanions per homodimer. Specific interaction partners of MopA and MopB were the molybdate transporter ATPase ModC and the molbindin-like Mop protein, respectively. Like other molbindins, the R. capsulatus Mop protein formed hexamers, which were stabilized by binding of six molybdate oxyanions per hexamer. Heteromer formation of MopA and MopB was shown by Y2H studies and copurification experiments. Reporter gene activity of a strictly MopA-dependent mop-lacZ fusion in mutant strains defective for either mopA, mopB, or both suggested that MopB negatively modulates expression of the mop promoter. We propose that depletion of the active MopA homodimer pool by formation of MopA-MopB heteromers might represent a fine-tuning mechanism controlling mop gene expression.
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Mutational analysis of the Candida albicans ammonium permease Mep2p reveals residues required for ammonium transport and signaling. EUKARYOTIC CELL 2008; 8:147-60. [PMID: 19060183 DOI: 10.1128/ec.00229-08] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The ammonium permease Mep2p mediates ammonium uptake and also induces filamentous growth in the human-pathogenic yeast Candida albicans in response to nitrogen limitation. The C-terminal cytoplasmic tail of Mep2p contains a signaling domain that is not required for ammonium transport but is essential for Mep2p-dependent morphogenesis. Progressive C-terminal truncations showed Y433 to be the last amino acid that is essential for the induction of filamentous growth, thereby delimiting the Mep2p signaling domain. To understand in more detail how the signaling activity of Mep2p is regulated by ammonium availability and transport, we mutated conserved amino acid residues that have been implicated in ammonium binding or uptake. Mutation of D180, which has been proposed to mediate initial contact with extracellular ammonium, or the pore-lining residues H188 and H342 abolished Mep2p expression, indicating that these residues are important for protein stability. Mutation of F239, which together with F126 is thought to form an extracytosolic gate to the conductance channel, abolished both ammonium uptake and Mep2p-dependent filament formation, despite proper localization of the protein. On the other hand, mutation of W167, which is assumed to participate with Y122, F126, and S243 in the recruitment and coordination of the ammonium ion at the extracytosolic side of the cell membrane, also abolished filament formation without having a strong impact on ammonium transport, demonstrating that extracellular alterations in Mep2p can affect intracellular signaling. Mutation of Y122 reduced ammonium uptake much more strongly than mutation of W167 but still allowed efficient filament formation, indicating that the signaling activity of Mep2p is not directly correlated with its transport activity. These results provide important insights into ammonium transport and control of morphogenesis by Mep2p in C. albicans.
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