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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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Williamson G, Bizior A, Harris T, Pritchard L, Hoskisson P, Javelle A. Biological ammonium transporters from the Amt/Mep/Rh superfamily: mechanism, energetics, and technical limitations. Biosci Rep 2024; 44:BSR20211209. [PMID: 38131184 PMCID: PMC10794816 DOI: 10.1042/bsr20211209] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 12/12/2023] [Accepted: 12/21/2023] [Indexed: 12/23/2023] Open
Abstract
The exchange of ammonium across cellular membranes is a fundamental process in all domains of life and is facilitated by the ubiquitous Amt/Mep/Rh transporter superfamily. Remarkably, despite a high structural conservation in all domains of life, these proteins have gained various biological functions during evolution. It is tempting to hypothesise that the physiological functions gained by these proteins may be explained at least in part by differences in the energetics of their translocation mechanisms. Therefore, in this review, we will explore our current knowledge of energetics of the Amt/Mep/Rh family, discuss variations in observations between different organisms, and highlight some technical drawbacks which have hampered effects at mechanistic characterisation. Through the review, we aim to provide a comprehensive overview of current understanding of the mechanism of transport of this unique and extraordinary Amt/Mep/Rh superfamily of ammonium transporters.
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Affiliation(s)
- Gordon Williamson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Adriana Bizior
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Thomas Harris
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Leighton Pritchard
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Paul A. Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
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Huang J, Zheng X, Tian M, Zhang K. Ammonia and Nematode Ascaroside Are Synergistic in Trap Formation in Arthrobotrys oligospora. Pathogens 2023; 12:1114. [PMID: 37764922 PMCID: PMC10536950 DOI: 10.3390/pathogens12091114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 08/28/2023] [Accepted: 08/30/2023] [Indexed: 09/29/2023] Open
Abstract
Nematode-trapping (NT) fungi are natural predators of the soil living nematodes. Diverse external signals mediate the generation of predatory devices of NT fungi. Among these, broad ascarosides and nitrogenous ammonia are highly efficient inducers for trap structure initiation. However, the overlay effect of ammonia and ascaroside on the trap morphogenesis remains unclear. This study demonstrated that the combination of nitrogenous substances with nematode-derived ascarosides led to higher trap production compared to the single inducing cues; notably, ammonia and Ascr#18 had the most synergistic effect on the trap in A. oligospora. Further, the deletion of ammonia transceptor Amt43 blocked trap formation against ammonia addition in A. oligospora but not for the ascaroside Ascr#18 induction. Moreover, ammonia addition could promote plasma endocytosis in the process of trap formation. In contrast, ascaroside addition would facilitate the stability of intracellular organization away from endocytosis. Therefore, there is a synergistic effect on trap induction from different nitrogenous and ascaroside signals.
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Affiliation(s)
- Jinrong Huang
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming 650091, China; (J.H.); (X.Z.)
| | - Xi Zheng
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming 650091, China; (J.H.); (X.Z.)
| | - Mengqing Tian
- Key Laboratory for Potato Biology of Yunnan Province, The CAAS-YNNU-YINMORE Joint Academy of Potato Science, Yunnan Normal University, Kunming 650091, China;
| | - Keqin Zhang
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming 650091, China; (J.H.); (X.Z.)
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Hu C, Dai W, Zhu X, Yao H, Lin Z, Dong Y, Lv L. Expression and Functional Analysis of AMT1 Gene Responding to High Ammonia Stress in Razor Clam ( Sinonovacula constricta). Animals (Basel) 2023; 13:ani13101638. [PMID: 37238069 DOI: 10.3390/ani13101638] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 05/01/2023] [Accepted: 05/11/2023] [Indexed: 05/28/2023] Open
Abstract
Ammonium transporter 1 (AMT1), a member of ammonia (NH3/NH4+) transport proteins, has been found to have ammonia transport activity in plants and microorganisms. However, the functional characteristics and molecular mechanisms of AMT1 in mollusks remain unclear. The razor clam (Sinonovacula constricta) is a suitable model species to explore the molecular mechanism of ammonia excretion because of the high concentration of ambient ammonia it is exposed to in the clam-fish-shrimp polyculture system. Here, the expression of AMT1 in S. constricta (Sc-AMT1) in response to high ammonia (12.85 mmol/L NH4Cl) stress was identified by real-time quantitative PCR (qRT-PCR), Western blotting, RNA interference, and immunofluorescence analysis. Additionally, the association between the SNP_g.15211125A > T linked with Sc-AMT1 and ammonia tolerance was validated by kompetitive allele-specific PCR (KASP). A significant upregulated expression of Sc-AMT1 was observed during ammonia exposure, and Sc-AMT1 was found to be localized in the flat cells of gill. Moreover, the interference with Sc-AMT1 significantly upregulated the hemolymph ammonia levels, accompanied by the increased mRNA expression of Rhesus glycoprotein (Rh). Taken together, our findings imply that AMT1 may be a primary contributor to ammonia excretion in S. constricta, which is the basis of their ability to inhabit benthic water with high ammonia levels.
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Affiliation(s)
- Chenxin Hu
- Key Laboratory of Aquatic Germplasm Resource of Zhejiang, College of Biological and Environmental Sciences, Zhejiang Wanli University, Ningbo 315100, China
| | - Wenfang Dai
- Ninghai Institute of Mariculture Breeding and Seed Industry, Zhejiang Wanli University, Ningbo 315604, China
| | - Xiaojie Zhu
- Key Laboratory of Aquatic Germplasm Resource of Zhejiang, College of Biological and Environmental Sciences, Zhejiang Wanli University, Ningbo 315100, China
| | - Hanhan Yao
- Key Laboratory of Aquatic Germplasm Resource of Zhejiang, College of Biological and Environmental Sciences, Zhejiang Wanli University, Ningbo 315100, China
| | - Zhihua Lin
- Key Laboratory of Aquatic Germplasm Resource of Zhejiang, College of Biological and Environmental Sciences, Zhejiang Wanli University, Ningbo 315100, China
- Ninghai Institute of Mariculture Breeding and Seed Industry, Zhejiang Wanli University, Ningbo 315604, China
| | - Yinghui Dong
- Ninghai Institute of Mariculture Breeding and Seed Industry, Zhejiang Wanli University, Ningbo 315604, China
| | - Liyuan Lv
- Ninghai Institute of Mariculture Breeding and Seed Industry, Zhejiang Wanli University, Ningbo 315604, China
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Densi A, Iyer RS, Bhat PJ. Synonymous and Nonsynonymous Substitutions in Dictyostelium discoideum Ammonium Transporter amtA Are Necessary for Functional Complementation in Saccharomyces cerevisiae. Microbiol Spectr 2023; 11:e0384722. [PMID: 36840598 PMCID: PMC10100761 DOI: 10.1128/spectrum.03847-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Accepted: 01/24/2023] [Indexed: 02/24/2023] Open
Abstract
Ammonium transporters are present in all three domains of life. They have undergone extensive horizontal gene transfer (HGT), gene duplication, and functional diversification and therefore offer an excellent paradigm to study protein evolution. We attempted to complement a mep1Δmep2Δmep3Δ strain of Saccharomyces cerevisiae (triple-deletion strain), which otherwise cannot grow on ammonium as a sole nitrogen source at concentrations of <3 mM, with amtA of Dictyostelium discoideum, an orthologue of S. cerevisiae MEP2. We observed that amtA did not complement the triple-deletion strain of S. cerevisiae for growth on low-ammonium medium. We isolated two mutant derivatives of amtA (amtA M1 and amtA M2) from a PCR-generated mutant plasmid library that complemented the triple-deletion strain of S. cerevisiae. amtA M1 bears three nonsynonymous and two synonymous substitutions, which are necessary for its functionality. amtA M2 bears two nonsynonymous substitutions and one synonymous substitution, all of which are necessary for functionality. Interestingly, AmtA M1 transports ammonium but does not confer methylamine toxicity, while AmtA M2 transports ammonium and confers methylamine toxicity, demonstrating functional diversification. Preliminary biochemical analyses indicated that the mutants differ in their conformations as well as their mechanisms of ammonium transport. These intriguing results clearly point out that protein evolution cannot be fathomed by studying nonsynonymous and synonymous substitutions in isolation. The above-described observations have significant implications for various facets of biological processes and are discussed in detail. IMPORTANCE Functional diversification following gene duplication is one of the major driving forces of protein evolution. While the role of nonsynonymous substitutions in the functional diversification of proteins is well recognized, knowledge of the role of synonymous substitutions in protein evolution is in its infancy. Using functional complementation, we isolated two functional alleles of the D. discoideum ammonium transporter gene (amtA), which otherwise does not function in S. cerevisiae as an ammonium transporters. One of them is an ammonium transporter, while the other is an ammonium transporter that also confers methylammonium (ammonium analogue) toxicity, suggesting functional diversification. Surprisingly, both alleles require a combination of synonymous and nonsynonymous substitutions for their functionality. These results bring out a hitherto-unknown pathway of protein evolution and pave the way for not only understanding protein evolution but also interpreting single nucleotide polymorphisms (SNPs).
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Affiliation(s)
- Asha Densi
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, India
| | - Revathi S. Iyer
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, India
| | - Paike Jayadeva Bhat
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, India
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6
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Williamson G, Brito AS, Bizior A, Tamburrino G, Dias Mirandela G, Harris T, Hoskisson PA, Zachariae U, Marini AM, Boeckstaens M, Javelle A. Coexistence of Ammonium Transporter and Channel Mechanisms in Amt-Mep-Rh Twin-His Variants Impairs the Filamentation Signaling Capacity of Fungal Mep2 Transceptors. mBio 2022; 13:e0291321. [PMID: 35196127 PMCID: PMC9040831 DOI: 10.1128/mbio.02913-21] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Accepted: 01/26/2022] [Indexed: 12/01/2022] Open
Abstract
Ammonium translocation through biological membranes, by the ubiquitous Amt-Mep-Rh family of transporters, plays a key role in all domains of life. Two highly conserved histidine residues protrude into the lumen of the pore of these transporters, forming the family's characteristic Twin-His motif. It has been hypothesized that the motif is essential to confer the selectivity of the transport mechanism. Here, using a combination of in vitro electrophysiology on Escherichia coli AmtB, in silico molecular dynamics simulations, and in vivo yeast functional complementation assays, we demonstrate that variations in the Twin-His motif trigger a mechanistic switch between a specific transporter, depending on ammonium deprotonation, to an unspecific ion channel activity. We therefore propose that there is no selective filter that governs specificity in Amt-Mep-Rh transporters, but the inherent mechanism of translocation, dependent on the fragmentation of the substrate, ensures the high specificity of the translocation. We show that coexistence of both mechanisms in single Twin-His variants of yeast Mep2 transceptors disrupts the signaling function and so impairs fungal filamentation. These data support a signaling process driven by the transport mechanism of the fungal Mep2 transceptors. IMPORTANCE Fungal infections represent a significant threat to human health and cause huge damage to crop yields worldwide. The dimorphic switch between yeast and filamentous growth is associated with the virulence of pathogenic fungi. Of note, fungal Mep2 proteins of the conserved Amt-Mep-Rh family play a transceptor role in the induction of filamentation; however, the signaling mechanism remains largely unknown. Amt-Mep-Rh proteins ensure the specific scavenging of NH4+ through a mechanism relying on substrate deprotonation, thereby preventing competition and translocation of similar-sized K+. Our multidisciplinary approaches using E. coli AmtB, Saccharomyces cerevisiae, and Candida albicans Mep2 show that double variation of the family-defining Twin-His motif triggers a mechanistic switch from a specific transporter to an unspecific ion channel with both mechanisms still coexisting in single variants. Moreover, we show that this mechanistic alteration is associated with loss of signaling ability of Mep2, supporting a transport mechanism-driven process in filamentation induction.
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Affiliation(s)
- Gordon Williamson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Ana Sofia Brito
- Biology of Membrane Transport Laboratory, Department of Molecular Biology, Université Libre de Bruxelles, Gosselies, Belgium
| | - Adriana Bizior
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Giulia Tamburrino
- Computational Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Gaëtan Dias Mirandela
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
- Biology of Membrane Transport Laboratory, Department of Molecular Biology, Université Libre de Bruxelles, Gosselies, Belgium
| | - Thomas Harris
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Paul A. Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Ulrich Zachariae
- Computational Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Anna Maria Marini
- Biology of Membrane Transport Laboratory, Department of Molecular Biology, Université Libre de Bruxelles, Gosselies, Belgium
| | - Mélanie Boeckstaens
- Biology of Membrane Transport Laboratory, Department of Molecular Biology, Université Libre de Bruxelles, Gosselies, Belgium
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
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Abstract
AbstractIt is crucial for the growth and development of an organism whether ammonium is transported across its membranes in a form of NH4+ or NH3. The transport of both molecules follows different pH-dependent gradients across membranes and transport of both substrates differentially affects the internal and external pH. As a consequence, they directly influence the physiology and organism development. CaMep2 from Candida albicans shows a dual transceptor function in ammonium transport and sensing. CaMep2 senses low ammonium availability and induces filamentous growth. CaMep1, by contrast, is only active in transport, but not involved in ammonium signaling. Here, both proteins were heterologously expressed in Xenopus laevis oocytes. This study identified electrogenic NH4+ transport by CaMep1 and electroneutral NH3 transport by CaMep2, which might be a prerequisite for the induction of pseudohyphal growth.
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Hao DL, Zhou JY, Yang SY, Huang YN, Su YH. Functional and Regulatory Characterization of Three AMTs in Maize Roots. FRONTIERS IN PLANT SCIENCE 2020; 11:884. [PMID: 32676086 PMCID: PMC7333355 DOI: 10.3389/fpls.2020.00884] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Accepted: 05/29/2020] [Indexed: 06/11/2023]
Abstract
Maize grows in nitrate-dominated dryland soils, but shortly upon localized dressing of nitrogen fertilizers, ammonium is retained as a noticeable form of nitrogen source available to roots. Thus in addition to nitrate, the absorption of ammonium can be an important strategy that promotes rapid plant growth at strong nitrogen demanding stages. The present study reports the functional characterization of three root-expressed ammonium transporters (AMTs), aiming at finding out functional and regulatory properties that correlate with efficient nitrogen acquisition of maize. Using a stable electrophysiological recording method we previously established in Xenopus laevis oocytes that integrates the capture of currents in response to voltage ramps with onsite stability controls, we demonstrate that all three ZmAMT1s engage NH4 + uniporting as ammonium uptake mechanisms. The K m value for ZmAMT1.1a, 1.1b, or ZmAMT1.3 is, respectively, 9.9, 15.6, or 18.6 μM, indicating a typical high-affinity transport of NH4 + ions. Importantly, the uptake currents of these ZmAMT1s are markedly amplified upon extracellular acidification. A pH drop from 7.4 to 5.4 results in a 140.8%, 64.1% or a 120.7% increase of ammonium uptake activity through ZmAMT1.1a, 1.1b, or ZmAMT1.3. Since ammonium uptake by plant roots accompanies a spontaneous acidification to the root medium, the functional promotion of ZmAMT1.1a, 1.1b, and ZmAMT1.3 by low pH is in line with the facilitated ammonium uptake activity in maize roots. Furthermore, the expression of the three ZmAMT1 genes is induced under ammonium-dominated conditions. Thus we describe a facilitated ammonium uptake strategy in maize roots by functional and expression regulations of ZmAMT1 transporters that may coordinate with efficient acquisition of this form of nitrogen source when available.
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Brito AS, Neuhäuser B, Wintjens R, Marini AM, Boeckstaens M. Yeast filamentation signaling is connected to a specific substrate translocation mechanism of the Mep2 transceptor. PLoS Genet 2020; 16:e1008634. [PMID: 32069286 PMCID: PMC7048316 DOI: 10.1371/journal.pgen.1008634] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 02/28/2020] [Accepted: 01/28/2020] [Indexed: 11/18/2022] Open
Abstract
The dimorphic transition from the yeast to the filamentous form of growth allows cells to explore their environment for more suitable niches and is often crucial for the virulence of pathogenic fungi. In contrast to their Mep1/3 paralogues, fungal Mep2-type ammonium transport proteins of the conserved Mep-Amt-Rh family have been assigned an additional receptor role required to trigger the filamentation signal in response to ammonium scarcity. Here, genetic, kinetic and structure-function analyses were used to shed light on the poorly characterized signaling role of Saccharomyces cerevisiae Mep2. We show that Mep2 variants lacking the C-terminal tail conserve the ability to induce filamentation, revealing that signaling can proceed in the absence of exclusive binding of a putative partner to the largest cytosolic domain of the protein. Our data support that filamentation signaling requires the conformational changes accompanying substrate translocation through the pore crossing the hydrophobic core of Mep2. pHluorin reporter assays show that the transport activity of Mep2 and of non-signaling Mep1 differently affect yeast cytosolic pH in vivo, and that the unique pore variant Mep2H194E, with apparent uncoupling of transport and signaling functions, acquires increased ability of acidification. Functional characterization in Xenopus oocytes reveals that Mep2 mediates electroneutral substrate translocation while Mep1 performs electrogenic transport. Our findings highlight that the Mep2-dependent filamentation induction is connected to its specific transport mechanism, suggesting a role of pH in signal mediation. Finally, we show that the signaling process is conserved for the Mep2 protein from the human pathogen Candida albicans. Fungal Mep2-type ammonium transport proteins of the conserved Mep-Amt-Rh family that includes human Rhesus factors are specifically required to allow filamentation in response to ammonium limitation. These proteins were therefore assigned a receptor role while the underlying mechanism of signal transduction remains poorly understood. The “transceptor” property has subsequently been proposed to concern transporters of all kind of micro- and macro- nutrients in eukaryotes, from fungi to human. However, bringing the firm demonstration of their existence remains challenging as variants with full uncoupling of transport and receptor functions are difficult to obtain. Our data question the involvement of the C-terminal extremity of Saccharomyces cerevisiae Mep2 in the signal mediation leading to filamentation. If signaling partners exist, they should also bind to cytosolic loops and/or membrane-embedded domains. The capacity of Mep2 to enable filamentation is closely intertwined to the mechanism of substrate translocation through the pore of the hydrophobic core of the protein. In Xenopus oocytes, the transport activity of non-signaling Mep1 is electrogenic while it is electroneutral for Mep2, the latter likely translocating the weak base NH3, but not the proton released after NH4+ recognition and depronotation. We propose that given consequences of a Mep2-specific transport process, such as an intracellular pH modification, could be the underlying cause of the filamentation signal ensured by Mep2-type proteins.
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Affiliation(s)
- Ana Sofia Brito
- Biology of Membrane Transport Laboratory, Molecular Biology Department, Université Libre de Bruxelles, Gosselies, Belgium
| | - Benjamin Neuhäuser
- Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, Stuttgart, Germany
| | - René Wintjens
- Unité Microbiologie, Chimie Bioorganique et Macromoléculaire, Département RD3, Faculté de Pharmacie, Université Libre de Bruxelles, Brussels, Belgium
| | - Anna Maria Marini
- Biology of Membrane Transport Laboratory, Molecular Biology Department, Université Libre de Bruxelles, Gosselies, Belgium
- * E-mail: (AMM); (MB)
| | - Mélanie Boeckstaens
- Biology of Membrane Transport Laboratory, Molecular Biology Department, Université Libre de Bruxelles, Gosselies, Belgium
- * E-mail: (AMM); (MB)
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10
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Hao DL, Yang SY, Liu SX, Zhou JY, Huang YN, Véry AA, Sentenac H, Su YH. Functional Characterization of the Arabidopsis Ammonium Transporter AtAMT1;3 With the Emphasis on Structural Determinants of Substrate Binding and Permeation Properties. FRONTIERS IN PLANT SCIENCE 2020; 11:571. [PMID: 32528489 PMCID: PMC7256485 DOI: 10.3389/fpls.2020.00571] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 04/17/2020] [Indexed: 05/13/2023]
Abstract
AtAMT1;3 is a major contributor to high-affinity ammonium uptake in Arabidopsis roots. Using a stable electrophysiological recording strategy, we demonstrate in Xenopus laevis oocytes that AtAMT1;3 functions as a typical high-affinity NH4 + uniporter independent of protons and Ca2+. The findings that AtAMT1;3 transports methylammonium (MeA+, a chemical analog of NH4 +) with extremely low affinity (K m in the range of 2.9-6.1 mM) led to investigate the mechanisms underlying substrate binding. Homologous modeling and substrate docking analyses predicted that the deduced substrate binding motif of AtAMT1;3 facilitates the binding of NH4 + ions but loosely accommodates the binding of MeA+ to a more superficial location of the permeation pathway. Amongst point mutations tested based on this analysis, P181A resulted in both significantly increased current amplitudes and substrate binding affinity, whereas F178I led to opposite effects. Thus these 2 residues, which flank W179, a major structural component of the binding site, are also important determinants of AtAMT1;3 transport capacity by being involved in substrate binding. The Q365K mutation neighboring the histidine residue H378, which confines the substrate permeation tunnel, affected only the current amplitudes but not the binding affinities, providing evidence that Q365 mainly controls the substrate diffusion rate within the permeation pathway.
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Affiliation(s)
- Dong-Li Hao
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
| | - Shun-Ying Yang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
| | - Shu-Xia Liu
- Department of Computational Biology, Beijing Computing Center, Beijing, China
| | - Jin-Yan Zhou
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
| | - Ya-Nan Huang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
| | - Anne-Aliénor Véry
- BPMP, Univ Montpellier, CNRS, INRAE, Institut Agro, Montpellier, France
| | - Hervé Sentenac
- BPMP, Univ Montpellier, CNRS, INRAE, Institut Agro, Montpellier, France
- *Correspondence: Hervé Sentenac,
| | - Yan-Hua Su
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
- Yan-Hua Su,
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11
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Mi J, Chen X, Liao X. Screening of single or combined administration of 9 probiotics to reduce ammonia emissions from laying hens. Poult Sci 2019; 98:3977-3988. [PMID: 30982063 DOI: 10.3382/ps/pez138] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2018] [Accepted: 03/07/2019] [Indexed: 12/11/2022] Open
Abstract
The effects of single/combined administration of 9 probiotics on ammonia (NH3) emissions during in vitro fermentation of the caecal contents of laying hens were studied. Not all of the probiotics reduced NH3 emissions. Pichia farinose, Bacillus coagulans, Lactobacillus plantarum, Pichia guilliermondii, and Bacillus subtilis reduced NH3 production by approximately 35.1 to 39%. Compared with the control group, the greatest NH3 inhibition was achieved via the combined application of P. guilliermondii, B. subtilis, and L. plantarum at 1:2:1, resulting in a 46% reduction. Effective probiotics use decreased crude protein digestibility, pH, ammonium nitrogen, valerate levels, and urease and uricase activity, but increased urea, purine trione, nitrate nitrogen, total volatile fatty acids, and acetate levels. The relative abundance of the bacteria responsible for fermenting carbohydrates to produce short fatty acids was increased. Under different treatments, the KEGG Orthology (KO) metabolic pathways of NH3 production and utilization were diverse. Hence, the application of probiotics to control NH3 emissions is dependent on the types and combined ratio of the organisms involved.
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Affiliation(s)
- Jiandui Mi
- College of Animal Science, National Engineering Research Center for Breeding Swine Industry, South China Agricultural University, Guangzhou 510642, China.,Ministry of Agriculture Key Laboratory of Tropical Agricultural Environment, South China Agricultural University, Guangzhou 510642, China.,Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding and Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou 510642, China
| | - Xi Chen
- College of Animal Science, National Engineering Research Center for Breeding Swine Industry, South China Agricultural University, Guangzhou 510642, China.,Ministry of Agriculture Key Laboratory of Tropical Agricultural Environment, South China Agricultural University, Guangzhou 510642, China.,Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding and Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou 510642, China
| | - Xindi Liao
- College of Animal Science, National Engineering Research Center for Breeding Swine Industry, South China Agricultural University, Guangzhou 510642, China.,Ministry of Agriculture Key Laboratory of Tropical Agricultural Environment, South China Agricultural University, Guangzhou 510642, China.,Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding and Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou 510642, China
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12
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Affiliation(s)
- Bert van den Berg
- Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Siobhan Lister
- Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Julian C. Rutherford
- Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
- * E-mail:
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13
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Brito AS, Soto Diaz S, Van Vooren P, Godard P, Marini AM, Boeckstaens M. Pib2-Dependent Feedback Control of the TORC1 Signaling Network by the Npr1 Kinase. iScience 2019; 20:415-433. [PMID: 31622882 PMCID: PMC6817644 DOI: 10.1016/j.isci.2019.09.025] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Revised: 05/10/2019] [Accepted: 09/13/2019] [Indexed: 01/21/2023] Open
Abstract
To adjust cell growth and metabolism according to environmental conditions, the conserved TORC1 signaling network controls autophagy, protein synthesis, and turnover. Here, we dissected the signals controlling phosphorylation and activity of the TORC1-effector kinase Npr1, involved in tuning the plasma membrane permeability to nitrogen sources. By evaluating a role of pH as a signal, we show that, although a transient cytosolic acidification accompanies nitrogen source entry and is correlated to a rapid TORC1-dependent phosphorylation of Npr1, a pH drop is not a prerequisite for TORC1 activation. We show that the Gtr1/Gtr2 and Pib2 regulators of TORC1 both independently and differently contribute to regulate Npr1 phosphorylation and activity. Finally, our data reveal that Npr1 mediates nitrogen-dependent phosphorylation of Pib2, as well as a Pib2-dependent inhibition of TORC1. This work highlights a feedback control loop likely enabling efficient downregulation and faster re-activation of TORC1 in response to a novel stimulating signal.
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Affiliation(s)
- Ana Sofia Brito
- Laboratory of Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Silvia Soto Diaz
- Laboratory of Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Pascale Van Vooren
- Laboratory of Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Patrice Godard
- UCB Pharma, Chemin du Foriest, 1420 Braine-l'Alleud, Belgium
| | - Anna Maria Marini
- Laboratory of Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Mélanie Boeckstaens
- Laboratory of Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium.
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14
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Rutherford JC, Bahn YS, van den Berg B, Heitman J, Xue C. Nutrient and Stress Sensing in Pathogenic Yeasts. Front Microbiol 2019; 10:442. [PMID: 30930866 PMCID: PMC6423903 DOI: 10.3389/fmicb.2019.00442] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 02/20/2019] [Indexed: 12/23/2022] Open
Abstract
More than 1.5 million fungal species are estimated to live in vastly different environmental niches. Despite each unique host environment, fungal cells sense certain fundamentally conserved elements, such as nutrients, pheromones and stress, for adaptation to their niches. Sensing these extracellular signals is critical for pathogens to adapt to the hostile host environment and cause disease. Hence, dissecting the complex extracellular signal-sensing mechanisms that aid in this is pivotal and may facilitate the development of new therapeutic approaches to control fungal infections. In this review, we summarize the current knowledge on how two important pathogenic yeasts, Candida albicans and Cryptococcus neoformans, sense nutrient availability, such as carbon sources, amino acids, and ammonium, and different stress signals to regulate their morphogenesis and pathogenicity in comparison with the non-pathogenic model yeast Saccharomyces cerevisiae. The molecular interactions between extracellular signals and their respective sensory systems are described in detail. The potential implication of analyzing nutrient and stress-sensing systems in antifungal drug development is also discussed.
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Affiliation(s)
- Julian C Rutherford
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Yong-Sun Bahn
- Department of Biotechnology, Yonsei University, Seoul, South Korea
| | - Bert van den Berg
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Joseph Heitman
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC, United States
| | - Chaoyang Xue
- Public Health Research Institute, Rutgers University, Newark, NJ, United States.,Department of Molecular Genetics, Biochemistry and Microbiology, Rutgers University, Newark, NJ, United States
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15
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Mirandela GD, Tamburrino G, Hoskisson PA, Zachariae U, Javelle A. The lipid environment determines the activity of the Escherichia coli ammonium transporter AmtB. FASEB J 2019; 33:1989-1999. [PMID: 30211659 PMCID: PMC6338640 DOI: 10.1096/fj.201800782r] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Accepted: 08/14/2018] [Indexed: 12/22/2022]
Abstract
The movement of ammonium across biologic membranes is a fundamental process in all living organisms and is mediated by the ubiquitous ammonium transporter/methylammonium permease/rhesus protein (Amt/Mep/Rh) family of transporters. Recent structural analysis and coupled mass spectrometry studies have shown that the Escherichia coli ammonium transporter AmtB specifically binds 1-palmitoyl-2-oleoyl phosphatidylglycerol (POPG). Upon POPG binding, several residues of AmtB undergo a small conformational change, which stabilizes the protein against unfolding. However, no studies have so far been conducted, to our knowledge, to explore whether POPG binding to AmtB has functional consequences. Here, we used an in vitro experimental assay with purified components, together with molecular dynamics simulations, to characterize the relation between POPG binding and AmtB activity. We show that the AmtB activity is electrogenic. Our results indicate that the activity, at the molecular level, of Amt in archaebacteria and eubacteria may differ. We also show that POPG is an important cofactor for AmtB activity and that, in the absence of POPG, AmtB cannot complete the full translocation cycle. Furthermore, our simulations reveal previously undiscovered POPG binding sites on the intracellular side of the lipid bilayer between the AmtB subunits. Possible molecular mechanisms explaining the functional role of POPG are discussed.-Mirandela, G. D., Tamburrino, G., Hoskisson, P. A., Zachariae, U., Javelle, A. The lipid environment determines the activity of the Escherichia coli ammonium transporter AmtB.
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Affiliation(s)
- Gaëtan Dias Mirandela
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Giulia Tamburrino
- Computational Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
- Physics, School of Science and Engineering, University of Dundee, Dundee, United Kingdom
| | - Paul A. Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Ulrich Zachariae
- Computational Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
- Physics, School of Science and Engineering, University of Dundee, Dundee, United Kingdom
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
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16
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Ariz I, Boeckstaens M, Gouveia C, Martins AP, Sanz-Luque E, Fernández E, Soveral G, von Wirén N, Marini AM, Aparicio-Tejo PM, Cruz C. Nitrogen isotope signature evidences ammonium deprotonation as a common transport mechanism for the AMT-Mep-Rh protein superfamily. SCIENCE ADVANCES 2018; 4:eaar3599. [PMID: 30214933 PMCID: PMC6135547 DOI: 10.1126/sciadv.aar3599] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/03/2017] [Accepted: 07/27/2018] [Indexed: 06/08/2023]
Abstract
Ammonium is an important nitrogen (N) source for living organisms, a key metabolite for pH control, and a potent cytotoxic compound. Ammonium is transported by the widespread AMT-Mep-Rh membrane proteins, and despite their significance in physiological processes, the nature of substrate translocation (NH3/NH4+) by the distinct members of this family is still a matter of controversy. Using Saccharomyces cerevisiae cells expressing representative AMT-Mep-Rh ammonium carriers and taking advantage of the natural chemical-physical property of the N isotopic signature linked to NH4+/NH3 conversion, this study shows that only cells expressing AMT-Mep-Rh proteins were depleted in 15N relative to 14N when compared to the external ammonium source. We observed 15N depletion over a wide range of external pH, indicating its independence of NH3 formation in solution. On the basis of inhibitor studies, ammonium transport by nonspecific cation channels did not show isotope fractionation but competition with K+. We propose that kinetic N isotope fractionation is a common feature of AMT-Mep-Rh-type proteins, which favor 14N over 15N, owing to the dissociation of NH4+ into NH3 + H+ in the protein, leading to 15N depletion in the cell and allowing NH3 passage or NH3/H+ cotransport. This deprotonation mechanism explains these proteins' essential functions in environments under a low NH4+/K+ ratio, allowing organisms to specifically scavenge NH4+. We show that 15N isotope fractionation may be used in vivo not only to determine the molecular species being transported by ammonium transport proteins, but also to track ammonium toxicity and associated amino acids excretion.
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Affiliation(s)
- Idoia Ariz
- Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - Mélanie Boeckstaens
- Biology of Membrane Transport, Department of Molecular Biology, Université Libre de Bruxelles, 6041 Gosselies, Belgium
| | - Catarina Gouveia
- Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - Ana Paula Martins
- iMed.ULisboa–Research Institute for Medicines, Faculdade de Farmácia da Universidade de Lisboa, 1649-003 Lisboa, Portugal
| | - Emanuel Sanz-Luque
- Department of Biochemistry and Molecular Biology, Univeristy of Córdoba, 14071 Cordoba, Spain
| | - Emilio Fernández
- Department of Biochemistry and Molecular Biology, Univeristy of Córdoba, 14071 Cordoba, Spain
| | - Graça Soveral
- iMed.ULisboa–Research Institute for Medicines, Faculdade de Farmácia da Universidade de Lisboa, 1649-003 Lisboa, Portugal
| | - Nicolaus von Wirén
- Department of Physiology and Cell Biology, Leibniz Institute for Plant Genetics and Crop Plant Research, Seeland, 06466 OT Gatersleben, Germany
| | - Anna M. Marini
- Biology of Membrane Transport, Department of Molecular Biology, Université Libre de Bruxelles, 6041 Gosselies, Belgium
| | | | - Cristina Cruz
- Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal
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17
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Gu J, Li Z, Mao Y, Struik PC, Zhang H, Liu L, Wang Z, Yang J. Roles of nitrogen and cytokinin signals in root and shoot communications in maximizing of plant productivity and their agronomic applications. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2018; 274:320-331. [PMID: 30080619 DOI: 10.1016/j.plantsci.2018.06.010] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 06/13/2018] [Accepted: 06/13/2018] [Indexed: 05/03/2023]
Abstract
Nitrogen is an essential, often limiting, factor in plant growth and development. To regulate growth under limited nitrogen supply, plants sense the internal and external nitrogen status, and coordinate various metabolic processes and developmental programs accordingly. This coordination requires the transmission of various signaling molecules that move across the entire plant. Cytokinins, phytohormones derived from adenine and synthesized in various parts of the plant, are considered major local and long-distance messengers. Cytokinin metabolism and signaling are closely associated with nitrogen availability. They are systemically transported via the vasculature from plant roots to shoots, and vice versa, thereby coordinating shoot and root development. Tight linkage exists between the nitrogen signaling network and cytokinins during diverse developmental and physiological processes. However, the cytokinin-nitrogen interactions and the communication systems involved in sensing rhizospheric nitrogen status and in regulating canopy development remain obscure. We review current knowledge on cytokinin biosynthesis, transport and signaling, nitrogen acquisition, metabolism and signaling, and their interactive roles in regulating root-shoot morphological and physiological characteristics. We also discuss the role of spatio-temporal regulation of cytokinins in enhancing beneficial crop traits of yield and nitrogen use efficiency.
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Affiliation(s)
- Junfei Gu
- Jiangsu Key Laboratory of Crop Genetics and Physiology / Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou 225009, China
| | - Zhikang Li
- Jiangsu Key Laboratory of Crop Genetics and Physiology / Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou 225009, China
| | - Yiqi Mao
- Jiangsu Key Laboratory of Crop Genetics and Physiology / Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou 225009, China
| | - Paul C Struik
- Centre for Crop Systems Analysis, Department of Plant Science, Wageningen University, PO Box 430, Wageningen, 6700 AK, The Netherlands
| | - Hao Zhang
- Jiangsu Key Laboratory of Crop Genetics and Physiology / Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou 225009, China
| | - Lijun Liu
- Jiangsu Key Laboratory of Crop Genetics and Physiology / Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou 225009, China
| | - Zhiqin Wang
- Jiangsu Key Laboratory of Crop Genetics and Physiology / Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou 225009, China
| | - Jianchang Yang
- Jiangsu Key Laboratory of Crop Genetics and Physiology / Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou 225009, China.
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18
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Mutlu N, Kumar A. Messengers for morphogenesis: inositol polyphosphate signaling and yeast pseudohyphal growth. Curr Genet 2018; 65:119-125. [PMID: 30101372 DOI: 10.1007/s00294-018-0874-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 08/06/2018] [Accepted: 08/07/2018] [Indexed: 12/20/2022]
Abstract
In response to various environmental stimuli and stressors, the budding yeast Saccharomyces cerevisiae can initiate a striking morphological transition from its classic growth mode as isolated single cells to a filamentous form in which elongated cells remain connected post-cytokinesis in multi-cellular pseudohyphae. The formation of pseudohyphal filaments is regulated through an expansive signaling network, encompassing well studied and highly conserved pathways enabling changes in cell polarity, budding, cytoskeletal organization, and cell adhesion; however, changes in metabolite levels underlying the pseudohyphal growth transition are less well understood. We have recently identified a function for second messenger inositol polyphosphates (InsPs) in regulating pseudohyphal growth. InsPs are formed through the cleavage of membrane-bound phosphatidylinositol 4,5-bisphosphate (PIP2), and these soluble compounds are now being appreciated as important regulators of diverse processes, from phosphate homeostasis to cell migration. We find that kinases in the InsP pathway are required for wild-type pseudohyphal growth, and that InsP species exhibit characteristic profiles under conditions promoting filamentation. Ratios of the doubly phosphorylated InsP7 isoforms 5PP-InsP5 to 1PP-InsP5 are elevated in mutants exhibiting exaggerated pseudohyphal growth. Interestingly, S. cerevisiae mutants deleted of the mitogen-activated protein kinases (MAPKs) Kss1p or Fus3p or the AMP-activated kinase (AMPK) family member Snf1p display mutant InsP profiles, suggesting that these signaling pathways may contribute to the regulatory mechanism controlling InsP levels. Consequently, analyses of yeast pseudohyphal growth may be informative in identifying mechanisms regulating InsPs, while indicating a new function for these conserved second messengers in modulating cell stress responses and morphogenesis.
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Affiliation(s)
- Nebibe Mutlu
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Anuj Kumar
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA.
- Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, MI, 48109, USA.
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19
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Xuan W, Beeckman T, Xu G. Plant nitrogen nutrition: sensing and signaling. CURRENT OPINION IN PLANT BIOLOGY 2017; 39:57-65. [PMID: 28614749 DOI: 10.1016/j.pbi.2017.05.010] [Citation(s) in RCA: 111] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Revised: 05/24/2017] [Accepted: 05/28/2017] [Indexed: 05/26/2023]
Abstract
In response to external fluctuations of nitrogen (N) supplies, plants can activate complex regulatory networks for optimizing N uptake and utilization. In this review, we highlight novel N-responsive sensors, transporters, and signaling molecules recently identified in the dicot Arabidopsis and the monocot rice, and discuss their potential roles in N sensing and signaling. Furthermore, over the last couple of years, N sensing has been shown to be affected by multiple external factors, which act as local signals to trigger systemic signaling coordinated by long-distance mobile signals. Understanding of this complex regulatory network provides a foundation for the development of novel strategies to increase the root N acquisition efficiency under varying N conditions for crop production.
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Affiliation(s)
- Wei Xuan
- State Key Laboratory of Crop Genetics and Germplasm Enhancement and MOA Key Laboratory of Plant Nutrition and Fertilization in Lower-Middle Reaches of the Yangtze River, Nanjing Agricultural University, Nanjing 210095, PR China
| | - Tom Beeckman
- Department of Plant Biotechnology and Bioinformatics, Ghent University, Technologiepark 927, B-9052 Ghent, Belgium; VIB-UGent Center for Plant Systems Biology, Technologiepark 927, B-9052 Ghent, Belgium
| | - Guohua Xu
- State Key Laboratory of Crop Genetics and Germplasm Enhancement and MOA Key Laboratory of Plant Nutrition and Fertilization in Lower-Middle Reaches of the Yangtze River, Nanjing Agricultural University, Nanjing 210095, PR China.
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20
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Koegel S, Mieulet D, Baday S, Chatagnier O, Lehmann MF, Wiemken A, Boller T, Wipf D, Bernèche S, Guiderdoni E, Courty PE. Phylogenetic, structural, and functional characterization of AMT3;1, an ammonium transporter induced by mycorrhization among model grasses. MYCORRHIZA 2017; 27:695-708. [PMID: 28667402 DOI: 10.1007/s00572-017-0786-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2017] [Accepted: 06/13/2017] [Indexed: 06/07/2023]
Abstract
In the arbuscular mycorrhizal (AM) symbiosis, plants satisfy part of their nitrogen (N) requirement through the AM pathway. In sorghum, the ammonium transporters (AMT) AMT3;1, and to a lesser extent AMT4, are induced in cells containing developing arbuscules. Here, we have characterized orthologs of AMT3;1 and AMT4 in four other grasses in addition to sorghum. AMT3;1 and AMT4 orthologous genes are induced in AM roots, suggesting that in the common ancestor of these five plant species, both AMT3;1 and AMT4 were already present and upregulated upon AM colonization. An artificial microRNA approach was successfully used to downregulate either AMT3;1 or AMT4 in rice. Mycorrhizal root colonization and hyphal length density of knockdown plants were not affected at that time, indicating that the manipulation did not modify the establishment of the AM symbiosis and the interaction between both partners. However, expression of the fungal phosphate transporter FmPT was significantly reduced in knockdown plants, indicating a reduction of the nutrient fluxes from the AM fungus to the plant. The AMT3;1 knockdown plants (but not the AMT4 knockdown plants) were significantly less stimulated in growth by AM fungal colonization, and uptake of both 15N and 33P from the AM fungal network was reduced. This confirms that N and phosphorus nutrition through the mycorrhizal pathway are closely linked. But most importantly, it indicates that AMT3;1 is the prime plant transporter involved in the mycorrhizal ammonium transfer and that its function during uptake of N cannot be performed by AMT4.
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Affiliation(s)
- Sally Koegel
- Department of Environmental Sciences, Botany, Zurich-Basel Plant Science Center, University of Basel, Hebelstrasse 1, 4056, Basel, Switzerland
| | | | - Sefer Baday
- SIB Swiss Institute of Bioinformatics and Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056, Basel, Switzerland
- Applied Informatics Department, Informatics Institute, Istanbul Technical University, 34469, Istanbul, Turkey
| | - Odile Chatagnier
- Agroécologie, AgroSupDijon, CNRS, INRA, Université de Bourgogne Franche-Comté, 21000, Dijon, France
| | - Moritz F Lehmann
- Department of Environmental Sciences, Aquatic and Stable Isotope Biogeochemistry, University of Basel, Basel, Switzerland
| | - Andres Wiemken
- Department of Environmental Sciences, Botany, Zurich-Basel Plant Science Center, University of Basel, Hebelstrasse 1, 4056, Basel, Switzerland
| | - Thomas Boller
- Department of Environmental Sciences, Botany, Zurich-Basel Plant Science Center, University of Basel, Hebelstrasse 1, 4056, Basel, Switzerland
| | - Daniel Wipf
- Agroécologie, AgroSupDijon, CNRS, INRA, Université de Bourgogne Franche-Comté, 21000, Dijon, France
| | - Simon Bernèche
- SIB Swiss Institute of Bioinformatics and Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056, Basel, Switzerland
| | | | - Pierre-Emmanuel Courty
- Department of Environmental Sciences, Botany, Zurich-Basel Plant Science Center, University of Basel, Hebelstrasse 1, 4056, Basel, Switzerland.
- Agroécologie, AgroSupDijon, CNRS, INRA, Université de Bourgogne Franche-Comté, 21000, Dijon, France.
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21
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Abstract
To respond to the changing environment, cells must be able to sense external conditions. This is important for many processes including growth, mating, the expression of virulence factors, and several other regulatory effects. Nutrient sensing at the plasma membrane is mediated by different classes of membrane proteins that activate downstream signaling pathways: nontransporting receptors, transceptors, classical and nonclassical G-protein-coupled receptors, and the newly defined extracellular mucin receptors. Nontransporting receptors have the same structure as transport proteins, but have lost the capacity to transport while gaining a receptor function. Transceptors are transporters that also function as a receptor, because they can rapidly activate downstream signaling pathways. In this review, we focus on these four types of fungal membrane proteins. We mainly discuss the sensing mechanisms relating to sugars, ammonium, and amino acids. Mechanisms for other nutrients, such as phosphate and sulfate, are discussed briefly. Because the model yeast Saccharomyces cerevisiae has been the most studied, especially regarding these nutrient-sensing systems, each subsection will commence with what is known in this species.
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22
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Jacquot A, Li Z, Gojon A, Schulze W, Lejay L. Post-translational regulation of nitrogen transporters in plants and microorganisms. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:2567-2580. [PMID: 28369438 DOI: 10.1093/jxb/erx073] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
For microorganisms and plants, nitrate and ammonium are the main nitrogen sources and they are also important signaling molecules controlling several aspects of metabolism and development. Over the past decade, numerous studies revealed that nitrogen transporters are strongly regulated at the transcriptional level. However, more and more reports are now showing that nitrate and ammonium transporters are also subjected to post-translational regulations in response to nitrogen availability. Phosphorylation is so far the most well studied post-translational modification for these transporters and it affects both the regulation of nitrogen uptake and nitrogen sensing. For example, in Arabidopsis thaliana, phosphorylation was shown to activate the sensing function of the root nitrate transporter NRT1.1 and to switch the transport affinity. Also, for ammonium transporters, a phosphorylation-dependent activation/inactivation mechanism was elucidated in recent years in both plants and microorganisms. However, despite the fact that these regulatory mechanisms are starting to be thoroughly described, the signaling pathways involved and their action on nitrogen transporters remain largely unknown. In this review, we highlight the inorganic nitrogen transporters regulated at the post-translational level and we compare the known mechanisms in plants and microorganisms. We then discuss how these mechanisms could contribute to the regulation of nitrogen uptake and/or nitrogen sensing.
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Affiliation(s)
- Aurore Jacquot
- Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes 'Claude Grignon', UMR CNRS/INRA/SupAgro/UM2, Place Viala, 34060 Montpellier cedex, France
| | - Zhi Li
- Institute of Physiology and Biotechnology of plants, Plant Systems Biology, University of Hohenheim, Garbenstrasse 30, D-70593, Stuttgart, Germany
| | - Alain Gojon
- Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes 'Claude Grignon', UMR CNRS/INRA/SupAgro/UM2, Place Viala, 34060 Montpellier cedex, France
| | - Waltraud Schulze
- Institute of Physiology and Biotechnology of plants, Plant Systems Biology, University of Hohenheim, Garbenstrasse 30, D-70593, Stuttgart, Germany
| | - Laurence Lejay
- Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes 'Claude Grignon', UMR CNRS/INRA/SupAgro/UM2, Place Viala, 34060 Montpellier cedex, France
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23
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Liu Y, von Wirén N. Ammonium as a signal for physiological and morphological responses in plants. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:2581-2592. [PMID: 28369490 DOI: 10.1093/jxb/erx086] [Citation(s) in RCA: 177] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Ammonium is a major inorganic nitrogen source for plants. At low external supplies, ammonium promotes plant growth, while at high external supplies it causes toxicity. Ammonium triggers rapid changes in cytosolic pH, in gene expression, and in post-translational modifications of proteins, leading to apoplastic acidification, co-ordinated ammonium uptake, enhanced ammonium assimilation, altered oxidative and phytohormonal status, and reshaped root system architecture. Some of these responses are dependent on AMT-type ammonium transporters and are not linked to a nutritional effect, indicating that ammonium is perceived as a signaling molecule by plant cells. This review summarizes current knowledge of ammonium-triggered physiological and morphological responses and highlights existing and putative mechanisms mediating ammonium signaling and sensing events in plants. We put forward the hypothesis that sensing of ammonium takes place at multiple steps along its transport, storage, and assimilation pathways.
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Affiliation(s)
- Ying Liu
- Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466 Stadt Seeland, OT Gatersleben, Germany
| | - Nicolaus von Wirén
- Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466 Stadt Seeland, OT Gatersleben, Germany
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24
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Pfannmüller A, Boysen JM, Tudzynski B. Nitrate Assimilation in Fusarium fujikuroi Is Controlled by Multiple Levels of Regulation. Front Microbiol 2017; 8:381. [PMID: 28352253 PMCID: PMC5348485 DOI: 10.3389/fmicb.2017.00381] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Accepted: 02/23/2017] [Indexed: 11/24/2022] Open
Abstract
Secondary metabolite production of the phytopathogenic ascomycete fungus Fusarium fujikuroi is greatly influenced by the availability of nitrogen. While favored nitrogen sources such as glutamine and ammonium are used preferentially, the uptake and utilization of nitrate is subject to a regulatory mechanism called nitrogen metabolite repression (NMR). In Aspergillus nidulans, the transcriptional control of the nitrate assimilatory system is carried out by the synergistic action of the nitrate-specific transcription factor NirA and the major nitrogen-responsive regulator AreA. In this study, we identified the main components of the nitrate assimilation system in F. fujikuroi and studied the role of each of them regarding the regulation of the remaining components. We analyzed mutants with deletions of the nitrate-specific activator NirA, the nitrate reductase (NR), the nitrite reductase (NiR) and the nitrate transporter NrtA. We show that NirA controls the transcription of the nitrate assimilatory genes NIAD, NIIA, and NRTA in the presence of nitrate, and that the global nitrogen regulator AreA is obligatory for expression of most, but not all NirA target genes (NIAD). By transforming a NirA-GFP fusion construct into the ΔNIAD, ΔNRTA, and ΔAREA mutant backgrounds we revealed that NirA was dispersed in the cytosol when grown in the presence of glutamine, but rapidly sorted to the nucleus when nitrate was added. Interestingly, the rapid and nitrate-induced nuclear translocation of NirA was observed also in the ΔAREA and ΔNRTA mutants, but not in ΔNIAD, suggesting that the fungus is able to directly sense nitrate in an AreA- and NrtA-independent, but NR-dependent manner.
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Affiliation(s)
- Andreas Pfannmüller
- Molecular Biology and Biotechnology of Fungi, Department of Biology, Institute of Biology and Biotechnology of Plants, University of Münster Münster, Germany
| | - Jana M Boysen
- Molecular Biology and Biotechnology of Fungi, Department of Biology, Institute of Biology and Biotechnology of Plants, University of Münster Münster, Germany
| | - Bettina Tudzynski
- Molecular Biology and Biotechnology of Fungi, Department of Biology, Institute of Biology and Biotechnology of Plants, University of Münster Münster, Germany
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25
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Lucas C, Ferreira C, Cazzanelli G, Franco-Duarte R, Tulha J, Roelink H, Conway SJ. Yeast Gup1(2) Proteins Are Homologues of the Hedgehog Morphogens Acyltransferases HHAT(L): Facts and Implications. J Dev Biol 2016; 4:E33. [PMID: 29615596 PMCID: PMC5831804 DOI: 10.3390/jdb4040033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Revised: 10/25/2016] [Accepted: 10/27/2016] [Indexed: 12/16/2022] Open
Abstract
In multiple tissues, the Hedgehog secreted morphogen activates in the receiving cells a pathway involved in cell fate, proliferation and differentiation in the receiving cells. This pathway is particularly important during embryogenesis. The protein HHAT (Hedgehog O-acyltransferase) modifies Hh morphogens prior to their secretion, while HHATL (Hh O-acyltransferase-like) negatively regulates the pathway. HHAT and HHATL are homologous to Saccharomyces cerevisiae Gup2 and Gup1, respectively. In yeast, Gup1 is associated with a high number and diversity of biological functions, namely polarity establishment, secretory/endocytic pathway functionality, vacuole morphology and wall and membrane composition, structure and maintenance. Phenotypes underlying death, morphogenesis and differentiation are also included. Paracrine signalling, like the one promoted by the Hh pathway, has not been shown to occur in microbial communities, despite the fact that large aggregates of cells like biofilms or colonies behave as proto-tissues. Instead, these have been suggested to sense the population density through the secretion of quorum-sensing chemicals. This review focuses on Gup1/HHATL and Gup2/HHAT proteins. We review the functions and physiology associated with these proteins in yeasts and higher eukaryotes. We suggest standardisation of the presently chaotic Gup-related nomenclature, which includes KIAA117, c3orf3, RASP, Skinny, Sightless and Central Missing, in order to avoid the disclosure of otherwise unnoticed information.
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Affiliation(s)
- Cândida Lucas
- CBMA—Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-054 Braga, Portugal; (G.C.); (R.F.-D.); (J.T.)
| | - Célia Ferreira
- CBMA—Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-054 Braga, Portugal; (G.C.); (R.F.-D.); (J.T.)
- School of Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK;
| | - Giulia Cazzanelli
- CBMA—Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-054 Braga, Portugal; (G.C.); (R.F.-D.); (J.T.)
| | - Ricardo Franco-Duarte
- CBMA—Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-054 Braga, Portugal; (G.C.); (R.F.-D.); (J.T.)
| | - Joana Tulha
- CBMA—Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-054 Braga, Portugal; (G.C.); (R.F.-D.); (J.T.)
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Hao D, Yang S, Huang Y, Su Y. Identification of structural elements involved in fine-tuning of the transport activity of the rice ammonium transporter OsAMT1;3. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2016; 108:99-108. [PMID: 27423220 DOI: 10.1016/j.plaphy.2016.07.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 07/01/2016] [Accepted: 07/03/2016] [Indexed: 05/13/2023]
Abstract
Ammonium transporters (AMTs) are major routes for plant uptake of the NH4+-form nitrogen. Plant AMTs mediate predominantly the uptake of NH4+ and to a lesser extent, its organic analog methylammonium (MeA+). Mutagenesis studies on potential phosphorylation residues have achieved solid recognition that alteration of the phosphorylation status can result in allosteric regulation and impair the functionality of plant AMTs. However, molecular insights to the fine-tuning of a functional ammonium transporter remain less clear. In this report, we demonstrate that the rice root expressed OsAMT1;3 (Oryza sativa ammonium transporter 1;3) functions as a typical high-affinity NH4+ transporter and is weakly permeable to MeA+ using growth assays in NH4+ uptake defective yeast cells and electrophysiological measurements in Xenopus oocytes. Upon screening of six point mutations generated with the transporter, we identified two amino acid residues involved in the functional modulation of OsAMT1;3. The H199E mutation caused loss of transport activity whereas other five mutations retained the functionality of OsAMT1;3. Furthermore, the L56F mutation enabled respectively 5- and 3.5 -fold increased capability for NH4+ and MeA+ uptake with several-fold decreased affinity (Km) and accelerated Vmax values. Surprisingly, yeast cells expressing the L56F mutation shown increased Na+ toxicity leading to a speculation that enhanced Na+ permeation occurred with this mutation. The phenomenon was further supported by the observation of significant Na+ uptake current in oocytes. Our results seemingly support a speculation that the L56F mutation of OsAMT1;3 widens the substrate passage tunnel and allows enhanced permeability to NH4+ and larger ions MeA+ and Na+.
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Affiliation(s)
- Dongli Hao
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shunying Yang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
| | - Yanan Huang
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yanhua Su
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
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In Vivo Analysis of NH 4+ Transport and Central Nitrogen Metabolism in Saccharomyces cerevisiae during Aerobic Nitrogen-Limited Growth. Appl Environ Microbiol 2016; 82:6831-6845. [PMID: 27637876 DOI: 10.1128/aem.01547-16] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2016] [Accepted: 09/08/2016] [Indexed: 11/20/2022] Open
Abstract
Ammonium is the most common N source for yeast fermentations. Although its transport and assimilation mechanisms are well documented, there have been only a few attempts to measure the in vivo intracellular concentration of ammonium and assess its impact on gene expression. Using an isotope dilution mass spectrometry (IDMS)-based method, we were able to measure the intracellular ammonium concentration in N-limited aerobic chemostat cultivations using three different N sources (ammonium, urea, and glutamate) at the same growth rate (0.05 h-1). The experimental results suggest that, at this growth rate, a similar concentration of intracellular (IC) ammonium, about 3.6 mmol NH4+/literIC, is required to supply the reactions in the central N metabolism, independent of the N source. Based on the experimental results and different assumptions, the vacuolar and cytosolic ammonium concentrations were estimated. Furthermore, we identified a futile cycle caused by NH3 leakage into the extracellular space, which can cost up to 30% of the ATP production of the cell under N-limited conditions, and a futile redox cycle between Gdh1 and Gdh2 reactions. Finally, using shotgun proteomics with protein expression determined relative to a labeled reference, differences between the various environmental conditions were identified and correlated with previously identified N compound-sensing mechanisms.IMPORTANCE In our work, we studied central N metabolism using quantitative approaches. First, intracellular ammonium was measured under different N sources. The results suggest that Saccharomyces cerevisiae cells maintain a constant NH4+ concentration (around 3 mmol NH4+/literIC), independent of the applied nitrogen source. We hypothesize that this amount of intracellular ammonium is required to obtain sufficient thermodynamic driving force. Furthermore, our calculations based on thermodynamic analysis of the transport mechanisms of ammonium suggest that ammonium is not equally distributed, indicating a high degree of compartmentalization in the vacuole. Additionally, metabolomic analysis results were used to calculate the thermodynamic driving forces in the central N metabolism reactions, revealing that the main reactions in the central N metabolism are far from equilibrium. Using proteomics approaches, we were able to identify major changes, not only in N metabolism, but also in C metabolism and regulation.
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28
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Boeckstaens M. [From the discovery of microbial Mep-Amt ammonium transporters to human Rhesus factors]. Med Sci (Paris) 2016; 32:394-400. [PMID: 27137697 DOI: 10.1051/medsci/20163204018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Ammonium, ubiquitous on Earth, plays major and distinct roles in most organisms. While it can be a nitrogen source for many microorganisms and plants, it is a cytotoxic metabolic product actively detoxified by the liver in animals. Furthermore, in the latter, ammonium synthesis in the kidney is involved in acid/base homeostasis. Ammonium transport is ensured by a family of proteins, called Mep-Amt-Rh. This family is conserved in all domains of life and comprises the human Rh factors, notably known in transfusional medicine. While the study of bacterial, fungal and vegetal Mep-Amt transporters reveals a fine-tuned and rapid regulation of these proteins in function of environmental changes, the regulation of animal Rh proteins has been poorly addressed. This review notably highlights the importance of the yeast model in the study of the regulation of these proteins as well as in the functional characterization of Mep-Amt-Rh members of diverse origins.
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Affiliation(s)
- Mélanie Boeckstaens
- Laboratoire de biologie du transport membranaire, IBMM, université Libre de Bruxelles, 12, rue des Professeurs Jeener et Brachet, 6041 Gosselies, Belgique
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29
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van den Berg B, Chembath A, Jefferies D, Basle A, Khalid S, Rutherford JC. Structural basis for Mep2 ammonium transceptor activation by phosphorylation. Nat Commun 2016; 7:11337. [PMID: 27088325 PMCID: PMC4852598 DOI: 10.1038/ncomms11337] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Accepted: 03/14/2016] [Indexed: 11/18/2022] Open
Abstract
Mep2 proteins are fungal transceptors that play an important role as ammonium sensors in fungal development. Mep2 activity is tightly regulated by phosphorylation, but how this is achieved at the molecular level is not clear. Here we report X-ray crystal structures of the Mep2 orthologues from Saccharomyces cerevisiae and Candida albicans and show that under nitrogen-sufficient conditions the transporters are not phosphorylated and present in closed, inactive conformations. Relative to the open bacterial ammonium transporters, non-phosphorylated Mep2 exhibits shifts in cytoplasmic loops and the C-terminal region (CTR) to occlude the cytoplasmic exit of the channel and to interact with His2 of the twin-His motif. The phosphorylation site in the CTR is solvent accessible and located in a negatively charged pocket ∼30 Å away from the channel exit. The crystal structure of phosphorylation-mimicking Mep2 variants from C. albicans show large conformational changes in a conserved and functionally important region of the CTR. The results allow us to propose a model for regulation of eukaryotic ammonium transport by phosphorylation.
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Affiliation(s)
- Bert van den Berg
- Institute for Cell and Molecular Biosciences, The Medical
School, Newcastle University, Newcastle upon Tyne
NE2 4HH, UK
| | - Anupama Chembath
- Institute for Cell and Molecular Biosciences, The Medical
School, Newcastle University, Newcastle upon Tyne
NE2 4HH, UK
| | - Damien Jefferies
- School of Chemistry, University of Southampton,
Highfield Campus, Southampton
SO17 1BJ, UK
| | - Arnaud Basle
- Institute for Cell and Molecular Biosciences, The Medical
School, Newcastle University, Newcastle upon Tyne
NE2 4HH, UK
| | - Syma Khalid
- School of Chemistry, University of Southampton,
Highfield Campus, Southampton
SO17 1BJ, UK
| | - Julian C. Rutherford
- Institute for Cell and Molecular Biosciences, The Medical
School, Newcastle University, Newcastle upon Tyne
NE2 4HH, UK
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30
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Availability of Amino Acids Extends Chronological Lifespan by Suppressing Hyper-Acidification of the Environment in Saccharomyces cerevisiae. PLoS One 2016; 11:e0151894. [PMID: 26991662 PMCID: PMC4798762 DOI: 10.1371/journal.pone.0151894] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 03/04/2016] [Indexed: 11/24/2022] Open
Abstract
The chronological lifespan of Saccharomyces cerevisiae represents the duration of cell survival in the postdiauxic and stationary phases. Using a prototrophic strain derived from the standard auxotrophic laboratory strain BY4742, we showed that supplementation of non-essential amino acids to a synthetic defined (SD) medium increases maximal cell growth and extends the chronological lifespan. The positive effects of amino acids can be reproduced by modulating the medium pH, indicating that amino acids contribute to chronological longevity in a cell-extrinsic manner by alleviating medium acidification. In addition, we showed that the amino acid-mediated effects on extension of chronological longevity are independent of those achieved through a reduction in the TORC1 pathway, which is mediated in a cell-intrinsic manner. Since previous studies showed that extracellular acidification causes mitochondrial dysfunction and leads to cell death, our results provide a path to premature chronological aging caused by differences in available nitrogen sources. Moreover, acidification of culture medium is generally associated with culture duration and cell density; thus, further studies are required on cell physiology of auxotrophic yeast strains during the stationary phase because an insufficient supply of essential amino acids may cause alterations in environmental conditions.
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31
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The TORC1 effector kinase Npr1 fine tunes the inherent activity of the Mep2 ammonium transport protein. Nat Commun 2015; 5:3101. [PMID: 24476960 DOI: 10.1038/ncomms4101] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Accepted: 12/13/2013] [Indexed: 12/30/2022] Open
Abstract
The TORC1 complex controls cell growth upon integrating nutritional signals including amino-acid availability. TORC1 notably adapts the plasma membrane protein content by regulating arrestin-mediated endocytosis of amino-acid transporters. Here we demonstrate that TORC1 further fine tunes the inherent activity of the ammonium transport protein, Mep2, a yeast homologue of mammalian Rhesus factors, independently of arrestin-mediated endocytosis. The TORC1 effector kinase Npr1 and the upstream TORC1 regulator Npr2 control Mep2 transport activity by phospho-silencing a carboxy-terminal autoinhibitory domain. Under poor nitrogen supply, Npr1 enables Mep2 S457 phosphorylation and thus ammonium transport activity. Supplementation of the preferred nitrogen source glutamine leads to Mep2 inactivation and instant S457 dephosphorylation via plasma membrane Psr1 and Psr2 redundant phosphatases. This study underscores that TORC1 also adjusts nutrient permeability to regulate cell growth in a fast and flexible response to environmental perturbation, establishing a hierarchy in the transporters to be degraded, inactivated or maintained active at the plasma membrane.
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32
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Boeckstaens M, Merhi A, Llinares E, Van Vooren P, Springael JY, Wintjens R, Marini AM. Identification of a Novel Regulatory Mechanism of Nutrient Transport Controlled by TORC1-Npr1-Amu1/Par32. PLoS Genet 2015; 11:e1005382. [PMID: 26172854 PMCID: PMC4501750 DOI: 10.1371/journal.pgen.1005382] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 06/22/2015] [Indexed: 01/12/2023] Open
Abstract
Fine-tuning the plasma-membrane permeability to essential nutrients is fundamental to cell growth optimization. Nutritional signals including nitrogen availability are integrated by the TORC1 complex which notably regulates arrestin-mediated endocytosis of amino-acid transporters. Ammonium is a ubiquitous compound playing key physiological roles in many, if not all, organisms. In yeast, it is a preferred nitrogen source transported by three Mep proteins which are orthologues of the mammalian Rhesus factors. By combining genetic, kinetic, biochemical and cell microscopy analyses, the current study reveals a novel mechanism enabling TORC1 to regulate the inherent activity of ammonium transport proteins, independently of arrestin-mediated endocytosis, identifying the still functional orphan Amu1/Par32 as a selective regulator intermediate. We show that, under poor nitrogen supply, the TORC1 effector kinase' Npr1' promotes phosphorylation of Amu1/Par32 which appears mainly cytosolic while ammonium transport proteins are active. Upon preferred nitrogen supplementation, like glutamine or ammonium addition, TORC1 upregulation enables Npr1 inhibition and Amu1/Par32 dephosphorylation. In these conditions, as in Npr1-lacking cells, hypophosphorylated Amu1/Par32 accumulates at the cell surface and mediates the inhibition of specific ammonium transport proteins. We show that the integrity of a conserved repeated motif of Amu1/Par32 is required for the interaction with these transport proteins. This study underscores the diversity of strategies enabling TORC1-Npr1 to selectively monitor cell permeability to nutrients by discriminating between transporters to be degraded or transiently inactivated and kept stable at the plasma membrane. This study further identifies the function of Amu1/Par32 in acute control of ammonium transport in response to variations in nitrogen availability. Cells have evolved a variety of mechanisms to control the permeability of the plasma membrane to face environmental perturbations. Transcriptional regulation, endocytosis, gating and activity control of channels and transporters enable global or specific responses to stressful conditions and focused variations in nutrient availability. Emerging data from the yeast model reveal that the conserved TORC1 pathway regulates arrestin-mediated endocytosis of amino-acid transporters. We provide genetic and biochemical evidence for a novel mechanism enabling TORC1 to regulate the inherent activity of transport proteins via the Amu1/Par32 regulator intermediate. This low complexity protein mediates inhibition of specific proteins dedicated to the transport of ammonium, a favored nitrogen source, underscoring that TORC1 selects transporters to be degraded or transiently inactivated and preserved at the cell surface according to the environmental situation. The here-revealed mechanism of transport inhibition by Amu/Par32 is reminiscent to the inhibition of prokaryotic ammonium transport proteins mediated by PII-type proteins, key nitrogen signal transducers widespread in bacteria and Archaea.
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Affiliation(s)
- Mélanie Boeckstaens
- Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, Gosselies, Belgium
| | - Ahmad Merhi
- Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, Gosselies, Belgium
| | - Elisa Llinares
- Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, Gosselies, Belgium
| | - Pascale Van Vooren
- Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, Gosselies, Belgium
| | | | - René Wintjens
- Laboratoire des Biopolymères et des nanomatériaux supramoléculaires, Université Libre de Bruxelles, Brussels, Belgium
| | - Anna Maria Marini
- Biology of Membrane Transport, IBMM, Université Libre de Bruxelles, Gosselies, Belgium
- * E-mail:
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33
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Pfannmüller A, Wagner D, Sieber C, Schönig B, Boeckstaens M, Marini AM, Tudzynski B. The General Amino Acid Permease FfGap1 of Fusarium fujikuroi Is Sorted to the Vacuole in a Nitrogen-Dependent, but Npr1 Kinase-Independent Manner. PLoS One 2015; 10:e0125487. [PMID: 25909858 PMCID: PMC4409335 DOI: 10.1371/journal.pone.0125487] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Accepted: 03/14/2015] [Indexed: 12/18/2022] Open
Abstract
The rice pathogenic fungus Fusarium fujikuroi is well known for the production of a broad spectrum of secondary metabolites (SMs) such as gibberellic acids (GAs), mycotoxins and pigments. The biosynthesis of most of these SMs strictly depends on nitrogen availability and of the activity of permeases of nitrogen sources, e.g. the ammonium and amino acid permeases. One of the three ammonium permeases, MepB, was recently shown to act not only as a transporter but also as a nitrogen sensor affecting the production of nitrogen-repressed SMs. Here we describe the identification of a general amino acid permease, FfGap1, among the 99 putative amino acid permeases (AAPs) in the genome of F. fujikuroi. FfGap1 is able to fully restore growth of the yeast gap1∆ mutant on several amino acids including citrulline and tryptophane. In S. cerevisiae, Gap1 activity is regulated by shuttling between the plasma membrane (nitrogen limiting conditions) and the vacuole (nitrogen sufficiency), which we also show for FfGap1. In yeast, the Npr1 serine/threonine kinase stabilizes the Gap1 position at the plasma membrane. Here, we identified and characterized three NPR1-homologous genes, encoding the putative protein kinases FfNpr1-1, FfNpr1-2 and FfNpr1-3 with significant similarity to yeast Npr1. Complementation of the yeast npr1Δ mutant with each of the three F. fujikuroi NPR1 homologues, resulted in partial restoration of ammonium, arginine and proline uptake by FfNPR1-1 while none of the three kinases affect growth on different nitrogen sources and nitrogen-dependent sorting of FfGap1 in F. fujikuroi. However, exchange of the putative ubiquitin-target lysine 9 (K9A) and 15 (K15A) residues of FfGap1 resulted in extended localization to the plasma membrane and increased protein stability independently of nitrogen availability. These data suggest a similar regulation of FfGap1 by nitrogen-dependent ubiquitination, but differences regarding the role of Fusarium Npr1 homologues compared to yeast.
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Affiliation(s)
- Andreas Pfannmüller
- Institut für Biologie und Biotechnologie der Pflanzen, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Dominik Wagner
- Institut für Biologie und Biotechnologie der Pflanzen, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Christian Sieber
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Neuherberg, Germany
| | - Birgit Schönig
- Institut für Biologie und Biotechnologie der Pflanzen, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Mélanie Boeckstaens
- Laboratoire de Biologie du Transport Membranaire, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, Gosselies, Belgium
| | - Anna Maria Marini
- Laboratoire de Biologie du Transport Membranaire, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, Gosselies, Belgium
| | - Bettina Tudzynski
- Institut für Biologie und Biotechnologie der Pflanzen, Westfälische Wilhelms-Universität Münster, Münster, Germany
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34
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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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35
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Bai L, Zhou Y, Ma X, Gao L, Song CP. Arabidopsis CAP1-mediated ammonium sensing required reactive oxygen species in plant cell growth. PLANT SIGNALING & BEHAVIOR 2014; 9:e29582. [PMID: 25763633 PMCID: PMC4205142 DOI: 10.4161/psb.29582] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 06/13/2014] [Accepted: 06/13/2014] [Indexed: 05/24/2023]
Abstract
[Ca(2+)]cyt-associated protein kinase (CAP) gene 1 is a receptor-like kinase that belongs to CrRLK1L (Catharanthus roseus Receptor like kinase) subfamily. CAP1 has been identified as a novel modulator of NH4(+) in the tonoplast, which regulates root hair growth by maintaining the cytoplasmic Ca(2+) gradients. Different expression pattern of tonoplast intrinsic protein (TIP2;3) in the CAP1 knock out mutant and wild type on Murashige and Skoog (MS) medium suggested that CAP1 influences transport activity to regulate the compartmentalization of NH4(+) into vacuole. Lower expression level of Oxidative Signal-Inducible1(OXI1) in the cap1-1 root and the abnormal reactive oxygen species (ROS) gradient in root hair of cap1-1 on MS medium indicated that ROS signaling involve in CAP1-regulated root hair growth. Wild-type-like ROS distribution pattern in the cap1-1 root hair can be reestablished in seedlings grown on NH4(+) deficient medium, which indicated that CAP1 functions as a sensor for NH4(+) signaling in maintaining tip-focused ROS gradient in root hairs polar growth.
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Abstract
For centuries yeast species have been popular hosts for classical biotechnology processes, such as baking, brewing, and wine making, and more recently for recombinant proteins production, thanks to the advantages of unicellular organisms (i.e., ease of genetic manipulation and rapid growth) together with the ability to perform eukaryotic posttranslational modifications. Moreover, yeast cells have been used for few decades as a tool for identifying the genes and pathways involved in basic cellular processes such as the cell cycle, aging, and stress response. In the budding yeast S. cerevisiae the Ras/cAMP/PKA pathway is directly involved in the regulation of metabolism, cell growth, stress resistance, and proliferation in response to the availability of nutrients and in the adaptation to glucose, controlling cytosolic cAMP levels and consequently the cAMP-dependent protein kinase (PKA) activity. Moreover, Ras signalling has been identified in several pathogenic yeasts as a key controller for virulence, due to its involvement in yeast morphogenesis. Nowadays, yeasts are still useful for Ras-like proteins investigation, both as model organisms and as a test tube to study variants of heterologous Ras-like proteins.
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Affiliation(s)
- Renata Tisi
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy
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van Heeswijk WC, Westerhoff HV, Boogerd FC. Nitrogen assimilation in Escherichia coli: putting molecular data into a systems perspective. Microbiol Mol Biol Rev 2013; 77:628-95. [PMID: 24296575 PMCID: PMC3973380 DOI: 10.1128/mmbr.00025-13] [Citation(s) in RCA: 159] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
We present a comprehensive overview of the hierarchical network of intracellular processes revolving around central nitrogen metabolism in Escherichia coli. The hierarchy intertwines transport, metabolism, signaling leading to posttranslational modification, and transcription. The protein components of the network include an ammonium transporter (AmtB), a glutamine transporter (GlnHPQ), two ammonium assimilation pathways (glutamine synthetase [GS]-glutamate synthase [glutamine 2-oxoglutarate amidotransferase {GOGAT}] and glutamate dehydrogenase [GDH]), the two bifunctional enzymes adenylyl transferase/adenylyl-removing enzyme (ATase) and uridylyl transferase/uridylyl-removing enzyme (UTase), the two trimeric signal transduction proteins (GlnB and GlnK), the two-component regulatory system composed of the histidine protein kinase nitrogen regulator II (NRII) and the response nitrogen regulator I (NRI), three global transcriptional regulators called nitrogen assimilation control (Nac) protein, leucine-responsive regulatory protein (Lrp), and cyclic AMP (cAMP) receptor protein (Crp), the glutaminases, and the nitrogen-phosphotransferase system. First, the structural and molecular knowledge on these proteins is reviewed. Thereafter, the activities of the components as they engage together in transport, metabolism, signal transduction, and transcription and their regulation are discussed. Next, old and new molecular data and physiological data are put into a common perspective on integral cellular functioning, especially with the aim of resolving counterintuitive or paradoxical processes featured in nitrogen assimilation. Finally, we articulate what still remains to be discovered and what general lessons can be learned from the vast amounts of data that are available now.
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Ellerbeck M, Schüßler A, Brucker D, Dafinger C, Loos F, Brachmann A. Characterization of three ammonium transporters of the glomeromycotan fungus Geosiphon pyriformis. EUKARYOTIC CELL 2013; 12:1554-62. [PMID: 24058172 PMCID: PMC3837933 DOI: 10.1128/ec.00139-13] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Accepted: 09/15/2013] [Indexed: 11/20/2022]
Abstract
Members of the Glomeromycota form the arbuscular mycorrhiza (AM) symbiosis. They supply plants with inorganic nutrients, including nitrogen, from the soil. To gain insight into transporters potentially facilitating nitrogen transport processes, ammonium transporters (AMTs) of Geosiphon pyriformis, a glomeromycotan fungus forming a symbiosis with cyanobacteria, were studied. Three AMT genes were identified, and all three were expressed in the symbiotic stage. The localization and functional characterization of the proteins in a heterologous yeast system revealed distinct characteristics for each of them. AMT1 of G. pyriformis (GpAMT1) and GpAMT2 were both plasma membrane localized, but only GpAMT1 transported ammonium. Neither protein transported the ammonium analogue methylammonium. Unexpectedly, GpAMT3 was localized in the vacuolar membrane, and it has as-yet-unknown transport characteristics. An unusual cysteine residue in the AMT signature of GpAMT2 and GpAMT3 was identified, and the corresponding residue was demonstrated to play an important role in ammonium transport. Surprisingly, each of the three AMTs of G. pyriformis had very distinct features. The localization of an AMT in the yeast vacuolar membrane is novel, as is the described amino acid residue that clearly influences ammonium transport. The AMT characteristics might reflect adaptations to the lifestyle of glomeromycotan fungi.
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Scherzer S, Krol E, Kreuzer I, Kruse J, Karl F, von Rüden M, Escalante-Perez M, Müller T, Rennenberg H, Al-Rasheid KAS, Neher E, Hedrich R. The Dionaea muscipula ammonium channel DmAMT1 provides NH₄⁺ uptake associated with Venus flytrap's prey digestion. Curr Biol 2013; 23:1649-57. [PMID: 23954430 DOI: 10.1016/j.cub.2013.07.028] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 05/07/2013] [Accepted: 07/03/2013] [Indexed: 01/07/2023]
Abstract
BACKGROUND Ammonium transporter (AMT/MEP/Rh) superfamily members mediate ammonium uptake and retrieval. This pivotal transport system is conserved among all living organisms. For plants, nitrogen represents a macronutrient available in the soil as ammonium, nitrate, and organic nitrogen compounds. Plants living on extremely nutrient-poor soils have developed a number of adaptation mechanisms, including a carnivorous lifestyle. This study addresses the molecular nature, function, and regulation of prey-derived ammonium uptake in the Venus flytrap, Dionaea muscipula, one of the fastest active carnivores. RESULTS The Dionaea muscipula ammonium transporter DmAMT1 was localized in gland complexes where its expression was upregulated upon secretion. These clusters of cells decorating the inner trap surface are engaged in (1) secretion of an acidic digestive enzyme cocktail and (2) uptake of prey-derived nutrients. Voltage clamp of Xenopus oocytes expressing DmAMT1 and membrane potential recordings with DmAMT1-expressing Dionaea glands were used to monitor and compare electrophysiological properties of DmAMT1 in vitro and in planta. DmAMT1 exhibited the hallmark biophysical properties of a NH4(+)-selective channel. At depolarized membrane potentials (Vm = 0), the Km (3.2 ± 0.3 mM) indicated a low affinity of DmAMT1 for ammonium that increased systematically with negative going voltages. Upon hyperpolarization to, e.g., -200 mV, a Km of 0.14 ± 0.015 mM documents the voltage-dependent shift of DmAMT1 into a NH4(+) transport system of high affinity. CONCLUSIONS We suggest that regulation of glandular DmAMT1 and membrane potential readjustments of the endocrine cells provide for effective adaptation to varying, prey-derived ammonium sources.
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Affiliation(s)
- Sönke Scherzer
- Institute for Molecular Plant Physiology and Biophysics, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany; Department for Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, 37077 Goettingen, Germany
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Deschuyteneer A, Boeckstaens M, De Mees C, Van Vooren P, Wintjens R, Marini AM. SNPs altering ammonium transport activity of human Rhesus factors characterized by a yeast-based functional assay. PLoS One 2013; 8:e71092. [PMID: 23967154 PMCID: PMC3742762 DOI: 10.1371/journal.pone.0071092] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 06/24/2013] [Indexed: 01/23/2023] Open
Abstract
Proteins of the conserved Mep-Amt-Rh family, including mammalian Rhesus factors, mediate transmembrane ammonium transport. Ammonium is an important nitrogen source for the biosynthesis of amino acids but is also a metabolic waste product. Its disposal in urine plays a critical role in the regulation of the acid/base homeostasis, especially with an acid diet, a trait of Western countries. Ammonium accumulation above a certain concentration is however pathologic, the cytotoxicity causing fatal cerebral paralysis in acute cases. Alteration in ammonium transport via human Rh proteins could have clinical outcomes. We used a yeast-based expression assay to characterize human Rh variants resulting from non synonymous single nucleotide polymorphisms (nsSNPs) with known or unknown clinical phenotypes and assessed their ammonium transport efficiency, protein level, localization and potential trans-dominant impact. The HsRhAG variants (I61R, F65S) associated to overhydrated hereditary stomatocytosis (OHSt), a disease affecting erythrocytes, proved affected in intrinsic bidirectional ammonium transport. Moreover, this study reveals that the R202C variant of HsRhCG, the orthologue of mouse MmRhcg required for optimal urinary ammonium excretion and blood pH control, shows an impaired inherent ammonium transport activity. Urinary ammonium excretion was RHcg gene-dose dependent in mouse, highlighting MmRhcg as a limiting factor. HsRhCG(R202C) may confer susceptibility to disorders leading to metabolic acidosis for instance. Finally, the analogous R211C mutation in the yeast ScMep2 homologue also impaired intrinsic activity consistent with a conserved functional role of the preserved arginine residue. The yeast expression assay used here constitutes an inexpensive, fast and easy tool to screen nsSNPs reported by high throughput sequencing or individual cases for functional alterations in Rh factors revealing potential causal variants.
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Affiliation(s)
- Aude Deschuyteneer
- Biologie du Transport Membranaire, Université Libre de Bruxelles, Gosselies, Belgium
| | - Mélanie Boeckstaens
- Biologie du Transport Membranaire, Université Libre de Bruxelles, Gosselies, Belgium
| | - Christelle De Mees
- Biologie du Transport Membranaire, Université Libre de Bruxelles, Gosselies, Belgium
| | - Pascale Van Vooren
- Biologie du Transport Membranaire, Université Libre de Bruxelles, Gosselies, Belgium
| | - René Wintjens
- Laboratoire des Biopolymères et des nanomatériaux supramoléculaires, Université Libre de Bruxelles, Brussels, Belgium
| | - Anna Maria Marini
- Biologie du Transport Membranaire, Université Libre de Bruxelles, Gosselies, Belgium
- * E-mail:
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41
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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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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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Wang J, Fulford T, Shao Q, Javelle A, Yang H, Zhu W, Merrick M. Ammonium transport proteins with changes in one of the conserved pore histidines have different performance in ammonia and methylamine conduction. PLoS One 2013; 8:e62745. [PMID: 23667517 PMCID: PMC3647058 DOI: 10.1371/journal.pone.0062745] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Accepted: 03/25/2013] [Indexed: 01/02/2023] Open
Abstract
Two conserved histidine residues are located near the mid-point of the conduction channel of ammonium transport proteins. The role of these histidines in ammonia and methylamine transport was evaluated by using a combination of in vivo studies, molecular dynamics (MD) simulation, and potential of mean force (PMF) calculations. Our in vivo results showed that a single change of either of the conserved histidines to alanine leads to the failure to transport methylamine but still facilitates good growth on ammonia, whereas double histidine variants completely lose their ability to transport both methylamine and ammonia. Molecular dynamics simulations indicated the molecular basis of the in vivo observations. They clearly showed that a single histidine variant (H168A or H318A) of AmtB confines the rather hydrophobic methylamine more strongly than ammonia around the mutated sites, resulting in dysfunction in conducting the former but not the latter molecule. PMF calculations further revealed that the single histidine variants form a potential energy well of up to 6 kcal/mol for methylamine, impairing conduction of this substrate. Unlike the single histidine variants, the double histidine variant, H168A/H318A, of AmtB was found to lose its unidirectional property of transporting both ammonia and methylamine. This could be attributed to a greatly increased frequency of opening of the entrance gate formed by F215 and F107, in this variant compared to wild-type, with a resultant lowering of the energy barrier for substrate to return to the periplasm.
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Affiliation(s)
- Jinan Wang
- Drug Discovery and Design Center, CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
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44
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Hall JA, Yan D. The molecular basis of K+ exclusion by the Escherichia coli ammonium channel AmtB. J Biol Chem 2013; 288:14080-14086. [PMID: 23546877 DOI: 10.1074/jbc.m113.457952] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Members of the Amt family of channels mediate the transport of ammonium. The form of ammonium, NH3 or NH4(+), carried by these proteins remains controversial, and the mechanism by which they select against K(+) ions is unclear. We describe here a set of Escherichia coli AmtB proteins carrying mutations at the conserved twin-histidine site within the conduction pore that have altered substrate specificity and now transport K(+). Subsequent work established that AmtB-mediated K(+) uptake occurred against a concentration gradient and was membrane potential-dependent. These findings indicate that the twin-histidine element serves as a filter to prevent K(+) conduction and strongly support the notion that Amt proteins transport cations (NH4(+) or, in mutant proteins, K(+)) rather than NH3 gas molecules through their conduction pores.
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Affiliation(s)
- Jason A Hall
- Division of Biological Sciences, University of California San Diego, La Jolla, California 92093-0374.
| | - Dalai Yan
- Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120
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45
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46
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Wang S, Orabi EA, Baday S, Bernèche S, Lamoureux G. Ammonium Transporters Achieve Charge Transfer by Fragmenting Their Substrate. J Am Chem Soc 2012; 134:10419-27. [DOI: 10.1021/ja300129x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Shihao Wang
- Department of Chemistry and
Biochemistry and Centre for Research in Molecular Modeling (CERMM), Concordia University, 7141 Sherbrooke Street West,
Montréal, Québec H4B 1R6, Canada
| | - Esam A. Orabi
- Department of Chemistry and
Biochemistry and Centre for Research in Molecular Modeling (CERMM), Concordia University, 7141 Sherbrooke Street West,
Montréal, Québec H4B 1R6, Canada
| | - Sefer Baday
- Swiss Institute of Bioinformatics
and Biozentrum, University of Basel, Klingelbergstrasse
50/70, CH-4056 Basel, Switzerland
| | - Simon Bernèche
- Swiss Institute of Bioinformatics
and Biozentrum, University of Basel, Klingelbergstrasse
50/70, CH-4056 Basel, Switzerland
| | - Guillaume Lamoureux
- Department of Chemistry and
Biochemistry and Centre for Research in Molecular Modeling (CERMM), Concordia University, 7141 Sherbrooke Street West,
Montréal, Québec H4B 1R6, Canada
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Abstract
Filamentous growth is a nutrient-regulated growth response that occurs in many fungal species. In pathogens, filamentous growth is critical for host-cell attachment, invasion into tissues, and virulence. The budding yeast Saccharomyces cerevisiae undergoes filamentous growth, which provides a genetically tractable system to study the molecular basis of the response. Filamentous growth is regulated by evolutionarily conserved signaling pathways. One of these pathways is a mitogen activated protein kinase (MAPK) pathway. A remarkable feature of the filamentous growth MAPK pathway is that it is composed of factors that also function in other pathways. An intriguing challenge therefore has been to understand how pathways that share components establish and maintain their identity. Other canonical signaling pathways-rat sarcoma/protein kinase A (RAS/PKA), sucrose nonfermentable (SNF), and target of rapamycin (TOR)-also regulate filamentous growth, which raises the question of how signals from multiple pathways become integrated into a coordinated response. Together, these pathways regulate cell differentiation to the filamentous type, which is characterized by changes in cell adhesion, cell polarity, and cell shape. How these changes are accomplished is also discussed. High-throughput genomics approaches have recently uncovered new connections to filamentous growth regulation. These connections suggest that filamentous growth is a more complex and globally regulated behavior than is currently appreciated, which may help to pave the way for future investigations into this eukaryotic cell differentiation behavior.
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48
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Pantoja O. High affinity ammonium transporters: molecular mechanism of action. FRONTIERS IN PLANT SCIENCE 2012; 3:34. [PMID: 22645581 PMCID: PMC3355798 DOI: 10.3389/fpls.2012.00034] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2011] [Accepted: 02/06/2012] [Indexed: 05/26/2023]
Abstract
The importance of the family of high affinity ammonium transporters is demonstrated by the presence of these proteins in all domains of life, including bacteria, archaea, fungi, plants, and humans. The majority of the proteins that have been studied from this family show high affinity and selectivity for ammonium, are impermeable to alkaline cations, saturate rapidly at low millimolar concentrations and most of them, are also permeable to methylammonium. Crystallization of homologue proteins from bacteria and archaea has demonstrated that the functional entity corresponds to a trimer, with each monomer maintaining a conductive pore. Through molecular modeling, it has been demonstrated that even though the identity of the proteins between bacteria/archaea with those from plants is below 25%, the latter seem to maintain similar tertiary and quaternary structures, an observation that has helped to address the functionality of conserved residues by means of mutational analysis. Results have shown that changes in the extracellular binding site of some plant transporters may result in their inhibition or reduction in transport activity, while in Escherichia coli, dissimilar replacements like Phe/Ala or Ser/Leu that eliminate possible π-interactions or H-bonds with ammonium, respectively, lead to more active transporters. Active mutants with changes in the pair of conserved His in the center of the transporter suggest these residues are dispensable. Additional mutations have identified other important amino acids, both in the entrance of the pore and in cytoplasmic loops. Regulation of this family of transporters can be achieved by interactions of the C-terminal with cytoplasmic loops within the same monomer, or with a neighbor in the trimer. Depending on the interacting residues, these contacts may lead to the activation or inhibition of the protein. The aim of this review is to critically evaluate the newest findings on the role of the proposed amino acids that structure the ammonium pathway, as well as highlight the importance of additional residues that have been identified through mutational analyses.
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Affiliation(s)
- Omar Pantoja
- Instituto de Biotecnología, Universidad Nacional Autónoma de MéxicoCuernavaca, México
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Ortiz-Ramirez C, Mora SI, Trejo J, Pantoja O. PvAMT1;1, a highly selective ammonium transporter that functions as H+/NH4(+) symporter. J Biol Chem 2011; 286:31113-22. [PMID: 21757699 PMCID: PMC3173114 DOI: 10.1074/jbc.m111.261693] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2011] [Revised: 07/04/2011] [Indexed: 01/26/2023] Open
Abstract
One of the main forms of nitrogen assimilated by microorganisms and plants is ammonium, despite its toxicity at low millimolar concentrations. Ammonium absorption has been demonstrated to be carried out by highly selective plasma membrane-located transporters of the AMT/MEP/Rh family and characterized by the presence of a well conserved hydrophobic pore through which ammonia is proposed to move. However, uncertainties exist regarding the exact chemical species transported by these membrane proteins, which can be in the form of either hydrophobic ammonia or charged ammonium. Here, we present the characterization of PvAMT1;1 from the common bean and demonstrate that it mediates the high affinity (micromolar), rapidly saturating (1 mM) electrogenic transport of ammonium. Activity of the transporter is enhanced by low extracellular pH, and associated with this acidic pH stimulation are changes in the reversal potential and cytoplasm acidification, indicating that PvAMT1;1 functions as an H(+)/NH(4)(+) symporter. Mutation analysis of a unique histidine present in PvAMT1;1 (H125R) leads to the stimulation of ammonium transport by decreasing the K(m) value by half and by increasing the V(max) 3-fold, without affecting the pH dependence of the symporter. In contrast, mutation of the first conserved histidine within the channel modifies the properties of PvAMT1;1, increasing its K(m) and V(max) values and transforming it into a pH-independent mechanism.
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Affiliation(s)
- Carlos Ortiz-Ramirez
- From the Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, A. P. 510-3, Colonia Miraval, Cuernavaca, Morelos 62250, México
| | - Silvia I. Mora
- From the Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, A. P. 510-3, Colonia Miraval, Cuernavaca, Morelos 62250, México
| | - Jorge Trejo
- From the Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, A. P. 510-3, Colonia Miraval, Cuernavaca, Morelos 62250, México
| | - Omar Pantoja
- From the Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, A. P. 510-3, Colonia Miraval, Cuernavaca, Morelos 62250, México
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The pivotal twin histidines and aromatic triad of the Escherichia coli ammonium channel AmtB can be replaced. Proc Natl Acad Sci U S A 2011; 108:13270-4. [PMID: 21775672 DOI: 10.1073/pnas.1108451108] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In Escherichia coli, each subunit of the trimeric channel protein AmtB carries a hydrophobic pore for transport of NH(4)(+) across the cytoplasmic membrane. Positioned along this substrate conduction pathway are two conserved elements--a pair of hydrogen-bonded histidines (H168/H318) located within the pore itself and a set of aromatic residues (F107/W148/F215) at its periplasmic entrance--thought to be critical to AmtB function. Using site-directed mutagenesis and suppressor genetics, we examined the requirement for these elements in NH(4)(+) transport. This analysis shows that AmtB can accommodate, by either direct substitution or suppressor generation, acidic residues at one or both positions of the H168/H318 twin-histidine site while retaining near wild-type activity. Similarly, study of the F107/W148/F215 triad indicates that good-to-excellent AmtB function is preserved upon individual and simultaneous replacement of these aromatic amino acids with aliphatic residues. Our findings lead us to conclude that these elements and their component parts are not required for AmtB function, but instead serve to optimize its performance.
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