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EcoSal Plus

Domain 3:

Metabolism

Ammonia Transport

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  • Author: Ned S. Wingreen1
  • Editor: Valley Stewart2
  • VIEW AFFILIATIONS HIDE AFFILIATIONS
    Affiliations: 1: Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014; 2: University of California, Davis, Davis, CA
  • Received 27 May 2004 Accepted 11 August 2004 Published 15 November 2004
  • Address correspondence to Ned S. Wingreen wingreen@princeton.edu
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  • Abstract:

    This review reviews the ammonium/methylammonium transport (Amt) proteins of and serovar Typhimurium. The Amt proteins and their homologs, the methylammonium/ammonium permease proteins of , constitute a distinct class of membrane-associated ammonia transporters. Members of the Amt family are found in archaea, bacteria, fungi, plants, and invertebrate animals. In and serovar Typhimurium, the Amt proteins are essential to maintain maximal growth at low concentrations of ammonia, the preferred nitrogen source. Soupene and coworkers showed that a mutant of with only the low-affinity glutamate dehydrogenase pathway for assimilation of ammonia, which therefore grows slowly at low ammonia concentrations, is not relieved of its growth defect by overexpression of AmtB. A recent study on an Amt protein from tomato concluded that it was a specific transporter for NH4. A trimeric stoichiometry for AmtB is supported by the observation of a direct interaction between AmtB and the trimeric signal-transduction protein GlnK. In , GlnK has been observed to associate with the membrane in an AmtB-dependent fashion. Both GlnK and GlnB are sensors of nitrogen status. Their interaction with AmtB suggests a role for AmtB in nitrogen regulation. In summary, AmtB is a membrane-associated ammonia transporter that is important for growth at external concentrations of the uncharged species (NH) below about 50 nM. The preponderance of evidence suggests that AmtB specifically transports the charged species (NH ) and that this transport is passive and, hence, bidirectional.

  • Citation: Wingreen N. 2004. Ammonia Transport, EcoSal Plus 2004; doi:10.1128/ecosalplus.3.3.2.1

Key Concept Ranking

Cold Shock Response
0.38103026
Nitrogen Sources
0.36401996
Saccharomyces cerevisiae
0.34848484
AmtB Protein
0.32492897
0.38103026

References

1. Soupene E, Lee H, Kustu S. 2002. Ammonium/methylammonium transport (Amt) proteins facilitate diffusion of NH3 bidirectionally. Proc Natl Acad Sci USA 99:3926–3931. [PubMed][CrossRef]
2. Ludewig U, von Wiren N, Frommer WB. 2002. Uniport of NH4+ by the root hair plasma membrane ammonium transporter LeAmt1;1. J Biol Chem 277:13548–13555. [PubMed][CrossRef]
3. Soupene E, He L, Yan D, Kustu S. 1998. Ammonia acquisition in enteric bacteria: Physiological role of the ammonium/methylammonium transport B (AmtB) protein. Proc Natl Acad Sci USA 95:7030–7034. [PubMed][CrossRef]
4. Soupene E, Ramirez RM, Kustu S. 2001. Evidence that fungal MEP proteins mediate diffusion of the uncharged species NH3 across the cytoplasmic membrane. Mol Cell Biol 21:5733–5741. [PubMed][CrossRef]
5. van Heeswijk WC, Hoving S, Molenaar D, Stegeman B, Kahn D, Westerhoff HV. 1996. An alternative PII protein in the regulation of glutamine synthetase in Escherichia coli. Mol Microbiol 21:133–146. [PubMed][CrossRef]
6. Thomas GH, Mullins JGL, Merrick M. 2000. Membrane topology of the Mep/Amt family of ammonium transporters. Mol Microbiol 37:331–344. [PubMed][CrossRef]
7. Blakey D, Leech A, Thomas GH, Coutts G, Findlay K, Merrick M. 2002. Purification of the Escherichia coli ammonium transporter AmtB reveals a trimeric stoichiometry. Biochem J 364:527–535. [PubMed][CrossRef]
8. Coutts G, Thomas G, Blakey D, Merrick M. 2002. Membrane sequestration of the signal transduction protein GlnK by the ammonium transporter AmtB. EMBO J 21:536–545. [PubMed][CrossRef]
9. Xu Y, Cheah E, Carr PD, van Heeswijk WC, Westerhoff HV, Vasudevan SG, Ollis D. 1998. GlnK, a PII-homologue: structure reveals ATP binding site and indicates how the T-loops may be involved in molecular recognition. J Mol Biol 282:149–165. [PubMed][CrossRef]
10. Carr PD, Cheah E, Suffolk PM, Vasudevan SG, Dixon NE, Ollis DL. 1996. X-ray structure of the signal transduction protein PII from Escherichia coli at 1.9 angstrom. Acta Crystallogr Sect D Biol Crystallogr 52:93–104. [CrossRef]
11. van Heeswijk WC, Wen D, Clancy P, Jaggi R, Ollis DL, Westerhoff HV, Vasudevan SG. 2000. The Escherichia coli signal transducers PII (GlnB) and GlnK form heterotrimers in vivo: fine tuning the nitrogen signal cascade. Proc Natl Acad Sci USA 97:3942–3947. [PubMed][CrossRef]
12. Blauwkamp TA, Ninfa AJ. 2003. Antagonism of PII signaling by the AmtB protein of Escherichia coli. Mol Microbiol 48:1017–1028. [PubMed][CrossRef]
13. Thomas GH, Coutts G, Merrick M. 2000. The glnKamtB operon a conserved gene pair in prokaryotes. Trends Genet 16:11–14. [PubMed][CrossRef]
14. Atkinson MR, Ninfa AJ. 1998. Role of the GlnK signal transduction protein in the regulation of nitrogen assimilation in Escherichia coli. Mol Microbiol 29:431–447. [PubMed][CrossRef]
15. Marini A-M, Urrestarazu A, Beauwens R, Andre B. 1997. The Rh (Rhesus) blood group polypeptides are related to NH4+ transporters. Trends Biochem Sci 22:460–461. [PubMed][CrossRef]
16. Soupene E, King N, Feild E, Liu P, Niyogi KK, Huang C-H, Kustu S. 2002. Rhesus expression in a green alga is regulated by CO2. Proc Natl Acad Sci USA 99:7769–7773. [PubMed][CrossRef]
17. Ikeda TP, Shauger AE, Kustu S. 1996. Salmonella typhimurium apparently perceives external nitrogen limitation as internal glutamine limitation. J Mol Biol 259:589–607. [PubMed][CrossRef]
18. Kleiner D. 1985. Bacterial ammonium transport. FEMS Microbiol Rev 32:87–100. [CrossRef]
19. Eigen M. 1967. Immeasurably fast reactions (Nobel Lecture). [online.] Nobel e-Museum. http://www.nobel.se/chemistry/laureates/1967/eigen-lecture.html.
20. Tajkhorshid E, Nollert P, Jensen MO, Miercke LJW, O’Connell J, Stroud RM, Schulten K. 2002. Control of the selectivity of the aquaporin water channel family by global orientational tuning. Science 296:525–530. [CrossRef]
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/content/journal/ecosalplus/10.1128/ecosalplus.3.3.2.1
2004-11-15
2017-05-29

Abstract:

This review reviews the ammonium/methylammonium transport (Amt) proteins of and serovar Typhimurium. The Amt proteins and their homologs, the methylammonium/ammonium permease proteins of , constitute a distinct class of membrane-associated ammonia transporters. Members of the Amt family are found in archaea, bacteria, fungi, plants, and invertebrate animals. In and serovar Typhimurium, the Amt proteins are essential to maintain maximal growth at low concentrations of ammonia, the preferred nitrogen source. Soupene and coworkers showed that a mutant of with only the low-affinity glutamate dehydrogenase pathway for assimilation of ammonia, which therefore grows slowly at low ammonia concentrations, is not relieved of its growth defect by overexpression of AmtB. A recent study on an Amt protein from tomato concluded that it was a specific transporter for NH4. A trimeric stoichiometry for AmtB is supported by the observation of a direct interaction between AmtB and the trimeric signal-transduction protein GlnK. In , GlnK has been observed to associate with the membrane in an AmtB-dependent fashion. Both GlnK and GlnB are sensors of nitrogen status. Their interaction with AmtB suggests a role for AmtB in nitrogen regulation. In summary, AmtB is a membrane-associated ammonia transporter that is important for growth at external concentrations of the uncharged species (NH) below about 50 nM. The preponderance of evidence suggests that AmtB specifically transports the charged species (NH ) and that this transport is passive and, hence, bidirectional.

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Figures

Image of Figure 1
Figure 1

Positively charged residues are shown in black. The overall charge of each loop is indicated. Thomas et al. ( 6 ).

Citation: Wingreen N. 2004. Ammonia Transport, EcoSal Plus 2004; doi:10.1128/ecosalplus.3.3.2.1
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