TU Darmstadt / ULB / TUbiblio

Different transport mechanisms in plant and human AMT/Rh-type ammonium transporters

Mayer, Maria and Schaaf, Gabriel and Mouro, Isabelle and Lopez, Claude and Colin, Yves and Neumann, Petra and Cartron, Jean-Pierre and Ludewig, Uwe (2006):
Different transport mechanisms in plant and human AMT/Rh-type ammonium transporters.
In: The Journal of general physiology, pp. 133-44, 127, (2), ISSN 0022-1295, [Article]

Abstract

The conserved family of AMT/Rh proteins facilitates ammonium transport across animal, plant, and microbial membranes. A bacterial homologue, AmtB, forms a channel-like structure and appears to function as an NH3 gas channel. To evaluate the function of eukaryotic homologues, the human RhCG glycoprotein and the tomato plant ammonium transporter LeAMT1;2 were expressed and compared in Xenopus oocytes and yeast. RhCG mediated the electroneutral transport of methylammonium (MeA), which saturated with Km = 3.8 mM at pHo 7.5. Uptake was strongly favored by increasing the pHo and was inhibited by ammonium. Ammonium induced rapid cytosolic alkalinization in RhCG-expressing oocytes. Additionally, RhCG expression was associated with an alkali-cation conductance, which was not significantly permeable to NH4+ and was apparently uncoupled from the ammonium transport. In contrast, expression of the homologous LeAMT1;2 induced pHo-independent MeA+ uptake and specific NH4+ and MeA+ currents that were distinct from endogenous currents. The different mechanisms of transport, including the RhCG-associated alkali-cation conductance, were verified by heterologous expression in appropriate yeast strains. Thus, homologous AMT/Rh-type proteins function in a distinct manner; while LeAMT1;2 carries specifically NH4+, or cotransports NH3/H+, RhCG mediates electroneutral NH3 transport.

Item Type: Article
Erschienen: 2006
Creators: Mayer, Maria and Schaaf, Gabriel and Mouro, Isabelle and Lopez, Claude and Colin, Yves and Neumann, Petra and Cartron, Jean-Pierre and Ludewig, Uwe
Title: Different transport mechanisms in plant and human AMT/Rh-type ammonium transporters
Language: English
Abstract:

The conserved family of AMT/Rh proteins facilitates ammonium transport across animal, plant, and microbial membranes. A bacterial homologue, AmtB, forms a channel-like structure and appears to function as an NH3 gas channel. To evaluate the function of eukaryotic homologues, the human RhCG glycoprotein and the tomato plant ammonium transporter LeAMT1;2 were expressed and compared in Xenopus oocytes and yeast. RhCG mediated the electroneutral transport of methylammonium (MeA), which saturated with Km = 3.8 mM at pHo 7.5. Uptake was strongly favored by increasing the pHo and was inhibited by ammonium. Ammonium induced rapid cytosolic alkalinization in RhCG-expressing oocytes. Additionally, RhCG expression was associated with an alkali-cation conductance, which was not significantly permeable to NH4+ and was apparently uncoupled from the ammonium transport. In contrast, expression of the homologous LeAMT1;2 induced pHo-independent MeA+ uptake and specific NH4+ and MeA+ currents that were distinct from endogenous currents. The different mechanisms of transport, including the RhCG-associated alkali-cation conductance, were verified by heterologous expression in appropriate yeast strains. Thus, homologous AMT/Rh-type proteins function in a distinct manner; while LeAMT1;2 carries specifically NH4+, or cotransports NH3/H+, RhCG mediates electroneutral NH3 transport.

Journal or Publication Title: The Journal of general physiology
Volume: 127
Number: 2
Divisions: 10 Department of Biology > Plant Nutrition and Biomass
?? fb10_botanik ??
10 Department of Biology
Date Deposited: 16 Mar 2010 14:05
Export:

Optionen (nur für Redakteure)

View Item View Item