Amt - Ammonia/Ammonium Transporter
Family:
Ammonia transporters
Members:
Amt (ammonia transporters) in bacteria and plants, MEPs (methylammonium/ammonium permeases) in yeast and Rh (Rhesus proteins) in chordates.
Description:
Ammonia transporters are structurally related membrane transport proteins called Amt proteins (ammonia transporters). The proteins of the Amt family vary in size from 391 to 622 amino acyl residues. Eukaryotic AmtB homologues, in general, are larger than the prokaryotic proteins. Most functionally characterized members of the family are ammonium uptake transporters. Some, but not other Amt proteins also transport methylammonium.
Amt Transporter Background Information
Overview:
In organisms from all kingdoms of life, ammonia and its conjugated ion ammonium are transported across membranes by proteins of the AMT family. The proteins of this family vary in size from 391 to 622 amino acyl residues and possess 11 (N-terminus out; most members) or 12 (N-terminus in) transmembrane α-helical spanners (TMSs). The E. coli AmtB appears to have dual functions, transporting NH4+ and regulating nitrogen metabolism by directly interacting with regulatory proteins.
Data Sheet:
Genes (selection):
AmtA, AmtB, AmtC, Amt1, Amt2, Amt3, MEP1, MEP2, MEP3, RhAG, RhBG, RhCG
Proteins (selection):
- UniProt: P69681 (Ammonia Channel; AmtB; Escherichia coli)
- UniProt: O67997 (Ammonium Transporter, amtB; Azospirillum brasilense)
- UniProt P40260 (Ammonium transporter MEP1, Saccharomyces cerevisiae)
- UniProt Q02094 (Ammonium transporter Rh type A,RHAG; Homo sapiens)
- UniProt Q8MXY0 (Ammonium transporter 3, amtC; Dictyostelium discoideum)
- UniProt Q9C0V1 (Ammonium transporter 1, amt1; Schizosaccharomyces pombe)
Topology:
The transporter exists as a homotrimer, each subunit contains 11 transmembrane (TM) segments and containining a pseudo two-fold symmetry. Each monomer contains a hydrophobic ammonia conducting pore. In Azospirillum brasilense, AmtB forms a ternary complex between AmtB, GlnZ.
Regulation:
The E. coli ammonium channel, AmtB, and the PII signal transduction protein, GlnK, constitute an ammonium sensory system that effectively couples the intracellular nitrogen regulation system to external changes in ammonium availability. Direct binding of GlnK to AmtB inactivates the channel, thereby controlling ammonium influx in response to the intracellular nitrogen status. The stoichiometry of the complex is 1:1 for AmtB:GlnK
Function:
Amt proteins facilitate ammonium ion transport across the membranes of plants, fungi, and bacteria. Soeme transporters has been shown to function both as a transporter and as a sensor.
Assays:
SSM-based assays on the SURFE²R instrument family
Reviews and Links
Recommended Reviews:
Transporter classification database:
UniProt (selection):
- Ammonia channel (AmtB, Escherichia coli)
- Ammonium transporter (AmtB, Azospirillum brasilense)
- Ammonium transporter MEP1 (MEP1, Saccharomyces cerevisiae)
- Ammonium transporter Rh type A (RHAG, Homo sapiens)
- Ammonium transporter 3 (amtC, Dictyostelium discoideum)
- Ammonium transporter 1 (amt1, Schizosaccharomyces pombe)
Data and Applications
AmtB - Substrate specificity
SURFE2R N1 data and applications:
Purified AmtB from E.Coli was incorporated into liposomes and used on the SURFE2R N1. AmtB substrate specificity. (A) Transient current measured after a 100 mM substrate jump. Ammonium (red), methylammonium (black), potassium (green) or sodium (purple). Potassium and sodium do not act as substrates for AmtB and methylammonium translocates but at a much reduced rate compared with ammonium. Insert: Normalised current after a 100 mM substrate jump. Ammonium (red), methylammonium (black).
Data from Mirandela et al, 2018
AmtB - Activation by ammonium
SURFE2R N1 data and applications:
Purified AmtB from E.Coli was incorporated into liposomes and used on the SURFE2R N1. Shown are transient currents measured after a 100 mM ammonium jump in empty liposomes (green) or proteoliposomes containing AmtB at a lipid protein ratio (LPR) of 50 (black), 10 (red) or 5 (blue). Insert: Normalized current measured in proteoliposomes containing AmtB at an LPR of 50 (black), 10 (red) or 5 (blue).
Data from Mirandela et al, 2018
Testimonials
Dr. Arnaud Javelle - Statement about the SURFE²R N1 Device
“Using the SURFE2R N1 we have recently obtained high quality data in a very short period of time. We have developed an assay to measure the activity of ammonium transporters from the Amt protein family. There has been considerable controversy over the mechanism of ammonium transport by Amt proteins and the controversy was due to the lack of quantitative kinetic data characterizing the activity of the proteins at the single channel level. The SSM technologies allows to overcome this hurdle and we are now capable of answering very challenging functional questions concerning the mechanisms and the energetics of these transporters."
Dr. Arnaud Javelle, Chancellor's fellow, Strathclyde Institute of Pharmacy and Biomedical Sciences
Publications
2020 - A two-lane mechanism for selective biological ammonium transport
SURFE²R N1 publication in eLife (2020)
Authors:
Williamson G., Tamburrino G., Bizior A., Boeckstaens M., Mirandela G.D., Bage M.G., Pisliakov A., Ives C.M., Terras E., Hoskisson P.A., Marini A.M., Zachariae U., Javelle A.
2018 - The lipid environment determines the activity of the E. coli ammonium transporter, AmtB
SURFE²R N1 publication in Faseb J. (2018)
Authors:
Mirandela G.D., Tamburrino G., Hoskisson P.A., Zachariae U., Javelle A.
2014 - Direct observation of electrogenic NH4(+) transport in ammonium transport (Amt) proteins
SURFE²R-technology (custom-built system) publication in PNAS (2014)
Authors:
Wacker T., Garcia-Celma J.J., Lewe P., Andrade S.L.