Amt - Ammonia/Ammonium Transporter
Amt (ammonia transporters) in bacteria and plants, MEPs (methylammonium/ammonium permeases) in yeast and Rh (Rhesus proteins) in chordates.
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
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.
AmtA, AmtB, AmtC, Amt1, Amt2, Amt3, MEP1, MEP2, MEP3, RhAG, RhBG, RhCG
- 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)
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.
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
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.
SSM-based assays on the SURFE²R instrument family
Reviews and Links
- Neuhäuser et al.: Switching substrate specificity of AMT/MEP/ Rh proteins (2014) Channels (Austin) 8(6):496-502. doi: 10.4161/19336950.2014.967618.
Transporter classification database:
- 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)