AmtB (PP_5233) is a high-affinity ammonium transporter of the Amt/Mep/Rh (ammonia transporter channel) superfamily located in the cytoplasmic (inner) membrane, where it is predicted to form a trimer with each protomer providing an 11-transmembrane-helix channel. It mediates uptake of ammonium across the membrane, scavenging low external ammonium to support nitrogen assimilation under nitrogen-limiting conditions; family members recruit NH4+ at a periplasmic site and conduct it through a hydrophobic pore (with conserved Phe-gate and twin-His motifs), with deprotonation to NH3 and growing evidence for electrogenic transport. In Pseudomonas putida KT2440, amtB is encoded in a glnK-amtB operon together with the PII-family nitrogen signaling protein GlnK; it is strongly induced (tens-of-fold) during nitrogen limitation under control of the NtrC/sigma-54 (RpoN) regulatory system, and, as in other Proteobacteria, AmtB transport activity can be gated post-translationally by GlnK binding to its cytoplasmic face.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: AmtB is a multi-pass cytoplasmic (inner) membrane transporter; plasma membrane localization is correct for this Amt-family protein. Reason: UniProt SUBCELLULAR LOCATION (RuleBase/ARBA) annotates AmtB as a multi-pass cell membrane protein, and the deep research describes AmtB as a cytoplasmic (inner) membrane ammonium transporter. The 11 predicted transmembrane helices in the UniProt record support membrane localization. |
| GO:0008519 ammonium channel activity | IEA GO_REF:0000120 | ACCEPT | Summary: AmtB is a member of the ammonia transporter channel (TC 1.A.11.2) family; ammonium channel activity is the appropriate molecular function for this protein. Reason: The Amt/Mep/Rh family is the canonical ammonium channel/transporter family, and AmtB carries the IPR001905/IPR018047/IPR024041 (Ammonium_transpt) domains plus the TC 1.A.11.2 family assignment. This is the standard, well-supported molecular function term for AmtB orthologs. Mechanistic debate over passive NH3 conduction versus electrogenic NH4+ transport does not change the family-level MF assignment. |
| GO:0016020 membrane | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Generic membrane localization; correct but subsumed by the more specific plasma membrane annotation. Reason: GO:0016020 (membrane) is a true but high-level parent of the more informative GO:0005886 (plasma membrane) annotation already present. It is an InterPro2GO electronic inference that is not incorrect, but adds little specificity; retained as non-core. |
| GO:0072488 ammonium transmembrane transport | IEA GO_REF:0000120 | ACCEPT | Summary: AmtB mediates transport of ammonium across the cytoplasmic membrane; this is the core biological process for the gene. Reason: Consistent with the molecular function (ammonium channel activity) and with KT2440-specific evidence that amtB is a high-affinity ammonium transporter strongly induced under nitrogen limitation to scavenge external ammonium for nitrogen assimilation. Supporting Evidence: PMID:17965157 amtB (PP5233) in P. putida KT2440 is the high-affinity ammonium transporter, induced ~62-fold under nitrogen limitation, supporting its role in ammonium uptake for nitrogen assimilation. |
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