Aer (PA1561, formerly TlpC) is the membrane-bound aerotaxis transducer of Pseudomonas aeruginosa PAO1, a methyl-accepting chemotaxis protein (MCP) with 45% identity to the Escherichia coli energy-taxis receptor Aer. It has an N-terminal cytoplasmic PAS domain, a pair of closely spaced transmembrane helices that anchor it in the inner membrane with almost no periplasmic segment, and a C-terminal cytoplasmic MCP signalling domain. Unlike classical chemoreceptors it has no periplasmic sensing domain; by analogy with E. coli Aer its PAS domain is expected to sense the cell's internal energy or redox state. Aer acts through the chemotaxis gene cluster 1 (cheYZABW) and CheR, and an aer mutant shows reduced aerotaxis, which is abolished when the soluble transducer Aer-2 (McpB) is also lost. Aer-mediated energy taxis is strong enough to mask chemotaxis mediated by other receptors. Expression of aer is induced on entry into stationary phase and requires the anaerobic regulator ANR.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004888 transmembrane signaling receptor activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO transmembrane signaling receptor activity from the chemotaxis methyl-accepting receptor signature, which covers all MCPs. Reason: Aer is a signalling receptor, but not a transmembrane one in the sense of the definition (signal received on one side of the membrane and transmitted to the other). Its only sensory domain, the PAS domain, lies N-terminal to the transmembrane pair and so in the cytoplasm, the two helices are separated by a loop of four residues, and the MCP signalling domain is also cytoplasmic. The membrane segment is an anchor, as in E. coli Aer, not a signal-transmitting element. The essence (signalling receptor) is sound, so the row is generalized to the parent term. Proposed replacements: signaling receptor activity Supporting Evidence: file:PSEAE/aer/aer-uniprot.txt TRANSMEM 147..169 file:PSEAE/aer/aer-uniprot.txt TRANSMEM 174..193 file:PSEAE/aer/aer-uniprot.txt PF08447; PAS_3 PMID:14987771 TlpC has 45% amino acid identity with the Escherichia coli aerotactic transducer Aer. |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Plasma membrane from the UniProt subcellular location (cell inner membrane, multi-pass). Reason: Two predicted transmembrane helices anchor the protein in the inner membrane; the paralogue Aer-2, which lacks them, is the soluble aerotaxis transducer. Supporting Evidence: file:PSEAE/aer/aer-uniprot.txt Cell inner membrane {ECO:0000305}; Multi-pass membrane protein {ECO:0000255}. file:PSEAE/aer/aer-uniprot.txt TRANSMEM 147..169 |
| GO:0006935 chemotaxis | IBA GO_REF:0000033 | TOO GENERAL | Summary: Chemotaxis propagated from PAINT node PTN001280296 (PTHR32089 MCP clade, 215 leaves in 22 taxa). Aer is one of the ten IBD seeds through its aerotaxis IMP rows (GO:0009454 aerotaxis is_a GO:0006935 chemotaxis), like the HemAT aerotaxis transducers among the other seeds. Reason: True, but GO:0052131 positive aerotaxis, accepted on this gene, is an is_a descendant (through aerotaxis and positive chemotaxis) and entails it. The IBD itself is sound and the node term suits an MCP clade that contains both chemoreceptors and aerotaxis transducers. |
| GO:0006935 chemotaxis | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO chemotaxis from the MCP signature. Reason: True, but GO:0052131 positive aerotaxis, accepted on this gene, is an is_a descendant and entails it. |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO signal transduction from the MCP signalling domain. Reason: Aer transduces an intracellular sensory signal through the CheA-CheW chemosensory array. Unlike the transmembrane chemoreceptors it does not sense at the cell surface, so cell surface receptor signaling pathway does not apply, and no other descendant is supported by data on this protein; the general term is as precise as the evidence allows. Supporting Evidence: PMID:14987771 Aerotaxis assays of a number of deletion-insertion mutants of Pseudomonas aeruginosa PAO1 revealed that the chemotaxis gene cluster 1 and cheR are required for aerotaxis. file:PSEAE/aer/aer-uniprot.txt PF00015; MCPsignal |
| GO:0009454 aerotaxis | IMP PMID:14987771 Chemotaxis proteins and transducers for aerotaxis in Pseudom... | TOO GENERAL | Summary: PseudoCAP IMP seed (with the CACAO positive aerotaxis IMP row) for the PAINT chemotaxis IBD at PTN001280296. The abstract states that a tlpC (aer) deletion mutant showed decreased aerotaxis and that a tlpC tlpG double mutant was negative for aerotaxis. Reason: Seed verdict SOUND: the transducer mutant loses aerotaxis, which is the gene's own process, and aerotaxis is_a chemotaxis, so it supports the chemotaxis IBD. The row is nevertheless entailed by GO:0052131 positive aerotaxis (is_a aerotaxis), accepted on this gene from the same paper. Supporting Evidence: PMID:14987771 Mutant strains which contained deletions in the methyl-accepting chemotaxis protein-like genes tlpC and tlpG showed decreased aerotaxis. PMID:14987771 A double mutant deficient in tlpC and tlpG was negative for aerotaxis. |
| GO:0016020 membrane | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO membrane location. Reason: True but uninformative; GO:0005886 plasma membrane, accepted on this gene, is an is_a descendant and entails it. |
| GO:0052131 positive aerotaxis | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA positive aerotaxis. Reason: Consistent with the IMP row for the same term. Supporting Evidence: PMID:14987771 A double mutant deficient in tlpC and tlpG was negative for aerotaxis. |
| GO:0052131 positive aerotaxis | IMP PMID:14987771 Chemotaxis proteins and transducers for aerotaxis in Pseudom... | ACCEPT | Summary: CACAO IMP; the aer mutant shows decreased migration towards oxygen in aerotaxis assays. Reason: Core process. Aerotaxis assays measure movement towards the preferred oxygen concentration, and the transducer mutant is defective; positive aerotaxis is the most precise supported term. Supporting Evidence: PMID:14987771 Mutant strains which contained deletions in the methyl-accepting chemotaxis protein-like genes tlpC and tlpG showed decreased aerotaxis. PMID:14987771 TlpC has 45% amino acid identity with the Escherichia coli aerotactic transducer Aer. |
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Download this section (compressed HTML)Q: Does the P. aeruginosa Aer PAS domain bind FAD and sense electron transport chain redox state, as E. coli Aer does, or does it sense oxygen directly?
Q: InterPro2GO assigns transmembrane signaling receptor activity to all MCP-signature proteins, including membrane-anchored cytoplasmic sensors such as Aer. Should the mapping be restricted to MCPs with a periplasmic sensing domain?
Experiment: Purify the Aer PAS domain and test for bound flavin, then measure aerotaxis of PAS mutants predicted to abolish FAD binding.
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