PctC (PA4307) is a methyl-accepting chemotaxis protein (MCP) of Pseudomonas aeruginosa PAO1, one of three paralogous amino acid chemoreceptors encoded in the pctC-pctA-pctB region. It is an inner-membrane receptor with two transmembrane helices flanking a periplasmic dCache_1 (double PDC) ligand binding region, followed by a cytoplasmic HAMP domain and the MCP signalling domain that couples to the CheA-CheW chemosensory array. Its ligand binding region binds L-histidine and L-proline and, with strong preference, gamma-aminobutyrate (GABA), and the receptor mediates chemotaxis towards these compounds. PctC also contributes, together with PctA and TlpQ, to chemotaxis towards histamine without binding it, and to repellent responses to trichloroethylene, chloroform and methylthiocyanate. PctC arose from a duplication of pctA in the common ancestor of the genus Pseudomonas.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| 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 bracket the periplasmic ligand binding region, the standard topology of an inner-membrane chemoreceptor; the periplasmic LBR binds the ligands. Supporting Evidence: file:PSEAE/pctC/pctC-uniprot.txt Cell inner membrane {ECO:0000305}; Multi-pass membrane protein {ECO:0000255}. PMID:23650915 We show that the recombinant ligand binding regions (LBRs) of PctA, PctB and PctC bind 17, 5 and 2 l-amino acids respectively. |
| GO:0006935 chemotaxis | IBA GO_REF:0000033 | ACCEPT | Summary: Chemotaxis propagated from PAINT node PTN001280296 (PTHR32089 MCP clade, 215 leaves in 22 taxa). PctC is itself one of the ten IBD seeds through its PseudoCAP IMP row; the other seeds include B. subtilis McpC (IDA/IMP positive chemotaxis) and the HemAT aerotaxis transducers of B. subtilis and H. salinarum (IDA aerotaxis). Reason: Core process. PctC's own complementation and mutant data show it mediates chemotaxis, and the IBD is grounded in several independent experimentally characterized MCPs, so the node placement is sound. The target's presence in WITH/FROM reflects its own experimental row, which is expected, not circular. Supporting Evidence: PMID:9353923 The pctB and pctC genes complemented the defect in chemotaxis to only seven (Ala, Arg, Glu, Lys, Met, Tyr, Gln) and two (His, Pro) L-amino acids, respectively. PMID:23650915 Bacteria were efficiently attracted to l-Gln and GABA, but mutation of pctB and pctC, respectively, abolished chemoattraction. |
| GO:0006935 chemotaxis | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA chemotaxis assignment for an MCP-family protein. Reason: Consistent with the experimental and IBA rows; PctC is a characterized chemoreceptor. Supporting Evidence: PMID:23650915 Bacteria were efficiently attracted to l-Gln and GABA, but mutation of pctB and pctC, respectively, abolished chemoattraction. |
| GO:0006935 chemotaxis | IMP PMID:9353923 Genetic identification of chemotactic transducers for amino ... | ACCEPT | Summary: PseudoCAP IMP seed for the PAINT IBD at PTN001280296. The abstract states that deletion of the whole pctC-orf1-pctA-pctB region abolished chemotaxis to all 20 L-amino acids and that pctC on a plasmid restored chemotaxis to His and Pro; a later pctC mutant lost chemoattraction to GABA (PMID:23650915). Reason: Seed verdict SOUND. Restoration of taxis by the cloned gene, for a receptor whose ligand binding region binds the same ligands, shows that PctC performs the sensing step of chemotaxis; this is not an indirect phenotype. Supporting Evidence: PMID:9353923 A null mutant strain PCT2, which contained a deletion in the entire pctC, orf1, pctA and pctB genes, did not show chemotaxis towards all 20 commonly occurring L-amino acids. PMID:9353923 The pctB and pctC genes complemented the defect in chemotaxis to only seven (Ala, Arg, Glu, Lys, Met, Tyr, Gln) and two (His, Pro) L-amino acids, respectively. PMID:23650915 Bacteria were efficiently attracted to l-Gln and GABA, but mutation of pctB and pctC, respectively, abolished chemoattraction. |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO signal transduction from the HAMP and MCP signalling domains. Reason: Correct but general. PctC is a transmembrane receptor that binds its ligands in the periplasm and signals across the inner membrane to the CheA-CheW array, so the more specific term is cell surface receptor signaling pathway (an is_a descendant), as used for other transmembrane MCPs. Proposed replacements: cell surface receptor signaling pathway Supporting Evidence: file:PSEAE/pctC/pctC-uniprot.txt Chemotactic-signal transducers respond to changes in the concentration of attractants and repellents in the environment, transduce a signal from the outside to the inside of the cell file:PSEAE/pctC/pctC-uniprot.txt PF00015; MCPsignal |
| 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. Supporting Evidence: file:PSEAE/pctC/pctC-uniprot.txt Cell inner membrane {ECO:0000305}; Multi-pass membrane protein {ECO:0000255}. |
| GO:0016597 amino acid binding | IDA PMID:23650915 Paralogous chemoreceptors mediate chemotaxis towards protein... | ACCEPT | Summary: Direct binding of two L-amino acids and of GABA to the recombinant ligand binding region (ITC). Reason: Direct binding assay on the purified sensor domain; GABA is itself an amino acid, so the term covers all three ligands. Ligand recognition is the receptor's sensing activity. Supporting Evidence: PMID:23650915 We show that the recombinant ligand binding regions (LBRs) of PctA, PctB and PctC bind 17, 5 and 2 l-amino acids respectively. PMID:23650915 In addition, PctC-LBR recognized GABA but not any other structurally related compound. |
| GO:0016597 amino acid binding | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA amino acid binding. Reason: Consistent with the IDA row for the same term. Supporting Evidence: PMID:23650915 In addition, PctC-LBR recognized GABA but not any other structurally related compound. |
| GO:0043200 response to amino acid | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA response to amino acid. Reason: Consistent with the IMP row; the chemotactic response to amino acids is the receptor's role, and GO has no amino-acid-specific chemotaxis term, so this pairing with chemotaxis is as precise as the ontology allows. Supporting Evidence: PMID:9353923 The pctB and pctC genes complemented the defect in chemotaxis to only seven (Ala, Arg, Glu, Lys, Met, Tyr, Gln) and two (His, Pro) L-amino acids, respectively. |
| GO:0043200 response to amino acid | IMP PMID:9353923 Genetic identification of chemotactic transducers for amino ... | ACCEPT | Summary: PseudoCAP IMP; complementation of the pct deletion mutant by pctC restores chemotactic responses to L-His and L-Pro. Reason: The response measured is the chemotactic response to amino acids, mediated by the receptor that binds them. GO has no term for chemotaxis to amino acids, so this term together with chemotaxis is the most precise available. Supporting Evidence: PMID:9353923 The pctB and pctC genes complemented the defect in chemotaxis to only seven (Ala, Arg, Glu, Lys, Met, Tyr, Gln) and two (His, Pro) L-amino acids, respectively. |
| GO:0004888 transmembrane signaling receptor activity | IC PMID:23650915 Paralogous chemoreceptors mediate chemotaxis towards protein... | NEW | Summary: Proposed core molecular function, absent from GOA for this gene although assigned to other P. aeruginosa transmembrane MCPs (for example CtpH and CtpM via InterPro2GO). Reason: Two independent lines agree. The protein has two transmembrane helices around a periplasmic dCache_1 ligand binding region that binds its ligands directly, and its cytoplasmic HAMP-MCP signalling domain mediates the chemotactic response in vivo. Ligand binding outside and signalling inside is the definition of transmembrane signaling receptor activity. IC because no single assay tests transmembrane signalling itself. Supporting Evidence: PMID:23650915 In addition, PctC-LBR recognized GABA but not any other structurally related compound. PMID:23650915 Bacteria were efficiently attracted to l-Gln and GABA, but mutation of pctB and pctC, respectively, abolished chemoattraction. file:PSEAE/pctC/pctC-uniprot.txt Chemotactic-signal transducers respond to changes in the concentration of attractants and repellents in the environment, transduce a signal from the outside to the inside of the cell |
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Download this section (compressed HTML)Q: PctC mediates histamine chemotaxis without binding histamine. Is the signal relayed by a periplasmic binding protein or by a histamine-derived ligand, or does PctC act through receptor array cooperativity with TlpQ?
Experiment: Test histamine chemotaxis of a PctC ligand binding site mutant that no longer binds GABA, in a tlpQ background, to see whether histamine sensing by PctC requires its own ligand pocket.
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