PctB (PA4310) 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. The recombinant ligand binding region binds five L-amino acids at its membrane-distal module, with L-glutamine bound most tightly, and the receptor mediates chemotaxis towards L-Gln, L-Arg, L-Ala, L-Glu, L-Lys, L-Met and L-Tyr. It also contributes to repellent responses to trichloroethylene, chloroform and methylthiocyanate. PctB arose from a duplication of pctA in the ancestor of P. aeruginosa.
| 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 amino acid ligands. Supporting Evidence: file:PSEAE/pctB/pctB-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). PctB 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. PctB's own mutant and complementation data show it mediates amino acid 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; PctB is a characterized amino acid chemoreceptor. 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: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 a deletion of the whole pctC-orf1-pctA-pctB region abolished chemotaxis to all 20 L-amino acids and that pctB on a plasmid restored chemotaxis to seven of them; a later pctB single mutant lost chemoattraction to L-Gln (PMID:23650915). Reason: Seed verdict SOUND. Loss of taxis in the mutant and restoration by the cloned gene, for a receptor whose ligand binding region binds the same amino acids, show that PctB does the sensing step of chemotaxis itself; 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. PctB 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/pctB/pctB-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/pctB/pctB-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/pctB/pctB-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 five L-amino acids to the recombinant ligand binding region (ITC), L-Gln binding most tightly; ligands bind the membrane-distal PDC module. Reason: Direct binding assay on the purified sensor domain; 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 l-Gln, one of the three amino acids that is not recognized by PctA-LBR, was the most tightly binding ligand to PctB |
| 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 We show that the recombinant ligand binding regions (LBRs) of PctA, PctB and PctC bind 17, 5 and 2 l-amino acids respectively. |
| 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 pctB restores chemotactic responses to seven L-amino acids. 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 present on its paralogues' family members (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 amino acid 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 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 Bacteria were efficiently attracted to l-Gln and GABA, but mutation of pctB and pctC, respectively, abolished chemoattraction. file:PSEAE/pctB/pctB-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: PANTHER places the Dictyostelium lysozyme-like proteins AlyL (Q54M35, F0ZEQ3), which lack an MCP signalling domain, under the chemotaxis node PTN001280296, so they inherit a chemotaxis IBA. Should these leaves be moved out of the MCP clade or the IBA blocked for them?
Experiment: Measure PctB-mediated L-Gln chemotaxis with ligand binding site mutants of the membrane-distal PDC module, to link the binding residues in the crystal structures to the in vivo response.
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