CtpL (PA4844) is a methyl-accepting chemotaxis protein (MCP) of Pseudomonas aeruginosa PAO1 and one of two chemoreceptors for inorganic phosphate. It is an inner-membrane receptor with two transmembrane helices around a periplasmic sensor region and a cytoplasmic HAMP and MCP signalling region. CtpL mediates chemotaxis towards low (micromolar) Pi concentrations, complementing CtpH, which senses high Pi. It does not bind Pi directly: the Pi-loaded periplasmic binding protein PstS of the Pst phosphate transporter binds CtpL and stimulates it. ctpL belongs to the Pho regulon and is induced by phosphate limitation through PhoB. CtpL also mediates positive chemotaxis to the aromatic pollutant 4-chloroaniline and to catechol.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004888 transmembrane signaling receptor activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO transmembrane signaling receptor activity from the MCP family signature. Reason: Core molecular function. CtpL has two transmembrane helices around a large periplasmic region (27-305) that is stimulated by the Pi-loaded periplasmic binding protein PstS, and a cytoplasmic HAMP-MCP signalling region that drives Pi taxis; ligand recognition outside and signalling inside is transmembrane receptor activity. Supporting Evidence: PMID:27353565 We identify the periplasmic ligand binding protein PstS as the protein that binds in its Pi loaded state to CtpL, resulting in receptor stimulation. PMID:10852870 Conversely, the ctpL single mutant could not respond to P(i) at the concentration of 0.01 mM. |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Plasma membrane from the UniProt subcellular location (cell inner membrane). Reason: Two predicted transmembrane helices bracket the periplasmic sensor region; inner membrane location is the standard topology for an MCP, and the periplasmic region interacts with PstS. Supporting Evidence: file:PSEAE/ctpL/ctpL-uniprot.txt Cell inner membrane PMID:27353565 We identify the periplasmic ligand binding protein PstS as the protein that binds in its Pi loaded state to CtpL, resulting in receptor stimulation. |
| GO:0006935 chemotaxis | IBA GO_REF:0000033 | ACCEPT | Summary: Chemotaxis propagated from PAINT node PTN001280296 (PTHR32089 MCP clade, 215 leaves in 22 taxa). CtpL is one of the ten IBD seeds through its PseudoCAP IMP row; the node is assessed in the pctB notes. Reason: Core process. CtpL mutants lose Pi taxis at low Pi and 4-chloroaniline taxis, and the IBD is also grounded in independent experimentally characterized MCPs (B. subtilis McpC, two HemAT aerotaxis transducers). The target in its own WITH/FROM reflects its own experimental row, which is expected. Supporting Evidence: PMID:10852870 Conversely, the ctpL single mutant could not respond to P(i) at the concentration of 0.01 mM. PMID:24038698 Molecular analysis of all 26 mutants with a disrupted methyl-accepting chemotaxis gene revealed that CtpL, a chromosomally encoded chemoreceptor, was responsible for the positive chemotactic response toward 4CA. |
| GO:0006935 chemotaxis | IEA GO_REF:0000120 | ACCEPT | Summary: Chemotaxis from the MCP family signature (UniProt combined automatic rule). Reason: Consistent with the experimental and IBA rows. Supporting Evidence: PMID:10852870 Conversely, the ctpL single mutant could not respond to P(i) at the concentration of 0.01 mM. file:PSEAE/ctpL/ctpL-uniprot.txt Chemoreceptor for inorganic phosphate, which is required |
| GO:0006935 chemotaxis | IMP PMID:10852870 Identification and characterization of two chemotactic trans... | ACCEPT | Summary: PseudoCAP IMP seed for the IBD at PTN001280296. The ctpL insertion mutant fails to respond to 0.01 mM Pi, and the ctpH ctpL double mutant is defective in Pi taxis at all concentrations. Reason: Seed verdict SOUND. Loss of Pi taxis in the receptor mutant, for a receptor later shown to be stimulated by Pi-loaded PstS, shows that CtpL performs the sensing step of chemotaxis itself. Supporting Evidence: PMID:10852870 Conversely, the ctpL single mutant could not respond to P(i) at the concentration of 0.01 mM. PMID:10852870 The ctpH ctpL double mutant was defective in P(i) taxis at any concentration ranging from 0.01 to 10 mM. PMID:27353565 We identify the periplasmic ligand binding protein PstS as the protein that binds in its Pi loaded state to CtpL, resulting in receptor stimulation. |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO signal transduction from the HAMP and MCP signalling domains. Reason: Correct but general. CtpL receives its stimulus in the periplasm and signals across the inner membrane to the chemosensory array, so cell surface receptor signaling pathway (an is_a descendant) is the specific term, as chosen for the sibling MCPs pctB and pctA. Proposed replacements: cell surface receptor signaling pathway Supporting Evidence: PMID:27353565 We identify the periplasmic ligand binding protein PstS as the protein that binds in its Pi loaded state to CtpL, resulting in receptor stimulation. file:PSEAE/ctpL/ctpL-uniprot.txt PF00015; MCPsignal |
| GO:0010247 detection of phosphate ion | IMP PMID:10852870 Identification and characterization of two chemotactic trans... | ACCEPT | Summary: PseudoCAP IMP; the ctpL mutant fails to respond to low Pi, and Pi detection by CtpL requires PhoU. Reason: CtpL is the receptor that converts the low-Pi stimulus into a chemotactic signal. Unlike CtpH it does not bind Pi itself but is stimulated by the Pi-loaded periplasmic binding protein PstS (PMID:27353565); detection of phosphate ion still describes CtpL step, since GO:0010247 covers receipt of the stimulus and its conversion into a signal, not only direct ligand contact. Consistent with the ctpH review. Supporting Evidence: PMID:10852870 Conversely, the ctpL single mutant could not respond to P(i) at the concentration of 0.01 mM. PMID:10852870 suggesting that the P(i) detection by CtpL requires PhoU PMID:27353565 We identify the periplasmic ligand binding protein PstS as the protein that binds in its Pi loaded state to CtpL, resulting in receptor stimulation. |
| 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/ctpL/ctpL-uniprot.txt Cell inner membrane |
| GO:0050918 positive chemotaxis | IMP PMID:24038698 Identification of CtpL as a chromosomally encoded chemorecep... | ACCEPT | Summary: PseudoCAP IMP; of 26 MCP mutants, only the ctpL mutant lost positive chemotaxis to 4-chloroaniline (and catechol). Reason: Screen of all MCP mutants identifies CtpL as the receptor for the attractant response to 4CA; positive chemotaxis also describes Pi taxis. The abstract calls the 4CA response fortuitous, so Pi sensing remains the main physiological role, but the attraction itself is a direct receptor function. Supporting Evidence: PMID:24038698 Molecular analysis of all 26 mutants with a disrupted methyl-accepting chemotaxis gene revealed that CtpL, a chromosomally encoded chemoreceptor, was responsible for the positive chemotactic response toward 4CA. |
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Download this section (compressed HTML)Q: Does CtpL recognise 4-chloroaniline and catechol through its periplasmic region directly, or, as for Pi, through a periplasmic binding protein?
Experiment: Test binding of 4-chloroaniline and catechol to the purified CtpL periplasmic region and to PstS by isothermal titration calorimetry, and measure 4CA taxis in a pstS mutant.
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