CtpH (PA2561) is a methyl-accepting chemotaxis protein (MCP) of Pseudomonas aeruginosa PAO1 that serves as a chemoreceptor for inorganic phosphate (Pi). It is an inner-membrane receptor with two transmembrane helices flanking a periplasmic ligand binding domain, followed by a cytoplasmic HAMP domain and the MCP signalling domain that couples to the CheA-CheW chemosensory array. The ligand binding domain binds Pi directly with modest affinity (KD about 22 uM), and Pi binding induces its dimerization; it also binds other pyrophosphate-containing compounds such as ATP and ADP. CtpH is constitutively expressed and mediates taxis at high Pi concentrations, whereas the Pho-regulated paralogue CtpL mediates taxis at low Pi through the Pi-loaded periplasmic binding protein PstS. PhoU has been proposed to exert negative post-transcriptional control on Pi detection by CtpH.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004888 transmembrane signaling receptor activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO transmembrane signaling receptor activity from the chemotaxis methyl-accepting receptor signature. Reason: Core function. CtpH binds Pi directly with its periplasmic ligand binding domain and mediates Pi chemotaxis through its cytoplasmic signalling domain, which is transmembrane signaling receptor activity. Supporting Evidence: PMID:27353565 We demonstrate that the ligand binding domain (LBD) of CtpH but not CtpL binds Pi directly. PMID:10852870 Computer-assisted capillary assays showed that the ctpH single mutant failed to exhibit P(i) taxis when the concentration of P(i) in the capillary was higher than 5 mM. |
| 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 Pi-binding domain, the standard topology of an inner-membrane chemoreceptor. Supporting Evidence: file:PSEAE/ctpH/ctpH-uniprot.txt Cell inner membrane {ECO:0000305|PubMed:27353565}; Multi-pass membrane protein |
| GO:0006935 chemotaxis | IBA GO_REF:0000033 | ACCEPT | Summary: Chemotaxis propagated from PAINT node PTN001280296 (PTHR32089 MCP clade, 215 leaves in 22 taxa). CtpH is itself one of the ten IBD seeds through its PseudoCAP IMP row. Reason: Core process. CtpH's own mutant data show it mediates Pi chemotaxis, and the IBD is grounded in several independent experimentally characterized MCPs (B. subtilis McpC, the HemAT transducers), 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:10852870 The ctpH ctpL double mutant was defective in P(i) taxis at any concentration ranging from 0.01 to 10 mM. |
| GO:0006935 chemotaxis | IEA GO_REF:0000120 | ACCEPT | Summary: Combined InterPro/ARBA chemotaxis assignment for an MCP-family protein. Reason: Consistent with the experimental and IBA rows. Supporting Evidence: PMID:10852870 The ctpH ctpL double mutant was defective in P(i) taxis at any concentration ranging from 0.01 to 10 mM. |
| GO:0006935 chemotaxis | IMP PMID:10852870 Identification and characterization of two chemotactic trans... | ACCEPT | Summary: PseudoCAP IMP seed for the PAINT IBD at PTN001280296. The abstract states that a ctpH insertion mutant lost Pi taxis at Pi concentrations above 5 mM and that a ctpH ctpL double mutant lost Pi taxis at all concentrations tested. Reason: Seed verdict SOUND. A receptor mutant losing taxis towards the ligand that the receptor later proved to bind directly (PMID:27353565) is direct evidence that CtpH does the sensing step of chemotaxis, not an indirect phenotype. Supporting Evidence: PMID:10852870 Computer-assisted capillary assays showed that the ctpH single mutant failed to exhibit P(i) taxis when the concentration of P(i) in the capillary was higher than 5 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 demonstrate that the ligand binding domain (LBD) of CtpH but not CtpL binds Pi directly. |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO signal transduction from the HAMP and MCP signalling domains. Reason: Correct but general. CtpH binds Pi in the periplasm and signals across the inner membrane, 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/ctpH/ctpH-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 PMID:27353565 We demonstrate that the ligand binding domain (LBD) of CtpH but not CtpL binds Pi directly. |
| GO:0010247 detection of phosphate ion | IMP PMID:10852870 Identification and characterization of two chemotactic trans... | ACCEPT | Summary: PseudoCAP IMP; the ctpH mutant fails to respond to high Pi in capillary assays. Reason: CtpH is the receptor that receives the Pi stimulus: its ligand binding domain binds Pi directly (PMID:27353565), so detection of phosphate ion describes the receptor's own step, not a downstream phenotype. Supporting Evidence: PMID:10852870 Computer-assisted capillary assays showed that the ctpH single mutant failed to exhibit P(i) taxis when the concentration of P(i) in the capillary was higher than 5 mM. PMID:27353565 Data analysis revealed that the binding of CtpH-LBD with Pi has a KD of 22 ΞΌM (Table 1). |
| 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/ctpH/ctpH-uniprot.txt Cell inner membrane {ECO:0000305|PubMed:27353565}; Multi-pass membrane protein |
| GO:0042301 phosphate ion binding | IDA PMID:27353565 Two different mechanisms mediate chemotaxis to inorganic pho... | NEW | Summary: Proposed molecular function from isothermal titration calorimetry of the purified CtpH ligand binding domain with Pi. Reason: Direct binding assay on the purified sensor domain (KD 22 uM), absent from GOA. Pi binding is the sensing activity of the receptor and explains its role in taxis at high Pi. Supporting Evidence: PMID:27353565 We demonstrate that the ligand binding domain (LBD) of CtpH but not CtpL binds Pi directly. PMID:27353565 Data analysis revealed that the binding of CtpH-LBD with Pi has a KD of 22 ΞΌM (Table 1). |
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Download this section (compressed HTML)Q: How does PhoU control Pi detection by CtpH post-transcriptionally, given that CtpH binds Pi directly and is constitutively expressed?
Experiment: Measure CtpH methylation and Pi taxis in phoU and pstS backgrounds with a CtpH Pi-binding-site mutant, to separate direct Pi sensing from PhoU-dependent modulation.
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