PlcH (PA0844) is the secreted haemolytic phospholipase C of Pseudomonas aeruginosa, the founding member of a bacterial PC-PLC/phosphatase superfamily that also contains the M. tuberculosis PlcA-D enzymes and plant non-specific phospholipases C. It is exported across the inner membrane by the Tat system and reaches the extracellular medium through the Xcp type II secretion system, and is purified from culture supernatants as a 1:1 complex with the chaperone PlcR2. PlcHR2 acts only on choline-containing phospholipids, hydrolysing phosphatidylcholine and sphingomyelin equally well (plasmenylcholine too) and releasing phosphocholine; purified PlcH also catalyses the reverse-type transfer reaction of a sphingomyelin synthase. The host-derived choline and glycine betaine released by PlcH feed P. aeruginosa metabolism and raise Anr activity, and PlcH contributes to haemolysis and to virulence in animal infection.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004629 C-type glycerophospholipase activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO, C-type glycerophospholipase activity. Reason: True; GO:0034480 phosphatidylcholine phospholipase C activity, accepted here, is_a descendant of it. |
| GO:0015628 protein secretion by the type II secretion system | IDA PMID:11726509 Involvement of the twin-arginine translocation system in pro... | MARK AS OVER ANNOTATED | Summary: PseudoCAP IDA; PlcH is a substrate of the Xcp secreton and uses the Tat system for the inner-membrane step. Reason: The biology is accepted: PlcH crosses the outer membrane through the type II secretion system. But a secreted substrate does none of the work of the secretion process; GO annotates the Xcp/Gsp machinery to this term, not its cargo. The same call was recorded for the other Xcp cargo in this repository (genes/PSEAE/lasB, genes/PSEAE/lap). Only the abstract was available, so the row is not removed. Supporting Evidence: PMID:11726509 two substrates for the Pseudomonas aeruginosa secreton, both phospholipases, use the twin-arginine translocation (Tat) system |
| GO:0016042 lipid catabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO, lipid catabolic process. Reason: Correct but general: the specific process shown for PlcH is hydrolysis of host phosphatidylcholine (and sphingomyelin), whose products feed choline and glycine betaine catabolism. Proposed replacements: phosphatidylcholine catabolic process Supporting Evidence: PMID:12410824 PlcHR2 is only active on choline-containing phospholipids. It is equally active on phosphatidylcholine (PC) and sphingomyelin (SM) and is able to hydrolyse plasmenylcholine phospholipids (plasmalogens) PMID:23667230 Pseudomonas aeruginosa hemolytic phospholipase C (PlcH) degrades phosphatidylcholine (PC), an abundant lipid in cell membranes and lung surfactant |
| GO:0016298 lipase activity | IDA PMID:2120196 Molecular comparison of a nonhemolytic and a hemolytic phosp... | TOO GENERAL | Summary: PseudoCAP IDA for lipase activity, from the paper comparing the haemolytic and non-haemolytic PLCs. Reason: True (abstract read) but entailed by the accepted GO:0034480, which the same paper supports. Supporting Evidence: PMID:2120196 PLC-H hydrolyzes sphingomyelin in addition to phosphatidylcholine |
| GO:0016788 hydrolase activity, acting on ester bonds | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO, hydrolase activity acting on ester bonds. Reason: Entailed by the accepted GO:0034480. |
| GO:0033188 sphingomyelin synthase activity | IDA PMID:12799377 Purification, characterization, and identification of a sphi... | KEEP AS NON CORE | Summary: PseudoCAP IDA; purified PlcH shows sphingomyelin synthase activity, and plcH operon mutants lose the activity from culture supernatants. Reason: Real measured activity on the purified protein and genetically attributed to plcH (abstract read), so the row is kept; but a secreted bacterial enzyme has no access to the ceramide and phosphatidylcholine pools of a cytoplasmic-leaflet synthase, and its physiological output is hydrolysis of host choline phospholipids. A genuine secondary (transferase) activity of the same catalytic machinery, not the function the enzyme evolved for. Supporting Evidence: PMID:12799377 Second, purified PlcH showed SM synthase activity PMID:12799377 SM synthase-like activity was found secreted in the culture medium of P. aeruginosa PMID:12799377 the Pseudomonas PlcH also exerts SM synthase activity |
| GO:0034480 phosphatidylcholine phospholipase C activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN001277563; PlcH is one of five seeds, with the four M. tuberculosis PlcA-D enzymes. Reason: Expected self-seed: PlcH has its own purified-enzyme evidence for the term, and the IBA adds that the activity is inherited in this small clade. The other four seeds (P9WIB5, P9WIB3, P9WIB1, P9WIA9) carry EXP/IMP annotations for GO:0034480 of their own, so the IBD does not rest on PlcH. Supporting Evidence: PMID:12410824 PlcHR2 is only active on choline-containing phospholipids. It is equally active on phosphatidylcholine (PC) and sphingomyelin (SM) and is able to hydrolyse plasmenylcholine phospholipids (plasmalogens) |
| GO:0034480 phosphatidylcholine phospholipase C activity | IDA PMID:12410824 A novel class of microbial phosphocholine-specific phospholi... | ACCEPT | Summary: PseudoCAP IDA (seed of both IBDs). 1,500-fold purified PlcHR2 hydrolyses phosphatidylcholine and sphingomyelin and no non-choline phospholipid. Reason: Direct assay on the purified enzyme (abstract read, and the same specificity was reported in the 1990 comparison with PLC-N). The seed is sound for both PTN001277539 (C-type glycerophospholipase) and PTN001277563 (phosphatidylcholine phospholipase C). Supporting Evidence: PMID:12410824 In this report we describe the 1,500-fold purification and characterization of the haemolytic phospholipase C (PLC) of Pseudomonas aeruginosa PMID:12410824 PlcHR2 is only active on choline-containing phospholipids. It is equally active on phosphatidylcholine (PC) and sphingomyelin (SM) and is able to hydrolyse plasmenylcholine phospholipids (plasmalogens) PMID:2120196 PLC-H hydrolyzes sphingomyelin in addition to phosphatidylcholine file:PSEAE/plcH/plcH-uniprot.txt Hydrolyzes sphingomyelin in addition to phosphatidylcholine. |
| GO:0034480 phosphatidylcholine phospholipase C activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined automated IEA for the same term. Reason: Agrees with the direct assay. Supporting Evidence: PMID:12410824 PlcHR2 is only active on choline-containing phospholipids. It is equally active on phosphatidylcholine (PC) and sphingomyelin (SM) and is able to hydrolyse plasmenylcholine phospholipids (plasmalogens) |
| GO:0044179 hemolysis in another organism | IDA PMID:12410824 A novel class of microbial phosphocholine-specific phospholi... | ACCEPT | Summary: PseudoCAP IDA; the purified PlcHR2 complex is haemolytic, and calcium inhibits that haemolytic activity. Reason: Haemolysis of host erythrocytes by the purified enzyme is directly measured in the same paper that establishes the substrate specificity (abstract read), and it is what the protein is named for. PlcH itself performs the membrane-lipid hydrolysis that lyses the cell, so the gene product does the work of the process. Supporting Evidence: PMID:12410824 While calcium has no detectable effect on enzymatic activity, it inhibits the haemolytic activity of PlcHR2 PMID:12410824 PlcHR2 is only active on choline-containing phospholipids. It is equally active on phosphatidylcholine (PC) and sphingomyelin (SM) and is able to hydrolyse plasmenylcholine phospholipids (plasmalogens) |
| GO:0044179 hemolysis in another organism | IMP PMID:23667230 Anr and its activation by PlcH activity in Pseudomonas aerug... | ACCEPT | Summary: PseudoCAP IMP citing Jackson et al. 2013, a plcHR deletion study of Anr activation and host colonization. Reason: The claim is true of PlcH and is directly supported on the IDA row above, so the row is kept and the action matches. The reference, however, looks like the wrong choice: in the cached full text Jackson et al. measure phosphatidylcholine degradation, Anr regulon expression, choline and glycine betaine catabolism, biofilm formation and virulence in a mouse pneumonia model, and mention haemolytic activity only in the enzyme's name. Queried as a reference defect. Supporting Evidence: PMID:23667230 Pseudomonas aeruginosa hemolytic phospholipase C (PlcH) degrades phosphatidylcholine (PC), an abundant lipid in cell membranes and lung surfactant PMID:23667230 A ΞplcHR mutant, known to be defective in virulence in animal models, was less able to colonize epithelial cell monolayers and was defective in biofilm formation on plastic when grown in lung surfactant |
| GO:0005576 extracellular region | IC PMID:12799377 Purification, characterization, and identification of a sphi... | NEW | Summary: Proposed location. PlcH has no cellular component annotation at present, although it is purified from culture supernatants and its secretion route is established. Reason: Two independent lines agree: the enzyme activity is recovered from the culture medium of PAO1 and PAK and purified from it, and PlcH carries a Tat signal peptide (UniProt SIGNAL 1-38) and crosses the outer membrane through the Xcp secreton. Its substrates are host membrane lipids, which only an extracellular enzyme can reach. Supporting Evidence: PMID:12799377 SM synthase-like activity was found secreted in the culture medium of P. aeruginosa PMID:11726509 two substrates for the Pseudomonas aeruginosa secreton, both phospholipases, use the twin-arginine translocation (Tat) system file:PSEAE/plcH/plcH-uniprot.txt Predicted to be exported by the Tat system |
Loading supporting contentβ¦
Download this section (compressed HTML)Q: Does the sphingomyelin synthase (transfer) reaction of PlcH occur at all outside the test tube, where ceramide and phosphatidylcholine are in separate host membrane leaflets?
Experiment: Assay purified PlcHR2 on host-cell membranes and lung surfactant for hydrolysis versus transfer products, to establish whether sphingomyelin synthesis is physiologically relevant.
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)