PldA (PA3487, also called Tle5a) is a 1099-residue eukaryotic-type phospholipase D of P. aeruginosa. It carries two HxKxxxxD (HKD) catalytic motifs, and its crystal structure shows an active-site arrangement closer to eukaryotic than to other bacterial phospholipases D. Purified PldA hydrolyses the head group of phosphatidylcholine, releasing choline, and it tolerates a range of phospholipid substrates; in target cells its principal substrate is phosphatidylethanolamine, whose conversion to phosphatidic acid destabilises the membrane and kills the cell. PldA is a type VI secretion system effector: release depends on its cognate spike protein VgrG4b and on the H2-T6SS, and the producing cell is protected by the adjacent immunity protein Tli5a (PA3488). Activity has also been detected in the periplasm of the producing cell, and the gene is present in only some strains, consistently linked to a vgr gene, which indicates horizontal acquisition. Its biological role is antagonism of competing bacteria, with a reported contribution to persistence in chronic pulmonary infection.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004630 D-type glycerophospholipase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from the PAINT IBD on PTN004499769, the PLD superfamily node, seeded by 24 members including human PLD1 (Q13393), yeast SPO14, rat Pld1/Pld2 and ten Arabidopsis PLDs. PldA carries two HKD motifs, and purified protein hydrolyses phosphatidylcholine with a strict requirement for His855, so the target sits squarely inside the clade. Q9HYC2 appearing in its own WITH/FROM reflects its experimental row and is expected. Reason: The inherited claim is the family-defining activity and is directly demonstrated for this protein. Supporting Evidence: PMID:23552891 Consistent with prior observations, Tle5PA catalyzes the release of choline from phosphatidylcholine (PC), in a manner dependent upon a predicted catalytic histidine residue (His855) |
| GO:0009395 phospholipid catabolic process | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: A second IBD on the same node, seeded only by plant and rat PLDs that hydrolyse the phospholipids of their own membranes in lipid turnover and signalling. PldA is a secreted T6SS toxin whose substrate is the phosphatidylethanolamine of a target cell; it is not part of P. aeruginosa's own phospholipid degradation. Reason: The chemistry is phospholipid hydrolysis, so the term is not simply false, but the process claim carries the endogenous lipid-turnover role of the eukaryotic seeds onto an interbacterial toxin. Kept consistent with the same row on PA5089 (pldB). Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: ROLE CONFLATION CONTEXT OR TISSUE MISMATCH Sources checked: PANTHER:PTN004499769 · PTN004499769 SUPPORTS SOURCE BUT NOT TARGET All four seeds of the GO:0009395 IBD are eukaryotic PLDs acting on their own membranes; the node also contains secreted bacterial toxins, for which the process reading does not hold. Supporting Evidence: PMID:23552891 Taken together, these data strongly suggest that Tle5PA-imposed cell death occurs through PA accumulation via PLD activity, primarily directed against PE. |
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO root-level catalytic activity from the PLD/transphosphatidylase signature. Reason: Root-of-branch term, entailed by the GO:0004630 activity accepted elsewhere in this review. |
| GO:0004630 D-type glycerophospholipase activity | IEA GO_REF:0000003 | ACCEPT | Summary: EC 3.1.4.4 to GO mapping, in agreement with the purified-enzyme data. Reason: The mapped activity is the one demonstrated for purified PldA. Supporting Evidence: PMID:11136451 The pldA gene was cloned and shown to express an approximately 116 kDa protein with calcium-regulated PLD activity that is localized to the periplasm. |
| GO:0004630 D-type glycerophospholipase activity | IMP PMID:24832454 A Pseudomonas aeruginosa type VI secretion phospholipase D e... | ACCEPT | Summary: PseudoCAP row on PA3487 and one of the 24 seeds of the PTN004499769 IBD. The term is correct for this gene, and better supported than the row claims - purified PldA hydrolyses phosphatidylcholine with a His855 requirement and the structure shows an intact HKD core. The citation, however, points to the paper that characterised PldB (PA5089), the paralogue that carries the identical row with the identical PMID. Reason: The claim is true and directly demonstrated, so the row stays; the defect is in its reference, recorded below for PseudoCAP to re-point. Deferring to the curator on the claim while flagging the citation keeps the IBD on this node intact. Supporting Evidence: PMID:23552891 Consistent with prior observations, Tle5PA catalyzes the release of choline from phosphatidylcholine (PC), in a manner dependent upon a predicted catalytic histidine residue (His855) PMID:11136451 The pldA gene was cloned and shown to express an approximately 116 kDa protein with calcium-regulated PLD activity that is localized to the periplasm. |
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Download this section (compressed HTML)Q: Does PldA have any substrate in the producing cell's own periplasm, where calcium-regulated activity was detected, or is the periplasmic pool simply an export intermediate held in check by Tli5a?
Q: Should GO offer a process term for delivery of an antibacterial effector into a target cell, so that T6SS toxins need not be annotated to the endogenous metabolic process that matches their chemistry?
Experiment: Quantify the phospholipid composition of a prey strain intoxicated by PldA versus PldB, side by side, to test whether the two effectors have distinct head-group preferences; pair with active-site mutants of each (His167/His855 for PldA, the predicted 642/644/649 site for PldB).
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