PA0920 encodes the alanyl-phosphatidylglycerol synthase (A-PGS) of Pseudomonas aeruginosa, an MprF-family integral inner-membrane protein with an N-terminal domain of 14 transmembrane helices and a C-terminal cytoplasmic catalytic domain. The catalytic domain transfers L-alanine from Ala-tRNA(Ala) to the head group of phosphatidylglycerol, forming 2'-alanyl-phosphatidylglycerol (A-PG), and specifically recognises the PG head group and the tRNA acceptor stem. Transcription is acid-induced, and A-PG makes up several percent of membrane lipid at low pH; a deletion mutant makes no A-PG. Together with the periplasmic A-PG hydrolase PA0919, which trims A-PG levels, it tunes membrane charge and lowers susceptibility to cationic antimicrobial peptides and other antimicrobials. Despite an automated "lysyltransferase" name, P. aeruginosa does not make lysyl-phosphatidylglycerol.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: SubCell mapping (from an ARBA cell-membrane prediction). Correct; the enzyme was shown experimentally to be an integral inner (cytoplasmic) membrane protein. Reason: Direct localisation (membrane fractionation and immunogold) places A-PGS in the inner membrane, with the catalytic domain on its cytosolic face, consistent with 14 predicted TM helices. Supporting Evidence: PMID:19087229 The enzyme was identified as an integral component of the inner membrane. PMID:21392131 almost exclusively decorate the cytosolic part of the inner membrane |
| GO:0047637 phosphatidylglycerol alanyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN005059806, whose sole seed is this gene's PseudoCAP IDA (PMID:26261323). The target appearing in its own WITH/FROM is expected. Reason: The activity is directly demonstrated for PA0920 (in vitro Ala-tRNA-dependent A-PG formation, heterologous A-PG formation in E. coli, loss in the deletion). The node is a clade of A-PGS-type MprF proteins; the propagation to other leaves deserves a check because A-PG vs L-PG specificity is not marked by a simple sequence motif, but for PA0920 itself the IBA is correct. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN005059806 · PTN005059806 SUPPORTS TRANSFER QuickGO (2026-10-28) lists 55 GO:0047637 leaves (worklist release 2), diverse bacteria and the archaeon Methanosarcina acetivorans. Specificity of other leaves is untested here. UniProtKB:Q9I537 · PA0920 SUPPORTS TRANSFER The target's own experimental annotation is the IBD seed; expected, not circular. Supporting Evidence: PMID:19087229 tRNA(Ala)-dependent catalysis was demonstrated. |
| GO:0047637 phosphatidylglycerol alanyltransferase activity | IDA PMID:26261323 Structures of two bacterial resistance factors mediating tRN... | ACCEPT | Summary: PseudoCAP IDA from the crystal structure and biochemical substrate-recognition study of the A-PGS catalytic domain. Sole seed of the GO:0047637 IBD at PTN005059806 and of GO:0016755 at PTN002162750. Reason: The paper assays the purified catalytic domain with aminoacylated tRNA and PG substrates, which is direct evidence for the activity; earlier papers from the same group show the activity in vitro and in vivo. Supporting Evidence: PMID:26261323 Here we present the X-ray crystallographic structure of the catalytic domain of A-PGS from the opportunistic human pathogen Pseudomonas aeruginosa. PMID:26261323 Substrate recognition of A-PGS versus L-PGS was investigated using misacylated tRNA variants. PMID:21392131 identify the minimal core domain of this transmembrane protein, which is capable of alanyl-phosphatidylglycerol biosynthesis |
| GO:0050071 phosphatidylglycerol lysyltransferase activity | IEA GO_REF:0000003 | REMOVE | Summary: EC2GO mapping from an ARBA-predicted EC 2.3.2.3 (lysyl-PG synthase). Contradicted by the characterised alanyl specificity of PA0920. Reason: PA0920 is the alanyl-PG synthase. The deletion mutant loses A-PG, the enzyme uses Ala-tRNA(Ala), and P. aeruginosa naturally makes A-PG; lysyl-PG appears only in engineered chimeric strains. The EC number and the RecName come from an ARBA rule for the MprF family that ignores the A-PGS/L-PGS split, so this is a demonstrably wrong electronic transfer. Supporting Evidence: PMID:22267511 chimeric mutant strains producing lysyl-phosphatidylglycerol (L-PG) instead of the naturally occurring alanyl-phosphatidylglycerol (A-PG) PMID:19087229 The P. aeruginosa deletion mutant DeltaPA0920 failed to synthesize A-PG. |
| GO:0055091 phospholipid homeostasis | IBA GO_REF:0000033 | MODIFY | Summary: PAINT IBA from PTN002162750, whose sole seed is this gene's PseudoCAP IDA to phospholipid homeostasis (PMID:26261323), which this review does not accept as the gene's own process. Reason: PA0920 catalyses one biosynthetic step, alanylation of PG; the steady-state level of A-PG is set by acid-induced expression together with the PA0919 A-PG hydrolase. The gene's own process is phospholipid (A-PG) biosynthesis, so the row is corrected laterally to GO:0008654. The node term is also unsuitable for the clade, which includes fungal ergosteryl-glycine synthases (ErgS) that modify a sterol, not a phospholipid. Propagation Review Root cause: SOURCE BAD Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002162750 · PTN002162750 SOURCE BAD QuickGO (2026-10-28) lists 26 GO:0055091 leaves, including A. fumigatus and Y. lipolytica ErgS (Q4WB70, Q6C7J3; ergosteryl-3beta-O-glycine synthases), S. aureus, B. subtilis and Listeria MprF (L-PGS) and M. tuberculosis Rv1619 (LysX2); none has experimental GO annotation of its own. UniProtKB:Q9I537 · PA0920 SOURCE BAD The seed's abstract reports in vitro structural and biochemical work that shows activity and describes no homeostasis assay (full text not read). Proposed replacements: phospholipid biosynthetic process Supporting Evidence: PMID:23792962 The elucidated enzymatic activity implies a new regulatory circuit for the appropriate tuning of cellular alanyl-PG concentrations. PMID:19087229 Heterologous overproduction of PA0920 in Escherichia coli resulted in the formation of significant amounts of A-PG, otherwise not synthesized by E. coli. |
| GO:0055091 phospholipid homeostasis | IDA PMID:26261323 Structures of two bacterial resistance factors mediating tRN... | MODIFY | Summary: PseudoCAP IDA citing the A-PGS catalytic-domain structure paper. Sole seed of the GO:0055091 IBD at PTN002162750. Reason: The abstract reports the enzyme's activity and substrate recognition in vitro and describes no measurement of phospholipid levels or their maintenance in cells (full text not read). The process PA0920 itself performs is synthesis of A-PG, a phospholipid, so the row is corrected to GO:0008654. Homeostasis of A-PG is a system property that also depends on the PA0919 hydrolase, which is the gene the authors associate with lipid homeostasis. Proposed replacements: phospholipid biosynthetic process Supporting Evidence: PMID:26261323 Aminoacylation of the polar head group of the phospholipid phosphatidylglycerol (PG) catalyzed by Ala-tRNA(Ala)-dependent alanyl-phosphatidylglycerol synthase (A-PGS) PMID:23792962 we make use of the opportunistic pathogen Pseudomonas aeruginosa to decode ORF PA0919-dependent lipid homeostasis |
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Download this section (compressed HTML)Q: Should GO have a term for aminoacyl-phosphatidylglycerol (alanyl-/lysyl-PG) biosynthesis, so that MprF-family synthases need not be annotated to the broad phospholipid biosynthetic process or to phospholipid homeostasis?
Q: Does the N-terminal transmembrane domain of PA0920 translocate A-PG to the outer leaflet, as the S. aureus MprF flippase domain does for lysyl-PG?
Experiment: Assay A-PG translocation across the inner membrane (e.g. TNBS accessibility or flippase reconstitution) in wild type and N-terminal-domain mutants of PA0920.
Type: biochemical/biophysical lipid translocation assay
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