PA5455 is a predicted GT-B fold glycosyltransferase of the GT4 family (Pfam PF13692, Glyco_trans_1_4; 542 residues) encoded in the pa5455-pa5459 operon next to the rmd-wbpZ cluster for the common polysaccharide antigen (CPA, A-band O antigen), a D-rhamnan homopolymer of the lipopolysaccharide of Pseudomonas aeruginosa. In-frame deletion of either PA5455 or its neighbour PA5456 abolishes CPA production, and complementation in trans restores it; co-overexpression of PA5455 and PA5456 shortens CPA chains, suggesting that one or both catalyse a chain-length-determining or chain-terminating step. The donor and acceptor substrates and the linkage formed are not known; the D-rhamnan repeat itself is built by the D-rhamnosyltransferases WbpZ, WbpY and WbpX.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0009103 lipopolysaccharide biosynthetic process | IMP PMID:23341552 Five new genes are important for common polysaccharide antig... | TOO GENERAL | Summary: PseudoCAP IMP. The in-frame deletion mutant lacks CPA LPS; complementation restores it. Reason: True, but GO:0009243 O antigen biosynthetic process (part_of GO:0009103), accepted below, is the specific claim the data support. |
| GO:0009243 O antigen biosynthetic process | IDA PMID:23341552 Five new genes are important for common polysaccharide antig... | ACCEPT | Summary: PseudoCAP row coded IDA. The supporting data are the in-frame deletion and complementation (loss and restoration of CPA, the A-band O antigen), which is mutant-phenotype evidence. As a predicted glycosyltransferase in the CPA operon whose loss abolishes the polymer, PA5455 very probably performs a step of CPA assembly, so the process claim is accepted. Reason: The process claim is supported by deletion and complementation plus the GT4 domain; the evidence code should be IMP, not IDA. Supporting Evidence: PMID:23341552 Mutation of either one of the two putative glycosyltransferase genes, pa5455 and pa5456, completely abrogated CPA biosynthesis |
| GO:0016757 glycosyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from the PTN002288302 IBD, whose only two seeds are PA5455 (Q9HTB5) and PA5456 (Q9HTB4), both from the PseudoCAP IDA rows on PMID:23341552. Those rows have no enzyme assay behind them (see the IDA row), so the IBD has no experimental seed. The term itself is very probably true for the clade: both seeds, and by PANTHER membership the descendants, carry the GT4 Glyco_trans_1_4 domain. Reason: Generic glycosyltransferase activity is as precise as the evidence allows and is supported by the GT4 domain; it is the core (if uncharacterised) activity of the protein. Accepted on sequence grounds, not on the IBD's nominal experimental basis, which is absent. The node-level GO_CENTRAL defect is recorded on this row. Supporting Evidence: file:PSEAE/PA5455/PA5455-uniprot.txt PF13692; Glyco_trans_1_4 PMID:23341552 Gene sequence analysis indicated that pa5455 and pa5456 encode putative glycosyltransferases. |
| GO:0016757 glycosyltransferase activity | IDA PMID:23341552 Five new genes are important for common polysaccharide antig... | ACCEPT | Summary: PseudoCAP IDA and one of the two seeds of PTN002288302. The paper (full text read) calls PA5455 a putative glycosyltransferase from sequence analysis and reports only genetics (deletion, complementation, overexpression). No glycosyltransferase assay was performed. Reason: Seed verdict UNVERIFIABLE as experimental evidence: the activity is predicted from the GT4 domain, not assayed, so the IDA code is wrong. The claim itself is plausible on sequence grounds and is kept (consistent with the IBA row). Supporting Evidence: PMID:23341552 Gene sequence analysis indicated that pa5455 and pa5456 encode putative glycosyltransferases. file:PSEAE/PA5455/PA5455-uniprot.txt PF13692; Glyco_trans_1_4 |
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Download this section (compressed HTML)Q: The PAINT IBD on PTN002288302 (glycosyltransferase activity, 57 leaf IBAs in 43 taxa) rests only on the PseudoCAP IDA rows for PA5455 and PA5456, which have no enzyme assay behind them. Should the IBD be re-based on the GT4 domain (or withdrawn until an experimental seed exists)?
Q: Do PA5455 and PA5456 form a complex, as the overexpression phenotype suggests, and does either add a non-rhamnose terminal residue to CPA?
Experiment: Express PA5455 and PA5456 (singly and together) and assay transfer from nucleotide sugars (GDP-D-Rha, GDP-D-Man, UDP-GlcNAc and others) to synthetic D-rhamnan acceptors such as those used for WbpX/WbpY/WbpZ, identifying products by MS and NMR.
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The sugar donor, acceptor and glycosidic linkage made by PA5455 are unknown, as is whether it acts at CPA chain initiation, elongation, capping or termination.
BIOLOGY
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