WbpL (PA3145) is a polytopic inner-membrane sugar-1-phosphate transferase of the WecA/MraY family (Pfam PF00953). It initiates O-antigen synthesis by transferring an N-acetylhexosamine-1-phosphate from a UDP-sugar to the lipid carrier undecaprenyl phosphate, giving the first sugar of the repeat unit. It is bifunctional: it starts the B-band (O-specific antigen) with Fuc2NAc and the A-band (common polysaccharide antigen) D-rhamnan with GlcNAc or GalNAc. wbpL mutants make neither form of O antigen, and E. coli WecA can substitute for it.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN000531998, seeded by E. coli WecA and S. aureus Q2FZ93, both polytopic membrane enzymes. Reason: WbpL has nine predicted TM helices and acts on the membrane-embedded lipid carrier undecaprenyl phosphate; the inner (plasma) membrane is where it works. Supporting Evidence: file:PSEAE/wbpL/wbpL-uniprot.txt TRANSMEM 48..65 PMID:9680202 through the addition of Fuc2NAc (2-acetamido-2,6-dideoxy-D-galactose) to undecaprenol phosphate (Und-P) |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Subcellular-location mapping (cell membrane, multi-pass). Reason: Consistent with the nine predicted TM helices and the Und-P acceptor. Supporting Evidence: file:PSEAE/wbpL/wbpL-uniprot.txt TRANSMEM 48..65 |
| GO:0009103 lipopolysaccharide biosynthetic process | IBA GO_REF:0000033 | TOO GENERAL | Summary: IBA from PTN000532005, seeded by WbpL itself (expected self-seed), E. coli WecA and Thermotoga Q9X1N5, each with experimental support. Reason: True, and the right level for the node (WecA-like initiators also start enterobacterial common antigen). For WbpL, the accepted GO:0009243 O antigen biosynthetic process (part_of lipopolysaccharide biosynthetic process) entails it. IBD sound (see notes). Supporting Evidence: PMID:9680202 chromosomal wbpL mutants were generated that did not express A band or B band, indicating that WbpL initiates the synthesis of both LPS molecules |
| GO:0009103 lipopolysaccharide biosynthetic process | IMP PMID:9680202 Three rhamnosyltransferases responsible for assembly of the ... | TOO GENERAL | Summary: PseudoCAP seed row for PTN000532005. wbpL mutants make neither A-band nor B-band LPS. Reason: Seed verdict SOUND: the gene performs the initiating step of both O antigens. The specific term GO:0009243, accepted below, entails this one. Supporting Evidence: PMID:9680202 chromosomal wbpL mutants were generated that did not express A band or B band, indicating that WbpL initiates the synthesis of both LPS molecules |
| GO:0009243 O antigen biosynthetic process | IDA PMID:9680202 Three rhamnosyltransferases responsible for assembly of the ... | ACCEPT | Summary: PseudoCAP row (also listed as seed support for PTN000532005). WbpL initiates both the B-band and the A-band O antigen. Reason: Core process. The abstract describes mutant and cross-complementation data, which would fit IMP or IGI better than IDA. The full text could not be read, so the code is not challenged here. Supporting Evidence: PMID:9680202 Cross-complementation experiments using WbpL and its homologue, Escherichia coli WecA, demonstrates that WbpL is bifunctional, initiating B-band synthesis with a Fuc2NAc residue and A-band synthesis with either a GlcNAc (N-acetylglucosamine) or GalNAc (N-acetylgalactosamine) residue. |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO membrane from the PF00953 family signature. Reason: Correct but general; the protein is in the inner (plasma) membrane, a term it already carries. Proposed replacements: plasma membrane Supporting Evidence: file:PSEAE/wbpL/wbpL-uniprot.txt TRANSMEM 48..65 |
| GO:0016757 glycosyltransferase activity | IMP PMID:9680202 Three rhamnosyltransferases responsible for assembly of the ... | MODIFY | Summary: PseudoCAP row. WbpL is a WecA homologue that adds the first sugar to undecaprenyl phosphate, as a sugar-1-phosphate (from a UDP-sugar). Reason: The family is called "glycosyl transferase 4" in Pfam, but the reaction of WecA-type enzymes (EC 2.7.8.33) is sugar-1-phosphate transfer to Und-P. GO places that under GO:0016780 phosphotransferase activity, for other substituted phosphate groups (as for WecA), not under glycosyltransferase activity. GO:0016780 is already on this gene. Proposed replacements: phosphotransferase activity, for other substituted phosphate groups Supporting Evidence: PMID:9680202 through the addition of Fuc2NAc (2-acetamido-2,6-dideoxy-D-galactose) to undecaprenol phosphate (Und-P) file:PSEAE/wbpL/wbpL-uniprot.txt UNDECAPRENYL-PHOSPHATE ALPHA-N-ACETYLGLUCOSAMINYL 1-PHOSPHATE TRANSFERASE |
| GO:0016780 phosphotransferase activity, for other substituted phosphate groups | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN000531998 (WecA/MraY family root), seeded by MraY and WecA enzymes with experimental activity. Reason: Core activity. GO has no term for undecaprenyl-phosphate Fuc2NAc-1-phosphate (or GalNAc-1-phosphate) transfer. The GlcNAc-specific GO:0036380 would cover only one of WbpL's substrates, and that one is not assayed directly, so this term is as specific as the evidence allows. Supporting Evidence: PMID:9680202 through the addition of Fuc2NAc (2-acetamido-2,6-dideoxy-D-galactose) to undecaprenol phosphate (Und-P) |
| GO:0016780 phosphotransferase activity, for other substituted phosphate groups | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA from the PF00953 family signature. Reason: Same claim as the IBA row; consistent with family membership. Supporting Evidence: file:PSEAE/wbpL/wbpL-uniprot.txt Pfam; PF00953; Glycos_transf_4 |
| GO:0044038 cell wall macromolecule biosynthetic process | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: IBA from the family root PTN000531998, seeded by WecA and Q9X1N5. Reason: WbpL makes the lipid-linked primer of O antigen, an outer-membrane LPS component, not a cell-wall (peptidoglycan or teichoic acid) polymer. Its own process is captured by GO:0009243. The node also covers MraY-like members that do make cell-wall precursors, so this is a mis-fit for WbpL's branch rather than a wrong node term; no defect filed from this gene. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN000531998 · PTN000531998 SUPPORTS SOURCE BUT NOT TARGET WecA/MraY family root. The cell-wall process fits MraY-like members but not the O-antigen-initiating WbpL branch. UniProtKB:P0AC78 · E. coli WecA SUPPORTS SOURCE BUT NOT TARGET WecA's own IDA (PMID:11700352) is not evidence that WbpL builds cell-wall polymers. UniProtKB:Q9X1N5 · Thermotoga maritima Q9X1N5 SUPPORTS SOURCE BUT NOT TARGET Supporting Evidence: PMID:9680202 chromosomal wbpL mutants were generated that did not express A band or B band, indicating that WbpL initiates the synthesis of both LPS molecules |
| GO:0071555 cell wall organization | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: IBA from PTN000531998, as for GO:0044038. Reason: Same reasoning as GO:0044038: WbpL's product is O antigen on outer-membrane LPS, not a cell-wall component. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN000531998 · PTN000531998 SUPPORTS SOURCE BUT NOT TARGET WecA/MraY family root. The cell-wall process fits MraY-like members but not the O-antigen-initiating WbpL branch. UniProtKB:P0AC78 · E. coli WecA SUPPORTS SOURCE BUT NOT TARGET WecA's own IDA (PMID:11700352) is not evidence that WbpL builds cell-wall polymers. UniProtKB:Q9X1N5 · Thermotoga maritima Q9X1N5 SUPPORTS SOURCE BUT NOT TARGET Supporting Evidence: PMID:9680202 chromosomal wbpL mutants were generated that did not express A band or B band, indicating that WbpL initiates the synthesis of both LPS molecules |
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Download this section (compressed HTML)Experiment: Assay purified or membrane-embedded WbpL with undecaprenyl phosphate and UDP-Fuc2NAc, UDP-GlcNAc or UDP-GalNAc to establish its donor specificity directly.
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