wbpY (PA5448, Q9HTB9) notes

No deep-research provider was available; literature research done manually (PubMed MCP + cached
publications).

Identity

UniProt Q9HTB9 (TrEMBL, unreviewed; PE 4), 375 aa, P. aeruginosa PAO1, locus PA5448, in the
A-band (common polysaccharide antigen, CPA) cluster next to wbpX (PA5449, G3XCU3) and wbpZ.
GT4 (CAZy) GT-B fold glycosyltransferase: Pfam PF13439 Glyco_transf_4 and PF00534
Glycos_transf_1; PANTHER PTHR46401 (GLYCOSYLTRANSFERASE WBBK-RELATED) SF2.

CPA is a D-rhamnan homopolymer of trisaccharide repeats [D-Rha a1-2 D-Rha a1-3 D-Rha a1-3]n
PMID:35166992.
1998 genetics: wbpX, wbpY and wbpZ mutants lack A-band LPS while B-band is unaffected; WbpY was
proposed to add alpha1-3 Rha PMID:9680202. Abstract only; the assignment of
activities in that paper was by sequence and phenotype.
WbpZ (the first D-RhaT) adds D-Rha a1-3 to GlcNAc/GalNAc-PP-lipid PMID:25845842.
2022 biochemistry: recombinant WbpY transfers one D-Rha from GDP-D-Rha in alpha1-3 linkage onto
the WbpZ product D-Rha a1-3 D-GlcNAc a-PP-lipid (NMR); WbpX adds a1-2 and a1-3 Rha; WbpX+WbpY
together make D-Rha oligomers non-processively PMID:35166992.
So WbpY is a GDP-D-rhamnose:D-Rha-a1,3-D-GlcNAc-PP-lipid a1,3-D-rhamnosyltransferase. GO has no
D-rhamnosyltransferase term; rhamnosyltransferase terms sit under GO:0016758 hexosyltransferase
activity, which is the most specific existing MF.

GO:0009243 O antigen biosynthetic process is part_of GO:0009103 lipopolysaccharide biosynthetic
process (OAK, sqlite:obo:go), so the LPS rows are correct but general for WbpY.

PTN node	node term	n_seeds	leaf IBAs	seed annotation (term, evidence, PMID)	verdict	rationale
PTN005302544	GO:0016757 glycosyltransferase activity	2 (WbpY, WbpX)	60 (22 taxa)	GO:0016757 glycosyltransferase activity, IMP, PMID:9680202	INDIRECT-PHENOTYPE (term correct)	As far as the abstract and the IMP code show (full text not read), the 1998 MF assignment rests on mutant LPS phenotype plus sequence similarity, not an activity assay. The term is nevertheless true: WbpY (and WbpX) were shown in vitro to be GDP-D-Rha rhamnosyltransferases (PMID:35166992). Node conclusion sound for a GT4 clade; re-seed with IDA from PMID:35166992.
PTN000749272	GO:0009103 lipopolysaccharide biosynthetic process	1 (sole seed)	51 (19 taxa)	GO:0009103 LPS biosynthetic process, IMP, PMID:9680202	SOUND	Mutants lack A-band (CPA) LPS and WbpY itself catalyses a chain-extension step of the CPA O antigen, so participation in LPS biosynthesis is direct. LPS biosynthesis is a reasonable breadth for a WbbK-related GT4 subclade from O-antigen clusters; members in other species could instead make capsule or exopolysaccharide, which was not checked.