MucB is a periplasmic co-antagonist of the ECF sigma factor AlgU: it binds the
anti-sigma factor MucA (MF: antisigma factor binding, GO:0045152) and shields it
from regulated intramembrane proteolysis. Alginate (polysaccharide) overproduction
in mucB mutants is the AlgU-regulon output in P. aeruginosa; it is a true
regulatory role of this gene, but it is not the conserved family function. In
E. coli and other enterobacteria, RseB controls the sigmaE envelope-stress
response, not polysaccharide synthesis.
| PTN node | node term | n_seeds | leaf IBAs | seed annotation (term, evidence, PMID) | verdict | rationale |
|---|---|---|---|---|---|---|
| PTN002215378 | GO:0032885 regulation of polysaccharide biosynthetic process | 1 (sole seed) | 7 (7 taxa) | GO:0032885 regulation of polysaccharide biosynthetic process, IMP, PMID:9171421 (PseudoCAP) | OVER-SPECIFIC | The seed is acceptable for MucB itself: mucB loss gives alginate overproduction because AlgU directly drives algD. But alginate control is a Pseudomonas-specific output of the AlgU regulon, not the RseB-family function. The node's other six leaves are enterobacterial/Vibrio/Shewanella/Haemophilus RseB orthologs (E. coli P0AFX9, Salmonella H9L461, Yersinia A0A2U2GWS2, Haemophilus P44792, Shewanella Q8EH85, Vibrio Q9KPA8) that regulate sigmaE, with no evidence of polysaccharide-synthesis control. The node term should not propagate; antisigma factor binding (already at this node, seeded by E. coli RseB) is the conserved claim. |
Node leaves were taken from the PAINT leaf GAF (.cache/paint/leaf.gaf.gz).
Audit of the leaf claims in the GO_CENTRAL source defect on PTN002215378.
Membership confirmed with
uv run python projects/PSEUDOCAP/panther_tree.py node PTN002215378 --leaves
(7 leaves, all PTHR38782:SF1); UniProt flat files fetched for all seven. All
seven are 310-321 aa and match Pfam PF03888 MucB_RseB plus PF17188
MucB_RseB_C; six also match NCBIfam NF006990 rseB (Shewanella Q8EH85 does not).
| Leaf | Name and its evidence | Experimental annotations | Verdict |
|---|---|---|---|
| P0AFX9 (E. coli RseB) | RecName, curated (Reviewed); PE 1 | GO:0045152 antisigma factor binding (IDA), GO:0050821 protein stabilization (IDA), GO:0042597 periplasmic space (EXP), GO:1903865 sigma factor antagonist complex (IPI), GO:0030288 (IDA); ECO:0000269 FUNCTION/SUBUNIT incl. LPS binding | "RseB ortholog" claim survives on evidence. No polysaccharide-related annotation of any kind |
| H9L461 (S. typhimurium) | RecName from ECO:0000256|ARBA (an association rule, not curation); PE 3 | none | Identity rests on the family signature, not on the name or on ARBA text |
| A0A2U2GWS2 (Y. pestis) | SubName {ECO:0000313|EMBL}; PE 3 | none | Same |
| P44792 (H. influenzae) | RecName, curated (Reviewed); PE 3 | none; FUNCTION all ECO:0000250 "By similarity" | Curated name, but no experimental data behind it |
| Q8EH85 (S. oneidensis) | SubName {ECO:0000313|EMBL}; PE 3 | none | Family signature only; lacks NF006990 |
| Q9KPA8 (V. cholerae) | SubName {ECO:0000313|EMBL}; PE 3 | none | Family signature only |
Outcome: the clade is genuinely homogeneous, so the "spans RseB orthologs"
observation survives — but on the domain architecture, not on the names (four of
six are SubName/ARBA). The load-bearing claim "with no reported role in
polysaccharide synthesis" does not survive as stated: it is an absence, and
there is a real counter-consideration. E. coli RseB binds LPS (curated
ECO:0000269 statements) and the sigmaE regulon includes LPS biogenesis genes, so
the broad GO:0032885 may be defensible for the enterobacterial leaves by a
mechanism unrelated to the seed's. What we can assert is narrower: the route
in the seed phenotype is lineage-restricted, because the alginate algD operon
is confined to Pseudomonas and Azotobacter.
Confidence lowered PROBABLE -> SUSPECTED, and the entry rewritten to query the
IBD rather than to assert the term is false for the other leaves.