PA4675 / ChtA (Q9HVC0) notes

Review session 2026-11-05 (PseudoCAP IBA-seed protocol, tier 2)

Fetched with just fetch-gene PSEAE Q9HVC0 --alias PA4675 (accession fetch). Accession
Q9HVC0 (unreviewed, PE3) matches the worklist. No deep-research keys; literature from the
cached seed paper (PMID:16549659, abstract-only, no PMC full text) and the UniProt record.

Identity

TonB-dependent outer-membrane receptor (TBDR). Signal peptide 1-28, plug domain 47-150,
TonB-dependent beta-barrel 244-699. PTHR30069:SF42 "FERRIC AEROBACTIN RECEPTOR"; Pfam
Plug + TonB_dep_Rec_b-barrel. No N-terminal signalling extension before the plug, so a
receptor-transporter, not a TonB-dependent transducer.

Literature

ChtA is the outer-membrane receptor for the citrate-hydroxamate xenosiderophores
PMID:16549659;
PMID:16549659;
no redundancy PMID:16549659;
TonB1-dependent PMID:16549659. Fur-regulated.

Annotation decisions

Cell outer membrane (IBA, IEA): ACCEPT. Siderophore uptake transmembrane transporter
activity (IBA, IMP): ACCEPT core. Siderophore-iron import into cell (IEA): ACCEPT.
Siderophore transmembrane transport (IBA): ACCEPT core process.
Siderophore-iron transmembrane transporter activity (IEA, GO:0015343): TOO_GENERAL
(GO:0015344 is its is_a descendant). Siderophore transport (IEA, IMP, GO:0015891):
TOO_GENERAL (GO:0044718 is its is_a descendant).
Signaling receptor activity (IEA, GO:0038023): REMOVE. The InterPro2GO mapping is wrong
for this member: ChtA has only a signal peptide then the plug, no signalling extension,
so it is not a TonB-dependent transducer. (Same decision as PfeA.)
Action counts: ACCEPT 6, TOO_GENERAL 3, REMOVE 1. Defects: none recorded (the signaling
row is an InterPro2GO electronic over-mapping handled by REMOVE, not a PseudoCAP/GO_CENTRAL
source defect; it is noted here and for the whole family).

PseudoCAP IBA-seed assessment

PTN node	node term	n_seeds	leaf IBAs	seed annotation (term, evidence, PMID)	verdict	rationale	other seeds	IBD stands without this seed?
PTN004738955	GO:0015344 siderophore uptake transmembrane transporter activity	4	142 (21 taxa)	GO:0015344, IMP, PMID:16549659	SOUND	chtA mutant cannot use aerobactin, rhizobactin 1021 or schizokinen (no redundancy), TonB1-dependent; ChtA is the outer-membrane receptor for these ferric siderophores.	PfeA (Q05098), FvbA (PA4156, Q9HWM5), PirA (Q9I527) — all PseudoCAP IMP; GO:0044718 at the same node seeded by E. coli CirA (P17315, IMP/IDA)	Yes

Node-level assessment, PTN004738955 (recorded here; cross-referenced from PA4156, pirA)

The GO:0015344 IBD at PTN004738955 (PTHR30069 TonB-dependent siderophore receptor clade,
142 leaves in 21 taxa) is seeded by four PAO1 receptors: PfeA (ferric enterobactin,
PMID:8419284), ChtA (this gene), FvbA (vibriobactin) and PirA (ferric enterobactin /
catecholamines). PfeA is independently reviewed (SOUND). The partner process IBD GO:0044718
at the same node is seeded by E. coli CirA (P17315), which carries experimental
GO:0015343/GO:0044718 (EcoCyc). Each seed is a characterized ferric-siderophore receptor, so
the IBD stands and the node term (siderophore uptake transmembrane transporter activity)
suits the clade; no GO_CENTRAL defect. The only caveat is the GO term itself: GO:0015344 is
defined by a proton-coupled ferrioxamine symport reaction (TC 2.A.1.16), which does not
describe a TonB-dependent outer-membrane receptor, yet it is the conventional term for them;
raised as a suggested question.

PANTHER note

UniProt currently assigns PA4675 to PTHR30069:SF42; the cell-outer-membrane IBA is on the
separate node PTN002824128 (seeded by E. coli FepA/BtuB/CirA/YncD), which is a general TBDR
localization node and is appropriate.