ctpL (PA4844, Q9HUW6) notes

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

Fetched with just fetch-gene PSEAE Q9HUW6 --alias ctpL (accession fetch after the
symbol query hit a UniProt 429). Accession Q9HUW6 matches the worklist. No deep-research
provider keys were available; literature is from the cached publications and the UniProt
record. Seed papers PMID:10852870, PMID:24038698 are abstract-only (PMC101905, PMC3837763
full text not retrievable through the PubMed MCP or Europe PMC); PMID:27353565 full text
is cached.

Identity

MCP chemoreceptor, PTHR32089:SF119. Two TM helices (6-26, 306-326) around a large
periplasmic region (27-305), then cytoplasmic HAMP (327-380) and MCPsignal (385-621)
domains. Belongs to the Pho regulon (induced by Pi limitation via PhoB; repressed by
PhoU) PMID:10852870.

Literature

Pi chemoreceptor. The ctpL mutant fails to respond to low (0.01 mM) Pi, and the ctpH
ctpL double mutant is defective in Pi taxis at all concentrations
PMID:10852870;
PMID:10852870.
Indirect sensing. CtpL does not bind Pi directly; the Pi-loaded periplasmic binding
protein PstS binds CtpL and stimulates it
PMID:27353565;
PMID:27353565.
Also the 4-chloroaniline / catechol chemoreceptor (screen of all 26 MCP mutants)
PMID:24038698.

Annotation decisions

Chemotaxis (IBA, IEA, IMP), detection of phosphate ion (IMP), positive chemotaxis
(IMP): ACCEPT (core). Transmembrane signaling receptor activity (IEA): ACCEPT core MF.
Plasma membrane (IEA): ACCEPT. Signal transduction (IEA): MODIFY to GO:0007166.
Membrane (IEA): TOO_GENERAL (plasma membrane entails it).
Action counts: ACCEPT 6, MODIFY 1, TOO_GENERAL 1.
No source defects; the PseudoCAP seed row is sound.

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?
PTN001280296	GO:0006935 chemotaxis	10	215 (22 taxa)	GO:0006935, IMP, PMID:10852870	SOUND	The ctpL mutant loses low-Pi taxis and the ctpH ctpL double mutant loses Pi taxis at all concentrations; CtpL is the receptor that transduces the stimulus (via Pi-loaded PstS). Also the 4CA/catechol receptor (PMID:24038698).	PctA, PctB, PctC, CtpH, CtpM, Aer (PseudoCAP IMP); B. subtilis McpC (IDA/IMP positive chemotaxis); B. subtilis and H. salinarum HemAT (IDA aerotaxis)	Yes; independent IDA seeds and six other PseudoCAP seeds

The node-level assessment of PTN001280296 is recorded once in pctB-notes.md (all five
chemoreceptors reviewed in that batch SOUND; node term chemotaxis suits the PTHR32089 MCP
clade; no GO_CENTRAL defect). ctpL is consistent with it. The only leaf oddity (Dictyostelium
AlyL lysozyme-like proteins placed in the clade) is a PANTHER family-placement issue raised
on pctB.