mexX (PA2019, G3XD21) notes

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

Fetched with just fetch-gene PSEAE G3XD21 --alias mexX; accession matches the
worklist. Reviewed Swiss-Prot entry. No deep-research provider was used. Cached
papers: PMID:10543738 and PMID:16030228 have full text; PMID:10952562,
PMID:11083635 and PMID:15325256 are abstract-only (the PMC copies returned no
text). The PubMed MCP search returned API errors.

Literature

MexX is the periplasmic adaptor (membrane fusion protein, MFP) of the tripartite
MexXY-OprM RND pump; it is a predicted inner-membrane lipoprotein (signal
peptide 1-23, lipidated Cys24, UniProt).
Discovery as an aminoglycoside efflux system in PAO1
PMID:10543738.
Isogenic deletion mutants
PMID:10952562;
MexX protein is induced by antibiotics
PMID:10952562.
Induction by ribosome-targeting antibiotics
PMID:16030228.
The assay measured mexY mRNA; mexX and mexY are one operon, so the induction
applies to MexX (MexX protein induction is shown in PMID:10952562).
Substrate range
PMID:11083635.
Assembly specificity
PMID:15325256.
Repressed by MexZ (reviewed separately in genes/PSEAE/mexZ).

Decisions

ACCEPT: plasma membrane (IBA, IDA x2, IEA); efflux transmembrane transporter
activity (IBA; MexX contributes as the adaptor); transmembrane transporter
binding (IPI, MexY); xenobiotic detoxification by transmembrane export across the
cell outer membrane (IBA); efflux pump complex (IDA).
KEEP_AS_NON_CORE: response to antibiotic (6 rows: EXP x2, IMP x2, IBA, IEA),
consistent with PA3677 (mexJ); periplasmic space (IEA).
TOO_GENERAL: membrane (IDA, IEA); transmembrane transporter activity (IEA);
transmembrane transport (IEA).
REMOVE: protein binding (IPI, OprM), per the protein-binding policy.
Counts: ACCEPT 8, KEEP_AS_NON_CORE 7, TOO_GENERAL 4, REMOVE 1.

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?
PTN001249140	GO:0046677 response to antibiotic	6	38 (12 taxa)	GO:0046677, IMP, PMID:10952562 (PseudoCAP)	SOUND	Abstract: isogenic mexXY deletion increases susceptibility of a MexAB-deficient strain to all agents tested.	E. coli AcrA (P0AE06; EcoCyc IMP PMID:8407802, IGI PMID:7651136), E. coli MdtE (P37636; EcoCyc IMP PMID:11566977, PMID:12937021), MexE (Q9I0Y9; UniProt IGI PMID:34680745), MexC (G3XD25; UniProt IGI PMID:12654738), MexA (P52477)	Yes
PTN001249140	GO:0046677 response to antibiotic	6	38 (12 taxa)	GO:0046677, EXP, PMID:10952562 (PseudoCAP)	SOUND	Same paper and claim as the IMP row; also shows MexX protein induced by tetracycline, erythromycin and gentamicin. EXP is a valid, less specific code.	as above	Yes
PTN001249140	GO:0046677 response to antibiotic	6	38 (12 taxa)	GO:0046677, EXP, PMID:16030228 (PseudoCAP)	SOUND	Full text read: mexXY is induced by ribosome-targeting antibiotics (mexY RT-PCR; operon). A genuine response to antibiotic.	as above	Yes

The UniProt IMP row (PMID:10543738, full text read) supports the same term
independently. No PSEUDOCAP and no GO_CENTRAL defect. The node is a clade of
membrane fusion proteins of RND multidrug pumps (AcrA, AcrE, MdtE, MexA, MexC,
MexE, MexX); a resistance-phenotype process term suits it and rests on several
independent E. coli and P. aeruginosa seeds. This is the node-level assessment for
the batch; mexA (genes/PSEAE/mexA/mexA-notes.md) cross-references it.