EmrAB-TolC multidrug efflux transport complex

cellstructuremech:emrab_tolc_multidrug_efflux_transport_complex · Other · Multiprotein complex · Proposed

An Escherichia coli MFS-family cell-envelope efflux pump complex composed of EmrA, EmrB, and TolC subunits that exports hydrophobic xenobiotics across the inner and outer membranes. [ComplexPortal:CPX-4268]

Synonyms: EmrAB-TolC multidrug efflux transport system

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
Multidrug export protein EmrA	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	emrA	6 copies in the E. coli K-12 Complex Portal CPX-4268 entry	ESSENTIAL	Periplasmic membrane-fusion adaptor subunit that links EmrB to the TolC outer-membrane channel in the EmrAB-TolC conduit. `ComplexPortal:CPX-4268` Complex Portal CPX-4268 curates P27303/EmrA as six copies in the E. coli K-12 EmrAB-TolC multidrug efflux transport system. `UniProtKB:P27303` UniProtKB P27303 is the reviewed E. coli K-12 entry for Multidrug export protein EmrA. `PDB:8ZAL` RCSB PDB:8ZAL is an EmrAB-TolC electron-microscopy structure with six modeled EmrA chains.
Multidrug export protein EmrB	Protein	part of	`InterPro:IPR004638`	emrB	1 copy in the E. coli K-12 Complex Portal CPX-4268 entry	ESSENTIAL	Inner-membrane MFS transporter subunit that forms the EmrAB core and exports hydrophobic xenobiotics through the EmrA/TolC conduit. `ComplexPortal:CPX-4268` Complex Portal CPX-4268 curates P0AEJ0/EmrB as the single E. coli K-12 EmrB copy in EmrAB-TolC. `UniProtKB:P0AEJ0` UniProtKB P0AEJ0 is the reviewed E. coli K-12 entry for Multidrug export protein EmrB. `InterPro:IPR004638` InterPro IPR004638 is the Drug resistance transporter EmrB-like family entry. `PDB:8ZAL` RCSB PDB:8ZAL is an EmrAB-TolC electron-microscopy structure with one modeled EmrB chain.
Outer membrane channel protein TolC	Protein	part of	`InterPro:IPR058622`	tolC	3 copies in the E. coli K-12 Complex Portal CPX-4268 entry	ESSENTIAL	Trimeric outer-membrane channel constituent that completes the EmrAB-TolC cell-envelope efflux conduit. `ComplexPortal:CPX-4268` Complex Portal CPX-4268 curates P02930/TolC as three copies in the E. coli K-12 EmrAB-TolC multidrug efflux transport system. `UniProtKB:P02930` UniProtKB P02930 is the reviewed E. coli K-12 entry for Outer membrane protein TolC. `InterPro:IPR058622` InterPro IPR058622 is the Outer membrane channel protein TolC family entry. `PDB:8ZAL` RCSB PDB:8ZAL is an EmrAB-TolC electron-microscopy structure with three modeled TolC chains.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

Multidrug export protein EmrA

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P27303`	Multidrug export protein EmrA	emrA	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) `UniProtKB:P27303` Reviewed Swiss-Prot entry EMRA_ECOLI is the E. coli K-12 EmrA accession and cross-references ComplexPortal:CPX-4268 and PDB:8ZAL.

Multidrug export protein EmrB

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0AEJ0`	Multidrug export protein EmrB	emrB	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) `UniProtKB:P0AEJ0` Reviewed Swiss-Prot entry EMRB_ECOLI is the E. coli K-12 EmrB accession and cross-references ComplexPortal:CPX-4268 and PDB:8ZAL.

Outer membrane channel protein TolC

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P02930`	Outer membrane protein TolC	tolC	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) `UniProtKB:P02930` Reviewed Swiss-Prot entry TOLC_ECOLI is the E. coli K-12 TolC accession and cross-references ComplexPortal:CPX-4268 and PDB:8ZAL.

Source composition assertions

EmrAB-TolC multidrug efflux transport system (ComplexPortal:CPX-4268)

Escherichia coli (strain K12) (NCBITaxon:83333) · Heterodecamer · ECO:0005547 · retrieved 2026-10-02

Participant	Source type	Source name	Stoichiometry
`UniProtKB:P27303` — Multidrug export protein EmrA	protein	emrA	6
`UniProtKB:P0AEJ0` — Multidrug export protein EmrB	protein	emrB	1
`UniProtKB:P02930` — Outer membrane protein TolC	protein	tolC	3

Curator-scoped import: E. coli K-12 EmrAB-TolC source composition for this record. Source evidence: inferred by curator. The accession was resolved through the Complex Portal accession endpoint; no equivalence xref was inferred.

Canonical examples

NCBITaxon:83333 Escherichia coli K-12 — Source strain for Complex Portal CPX-4268, which curates the heterodecameric EmrAB-TolC pump with six EmrA, one EmrB, and three TolC subunits. [ComplexPortal:CPX-4268]

Functions

xenobiotic transmembrane transporter activity GO:0042910 — The EmrAB-TolC complex exports hydrophobic xenobiotics across the E. coli inner and outer membranes through the coupled EmrB transporter, EmrA adaptor, and TolC channel.
- GO:0042910 GO:0042910 is the molecular-function term for xenobiotic transmembrane transporter activity.
- ComplexPortal:CPX-4268 Complex Portal cross-references GO:0042910 for the E. coli K-12 EmrAB-TolC multidrug efflux transport system.
- PMID:33065135 Yousefian et al. 2021 structurally characterized the EmrAB-TolC efflux complex from E. coli.

Physical properties

SUBUNIT_COUNT: 10 (E. coli K-12 6xEmrA:1xEmrB:3xTolC heterodecamer in ComplexPortal:CPX-4268) [ComplexPortal:CPX-4268]

Mechanism graphs

EmrAB-TolC exports hydrophobic xenobiotics across the cell envelope (FUNCTION)

EmrB, EmrA, and TolC form an envelope-spanning MFS-type efflux pump that exports hydrophobic xenobiotics from E. coli.

Subject	Predicate	Object	Evidence
Multidrug export protein EmrB	couples to	Multidrug export protein EmrA	`ComplexPortal:CPX-4268` CPX-4268 curates EmrA and EmrB as participants in the E. coli EmrAB-TolC pump.
Multidrug export protein EmrA	couples to	Outer membrane channel protein TolC	`PMID:33065135` Yousefian et al. 2021 structurally characterized the EmrAB-TolC complex.
EmrAB-TolC multidrug efflux transport complex	enables	xenobiotic transmembrane transporter activity	`ComplexPortal:CPX-4268` Complex Portal cross-references GO:0042910 for the EmrAB-TolC complex.
xenobiotic transmembrane transporter activity	transports	hydrophobic xenobiotic substrate	`ComplexPortal:CPX-4268` CPX-4268 summarizes the EmrAB-TolC system as transporting hydrophobic xenobiotics such as CCCP and steroid hormones.
xenobiotic detoxification by transmembrane export across the cell outer membrane	targets	cell exterior	`GO:0140330` GO:0140330 describes reducing xenobiotic toxicity by export through the outer membrane.

Discussions

CURATION_TODO (OPEN): Resolve an exact source-neutral EmrA protein family before replacing the reviewed-label-only component row. ComplexPortal:CPX-4268 and the reviewed E. coli K-12 UniProt record exactly identify EmrA, but no InterPro, Pfam, NCBIfam, or GO accession was verified as an exact source-neutral family for this named pump constituent; EmrB and TolC are grounded to InterPro:IPR004638 and InterPro:IPR058622.

Evidence

ComplexPortal:CPX-4268 Complex Portal entry for the E. coli K-12 EmrAB-TolC multidrug efflux transport system.
GO:1990281 Gene Ontology cellular-component parent term for efflux pump complexes.
GO:0042910 Gene Ontology molecular-function term for xenobiotic transmembrane transporter activity.
GO:0140330 Gene Ontology biological-process term for xenobiotic detoxification by transmembrane export across the cell outer membrane.
InterPro:IPR004638 InterPro family entry for Drug resistance transporter EmrB-like.
InterPro:IPR058622 InterPro family entry for Outer membrane channel protein TolC.
UniProtKB:P27303 Reviewed E. coli K-12 EmrA UniProtKB entry.
UniProtKB:P0AEJ0 Reviewed E. coli K-12 EmrB UniProtKB entry.
UniProtKB:P02930 Reviewed E. coli K-12 TolC UniProtKB entry.
PDB:8ZAL RCSB Protein Data Bank entry for the EmrAB-TolC MFS-type tripartite multidrug efflux pump EA electron-microscopy model.
PMID:33065135 PubMed identifier for Yousefian et al. 2021, Structural characterization of the EmrAB-TolC efflux complex from E. coli.
DOI:10.1016/j.bbamem.2020.183488 DOI for Yousefian et al. 2021, Structural characterization of the EmrAB-TolC efflux complex from E. coli.
PMID:12482849 PubMed identifier for Borges-Walmsley et al. 2003, Identification of oligomerization and drug-binding domains of the membrane fusion protein EmrA.
DOI:10.1074/jbc.M209457200 DOI for Borges-Walmsley et al. 2003, Identification of oligomerization and drug-binding domains of the membrane fusion protein EmrA.
PMID:41839863 PubMed identifier for Zhong et al. 2026, A model for drug transport across two membranes of Gram-negative bacteria by an MFS tripartite assembly.
DOI:10.1038/s41467-026-70500-5 DOI for Zhong et al. 2026, A model for drug transport across two membranes of Gram-negative bacteria by an MFS tripartite assembly.

Curation history

2026-10-02T10:09:54Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-02T10:11:12Z codex · EXPANDED_RECORD — Added CPX-4268/GO efflux-pump parentage, EmrA, EmrB, and TolC component rows with E. coli K-12 reviewed UniProt examples, exact InterPro groundings for EmrB and TolC, PDB/PubMed evidence, a compact xenobiotic export graph, the exact Complex Portal heterodecamer source composition, and an EmrA component-family grounding TODO.

Source: data/structures/other/emrab_tolc_multidrug_efflux_transport_complex.yaml