MsbA transporter complex

GO:1990199 · Other · Multiprotein complex · Proposed

An ATP-binding cassette (ABC) transporter complex made up of a dimer of MsbA. Facilitates the export across the plasma membrane of, amongst others, lipid A and lipopolysaccharide. In contrast to most ABC transporter complexes, each chain of the homodimer contains both the transmembrane domain (TMD) and the cytoplasmic ATP-binding domain (NBD). [GO:1990199]

Synonyms: MsbA complex; MsbA dimer

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
ABC transporter, lipid A-core flippase, MsbA	Protein	part of	`InterPro:IPR011917`	msbA	2 copies per E. coli MsbA homodimer in PDB:3B5W biological assembly 1	UNKNOWN	ATP-binding inner-membrane flippase subunit that homodimerizes to form the MsbA lipid A-core and lipopolysaccharide transporter. `GO:1990199` GO:1990199 defines the MsbA transporter complex as a dimer of MsbA. `InterPro:IPR011917` InterPro IPR011917 is the ABC transporter, lipid A-core flippase, MsbA family entry. `PDB:3B5W` RCSB describes PDB:3B5W biological assembly 1 as an E. coli MsbA homo-2-mer.

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.

ABC transporter, lipid A-core flippase, MsbA

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P60752`	ATP-dependent lipid A-core flippase	msbA	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (2 references) Reviewed E. coli K-12 MsbA accession mapped by RCSB to the homodimeric polymer entity in PDB:3B5W. `UniProtKB:P60752` UniProtKB P60752 is the reviewed E. coli K-12 entry for MsbA. `PDB:3B5W` RCSB maps PDB:3B5W polymer entity 1 to UniProtKB:P60752.

Canonical examples

NCBITaxon:562 Escherichia coli — E. coli source of the homodimeric MsbA transporter structure deposited as PDB:3B5W. [PDB:3B5W]

Functions

lipopolysaccharide floppase activity GO:0015437 — MsbA flips lipid A-core lipopolysaccharide from the cytosolic to the exoplasmic leaflet of the E. coli inner membrane.
- GO:1990199 GO:1990199 defines the MsbA transporter complex by export of lipid A and lipopolysaccharide across the plasma membrane.
- GO:0015437 GO:0015437 is the molecular-function term for ATP-dependent lipopolysaccharide floppase activity.

Physical properties

SUBUNIT_COUNT: 2 (E. coli MsbA homodimer in PDB:3B5W biological assembly 1) [PDB:3B5W]

Evidence

GO:1990199 Gene Ontology cellular-component term for the MsbA transporter complex.
GO:1902495 QuickGO reports GO:1990199 as an is-a descendant of GO:1902495 transmembrane transporter complex.
GO:0015437 Gene Ontology molecular-function term for lipopolysaccharide floppase activity.
InterPro:IPR011917 InterPro family entry for ABC transporter, lipid A-core flippase, MsbA.
UniProtKB:P60752 UniProtKB reviewed E. coli K-12 MsbA entry.
PDB:3B5W RCSB structure entry for the homodimeric E. coli MsbA transporter.
PMID:18024585 PubMed identifier for the PDB:3B5W MsbA flexibility study cited by GO:1990199.
DOI:10.1073/pnas.0709388104 DOI for the PDB:3B5W primary citation as reported by RCSB and PubMed.

Curation history

2026-10-01T21:01:29Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-01T21:03:31Z codex · EXPANDED_RECORD — Added GO exact synonyms and transmembrane-transporter parentage, an InterPro-grounded MsbA component with a reviewed E. coli K-12 UniProt example, an E. coli PDB-backed canonical example, lipopolysaccharide floppase activity, homodimer subunit count, and PMID/DOI evidence.

Source: data/structures/other/msba_transporter_complex.yaml