MacAB-TolC complex

GO:1990196 · Other · Multiprotein complex · Proposed

The MacAB-TolC complex is a macrolide transporter complex found in E.coli and related gram-negative bacteria. Its transport activity is specific to macrolide compounds containing 14- and 15-membered lactones. It consists of the dimeric inner membrane ATPase MacB, the hexameric, periplasmic membrane fusion protein MacA and the trimeric outer membrane factor TolC. [GO:1990196]

Synonyms: macrolide transporter MacAB-TolC complex

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
Macrolide export protein MacA	Protein	part of	`InterPro:IPR058623`	macA	6 copies per E. coli MacAB-TolC assembly in PDB:5NIK biological assembly 1	UNKNOWN	Hexameric periplasmic membrane-fusion constituent that links the inner-membrane MacB dimer to the TolC outer-membrane channel. `GO:1990196` GO:1990196 defines MacA as the hexameric periplasmic membrane-fusion protein in the MacAB-TolC complex. `InterPro:IPR058623` InterPro IPR058623 is the Macrolide export protein MacA family entry. `PDB:5NIK` RCSB describes six MacA chains in PDB:5NIK biological assembly 1.
Macrolide Exporter MacB	Protein	part of	`InterPro:IPR050250`	macB	2 copies per E. coli MacAB-TolC assembly in PDB:5NIK biological assembly 1	UNKNOWN	Dimeric inner-membrane ABC transporter constituent that hydrolyzes ATP and forms the MacAB-TolC translocation path. `GO:1990196` GO:1990196 defines MacB as the dimeric inner-membrane ATPase in the MacAB-TolC complex. `InterPro:IPR050250` InterPro IPR050250 is the Macrolide Exporter MacB family entry. `PDB:5NIK` RCSB describes two MacB chains in PDB:5NIK biological assembly 1.
Outer membrane channel protein TolC	Protein	part of	`InterPro:IPR058622`	tolC	3 copies per E. coli MacAB-TolC assembly in PDB:5NIK biological assembly 1	UNKNOWN	Trimeric outer-membrane channel constituent that completes the MacAB-TolC efflux conduit. `GO:1990196` GO:1990196 defines TolC as the trimeric outer-membrane factor in the MacAB-TolC complex. `InterPro:IPR058622` InterPro IPR058622 is the Outer membrane channel protein TolC family entry. `PDB:5NIK` RCSB describes three TolC chains in PDB:5NIK biological assembly 1.

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.

Macrolide export protein MacA

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P75830`	Macrolide export protein MacA	macA	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (2 references) Reviewed E. coli K-12 MacA accession mapped by RCSB to the MacA polymer entity in PDB:5NIK. `UniProtKB:P75830` UniProtKB P75830 is the reviewed E. coli K-12 entry for MacA. `PDB:5NIK` RCSB maps PDB:5NIK polymer entity 2 to UniProtKB:P75830.

Macrolide Exporter MacB

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P75831`	Macrolide export ATP-binding/permease protein MacB	macB	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (2 references) Reviewed E. coli K-12 MacB accession mapped by RCSB to the MacB polymer entity in PDB:5NIK. `UniProtKB:P75831` UniProtKB P75831 is the reviewed E. coli K-12 entry for MacB. `PDB:5NIK` RCSB maps PDB:5NIK polymer entity 3 to UniProtKB:P75831.

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 (2 references) Reviewed E. coli K-12 TolC accession mapped by RCSB to the TolC polymer entity in PDB:5NIK. `UniProtKB:P02930` UniProtKB P02930 is the reviewed E. coli K-12 entry for TolC. `PDB:5NIK` RCSB maps PDB:5NIK polymer entity 1 to UniProtKB:P02930.

Taxonomic distribution

NCBITaxon:2 Bacteria — VARIABLE: GO:1990196 frames MacAB-TolC as a macrolide transporter found in E. coli and related Gram-negative bacteria, so it is represented as variable within Bacteria. [GO:1990196]

Canonical examples

NCBITaxon:562 Escherichia coli — E. coli source of the MacAB-TolC ABC-type tripartite multidrug efflux pump structure deposited as PDB:5NIK. [PDB:5NIK]

Functions

ABC-type xenobiotic transporter activity GO:0008559 — MacAB-TolC uses the MacB ABC transporter to export macrolide antibiotics and other xenobiotics through the MacA adaptor and TolC outer-membrane channel.
- GO:1990196 GO:1990196 defines MacAB-TolC by its 14- and 15-membered macrolide transport specificity.
- PMID:18955484 Tikhonova et al. 2009 reported that E. coli MacB is a dimeric ABC transporter whose ATPase activity and macrolide-binding capacity are regulated by MacA.

Physical properties

SUBUNIT_COUNT: 11 (E. coli MacAB-TolC hetero-11-mer in PDB:5NIK biological assembly 1) [PDB:5NIK]

Evidence

GO:1990196 Gene Ontology cellular-component term for the MacAB-TolC complex.
GO:1990195 QuickGO reports GO:1990196 as an is-a child of GO:1990195 macrolide transmembrane transporter complex.
GO:0008559 Gene Ontology molecular-function term for ABC-type xenobiotic transporter activity.
InterPro:IPR058623 InterPro family entry for Macrolide export protein MacA.
InterPro:IPR050250 InterPro family entry for Macrolide Exporter MacB.
InterPro:IPR058622 InterPro family entry for Outer membrane channel protein TolC.
UniProtKB:P75830 UniProtKB reviewed E. coli K-12 MacA entry.
UniProtKB:P75831 UniProtKB reviewed E. coli K-12 MacB entry.
UniProtKB:P02930 UniProtKB reviewed E. coli K-12 TolC entry.
PDB:5NIK RCSB Protein Data Bank entry for the E. coli MacAB-TolC ABC-type tripartite multidrug efflux pump structure.
PMID:28504659 PubMed identifier for the 2017 MacAB-TolC structural paper cited by PDB:5NIK.
DOI:10.1038/nmicrobiol.2017.70 DOI for 'Structure of the MacAB-TolC ABC-type tripartite multidrug efflux pump' as reported by RCSB and PubMed.
PMID:18955484 PubMed identifier for the 2009 Journal of Biological Chemistry paper showing that MacA regulates MacB ATPase activity and macrolide binding.

Curation history

2026-10-01T19:20:53Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-01T19:22:57Z codex · EXPANDED_RECORD — Added GO synonymy and macrolide-transporter parentage, MacA/MacB/TolC components with exact InterPro groundings and reviewed E. coli K-12 UniProt examples, the PDB:5NIK hetero-11-mer, function, taxonomy, and authority evidence.

Source: data/structures/other/macab_tolc_complex.yaml