Bam protein complex

GO:1990063 · Other · Multiprotein complex · Proposed

A bacterial outer-membrane beta-barrel protein assembly machine in which the BamA beta-barrel core and associated outer-membrane lipoproteins fold and insert beta-barrel proteins into the outer membrane. [DOI:10.1146/annurev-biochem-061408-144611]

Synonyms: BAM complex; beta-barrel assembly machinery complex; OMP complex

Part of: cell outer membrane (GO:0009279)

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
BamA beta-barrel core	Protein	part of	`InterPro:IPR023707`	bamA	UNKNOWN	Integral outer-membrane beta-barrel core and POTRA-domain platform that binds the lipoprotein partners and forms the gated membrane-embedded part of the machine. `DOI:10.1146/annurev-biochem-061408-144611` Hagan, Silhavy and Kahne 2011 review BamA as the conserved outer-membrane beta-barrel subunit of the bacterial Bam complex. `DOI:10.1038/nature17199` Gu et al. 2016 solved E. coli BAM structures with BamA and four associated lipoproteins.
BamB lipoprotein	Protein	part of	`InterPro:IPR017687`	bamB	UNKNOWN	Accessory outer-membrane lipoprotein in the periplasmic BamA-lipoprotein assembly. `GO:1990063` GO describes E. coli BamB as one of the four lipoproteins in the Bam protein complex. `DOI:10.1038/ncomms12865` Iadanza et al. 2016 resolved BamB in an intact BamABCDE cryo-EM structure.
BamC lipoprotein	Protein	part of	`InterPro:IPR014524`	bamC	UNKNOWN	Accessory outer-membrane lipoprotein associated with the BamCDE subcomplex. `GO:1990063` GO describes E. coli BamC as one of the four lipoproteins in the Bam protein complex. `DOI:10.1038/nature17199` Gu et al. 2016 report BamC in E. coli five-subunit BAM crystal structures.
BamD lipoprotein	Protein	part of	`InterPro:IPR017689`	bamD	UNKNOWN	Lipoprotein partner of BamA and the BamCDE subcomplex in the periplasmic ring. `GO:1990063` GO describes E. coli BamD as one of the four lipoproteins in the Bam protein complex. `DOI:10.1126/science.aad3460` Bakelar, Buchanan and Noinaj 2016 solved a BamACDE structure containing BamD.
BamE lipoprotein	Protein	part of	`InterPro:IPR026592`	bamE	UNKNOWN	Accessory outer-membrane lipoprotein associated with BamC and BamD. `GO:1990063` GO describes E. coli BamE as one of the four lipoproteins in the Bam protein complex. `DOI:10.1038/nature17199` Gu et al. 2016 report BamE in E. coli five-subunit BAM crystal structures.

Taxonomic distribution

NCBITaxon:2 Bacteria — VARIABLE: The bacterial Bam complex acts in the outer membrane of Gram-negative bacteria; monoderm lineages lack this outer-membrane machine. [DOI:10.1146/annurev-biochem-061408-144611]

Canonical examples

NCBITaxon:562 Escherichia coli — The purified E. coli BamA-E complex was reconstituted in proteoliposomes and shown to assemble the OmpT beta-barrel substrate. [DOI:10.1126/science.1188919]

Functions

outer-membrane beta-barrel protein folding and insertion — Folds and inserts beta-barrel outer-membrane protein substrates into the bacterial cell outer membrane.
- DOI:10.1126/science.1188919 Hagan, Kim and Kahne 2010 reconstituted E. coli outer-membrane beta-barrel protein assembly from purified BAM components.
- DOI:10.1146/annurev-biochem-061408-144611 Hagan, Silhavy and Kahne 2011 review beta-barrel membrane-protein assembly by the Bam complex.

Physical properties

MOLECULAR_MASS: ~203 UO:0000222 (E. coli BamABCDE complex) [DOI:10.1038/ncomms12865]

Mechanism graphs

BAM folds and inserts beta-barrel OMP substrates (FUNCTION)

The outer-membrane BamA beta barrel and associated BamB-E lipoproteins form a machine that receives unfolded beta-barrel substrates and catalyzes their folding and insertion into the outer membrane.

Subject	Predicate	Object	Evidence
BamA beta-barrel core	organizes with	BamB-E lipoproteins	`GO:1990063` The GO Bam protein complex definition states that E. coli BamA interacts directly with BamB and with the BamCDE subcomplex.
BamA beta-barrel core	forms core of	Bam protein complex	`DOI:10.1038/nature17199` Gu et al. 2016 resolved the BamA barrel and POTRA domains within E. coli BAM structures.
BamB-E lipoproteins	assemble with	BamA beta-barrel core	`DOI:10.1038/ncomms12865` Iadanza et al. 2016 captured the intact BamABCDE complex by cryo-EM.
Bam protein complex	folds and inserts	unfolded outer-membrane beta-barrel protein substrate	`DOI:10.1126/science.1188919` Hagan, Kim and Kahne 2010 reconstituted OmpT folding and insertion with purified E. coli BAM components.
Bam protein complex	samples	laterally open BamA barrel	`DOI:10.1038/ncomms12865` Iadanza et al. 2016 observed a laterally open BamA barrel in an intact BamABCDE cryo-EM structure. `DOI:10.1038/nature17199` Gu et al. 2016 reported E. coli BAM crystal structures in inward-open and lateral-open states.
Bam protein complex	inserts	assembled outer-membrane beta-barrel protein	`DOI:10.1146/annurev-biochem-061408-144611` Hagan, Silhavy and Kahne 2011 review Bam-mediated beta-barrel assembly in the Gram-negative outer membrane.
assembled outer-membrane beta-barrel protein	embeds in	cell outer membrane	`DOI:10.1126/science.1188919` Hagan, Kim and Kahne 2010 used proteoliposomes to reconstitute E. coli outer-membrane protein assembly.

Discussions

CURATION_TODO (RESOLVED): Keep SurA and other soluble periplasmic chaperones out of the Bam protein complex component list. Hagan, Kim and Kahne 2010 required a soluble chaperone in the reconstituted OMP assembly assay, but that chaperone acts on the substrate before BAM-mediated membrane insertion and is not a constituent of the BamABCDE complex.

Evidence

DOI:10.1146/annurev-biochem-061408-144611 Hagan CL, Silhavy TJ and Kahne D 2011, 'beta-Barrel Membrane Protein Assembly by the Bam Complex', Annual Review of Biochemistry.
DOI:10.1126/science.1188919 Hagan CL, Kim S and Kahne D 2010, 'Reconstitution of Outer Membrane Protein Assembly from Purified Components', Science.
DOI:10.1038/nature17199 Gu Y et al. 2016, 'Structural basis of outer membrane protein insertion by the BAM complex', Nature.
DOI:10.1038/ncomms12865 Iadanza MG et al. 2016, 'Lateral opening in the intact beta-barrel assembly machinery captured by cryo-EM', Nature Communications.

Curation history

2026-09-12T02:41:32Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-12T02:42:43Z codex · EXPANDED_RECORD — Added BAM synonyms, outer-membrane parentage, BamA-E components, bacterial distribution, E. coli exemplar, beta-barrel assembly function, physical property, nonmechanistic assembly/function graph, evidence, and component-boundary discussions.
2026-09-12T02:46:16Z codex · FIX_DISCUSSION_ANCHOR — Pointed the SurA boundary discussion at concrete BamA-E component anchors.
2026-09-12T02:50:10Z codex · ADDRESS_REVIEW — Resolved review issues #568 and #569 by grounding BamA-E to exact InterPro family terms and correcting BAM function graph edge directions.

Source: data/structures/other/bam_protein_complex.yaml