lipopolysaccharide transport system

GO:0062051 · Other · Multiprotein complex · Proposed

A protein-containing complex that functions to transport lipopolysaccharide from its site of synthesis at the cytoplasmic membrane across the periplasm to the outer membrane in an ATP-dependent manner. [GO:0062051]

Synonyms: Lpt machinery; Lpt transenvelope complex

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Role
LptA periplasmic bridge protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	lptA	Periplasmic bridge constituent that polymerizes between the inner-membrane and outer-membrane Lpt subcomplexes. `DOI:10.1128/JB.01126-06` Sperandeo et al. 2007 identified E. coli LptA as a periplasmic protein implicated in LPS transport from the inner to the outer membrane. `DOI:10.1126/science.aar1886` Sherman et al. 2018 reconstituted membrane-to-membrane LPS movement through an Lpt protein bridge.
LptB cytoplasmic ATPase	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	lptB	Cytoplasmic ATPase constituent that powers LPS extraction by the inner-membrane LptBFGC subcomplex. `DOI:10.1128/JB.01126-06` Sperandeo et al. 2007 identified E. coli LptB as an essential protein implicated in LPS transport to the outer membrane. `DOI:10.1126/science.1228984` Okuda, Freinkman and Kahne 2012 showed that cytoplasmic ATP hydrolysis powers E. coli LPS transport across the periplasm.
LptC inner-membrane adapter	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	lptC	Inner-membrane adapter constituent of LptB2FGC that contacts the periplasmic LptA bridge. `DOI:10.1016/j.febslet.2009.05.051` Narita and Tokuda 2009 biochemically characterized the E. coli LptBFGC inner-membrane ABC transporter complex. `DOI:10.1074/jbc.R117.802512` Sperandeo, Martorana and Polissi 2017 review LptC as the inner-membrane Lpt component that bridges LptBFG and LptA.
LptD outer-membrane beta-barrel	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	lptD	Outer-membrane beta-barrel constituent that receives LPS from the periplasmic bridge and participates in final outer-membrane insertion. `DOI:10.1073/pnas.0604744103` Wu et al. 2006 identified the E. coli outer-membrane Imp/RlpB, now LptD/LptE, protein complex that assembles LPS in the outer membrane. `DOI:10.1073/pnas.0912872107` Chng et al. 2010 characterized LptD as part of the two-protein outer-membrane LptDE complex in E. coli.
LptE outer-membrane lipoprotein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	lptE	Outer-membrane lipoprotein constituent that complexes with LptD in the LPS insertion site. `DOI:10.1073/pnas.0604744103` Wu et al. 2006 identified RlpB, now LptE, as the lipoprotein partner of the E. coli outer-membrane LPS assembly complex. `DOI:10.1073/pnas.0912872107` Chng et al. 2010 characterized LptE as part of the two-protein outer-membrane LptDE complex in E. coli.
LptF inner-membrane permease	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	lptF	Inner-membrane permease constituent of the LptB2FGC ABC transporter. `DOI:10.1073/pnas.0801196105` Ruiz et al. 2008 identified LptF as one of two inner-membrane proteins required for LPS transport to the E. coli outer membrane. `DOI:10.1016/j.febslet.2009.05.051` Narita and Tokuda 2009 biochemically characterized the E. coli LptBFGC inner-membrane ABC transporter complex.
LptG inner-membrane permease	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	lptG	Inner-membrane permease constituent of the LptB2FGC ABC transporter. `DOI:10.1073/pnas.0801196105` Ruiz et al. 2008 identified LptG as one of two inner-membrane proteins required for LPS transport to the E. coli outer membrane. `DOI:10.1016/j.febslet.2009.05.051` Narita and Tokuda 2009 biochemically characterized the E. coli LptBFGC inner-membrane ABC transporter complex.

Taxonomic distribution

NCBITaxon:2 Bacteria — VARIABLE: The Lpt machinery assembles in Gram-negative diderm bacteria that transport LPS to an outer membrane, so it is represented as variable within Bacteria rather than universal. [DOI:10.1074/jbc.R117.802512]

Canonical examples

NCBITaxon:562 Escherichia coli — E. coli LptA-G constitute the model LPS transport system used to reconstitute membrane-to-membrane LPS movement. [DOI:10.1126/science.aar1886]

Functions

ATP-dependent lipopolysaccharide transport to the outer membrane — Extracts LPS from the cytoplasmic membrane and transports it through a periplasmic LptA bridge to the LptDE outer-membrane insertion site.
- GO:0062051 GO:0062051 defines the system by ATP-dependent LPS transport from its cytoplasmic-membrane synthesis site across the periplasm to the outer membrane.
- DOI:10.1126/science.aar1886 Sherman et al. 2018 reconstituted LPS transport between inner- and outer-membrane Lpt complexes in separate proteoliposomes.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral family groundings for LptA, LptB, LptC, LptD, LptE, LptF, and LptG in the LPS transport system. The first record uses reviewed gene-family labels from E. coli Lpt literature and avoids mapping to broad ABC transporter, periplasmic beta-jellyroll, lipoprotein, or beta-barrel signatures that would overgeneralize an individual Lpt constituent.
INTERPRETATION (RESOLVED): Should MsbA be curated as a constituent of the lipopolysaccharide transport system? MsbA flips nascent LPS across the inner membrane before the Lpt machine extracts LPS and transports it across the periplasm to the outer membrane. MsbA is therefore upstream of, rather than a constituent of, the Lpt transport system.

Evidence

GO:0062051 GO:0062051 is an active cellular-component term for the lipopolysaccharide transport system and is_a GO:1990351 transporter complex.
DOI:10.1074/jbc.R117.802512 Sperandeo, Martorana and Polissi 2017 review the Lpt machinery that transports LPS to the outer membrane of Gram-negative bacteria.
DOI:10.1126/science.aar1886 Sherman et al. 2018 reconstituted Lpt-dependent transport of LPS to the cell surface through a membrane-to-membrane protein bridge.
DOI:10.1021/bi100493e Chng, Gronenberg and Kahne 2010 reported that the E. coli proteins required for LPS assembly form a transenvelope complex.

Curation history

2026-10-01T15:52:11Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-01T15:54:30Z codex · EXPANDED_RECORD — Added Lpt synonymy, GO transporter-complex parentage, LptA-G reviewed-label-only components, bacterial taxonomy, E. coli canonical example, ATP-dependent LPS transport function, evidence, and component grounding/boundary discussions.

Source: data/structures/other/lipopolysaccharide_transport_system.yaml