Bacterial Mla intermembrane phospholipid transport

A species-neutral diderm-bacterial module for phospholipid exchange across the cell envelope through an outer-membrane MlaA/VacJ interface, a soluble periplasmic MlaC carrier, and an ATP-coupled inner-membrane MlaFEDB complex. The module represents the conserved transport architecture without forcing a universal retrograde or anterograde net direction.

MODULE:bacterial_mla_intermembrane_phospholipid_transportDRAFTBiological Processmodules/bacterial_mla_intermembrane_phospholipid_transport.yaml
intermembrane phospholipid transferGO:0120010
PMID:33236984
Structure of bacterial phospholipid transporter MlaFEDB with substrate bound.
Cryo-EM defines the MlaFEDB architecture and a continuous phospholipid pathway through MlaE and MlaD.
A continuous transport pathway extends from the MlaE substrate-binding site, through the channel of MlaD, and into the periplasm.
PMID:33837253
The Pseudomonas aeruginosa substrate-binding protein Ttg2D functions as a general glycerophospholipid transporter across the periplasm.
Direct work on a Pseudomonas Ttg2D ortholog establishes a soluble periplasmic glycerophospholipid carrier.
In Pseudomonas aeruginosa, Ttg2D is the soluble periplasmic phospholipid-binding component of an ABC transport system thought to be involved in maintaining the asymmetry of the outer membrane.
PMID:34873038
ATP disrupts lipid-binding equilibrium to drive retrograde transport critical for bacterial outer membrane asymmetry.
Reconstituted transfer assays support ATP-enhanced retrograde transport while also detecting spontaneous bidirectional exchange.
We further demonstrate that spontaneous PL transfer also occurs from MlaFEDB to MlaC, but such anterograde movement is instead abolished by ATP hydrolysis.
GO:0120010
intermembrane phospholipid transfer
Defines phospholipid transfer between the two membranes of the diderm bacterial envelope.
file:PSEPK/ttg2D/ttg2D-uniprot.txt
PSEPK Ttg2D/MlaC UniProt record
Q88P91 is a structurally characterized MlaC-family phospholipid-binding protein.
file:PSEPK/mlaF/mlaF-uniprot.txt
PSEPK MlaF UniProt record
Q88P94 is the ATPase subunit of the MlaFEDB inner-membrane complex.
file:projects/P_PUTIDA/deep-research/PSEPK__bacterial_mla_intermembrane_phospholipid_transport__ppu02010-deep-research-openscientist.md
OpenScientist PSEPK Mla pathway satisfiability research
Supports complete coverage by PP_0958-PP_0962 plus unlinked VacJ PP_2163, while distinguishing the PP_0140-PP_0142 Mce-like system and unresolved PP_1737 MlaA-family paralog from the core Mla route.
file:modules/bacterial_mla_intermembrane_phospholipid_transport-deep-research-openscientist.md
OpenScientist generic Mla module research
Supports the three-interface boundary, direction-neutral architecture, MlaB accessory role, MlaA lineage variation, and separation from parallel phospholipase-based outer-membrane repair.

Pseudomonas putida KT2440 names the MlaC- and MlaB-equivalent operon products Ttg2D and Ttg2E. The module uses their conserved family roles while retaining the exact local gene names. Transport direction is deliberately unresolved: current biochemical evidence favors retrograde transport, but published work has supported multiple direction models and direction may vary with biological context. The reusable module therefore remains direction-neutral. The species-aware report confirms that legacy Ttg2D and Ttg2E names correspond to MlaC and MlaB roles by domain, KEGG orthology, and contiguous operon context. Shared MlaF/E/D-like domains or KOs alone are insufficient because PP_0140-PP_0142 encode a separate Mce-like system. OmpC/OmpF names describe characterized canonical porin partners rather than a universally required named porin in every lineage.

4Nodes
3Parts
0Variant Sets
0Variants
3Annotons
0Connections

Derived QC

Recommended-field compliance

52.9% recommended fields populated
  • module.knowledge_gaps[0] · status (0/1)
  • module.knowledge_gaps[0] · provenance (0/1)
  • module.knowledge_gaps[1] · status (0/1)
  • module.knowledge_gaps[1] · provenance (0/1)
  • module.knowledge_gaps[2] · status (0/1)
  • module.knowledge_gaps[2] · provenance (0/1)
  • module.knowledge_gaps[3] · status (0/1)
  • module.knowledge_gaps[3] · provenance (0/1)

Module deep research

✓ present

  • bacterial_mla_intermembrane_phospholipid_transport-deep-research-openscientist.md (openscientist)

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Gene-review completeness (6/6 grounded genes reviewed)

6 complete review(s) · 6 with deep research · 0 missing review · 0 reviewed but lacking deep research

Gene Review Complete Deep research
mlaD Q88P92 ✓ ✓ ✓
mlaE Q88P93 ✓ ✓ ✓
mlaF Q88P94 ✓ ✓ ✓
ttg2D Q88P91 ✓ ✓ ✓
ttg2E Q88P90 ✓ ✓ ✓
vacJ Q88KX6 ✓ ✓ ✓

Details

Context
diderm bacteriaNCBITaxon:2
Bacterial Mla intermembrane phospholipid transportBiological Processbacterial_mla_intermembrane_phospholipid_transport
intermembrane phospholipid transferGO:0120010
Context
diderm bacteriaNCBITaxon:2
Part 1: Outer-membrane phospholipid handling
MlaA/VacJ outer-membrane interfaceTransport Stepmlaa_outer_membrane_interface

Annotons

MlaA/VacJ outer-membrane phospholipid interface
mlaa_outer_membrane_lipoprotein
Participant: Family: MlaA/VacJ family
Family:
MlaA/VacJ familyPANTHER:PTHR30035:SF3
Representative Members: PSEPK VacJ/MlaA exemplarUniProtKB:Q88KX6

Function

outer-membrane phospholipid handling activity

Processes

intermembrane phospholipid transferGO:0120010

Locations

cell outer membraneGO:0009279

Couples outer-membrane phospholipid access to exchange with the periplasmic carrier.

Part 2: Periplasmic phospholipid shuttling
MlaC periplasmic phospholipid shuttleTransport Stepmlac_periplasmic_shuttle

Annotons

MlaC-family periplasmic phospholipid carrier
mlac_phospholipid_carrier
Participant: Family: MlaC phospholipid-carrier family
Family:
MlaC phospholipid-carrier familyPANTHER:PTHR36573:SF1
Representative Members: PSEPK Ttg2D/MlaC exemplarUniProtKB:Q88P91

Function

phospholipid bindingGO:0005543

Processes

intermembrane phospholipid transferGO:0120010

Locations

outer membrane-bounded periplasmic spaceGO:0030288

Shields phospholipid cargo while shuttling between outer- and inner-membrane interfaces.

Part 3: ATP-coupled inner-membrane phospholipid handling
MlaFEDB inner-membrane complexTransport Stepmlafedb_inner_membrane_complex

Annotons

MlaFEDB phospholipid transport complex
mlafedb_phospholipid_transporter
Participant: Protein Complex: MlaFEDB ABC phospholipid transport complex
Protein Complex:
MlaFEDB ABC phospholipid transport complex
Active units:
MlaF ATPase
Participant: Family: MlaF family
Family:
MlaF familyPANTHER:PTHR43023:SF6
Representative Members: PSEPK MlaF exemplarUniProtKB:Q88P94
Role: ATP hydrolysis and energy coupling.
Function:
ATP hydrolysis activityGO:0016887
MlaE permease
Participant: Family: MlaE permease family
Family:
MlaE permease familyPANTHER:PTHR30188:SF4
Representative Members: PSEPK MlaE exemplarUniProtKB:Q88P93
Role: Integral membrane phospholipid-translocation subunit.
MlaD MCE-domain unit
Participant: Family: MlaD MCE-domain family
Family:
MlaD MCE-domain familyPANTHER:PTHR33371:SF4
Representative Members: PSEPK MlaD exemplarUniProtKB:Q88P92
Role: Periplasm-facing phospholipid-binding interface.
Function:
phospholipid bindingGO:0005543
MlaB-like STAS accessory subunit
Participant: Family: MlaB-like STAS-domain family
Family:
MlaB-like STAS-domain family
Representative Members: PSEPK Ttg2E/MlaB exemplarUniProtKB:Q88P90
Role: Cytoplasmic accessory subunit supporting complex assembly or regulation.

Function

phospholipid transfer activityGO:0120014

Processes

intermembrane phospholipid transferGO:0120010

Locations

plasma membraneGO:0005886

Exchanges phospholipid with the periplasmic MlaC-family carrier using MlaF ATP hydrolysis.