Alginate polymerization and export

A synthase-dependent bacterial exopolysaccharide module in which the inner-membrane Alg8-Alg44 complex polymerizes GDP-mannuronate, periplasmic proteins guide and modify the nascent alginate chain, AlgL removes escaped polymer, and the AlgE outer-membrane channel exports the product. Precursor synthesis, O-acetylation chemistry, and transcriptional regulation are separate modules.

MODULE:alginate_polymerization_exportDRAFTCONCRETEMetabolic Pathwaymodules/alginate_polymerization_export.yaml
alginic acid biosynthetic processGO:0042121
GO:0042121
alginic acid biosynthetic process
Defines production of the alginate polysaccharide.
GO:0047643
alginate synthase activity
Defines the polymerization function contributed by the Alg8-Alg44 complex.
RHEA:45572
mannuronan C5-epimerase reaction
Defines AlgG conversion of mannuronate residues to guluronate residues in alginate.
file:projects/P_PUTIDA/deep-research/PSEPK__alginate-polymerization-export__ppu00543-deep-research-openscientist.md
OpenScientist PSEPK alginate polymerization and export synthesis
Species-aware retrieval resolves the dedicated alginate operon from the broad exopolysaccharide overview map.
UniProtKB:Q88NC5
Reviewed Pseudomonas putida KT2440 Alg8 exemplar
Anchors the concrete module to the reviewed KT2440 glycosyltransferase Alg8 sequence.
UniProtKB:Q52463
Reviewed Pseudomonas aeruginosa Alg8 exemplar
Provides a characterized mannuronan-synthase family exemplar for the catalytic subunit.
UniProtKB:P18895
Reviewed Pseudomonas aeruginosa AlgE exemplar
Provides a reviewed alginate outer-membrane channel exemplar.
PMID:25968647
Alginate Polymerization and Modification Are Linked in Pseudomonas aeruginosa.
Directly supports the membrane-embedded Alg8-Alg44 polymerase-copolymerase partnership.
Alg8 directly interacts with the proposed copolymerase Alg44 while embedded in the cytoplasmic membrane.
PMID:25817996
Dimeric c-di-GMP is required for post-translational regulation of alginate production in Pseudomonas aeruginosa.
Defines cytoplasmic dimeric c-di-GMP sensing by the Alg44 PilZ domain.
structure of the cytoplasmic region of Alg44 in complex with dimeric self-intercalated c-di-GMP
PMID:23503314
Insights into the assembly of the alginate biosynthesis machinery in Pseudomonas aeruginosa.
Supports an envelope-spanning Alg8-Alg44-AlgK-AlgX-AlgE complex.
Overall experimental evidence was provided for the existence of a multiprotein complex required for alginate polymerization and secretion.

The polymerase is modeled as a two-part synthase complex: Alg8 supplies catalysis and Alg44 binds cyclic-di-GMP and contributes regulatory copolymerase function. AlgG maturation and AlgL quality control are optional parts because polymerization/export can be distinguished from product composition and escaped-polymer removal. AlgI, AlgJ, AlgF, and the O-acetyltransferase activity of AlgX belong to the separate alginate O-acetylation module.

6Nodes
5Parts
0Variant Sets
0Variants
6Annotons
5Connections

Derived QC

Recommended-field compliance

60.0% 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] · reference_section_type (0/1)

Module deep research

✗ none found

No MODULE:alginate_polymerization_export deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Reaction chaining (advisory)

✓ every PRECEDES step chains, or its break is acknowledged via chaining_status.

  • alg8_alg44_synthase → algK_scaffold [NOT_CHECKED]
    Polymer made at the inner membrane enters the periplasmic guidance apparatus.
  • algG_maturation → algK_scaffold [NOT_CHECKED]
    Epimerization occurs during periplasmic passage before final outer-membrane export.
  • algK_scaffold → algE_export [NOT_CHECKED]
    The periplasmic scaffold delivers polymer to the AlgE outer-membrane channel.

Gene-review completeness (6/11 grounded genes reviewed)

6 complete review(s) · 3 with deep research · 5 missing review · 3 reviewed but lacking deep research

Gene Review Complete Deep research
alg44 Q88NC6 ✓ ✓ ✗
alg8 Q88NC5 ✓ ✓ ✗
algE Q88NC8 ✓ ✓ ✓
algG Q88NC9 ✓ ✓ ✓
algK Q88NC7 ✓ ✓ ✓
algL Q88ND1 ✓ ✓ ✗
Pseudomonas aeruginosa AlgE P18895 ✗ — —
Pseudomonas aeruginosa AlgK P96956 ✗ — —
Pseudomonas aeruginosa AlgL Q06749 ✗ — —
Pseudomonas aeruginosa AlgG Q51371 ✗ — —
Pseudomonas aeruginosa Alg44 Q9HY69 ✗ — —

Details

Alginate polymerization and exportMetabolic Pathwayalginate_polymerization_export
alginic acid biosynthetic processGO:0042121

Connections

alg8_alg44_synthase -> algG_maturation Provides Input For
Part 1: inner-membrane alginate polymerization
Alg8-Alg44 alginate synthase complexProtein Complexalg8_alg44_synthase

Annotons

Alg8 catalytic polymerase
alg8_polymerase_activity
Participant: Ortholog Of: Pseudomonas putida KT2440 Alg8
Ortholog Of:
Pseudomonas putida KT2440 Alg8UniProtKB:Q88NC5 Orthologs of the reviewed KT2440 Alg8 that retain alginate-operon context and an Alg44 partner. Pseudomonas aeruginosa Q52463 is the characterized functional comparator. The mixed PTHR22913:SF12 export is not a safe selector because it also contains NodC and hyaluronan synthases.

Function

alginate synthase activityGO:0047643
Substrates: GDP-mannuronate
Products: nascent poly-beta-D-mannuronate

Processes

alginic acid biosynthetic processGO:0042121

Locations

plasma membraneGO:0005886

Multi-pass GT2 catalytic subunit of the synthase.

Alg44 regulatory copolymerase
alg44_copolymerase_activity
Participant: Family: Alg44 family
Family:
Alg44 familyInterPro:IPR058834
Representative Members: PSEPK Alg44UniProtKB:Q88NC6 Pseudomonas aeruginosa Alg44UniProtKB:Q9HY69

Function

cyclic-di-GMP bindingGO:0035438
Substrates: cyclic-di-GMP

Processes

alginic acid biosynthetic processGO:0042121

Locations

plasma membraneGO:0005886

Non-catalytic c-di-GMP-responsive subunit that activates and organizes Alg8 polymerization.

Part 2: optional mannuronate C5 epimerization (optional)
AlgG periplasmic epimerizationReactionalgG_maturation

Annotons

Mannuronan C5-epimerase
algG_epimerase_activity
Participant: Family: mannuronan C5-epimerase family
Family:
mannuronan C5-epimerase familyInterPro:IPR053409
Representative Members: PSEPK AlgGUniProtKB:Q88NC9 Pseudomonas aeruginosa AlgGUniProtKB:Q51371

Function

carbohydrate epimerase activityGO:0016857
Substrates: beta-D-mannuronate residues in nascent alginate
Products: alpha-L-guluronate residues in alginate

Processes

alginic acid biosynthetic processGO:0042121

Locations

periplasmic spaceGO:0042597

Adjusts mannuronate/guluronate composition after polymerization.

Part 3: periplasmic polymer guidance
AlgK secretion scaffoldProtein ComplexalgK_scaffold

Annotons

AlgK outer-membrane-anchored scaffold
algK_scaffold_role
Participant: Family: AlgK scaffold family
Family:
AlgK scaffold familyInterPro:IPR053440
Representative Members: PSEPK AlgKUniProtKB:Q88NC7 Pseudomonas aeruginosa AlgKUniProtKB:P96956

Processes

alginic acid biosynthetic processGO:0042121

Locations

cell outer membraneGO:0009279

TPR-rich lipoprotein scaffold that guides nascent alginate toward the outer-membrane channel.

Part 4: optional periplasmic escaped-polymer quality control (optional)
AlgL periplasmic alginate cleavageReactionalgL_quality_control

Annotons

Poly-beta-D-mannuronate lyase
algL_lyase_activity
Participant: Family: AlgL alginate lyase family
Family:
AlgL alginate lyase familyInterPro:IPR022859
Representative Members: PSEPK AlgLUniProtKB:Q88ND1 Pseudomonas aeruginosa AlgLUniProtKB:Q06749

Function

poly-beta-D-mannuronate lyase activityGO:0045135
Substrates: mislocalized periplasmic alginate
Products: unsaturated alginate oligosaccharides

Processes

alginic acid biosynthetic processGO:0042121

Locations

periplasmic spaceGO:0042597

Removes alginate that escapes the protected secretion conduit.

Part 5: outer-membrane alginate export
AlgE outer-membrane channelTransport StepalgE_export

Annotons

AlgE alginate permeability channel
algE_channel_role
Participant: Family: AlgE alginate channel family
Family:
AlgE alginate channel familyInterPro:IPR053728
Representative Members: PSEPK AlgEUniProtKB:Q88NC8 Pseudomonas aeruginosa AlgEUniProtKB:P18895

Processes

alginic acid biosynthetic processGO:0042121

Locations

cell outer membraneGO:0009279

Beta-barrel channel that translocates alginate across the outer membrane.