algJ

UniProt ID: Q88ND3
Organism: Pseudomonas putida (strain ATCC 47054 / DSM 6125 / CFBP 8728 / NCIMB 11950 / KT2440)
Review Status: DRAFT
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Gene Description

AlgJ is an SGNH-family, peripheral inner-membrane protein exposed on the periplasmic side. It acts with AlgI and AlgF in the acetyl-transfer relay that supplies AlgX-mediated O-acetylation of mannuronate residues in nascent alginate; its precise in-vivo relay chemistry is not yet resolved.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0005886 plasma membrane
IEA
GO_REF:0000044 		ACCEPT
Summary: AlgJ is peripherally associated with the bacterial inner membrane.
Reason: The reviewed topology places AlgJ at the inner membrane on its periplasmic side.
Supporting Evidence:
file:PSEPK/algJ/algJ-uniprot.txt
SUBCELLULAR LOCATION: Cell inner membrane
GO:0042121 alginic acid biosynthetic process
IEA
GO_REF:0000120 		KEEP AS NON CORE
Summary: AlgJ acts in post-polymerization alginate maturation rather than polymer formation itself.
Reason: GO:0051979 is not an ontology descendant of GO:0042121, so replacing this row would discard broader alginate-pathway context. The parent is retained as non-core and the exact acetylation process is added separately. Although AlgJ has acetylesterase activity in vitro, its physiological relay substrate is unresolved, so no molecular function is proposed here.
Supporting Evidence:
PMID:8636017
This indicated that the algIJF gene products were not required for polymer biosynthesis.
GO:0051979 alginic acid acetylation
ISS
PMID:12003941
Mutant analysis and cellular localization of the AlgI, AlgJ,... 		NEW
Summary: AlgJ is an essential periplasm-facing component of the alginate O-acetylation relay.
Reason: P. aeruginosa deletion and complementation establish the ortholog role; Q88ND3 is the syntenic KT2440 AlgJ and its soluble domain was directly structurally characterized in PMID:25165982.
Supporting Evidence:
PMID:12003941
each mutant produced alginate lacking O-acetyl groups.
GO:0042597 periplasmic space
IEA
GO_REF:0000044 		ACCEPT
Summary: The functional domain of membrane-associated AlgJ is exposed to the periplasm.
Reason: This location complements rather than duplicates the inner-membrane annotation by specifying sidedness.
Supporting Evidence:
file:PSEPK/algJ/algJ-uniprot.txt
Periplasmic side

Core Functions

Periplasm-facing, inner-membrane-associated SGNH-family component of the AlgI-AlgJ-AlgF acetyl-transfer relay for alginate O-acetylation.

Directly Involved In:
alginic acid acetylation
Cellular Locations:
plasma membrane periplasmic space
Supporting Evidence:

References

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Suggested Questions for Experts

Q: Does KT2440 AlgJ transfer an acetyl intermediate in vivo, or primarily provide esterase-like processing within the relay?

Suggested Experiments

Experiment: Compare acetyl-transfer and esterase activities of purified AlgJ and catalytic-triad variants in the presence of AlgI and AlgF.

Type: enzyme relay reconstruction

Knowledge Gaps

What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).

Gap: The physiological substrate and direction of the AlgJ-catalyzed step in the periplasmic acetyl relay are unresolved.

BIOLOGYCURATION

What is known: Q88ND3 has a directly solved SGNH-like structure, and the characterized Pseudomonas proteins show acetylesterase activity in vitro and an in-vivo requirement for alginate acetylation; these observations do not yet establish a specific physiological molecular function.

Provenance (the field's own admissions):

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Notes

(algJ-notes.md)

algJ curation notes

  • PMID:25165982 directly crystallized the soluble domain of KT2440 AlgJ/Q88ND3
    (PpAlgJ75-370; PDB 4O8V), providing target-specific structural evidence.
  • P. aeruginosa algJ deletion produces non-acetylated alginate and is rescued by
    complementation [PMID:12003941, "each mutant produced alginate lacking
    O-acetyl groups"].
  • AlgJ has acetylesterase activity in vitro, but it binds polymannuronate weakly
    or not detectably and its physiological relay substrate remains unknown
    [PMID:25165982, "AlgJ exhibits either weak or no detectable polymer binding"].
  • Because the in-vivo reaction is unresolved, the review adds the exact
    acetylation process without assigning a speculative hydrolase or transferase
    molecular function.

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