Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0042121 alginic acid biosynthetic process	IEA GO_REF:0000120	ACCEPT	Summary: AlgX has both polymer-modification and chain-protection roles in alginate biosynthesis. Reason: The broad process remains appropriate for the dual function, while GO:0051979 is added for the specific O-acetylation branch. Supporting Evidence: file:PSEPK/algX/algX-uniprot.txt Plays two roles in the biosynthesis of the exopolysaccharide PMID:23779107 this protein is essential for polymer production
GO:0042597 periplasmic space	IEA GO_REF:0000044	ACCEPT	Summary: AlgX modifies and protects alginate in the periplasm. Reason: The signal peptide, reviewed location, and solved P. putida AlgX structure support this compartment. Supporting Evidence: file:PSEPK/algX/algX-uniprot.txt SUBCELLULAR LOCATION: Periplasm
GO:0016413 O-acetyltransferase activity	ISS PMID:25165982 P. aeruginosa SGNH hydrolase-like proteins AlgJ and AlgX hav...	NEW	Summary: AlgX is the probable terminal polymer O-acetyltransferase in the Pseudomonas machinery. Reason: The characterized P. aeruginosa Q51372 ortholog directly O-acetylates polymannuronate in vitro. No alginate-substrate-specific MF term exists, so the valid generic term is paired with exact substrate and process context. Supporting Evidence: PMID:25165982 AlgX was capable of utilizing the surrogate acetyl-donor 4-nitrophenyl acetate to catalyze the O-acetylation of polymannuronic acid.
GO:0030247 polysaccharide binding	ISS PMID:25165982 P. aeruginosa SGNH hydrolase-like proteins AlgJ and AlgX hav...	NEW	Summary: The AlgX carbohydrate-binding module recognizes mannuronate oligomers in alginate. Reason: Direct binding measurements on the P. aeruginosa Q51372 ortholog show specific, length-dependent polymannuronate binding, and Q88ND0 retains the corresponding C-terminal carbohydrate-binding module. Supporting Evidence: PMID:25165982 AlgX binds polymannuronic acid specifically in a length-dependent manner.
GO:0051979 alginic acid acetylation	ISS PMID:23779107 Structural and functional characterization of Pseudomonas ae...	NEW	Summary: AlgX performs the terminal transfer to mannuronate residues in the alginate polymer. Reason: This specific process term captures the experimentally defined ortholog role and conserved KT2440 machinery. Supporting Evidence: PMID:23779107 site-specific mutation of these residues results in non-acetylated alginate.

Core Functions

Probable periplasmic alginate O-acetyltransferase that modifies O-2 and O-3 positions of mannuronate residues.

Molecular Function:

O-acetyltransferase activity

Directly Involved In:

alginic acid acetylation

Cellular Locations:

periplasmic space

Supporting Evidence:

PMID:23779107
site-specific mutation of these residues results in non-acetylated alginate.
PMID:25165982
AlgX was capable of utilizing the surrogate acetyl-donor 4-nitrophenyl acetate to catalyze the O-acetylation of polymannuronic acid.

Alginate-binding maturation factor that protects nascent polymer from AlgL during periplasmic transit.

Molecular Function:

polysaccharide binding

Directly Involved In:

alginic acid biosynthetic process

Cellular Locations:

periplasmic space

Supporting Evidence:

PMID:25165982
AlgX binds polymannuronic acid specifically in a length-dependent manner.
file:PSEPK/algX/algX-uniprot.txt
protects alginate from degradation

References

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Suggested Experiments

Experiment: Compare alginate acetylation, binding, and AlgL protection using catalytic-triad and carbohydrate-binding-module mutants of Q88ND0.

Type: structure-guided mutagenesis and polymer assays

📚 Additional Documentation

Notes

(algX-notes.md)

algX curation notes

Q88ND0 is curated by explicit transfer from reviewed P. aeruginosa AlgX
Q51372, not from the target UniProt record's circular "By similarity" line.
Catalytic-triad substitutions in Q51372 produce non-acetylated alginate in
vivo [PMID:23779107, "site-specific mutation of these residues results in
non-acetylated alginate"].
Purified Q51372 binds polymannuronic acid in a length-dependent manner and
O-acetylates it with a surrogate donor [PMID:25165982, "AlgX binds
polymannuronic acid specifically in a length-dependent manner"].
GO:0016413 captures the demonstrated transferase class, GO:0030247 captures
polymer binding, and GO:0051979 supplies alginate-specific process context.

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