AlgD is the GDP-mannose 6-dehydrogenase that converts GDP-mannose to GDP-mannuronate, the committed precursor-forming step in alginate biosynthesis. In Pseudomonas putida KT2440, alginate production and algD expression are most prominent under water-limiting conditions, where alginate contributes to hydrated biofilm microenvironments and protection from dehydration-associated stress, while playing a comparatively minor role in standard biofilm stability assays.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016616 oxidoreductase activity, acting on the CH-OH group of donors, NAD or NADP as acceptor | IEA GO_REF:0000120 | ACCEPT | Summary: This mechanistic parent term is correct for AlgD. The enzyme oxidizes the CH-OH group of GDP-mannose using NAD+ as electron acceptor to generate GDP-mannuronate. It is less specific than GO:0047919 but still accurately describes the reaction chemistry. Supporting Evidence: file:PSEPK/algD/algD-uniprot.txt Reaction=GDP-alpha-D-mannose + 2 NAD(+) + H2O = GDP-alpha-D-mannuronate file:PSEPK/algD/algD-uniprot.txt Catalyzes the oxidation of guanosine diphospho-D-mannose...to GDP-D-mannuronic acid, a precursor for alginate polymerization. file:PSEPK/algD/algD-deep-research-manual.md The most defensible direct function assignment is GDP-mannose 6-dehydrogenase activity. file:PSEPK/algD/algD-deep-research-falcon.md The reaction is **NAD+-dependent**, and activity is commonly monitored by **NADH formation** (A340). |
| GO:0042121 alginic acid biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: This annotation is correct and captures the direct pathway role of AlgD. AlgD generates GDP-mannuronate, the committed precursor for alginate synthesis. KT2440 literature shows alginate production and algD-pathway expression under water-limiting conditions, although alginate is not the dominant exopolysaccharide in every biofilm assay. Supporting Evidence: file:PSEPK/algD/algD-uniprot.txt PATHWAY: Glycan biosynthesis; alginate biosynthesis. PMID:20236161 Under water-limiting conditions Pseudomonas putida produces the exopolysaccharide alginate, which influences biofilm development and facilitates maintaining a hydrated microenvironment. PMID:22138988 Upregulation of alginate genes was notable in this early response. file:PSEPK/algD/algD-deep-research-manual.md AlgD is directly involved in alginate biosynthesis because it generates GDP-mannuronate, the committed precursor for alginate polymerization. file:PSEPK/algD/algD-deep-research-falcon.md PP_1288 is explicitly annotated as algD (GDP-mannose 6-dehydrogenase) file:PSEPK/algD/algD-deep-research-falcon.md algD/PP_1288 is reported as significantly induced under water-limited conditions, with a reported **log2 fold-change of 3.26** in wild type at **0.4 MPa** matric potential |
| GO:0047919 GDP-mannose 6-dehydrogenase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is the most specific and best supported molecular function term for AlgD. The UniProt record identifies the protein as GDP-mannose 6-dehydrogenase and gives the expected NAD-dependent oxidation of GDP-mannose to GDP-mannuronate. This is the core catalytic activity of the gene product. Supporting Evidence: file:PSEPK/algD/algD-uniprot.txt Full=GDP-mannose 6-dehydrogenase; file:PSEPK/algD/algD-uniprot.txt Reaction=GDP-alpha-D-mannose + 2 NAD(+) + H2O = GDP-alpha-D-mannuronate file:PSEPK/algD/algD-deep-research-manual.md The most defensible direct function assignment is GDP-mannose 6-dehydrogenase activity. file:PSEPK/algD/algD-deep-research-falcon.md AlgD catalyzes the **irreversible oxidation of GDP-mannose to GDP-mannuronate (GDP-mannuronic acid; GDP-ManA)**, supplying the activated uronic-acid building block used for polymer formation. file:PSEPK/algD/algD-deep-research-falcon.md AlgD (GDP-mannose 6-dehydrogenase; GMD) is a cytosolic enzyme in the **UDP-glucose/GDP-mannose dehydrogenase family** that catalyzes the **precursor-forming step** for bacterial alginate biosynthesis. |
| GO:0051287 NAD binding | IEA GO_REF:0000002 | ACCEPT | Summary: This annotation is correct as a supporting molecular function. AlgD is an NAD-dependent dehydrogenase with an N-terminal Rossmann-like nucleotide-binding domain, and the UniProt record lists multiple NAD(+) binding residues. This term is less informative than the catalytic activity term but remains valid. Supporting Evidence: file:PSEPK/algD/algD-uniprot.txt NAD(P)-binding Rossmann-like Domain file:PSEPK/algD/algD-uniprot.txt ligand="NAD(+)" file:PSEPK/algD/algD-deep-research-manual.md The presence of an NAD(P)-binding Rossmann-like domain and annotated NAD(+) binding residues supports the NAD-binding annotation. file:PSEPK/algD/algD-deep-research-falcon.md The enzyme is described as having an **N-terminal domain** that binds **NAD+ and GDP-mannose**, and a **C-terminal domain** containing an essential catalytic **cysteine** (reported as Cys268 in that article). |
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Download this section (compressed HTML)Q: Which environmental and regulatory inputs beyond water limitation most strongly control algD expression in Pseudomonas putida KT2440?
Q: In which habitats or growth states does alginate become a major, rather than minor, matrix component in KT2440 relative to other exopolysaccharides such as Pea and Peb?
Q: Are there measurable differences in catalytic efficiency or regulation between KT2440 AlgD and the better-studied Pseudomonas aeruginosa homologs?
Experiment: Purify KT2440 AlgD and measure GDP-mannose to GDP-mannuronate conversion in vitro with NAD+ to obtain direct kinetic evidence for the predicted catalytic activity in this strain.
Hypothesis: KT2440 AlgD is an NAD-dependent GDP-mannose 6-dehydrogenase with substrate specificity matching the UniProt-assigned reaction.
Type: Enzyme purification and steady-state kinetics
Experiment: Compare wild type, deltaalgD, and complemented strains under matric versus solute stress while quantifying alginate, biofilm architecture, and desiccation survival.
Hypothesis: algD-dependent alginate production specifically improves fitness under water-limiting conditions more than under purely osmotic stress.
Type: Mutant/complementation biofilm stress assay
Experiment: Use promoter-reporter fusions and RNA-seq in KT2440 across defined hydration states and carbon sources to map the upstream regulatory logic controlling algD expression.
Hypothesis: algD induction is driven by a specific dehydration-responsive regulatory program rather than by generic slowing of metabolism.
Type: Reporter assay and transcriptomics
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