id: A0A3B6NKR6 gene_symbol: A0A3B6NKR6 product_type: PROTEIN status: COMPLETE taxon: id: NCBITaxon:4565 label: Triticum aestivum description: >- A0A3B6NKR6 (TraesCS6A02G071400, chromosome 6A) is a 360-residue bread wheat member of the plant glucuronokinase family (PANTHER PTHR38710, subfamily SF1) within the GHMP kinase superfamily. It has the GHMP kinase N-terminal and C-terminal domains and the conserved glycine-rich phosphate-binding loop, and is full length relative to the characterised Arabidopsis glucuronokinases GLCAK1 and GLCAK2, with which it shares about 65% identity. By orthology to Arabidopsis GLCAK1 (and the enzyme purified from lily pollen), it is expected to phosphorylate D-glucuronic acid at C1 with ATP to give 1-phospho-alpha-D-glucuronate. This is the step that links the myo-inositol oxygenation pathway, and glucuronic-acid salvage, to UDP-glucuronic acid, the precursor of UDP-xylose, UDP-arabinose and UDP-galacturonic acid for cell-wall polysaccharides. The protein has no predicted signal peptide, transit peptide or transmembrane segment and is expected to be cytosolic. The wheat protein itself has not been characterised experimentally. existing_annotations: - term: id: GO:0005829 label: cytosol evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: is_active_in review: summary: >- Cytosolic localisation fits a soluble sugar-1-kinase that has no predicted targeting or membrane-spanning sequence. The characterised Arabidopsis ortholog was likewise predicted to be cytosolic. However, the PAINT node behind this IBA (PTN000048555) is seeded by mevalonate kinases (mouse and rat Mvk, yeast ERG12), not by glucuronokinases, and it does not occur in the PTHR38710 tree. The inference therefore rests on the GHMP superfamily, not on the glucuronokinase clade. One experimental report placed a YFP-tagged Arabidopsis paralog GLCAK2 at the plasma membrane, ER and tonoplast in transient tobacco expression; that has not been reproduced and does not fit the protein's lack of membrane features. action: ACCEPT reason: >- Cytosol is the most plausible compartment for this soluble enzyme. It is consistent with the sequence features and with the prediction made for the characterised Arabidopsis ortholog, so I accept it. The donor node is a mevalonate-kinase node (recorded in the bioinformatics results); this is a weakness of the provenance but not evidence against the location. supported_by: - reference_id: PMID:19951951 supporting_text: The protein is assumed to be localized in the cytosol as no transmembrane spanning domains and transit peptides are predicted (iPSORT software). - reference_id: file:WHEAT/A0A3B6NKR6/A0A3B6NKR6-bioinformatics/RESULTS-rereview.md supporting_text: The cytosol IBA that A0A3B6NKR6 (and both Arabidopsis - term: id: GO:0005524 label: ATP binding evidence_type: IEA original_reference_id: GO_REF:0000002 qualifier: enables review: summary: >- ATP binding is correct for a GHMP kinase. The characterised Arabidopsis ortholog uses ATP as the phosphate donor (Km 0.56 mM), and the wheat protein keeps the GHMP glycine-rich phosphate-binding loop (GLSGSSA). action: KEEP_AS_NON_CORE reason: >- ATP binding is true but only part of the catalytic activity. The informative function is glucuronokinase activity, proposed below. ATP binding is not a parent term of that activity, so it is kept as non-core rather than modified. supported_by: - reference_id: PMID:19951951 supporting_text: It requires ATP as phosphate donor (K(m) 0.56 mm). - reference_id: file:WHEAT/A0A3B6NKR6/A0A3B6NKR6-bioinformatics/RESULTS-rereview.md supporting_text: The GHMP phosphate-binding glycine-rich loop motif GLSGSSA is conserved in all three - term: id: GO:0019287 label: isopentenyl diphosphate biosynthetic process, mevalonate pathway evidence_type: IEA original_reference_id: GO_REF:0000041 qualifier: involved_in review: summary: >- This row comes from a UniPathway cross-reference (UPA00057, isopentenyl diphosphate biosynthesis via the mevalonate pathway). That pathway mapping appears to be inherited from mevalonate kinase, another GHMP family. The same PANTHER data list a PAINT node, PTN000048555, seeded by mevalonate kinases, with GO:0019287 and mevalonate kinase activity. A0A3B6NKR6 belongs to the glucuronokinase family PTHR38710, not to the mevalonate kinase family. Its characterised Arabidopsis ortholog is a sugar-1-kinase that is highly specific for D-glucuronic acid. Neither Arabidopsis glucuronokinase carries a mevalonate-pathway annotation in GOA. action: REMOVE reason: >- The electronic pathway mapping is demonstrably wrong for this family. Glucuronokinase phosphorylates D-glucuronic acid and acts in nucleotide-sugar metabolism, not in isoprenoid precursor synthesis. Plants make mevalonate with a separate mevalonate kinase from a different GHMP family. The annotation comes from GHMP-superfamily membership rather than from the glucuronokinase clade. supported_by: - reference_id: PMID:19951951 supporting_text: The Arabidopsis enzyme only catalyzed the conversion of d-GlcA into its corresponding sugar-1-phosphate but failed to utilize any other monosaccharide tested in the assays, indicating a very high substrate specificity of AtGlcAK for the sugar d-GlcA. - reference_id: file:WHEAT/A0A3B6NKR6/A0A3B6NKR6-bioinformatics/RESULTS-rereview.md supporting_text: It is a node seeded by - term: id: GO:0047940 label: glucuronokinase activity evidence_type: ISS original_reference_id: PMID:19951951 qualifier: enables review: summary: >- A0A3B6NKR6 is in the same PANTHER subfamily (PTHR38710:SF1) as Arabidopsis GLCAK1 (Q93ZC9). GLCAK1 was cloned from peptides of the enzyme purified from lily pollen and shown with recombinant protein to phosphorylate D-glucuronic acid to D-glucuronate-1-phosphate. In the PANTHER tree the plant glucuronokinases form one seed-plant clade with only speciation events between grasses and eudicots, so the wheat protein is an ortholog. It is full length, with both GHMP domains and the phosphate-binding loop. PAINT curators have placed a glucuronokinase-activity IBD at node PTN008680403, seeded by AT3G01640 (2026), but the wheat GOA snapshot does not yet carry the resulting IBA. action: NEW reason: >- The defining activity of this protein is missing from GOA. Subfamily-level orthology to the biochemically characterised enzyme supports the transfer, and so do the conserved catalytic motifs and the PAINT curators' own glucuronokinase IBD in this family. supported_by: - reference_id: PMID:19951951 supporting_text: AtGlcAK is a novel plant sugar kinase able to phosphorylate d-GlcA to d-GlcA-1-phosphate in the presence of ATP. - reference_id: file:WHEAT/A0A3B6NKR6/A0A3B6NKR6-bioinformatics/RESULTS-rereview.md supporting_text: So there is no duplication separating - term: id: GO:0006065 label: UDP-glucuronate biosynthetic process evidence_type: ISS original_reference_id: PMID:19951951 qualifier: involved_in review: summary: >- Glucuronokinase catalyses a step of UDP-glucuronate synthesis by the myo-inositol oxygenation route. It makes GlcA-1-phosphate, which UDP-sugar pyrophosphorylase then converts to UDP-GlcA. The gene product therefore does part of the work of the pathway itself; it is not merely a required input. Comparator check: the Arabidopsis UDP-glucose dehydrogenases (UGD2, UGD4), which catalyse the other route to UDP-GlcA, carry GO:0006065 by IDA. Arabidopsis GLCAK1 currently has only TAS inositol-metabolism and cell-wall terms, so this process term is not yet on the characterised ortholog. action: NEW reason: >- This is a catalytic participation in the pathway, which meets the participation test. It is proposed conservatively at the level of the UDP-GlcA product, not of downstream cell-wall or pollen phenotypes. supported_by: - reference_id: PMID:19951951 supporting_text: It is the last missing enzyme in the myo-inositol oxygenation pathway to UDP-GlcA core_functions: - description: >- ATP-dependent glucuronokinase that phosphorylates D-glucuronic acid at C1 to give 1-phospho-alpha-D-glucuronate in the cytosol. This step of the myo-inositol oxygenation and glucuronate-salvage route to UDP-glucuronic acid supplies nucleotide-sugar precursors for cell-wall polysaccharides. The function is inferred by subfamily-level orthology to biochemically characterised Arabidopsis GLCAK1. supported_by: - reference_id: PMID:19951951 supporting_text: AtGlcAK is a novel plant sugar kinase able to phosphorylate d-GlcA to d-GlcA-1-phosphate in the presence of ATP. - reference_id: file:WHEAT/A0A3B6NKR6/A0A3B6NKR6-bioinformatics/RESULTS-rereview.md supporting_text: So there is no duplication separating molecular_function: id: GO:0047940 label: glucuronokinase activity directly_involved_in: - id: GO:0006065 label: UDP-glucuronate biosynthetic process locations: - id: GO:0005829 label: cytosol references: - id: file:WHEAT/A0A3B6NKR6/A0A3B6NKR6-deep-research-falcon.md title: Deep research report for A0A3B6NKR6 (GHMP kinase N-terminal domain-containing protein) in Triticum aestivum reference_review: relevance: MEDIUM correctness: UNVERIFIED review_notes: >- Automated deep-research summary. Its domain-level conclusions match the primary literature, but it does not cite the primary glucuronokinase paper (PMID:19951951). Its localisation statement is a pathway-level inference. In the 2026-10-21 re-review it is no longer used as support; the primary paper and the bioinformatics re-analysis replace it. findings: - statement: >- A0A3B6NKR6 contains GHMP kinase N-terminal, C-terminal, and glucuronokinase-like domains, and is most plausibly annotated as a putative glucuronokinase involved in UDP-glucuronic acid biosynthesis via the myo-inositol oxidation pathway. reference_section_type: RESULTS - statement: >- The myo-inositol oxidation pathway operates in the cytosol: myo-inositol is converted to D-glucuronic acid (via MIOX), then to D-glucuronate-1-phosphate (via glucuronokinase), then to UDP-glucuronic acid. This pathway provides metabolic flexibility as an alternative to the UDP-glucose dehydrogenase route. reference_section_type: RESULTS - statement: >- The closest characterized ortholog identified by phmmer is Arabidopsis GLAK2 (Q9LY82, probable glucuronokinase 2, EC 2.7.1.43), sharing the same GHMP kinase domain architecture and glucuronokinase-like family membership. reference_section_type: RESULTS - id: PMID:19951951 title: Cloning of Glucuronokinase from Arabidopsis thaliana, the last missing enzyme of the myo-inositol oxygenase pathway to nucleotide sugars. reference_review: relevance: HIGH correctness: VERIFIED review_notes: >- Full text cached (PMC2823444). The authors purified the lily pollen enzyme, cloned Arabidopsis At3g01640 (GLCAK1, Q93ZC9) and characterised the recombinant protein: strict D-GlcA specificity, ATP as donor, Mg2+. This is the experimental source for the orthology-based transfer. findings: - statement: Recombinant Arabidopsis glucuronokinase phosphorylates D-glucuronic acid to D-glucuronic acid-1-phosphate using ATP, with strict substrate specificity. supporting_text: The Arabidopsis enzyme only catalyzed the conversion of d-GlcA into its corresponding sugar-1-phosphate but failed to utilize any other monosaccharide tested in the assays reference_section_type: RESULTS - statement: The enzyme is predicted to be cytosolic. supporting_text: The protein is assumed to be localized in the cytosol as no transmembrane spanning domains and transit peptides are predicted (iPSORT software). reference_section_type: RESULTS - id: PMID:36464707 title: AHL-Priming Protein 1 mediates N-3-oxo-tetradecanoyl-homoserine lactone priming in Arabidopsis. reference_review: relevance: LOW correctness: VERIFIED review_notes: >- Concerns the Arabidopsis paralog At5g14470 (GLCAK2/ALI1), not its kinase activity. It reports YFP-ALI1 at the plasma membrane, ER and tonoplast in transient tobacco expression, and a role in AHL priming. It is cited only as context for the cytosol row. The AHL-priming role is a GLCAK2-specific phenotype and is not transferred. findings: - statement: Transiently expressed YFP-tagged Arabidopsis GLCAK2/ALI1 colocalised with plasma membrane, ER and partly tonoplast markers in tobacco leaves. supporting_text: The results revealed that the YFP-ALI1 fusion protein colocalized with the plasma membrane, endoplasmic reticulum (ER), and partially with the tonoplast reference_section_type: RESULTS - id: file:WHEAT/A0A3B6NKR6/A0A3B6NKR6-bioinformatics/RESULTS-rereview.md title: A0A3B6NKR6 re-review bioinformatics (PANTHER tree placement, PAINT nodes, pairwise identity) findings: - statement: A0A3B6NKR6 shares PANTHER subfamily PTHR38710:SF1 with Arabidopsis GLCAK1 and GLCAK2 and is about 65% identical to each; it is full length and keeps the GHMP phosphate-binding loop. - statement: The cytosol IBA and the mevalonate-pathway mapping derive from a PAINT node seeded by mevalonate kinases (PTN000048555) that is absent from the PTHR38710 tree. - id: GO_REF:0000002 title: Gene Ontology annotation through association of InterPro records with GO terms findings: [] - id: GO_REF:0000033 title: Annotation inferences using phylogenetic trees findings: [] - id: GO_REF:0000041 title: Gene Ontology annotation based on UniPathway vocabulary mapping findings: [] suggested_questions: - question: >- PAINT node PTN000048555, seeded by mevalonate kinases, is attached to PTHR38710 and propagates cytosol to glucuronokinases. Should the cytosol IBD for glucuronokinases be re-anchored on a glucuronokinase node, for example PTN008680403? - question: >- Does UniPathway UPA00057, the mevalonate pathway, still map to PTHR38710 members, and can that pathway cross-reference be withdrawn for the glucuronokinase family? suggested_experiments: - description: >- Express recombinant A0A3B6NKR6 and assay ATP-dependent phosphorylation of D-glucuronic acid, with D-galacturonic acid, galactose and mevalonate as negative controls. This would confirm the orthology-based assignment in a grass.