Glk is the cytosolic glucokinase of Pseudomonas putida KT2440. It phosphorylates imported glucose to glucose-6-phosphate using ATP and feeds the phosphorylative branch of glucose assimilation into the Entner-Doudoroff-centered carbohydrate catabolic network. In KT2440, glk is part of the edd-glk operon and mutant and flux analyses indicate that the glucokinase branch is quantitatively important for growth on glucose even though P. putida can also oxidize glucose through periplasmic gluconate and 2-ketogluconate routes.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004340 glucokinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is the core molecular function of glk. UniProt assigns the protein as glucokinase (EC 2.7.1.2), and pathway work in KT2440 places Glk at the ATP-dependent phosphorylation step that converts cytoplasmic glucose to glucose-6-phosphate. Reason: This term is specific, mechanistically correct, and central to the gene's function. Supporting Evidence: file:PSEPK/glk/glk-uniprot.txt RecName: Full=Glucokinase file:PSEPK/glk/glk-uniprot.txt Reaction=D-glucose + ATP = D-glucose 6-phosphate + ADP + H(+); file:PSEPK/glk/glk-notes.md In KT2440, glucose imported into the cytoplasm is phosphorylated by glucokinase to glucose-6-phosphate before conversion to 6-phosphogluconate. file:PSEPK/glk/glk-deep-research-falcon.md The UniProt target **Q88P42** corresponds to **glk** in *Pseudomonas putida* KT2440 (ordered locus **PP_1011**) encoding the cytosolic enzyme **glucokinase (Glk)**, which phosphorylates imported glucose to **glucose‑6‑phosphate (G6P)** as the entry step of the phosphorylative branch of glucose catabolism. |
| GO:0005524 ATP binding | IEA GO_REF:0000120 | MARK AS OVER ANNOTATED | Summary: ATP binding is mechanistically true for a kinase, but it is much less informative than the specific catalytic term glucokinase activity and is redundant for describing the core function of this enzyme. Reason: The catalytic activity term already captures the biologically informative function. Supporting Evidence: file:PSEPK/glk/glk-uniprot.txt /ligand="ATP" file:PSEPK/glk/glk-notes.md ATP binding and D-glucose binding are mechanistically true but substantially less informative than the specific catalytic term glucokinase activity. |
| GO:0005536 D-glucose binding | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Substrate recognition is implicit in glucokinase activity, so this term is not wrong but is less informative than the specific catalytic annotation. Reason: This binding term adds little beyond the core enzymatic activity term. Supporting Evidence: file:PSEPK/glk/glk-notes.md In KT2440, glucose imported into the cytoplasm is phosphorylated by glucokinase to glucose-6-phosphate before conversion to 6-phosphogluconate. file:PSEPK/glk/glk-notes.md ATP binding and D-glucose binding are mechanistically true but substantially less informative than the specific catalytic term glucokinase activity. |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | MODIFY | Summary: Glk is a soluble intracellular enzyme and cytoplasmic localization is correct, but the more precise term in this context is cytosol. Reason: Cytoplasm is broader than needed for a soluble bacterial enzyme. Proposed replacements: cytosol Supporting Evidence: file:PSEPK/glk/glk-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm file:PSEPK/glk/glk-notes.md For cellular component, cytosol is the more specific GO term for a soluble bacterial cytoplasmic enzyme, while cytoplasm is acceptable but broader. |
| GO:0005829 cytosol | IEA GO_REF:0000118 | ACCEPT | Summary: This is the preferred cellular component term for a soluble cytoplasmic enzyme such as Glk and is more precise than the broader term cytoplasm. Reason: Specific and biologically appropriate localization term. Supporting Evidence: file:PSEPK/glk/glk-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm file:PSEPK/glk/glk-notes.md For cellular component, cytosol is the more specific GO term for a soluble bacterial cytoplasmic enzyme, while cytoplasm is acceptable but broader. |
| GO:0006096 glycolytic process | IEA GO_REF:0000120 | ACCEPT | Summary: Glk participates in glucose catabolism to pyruvate; in P. putida KT2440 that flux is routed through the Entner-Doudoroff-centered network. GO has now folded the ED-routed glycolysis variant (GO:0061688) back into this term, so the existing annotation is the appropriate process term for the glucokinase entry step. Reason: This review originally proposed MODIFY to GO:0061688 glycolytic process via Entner-Doudoroff Pathway, but GO:0061688 is obsolete in the GO release 2026-07-26 with replaced_by GO:0006096, noting that pathway variants are better represented as GO-CAMs than as nested terms. GO:0061688 was an is_a child of GO:0006096 that started with GO:0061678 Entner-Doudoroff pathway; Glk phosphorylates glucose upstream of the ED dehydration and aldol-cleavage steps and performs none of them, so the ED pathway term itself is not appropriate. (The is_a placement of GO:0061688 is read from the pre-obsoletion GO release; the term no longer exists in current releases.) GO:0006096 is therefore retained, supported by the glucokinase entry step being required for glucose catabolism in KT2440. Supporting Evidence: PMID:17483213 is then phosphorylated by glucokinase (encoded by the glk gene) and converted by glucose-6-phosphate dehydrogenase (encoded by the zwf genes) to 6-phosphogluconate PMID:17483213 It can therefore be concluded that the glucokinase pathway is a sine qua non condition for P. putida to grow with glucose. |
| GO:0051156 glucose 6-phosphate metabolic process | IEA GO_REF:0000002 | ACCEPT | Summary: This term accurately reflects the immediate pathway context of Glk, which generates glucose-6-phosphate from glucose and ATP. Reason: Directly describes the metabolic process in which the enzymatic reaction participates. Supporting Evidence: file:PSEPK/glk/glk-uniprot.txt Reaction=D-glucose + ATP = D-glucose 6-phosphate + ADP + H(+); file:PSEPK/glk/glk-notes.md In KT2440, glucose imported into the cytoplasm is phosphorylated by glucokinase to glucose-6-phosphate before conversion to 6-phosphogluconate. |
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Download this section (compressed HTML)Q: How does flux through the glucokinase branch versus the periplasmic gluconate and 2-ketogluconate branches change across different glucose concentrations and oxygen or redox conditions in KT2440?
Q: Does Glk have kinetic or regulatory specialization that distinguishes it from glucokinases in other pseudomonads that use different balances of oxidative and phosphorylative glucose uptake?
Q: How strongly does HexR-mediated control of the edd-glk operon constrain mixed-substrate utilization when glucose and gluconate are simultaneously available?
Experiment: Purify PP_1011 and measure steady-state kinetics for glucose and ATP, substrate specificity, and cofactor dependence under physiologically relevant ionic conditions.
Type: Enzyme biochemistry
Experiment: Construct a clean glk deletion and complemented strain, then quantify growth and intracellular carbon flux on glucose, gluconate, and mixed carbon sources using isotopic tracer experiments.
Type: Genetic perturbation and flux analysis
Experiment: Use promoter reporters or RNA-seq in wild type and hexR backgrounds to quantify how glucose, gluconate, 2-ketogluconate, and KDPG-related perturbations regulate the edd-glk-gltR2-gltS operon.
Type: Operon regulation
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