GlgX (PP_4055) is a predicted bacterial glycogen-debranching enzyme. Its GlgX-specific GH13 architecture supports hydrolysis of short alpha-1,6-linked branches from phosphorylase-limit glycogen during mobilization, producing a more linear alpha-1,4-glucan substrate for continued phosphorylase action. Q88FN4 has not been assayed directly, but characterized GlgX enzymes and the close Pseudomonas aeruginosa homolog have the short-chain debranching activity now classified as EC 3.2.1.196.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004135 amylo-alpha-1,6-glucosidase activity | IEA GO_REF:0000120 | MODIFY | Summary: This legacy term describes a different debranching reaction and should be replaced by the bacterial GlgX activity. Reason: GO:0004135/EC 3.2.1.33 releases free glucose from a residual single glucosyl stub, whereas bacterial GlgX/EC 3.2.1.196 releases a DP3-DP4 branch intact. These are distinct reactions, not a parent-child term pair. The Q88FN4 assignment derives from an ECO:0000313 submitted-name EC mapping, while its GlgX-specific family membership and characterized bacterial homologs support GO:0120549. Proposed replacements: limit dextrin alpha-1,6-maltotetraose-hydrolase activity Supporting Evidence: file:PSEPK/glgX/glgX-uniprot.txt DR GO; GO:0004135; F:amylo-alpha-1,6-glucosidase activity; IEA:UniProtKB-EC. PMID:15687211 debranching enzyme with high specificity for hydrolysis of chains consisting of three or four glucose residues PMID:33872310 MALDI-MS showed that the enzyme preferentially liberated a maltooligosaccharide with a DP of 4 and significantly less material with a DP of 5 and above (Fig 7), supporting its role as a debranching enzyme with a short chain-length specificity. |
| GO:0004553 hydrolase activity, hydrolyzing O-glycosyl compounds | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: This broad GH13 hydrolase term is compatible but non-specific. Reason: Hydrolysis of an alpha-1,6-glucosidic linkage is within this parent class, while GO:0120549 captures the informative branch-point reaction. Supporting Evidence: file:PSEPK/glgX/glgX-uniprot.txt DR InterPro; IPR011837; Glycogen_debranch_GlgX. |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: GlgX acts on a carbohydrate polymer, but this process term is broad. Reason: The annotation is directionally correct and can be retained as non-core; glycogen catabolic process is the informative pathway role. Supporting Evidence: file:PSEPK/glgX/glgX-uniprot.txt DR InterPro; IPR011837; Glycogen_debranch_GlgX. |
| GO:0005980 glycogen catabolic process | IEA GO_REF:0000002 | ACCEPT | Summary: Glycogen debranching is a direct step in glycogen catabolism. Reason: The GlgX-specific domain and EC assignment support removal of glycogen alpha-1,6 branch points, which is required for complete mobilization of branched glycogen. Supporting Evidence: file:PSEPK/glgX/glgX-uniprot.txt DR GO; GO:0005980; P:glycogen catabolic process; IEA:InterPro. |
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Download this section (compressed HTML)Q: Does Q88FN4 preferentially debranch glycogen made by GlgA or alpha-glucan made by GlgE?
Experiment: Compare purified Q88FN4 activity on defined branched glycogen and GlgE-derived alpha-glucan substrates, and profile polymer structure and mobilization in a glgX deletion strain.
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