ispG encodes the [4Fe-4S]-dependent reductive enzyme of the methylerythritol phosphate pathway that converts methylerythritol 2,4-cyclodiphosphate to HMBPP using reduced flavodoxin. Its product is the substrate for the terminal IspH reaction that forms isopentenyl and dimethylallyl diphosphate.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005506 iron ion binding | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Generic iron binding is redundant beside the specific [4Fe-4S] cluster term. Reason: UniProt records one [4Fe-4S] cluster as the catalytic cofactor, so the cluster-binding term is more informative than generic iron binding. Supporting Evidence: file:PSEPK/ispG/ispG-uniprot.txt Binds 1 [4Fe-4S] cluster. |
| GO:0008299 isoprenoid biosynthetic process | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Isoprenoid biosynthesis is correct but broader than the MEP pathway term. Reason: GO:0019288 captures the specific precursor-biosynthesis route in which IspG acts. HAMAP places IspG at a specific step of the DXP/MEP pathway. Supporting Evidence: file:PSEPK/ispG/ispG-uniprot.txt PATHWAY: Isoprenoid biosynthesis; isopentenyl diphosphate biosynthesis via DXP pathway |
| GO:0016114 terpenoid biosynthetic process | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Terpenoid biosynthesis is correct but broader than the MEP pathway term. Reason: GO:0019288 provides the pathway-specific process annotation and makes this broad parent redundant. HAMAP places IspG at a specific step of the DXP/MEP pathway. Supporting Evidence: file:PSEPK/ispG/ispG-uniprot.txt PATHWAY: Isoprenoid biosynthesis; isopentenyl diphosphate biosynthesis via DXP pathway |
| GO:0019288 isopentenyl diphosphate biosynthetic process, methylerythritol phosphate pathway | IEA GO_REF:0000120 | ACCEPT | Summary: The methylerythritol phosphate pathway is the core process for IspG. Reason: UniProt places IspG at step 5 of the six-reaction route from DXP to isopentenyl diphosphate. Supporting Evidence: file:PSEPK/ispG/ispG-uniprot.txt isopentenyl diphosphate biosynthesis via DXP pathway |
| GO:0046429 4-hydroxy-3-methylbut-2-en-1-yl diphosphate synthase activity (ferredoxin) | IEA GO_REF:0000120 | REMOVE | Summary: Remove the unsupported ferredoxin-specific IEA; the exact flavodoxin-coupled activity is independently retained below. Reason: The curated exact-reaction mapping for Q88PJ7 is EC 1.17.7.3/Rhea 43604 with flavodoxin, while no target-specific ferredoxin evidence was located. GO:0141197 is already present as a separate annotation, so modifying this row would only duplicate the retained exact activity. Supporting Evidence: file:PSEPK/ispG/ispG-uniprot.txt oxidized [flavodoxin] |
| GO:0051539 4 iron, 4 sulfur cluster binding | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: The [4Fe-4S] cluster is required catalytic cofactor context for IspG. Reason: UniProt records one [4Fe-4S] cluster, while the substrate- and electron-carrier-specific synthase term captures the evolved core function. Supporting Evidence: file:PSEPK/ispG/ispG-uniprot.txt Binds 1 [4Fe-4S] cluster. |
| GO:0141197 4-hydroxy-3-methylbut-2-enyl-diphosphate synthase activity (flavodoxin) | IEA GO_REF:0000120 | ACCEPT | Summary: Flavodoxin-dependent HMBPP synthase activity is the specific function of IspG. Reason: UniProt assigns EC 1.17.7.3 and Rhea 43604 for the flavodoxin-coupled conversion between ME-CPP and HMBPP. Supporting Evidence: file:PSEPK/ispG/ispG-uniprot.txt Converts 2C-methyl-D-erythritol 2,4-cyclodiphosphate file:PSEPK/ispG/ispG-deep-research-openscientist.md *ispG* encodes **(E)-4-hydroxy-3-methylbut-2-en-1-yl diphosphate synthase (HMBPP synthase / GcpE)** |
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