ispH encodes the [4Fe-4S]-dependent terminal reductase of the methylerythritol phosphate pathway. It reduces HMBPP to a mixture of isopentenyl diphosphate and dimethylallyl diphosphate, the universal five-carbon precursors used for downstream isoprenoid synthesis.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016114 terpenoid biosynthetic process | IEA GO_REF:0000104 | MARK AS OVER ANNOTATED | Summary: Terpenoid biosynthesis is correct but broader than the product-specific terms. Reason: GO:0019288 and GO:0050992 capture the specific IPP and DMAPP biosynthetic roles of IspH, making this broad parent redundant. Supporting Evidence: file:PSEPK/ispH/ispH-uniprot.txt DOXP/MEP pathway for isoprenoid precursor biosynthesis. |
| GO:0019288 isopentenyl diphosphate biosynthetic process, methylerythritol phosphate pathway | IEA GO_REF:0000120 | ACCEPT | Summary: The methylerythritol phosphate pathway is a core process for IspH. Reason: UniProt places IspH at the terminal step of the six-reaction route from DXP to isopentenyl diphosphate. Supporting Evidence: file:PSEPK/ispH/ispH-uniprot.txt isopentenyl diphosphate biosynthesis via DXP pathway |
| GO:0046872 metal ion binding | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Generic metal binding is redundant beside the specific [4Fe-4S] cluster term. Reason: UniProt identifies one [4Fe-4S] cluster as the catalytic cofactor, so generic metal binding adds no useful specificity. Supporting Evidence: file:PSEPK/ispH/ispH-uniprot.txt Binds 1 [4Fe-4S] cluster per subunit. |
| GO:0050992 dimethylallyl diphosphate biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: DMAPP biosynthesis is a direct core pathway output of IspH. Reason: The IspH reaction produces DMAPP as one of two products from HMBPP, and UniProt assigns the corresponding one-step DMAPP biosynthetic pathway. Supporting Evidence: file:PSEPK/ispH/ispH-uniprot.txt and dimethylallyl diphosphate (DMAPP) |
| 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 IspH. Reason: UniProt records one [4Fe-4S] cluster per subunit, while the substrate-specific reductase term captures the evolved core function. Supporting Evidence: file:PSEPK/ispH/ispH-uniprot.txt Binds 1 [4Fe-4S] cluster per subunit. |
| GO:0051745 4-hydroxy-3-methylbut-2-enyl diphosphate reductase activity | IEA GO_REF:0000120 | ACCEPT | Summary: HMBPP reductase activity is the specific catalytic function of IspH. Reason: UniProt assigns EC 1.17.7.4 and Rhea 24488/24825 for reduction of HMBPP to IPP and DMAPP with a ferredoxin electron donor. Supporting Evidence: file:PSEPK/ispH/ispH-uniprot.txt Catalyzes the conversion of 1-hydroxy-2-methyl-2-(E)-butenyl file:PSEPK/ispH/ispH-deep-research-openscientist.md IspH (LytB/HDR, EC 1.17.7.4) catalyzes the **last of the seven steps** of the MEP (DOXP/non-mevalonate) pathway. |
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