SepB is a trifunctional heptose precursor biosynthetic enzyme of Streptomyces fimbriatus CGMCC 4.1598. Its N-terminal sedoheptulose 7-phosphate isomerase domain and HldE-like kinase and adenylyltransferase domains catalyze three reactions that, together with the SepL phosphatase, produce ADP-D-glycero-beta-D-manno-heptose. SepC then epimerizes this nucleotide sugar to the L-glycero form used in septacidin biosynthesis. This Gram-positive secondary-metabolite pathway uses the same precursor chemistry as bacterial LPS heptose synthesis.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | MODIFY | Summary: Resolve the broad catalytic activity into the three experimentally established SepB reactions. Reason: The original study reconstituted ADP-D-glycero-beta-D-manno-heptose production with SepB and SepL. Reciprocal substitution with E. coli GmhA, HldE and GmhB identifies the fused isomerase, kinase and adenylyltransferase functions; full-length sequence identity links the assayed SepB to this accession. Proposed replacements: D-sedoheptulose 7-phosphate isomerase activity heptose 7-phosphate kinase activity heptose-1-phosphate adenylyltransferase activity Supporting Evidence: PMID:29483275 SepB, SepL, and SepC can convert d-sedoheptulose-7-phosphate (S-7-P) to ADP-l-glycero-Ξ²-d-manno-heptose file:STRFI/sepB/sepB-bioinformatics/RESULTS.md SepB A0A2P1G6C0 is identical over all 707 residues to AVM80385.1, the sepB translation in the original MF372757.1 septacidin cluster. |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000120 | MODIFY | Summary: Specify the activated heptose precursor biosynthetic pathway. Reason: SepB catalyzes three steps of ADP-L-glycero-beta-D-manno-heptose precursor synthesis; SepL and SepC complete the pathway. The downstream biological context is septacidin production, not LPS synthesis. This refinement identifies the chemically defined carbohydrate-derivative process. Proposed replacements: ADP-L-glycero-beta-D-manno-heptose biosynthetic process Supporting Evidence: PMID:29483275 SepB, SepL, and SepC can convert d-sedoheptulose-7-phosphate (S-7-P) to ADP-l-glycero-Ξ²-d-manno-heptose file:STRFI/sepB/sepB-bioinformatics/RESULTS.md SepB A0A2P1G6C0 is identical over all 707 residues to AVM80385.1, the sepB translation in the original MF372757.1 septacidin cluster. |
| GO:0016772 transferase activity, transferring phosphorus-containing groups | IEA GO_REF:0000117 | MODIFY | Summary: Specify the two phosphorus-transfer reactions of SepB. Reason: Independent biochemical evidence supports both ATP-dependent heptose phosphorylation and heptose-1-phosphate adenylylation. Both specific activities are needed to refine this broad transferase claim; the ARBA prediction is not the supporting evidence. Proposed replacements: heptose 7-phosphate kinase activity heptose-1-phosphate adenylyltransferase activity Supporting Evidence: PMID:29483275 SepB, SepL, and SepC can convert d-sedoheptulose-7-phosphate (S-7-P) to ADP-l-glycero-Ξ²-d-manno-heptose file:STRFI/sepB/sepB-bioinformatics/RESULTS.md SepB A0A2P1G6C0 is identical over all 707 residues to AVM80385.1, the sepB translation in the original MF372757.1 septacidin cluster. |
| GO:0016773 phosphotransferase activity, alcohol group as acceptor | IEA GO_REF:0000002 | MODIFY | Summary: Specify heptose 7-phosphate kinase activity. Reason: SepB phosphorylates the C1 hydroxyl of the heptose 7-phosphate intermediate using ATP. Coupled reconstruction and enzyme substitution establish this reaction within the trifunctional enzyme. Proposed replacements: heptose 7-phosphate kinase activity Supporting Evidence: PMID:29483275 SepB, SepL, and SepC can convert d-sedoheptulose-7-phosphate (S-7-P) to ADP-l-glycero-Ξ²-d-manno-heptose file:STRFI/sepB/sepB-bioinformatics/RESULTS.md SepB A0A2P1G6C0 is identical over all 707 residues to AVM80385.1, the sepB translation in the original MF372757.1 septacidin cluster. |
| GO:0016779 nucleotidyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: Specify heptose-1-phosphate adenylyltransferase activity. Reason: The HldE-like C-terminal region supplies AMP transfer from ATP to heptose 1-phosphate after SepL removes the C7 phosphate, yielding the ADP-D,D-heptose product identified against authentic standards. Proposed replacements: heptose-1-phosphate adenylyltransferase activity Supporting Evidence: PMID:29483275 SepB, SepL, and SepC can convert d-sedoheptulose-7-phosphate (S-7-P) to ADP-l-glycero-Ξ²-d-manno-heptose file:STRFI/sepB/sepB-bioinformatics/RESULTS.md SepB A0A2P1G6C0 is identical over all 707 residues to AVM80385.1, the sepB translation in the original MF372757.1 septacidin cluster. |
| GO:0030246 carbohydrate binding | IEA GO_REF:0000104 | MODIFY | Summary: Describe the phosphorylated-sugar substrates as carbohydrate derivatives. Reason: The demonstrated ligands are sugar phosphates and nucleotide sugars. Carbohydrate derivative binding expresses this chemistry more accurately than binding to an unmodified carbohydrate; this is a substrate-class correction, not an is_a refinement. Proposed replacements: carbohydrate derivative binding Supporting Evidence: PMID:29483275 SepB, SepL, and SepC can convert d-sedoheptulose-7-phosphate (S-7-P) to ADP-l-glycero-Ξ²-d-manno-heptose file:STRFI/sepB/sepB-bioinformatics/RESULTS.md SepB A0A2P1G6C0 is identical over all 707 residues to AVM80385.1, the sepB translation in the original MF372757.1 septacidin cluster. |
| GO:0097367 carbohydrate derivative binding | IEA GO_REF:0000002 | ACCEPT | Summary: Binding of carbohydrate derivatives is intrinsic to the measured catalytic reactions. Reason: The enzyme acts directly on sedoheptulose 7-phosphate and phosphorylated heptose intermediates. This binding claim is supported mechanistically by reconstituted catalysis; no independent lectin or polysaccharide-binding role is inferred. No single more specific binding term captures the distinct sugar-phosphate substrates. Supporting Evidence: PMID:29483275 SepB, SepL, and SepC can convert d-sedoheptulose-7-phosphate (S-7-P) to ADP-l-glycero-Ξ²-d-manno-heptose file:STRFI/sepB/sepB-bioinformatics/RESULTS.md SepB A0A2P1G6C0 is identical over all 707 residues to AVM80385.1, the sepB translation in the original MF372757.1 septacidin cluster. |
| GO:1901135 carbohydrate derivative metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: Specify the experimentally reconstructed ADP-L-heptose biosynthetic pathway. Reason: SepB performs three precursor-synthesis steps, with SepL phosphatase and SepC epimerase completing ADP-L-glycero-beta-D-manno-heptose synthesis. This is direct catalytic participation rather than an indirect requirement or substrate-only relationship. Proposed replacements: ADP-L-glycero-beta-D-manno-heptose biosynthetic process Supporting Evidence: PMID:29483275 SepB, SepL, and SepC can convert d-sedoheptulose-7-phosphate (S-7-P) to ADP-l-glycero-Ξ²-d-manno-heptose file:STRFI/sepB/sepB-bioinformatics/RESULTS.md SepB A0A2P1G6C0 is identical over all 707 residues to AVM80385.1, the sepB translation in the original MF372757.1 septacidin cluster. |
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