LipA (also known as yutB) is a lipoyl synthase belonging to the radical SAM superfamily that catalyzes the final step of de novo lipoate biosynthesis in Bacillus subtilis. The enzyme inserts two sulfur atoms into the C6 and C8 positions of protein-bound octanoyl groups (attached to lipoyl domains of acceptor proteins such as GcvH and E2 subunits of 2-oxoacid dehydrogenase complexes), converting them to lipoyl cofactors. LipA contains two [4Fe-4S] clusters: a radical-SAM cluster for generating 5'-deoxyadenosyl radicals from S-adenosyl-L-methionine, and an auxiliary cluster that serves as the sacrificial sulfur donor. In B. subtilis, LipA functions in a pathway where LipM first transfers octanoyl from ACP to GcvH, LipA then inserts sulfurs to form lipoyl-GcvH, and LipL transfers the lipoyl moiety to E2 domains. Disruption of lipA causes lipoate auxotrophy and severely impairs growth in minimal medium due to defective lipoate-dependent enzymes, leading to impaired branched-chain fatty acid biosynthesis.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | MODIFY | Summary: This annotation from InterPro mapping assigns the very general term "catalytic activity" based on the presence of radical SAM domains. LipA is indeed a catalyst (lipoyl synthase, EC 2.8.1.8), but this term is far too general and uninformative. Reason: LipA has well-established lipoyl synthase activity (EC 2.8.1.8). The term "catalytic activity" is overly broad and should be replaced with the specific molecular function term GO:0016992 (lipoate synthase activity) which accurately describes LipA's enzymatic function. Proposed replacements: lipoate synthase activity |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: This annotation assigns cytoplasmic localization based on UniProt subcellular location annotation and UniRule. In B. subtilis (a Gram-positive bacterium lacking membrane-bound organelles), LipA and partner enzymes function in the cytosol where they act on soluble lipoyl domains of central metabolic complexes. Reason: Cytoplasmic localization is correct for B. subtilis LipA. The enzyme acts on cytosolic acceptor proteins including GcvH and E2 subunits of pyruvate dehydrogenase, 2-oxoglutarate dehydrogenase, and branched-chain 2-oxoacid dehydrogenase complexes (Cronan 2024; Christensen 2011). Supporting Evidence: PMID:19820084 The function of lipA was inferred from the results of genetic and physiological experiments file:BACSU/lipA/lipA-deep-research-falcon.md See deep research file for comprehensive analysis |
| GO:0009107 lipoate biosynthetic process | IEA GO_REF:0000120 | MODIFY | Summary: This IEA annotation assigns involvement in lipoate biosynthesis based on InterPro lipoyl synthase domain and UniRule mapping. LipA catalyzes the final step of de novo lipoate biosynthesis by inserting sulfur atoms into octanoyl groups. Reason: LipA is the key enzyme for de novo lipoate biosynthesis, catalyzing sulfur insertion into protein-bound octanoyl groups. This is the core biological process of the enzyme and is well supported by the literature (Cronan 2024; Christensen 2010). GO:0009107 was obsoleted by GO (2026-08-22, replaced_by GO:0009249 protein lipoylation, obsoleted because term usage was inconsistent), so the annotation should move to the replacement term. GOA already carries independent GO:0009249 rows for this gene, so the replacement merges onto an existing annotation rather than asserting a new one. Proposed replacements: protein lipoylation Supporting Evidence: PMID:19820084 We report the characterization of a Bacillus subtilis mutant obtained by disruption of the lipA (yutB) gene, which encodes lipoyl synthase (LipA), the enzyme that catalyzes the final step in the de novo biosynthesis of this cofactor. |
| GO:0009249 protein lipoylation | IEA GO_REF:0000104 | ACCEPT | Summary: This annotation assigns involvement in protein lipoylation based on UniRule transfer. LipA directly modifies protein-bound octanoyl groups on lipoyl domains, converting them to lipoyl groups covalently attached to lysine residues. Reason: LipA functions specifically on protein substrates (octanoyl-GcvH, octanoyl-E2), not free octanoate, and its product is a protein-bound lipoyl cofactor. This annotation accurately reflects the enzyme's role in the post-translational lipoylation of proteins (Douglas 2008; Cronan 2024). Supporting Evidence: PMID:19820084 lipoyl synthase (LipA), the enzyme that catalyzes the final step in the de novo biosynthesis of this cofactor |
| GO:0016740 transferase activity | IEA GO_REF:0000043 | ACCEPT | Summary: This annotation assigns transferase activity based on UniProt keyword mapping (Transferase KW-0808). LipA is classified as EC 2.8.1.8, which is a sulfurtransferase that transfers sulfur atoms to octanoyl groups. Reason: LipA is a sulfurtransferase (EC 2.8.1.8) and thus correctly annotated as having transferase activity. While this is a general parent term, it is accurate and provides useful hierarchical information complementing the more specific lipoate synthase activity annotation. |
| GO:0016783 sulfurtransferase activity | IEA GO_REF:0000104 | ACCEPT | Summary: This annotation assigns sulfurtransferase activity based on UniRule mapping. LipA inserts sulfur atoms from its auxiliary [4Fe-4S] cluster into octanoyl substrates at C6 and C8 positions, making it a sulfurtransferase by definition. Reason: LipA is classified as EC 2.8.1.8 (sulfurtransferase class). The enzyme transfers sulfur atoms from its sacrificial auxiliary [4Fe-4S] cluster to the C6 and C8 positions of protein-bound octanoyl groups (Cronan 2024; Lee et al. 2008). |
| GO:0016992 lipoate synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This IEA annotation assigns lipoate synthase activity based on InterPro domain mapping and UniRule. This is the correct, specific molecular function term for LipA. Reason: GO:0016992 (lipoate synthase activity) is the most specific and accurate molecular function term for LipA. The enzyme catalyzes sulfur insertion into octanoyl groups to form lipoyl cofactors (EC 2.8.1.8). This is a core function annotation (Cronan 2024). Supporting Evidence: PMID:19820084 lipoyl synthase (LipA), the enzyme that catalyzes the final step in the de novo biosynthesis of this cofactor |
| GO:0046872 metal ion binding | IEA GO_REF:0000043 | ACCEPT | Summary: This annotation assigns metal ion binding based on UniProt keyword mapping. LipA binds two [4Fe-4S] clusters which contain iron ions. Reason: LipA binds iron as part of its two [4Fe-4S] clusters. The annotation is correct but general; it is complemented by the more specific iron-sulfur cluster binding annotations which provide better functional context. |
| GO:0051536 iron-sulfur cluster binding | IEA GO_REF:0000120 | ACCEPT | Summary: This annotation assigns iron-sulfur cluster binding based on InterPro radical SAM domains and UniProt keyword. LipA contains two distinct [4Fe-4S] clusters essential for its catalytic mechanism. Reason: LipA binds two [4Fe-4S] clusters: a radical-SAM cluster coordinated by a CysXXXCysXXCys motif for generating 5'-deoxyadenosyl radicals, and an auxiliary cluster that serves as the sulfur donor (Lee et al. 2008; Lanz 2015). This is a core property of the enzyme. |
| GO:0051539 4 iron, 4 sulfur cluster binding | IEA GO_REF:0000120 | ACCEPT | Summary: This annotation specifically assigns [4Fe-4S] cluster binding based on InterPro lipoyl synthase domain and UniProt keywords. LipA contains two [4Fe-4S] clusters. Reason: LipA specifically binds [4Fe-4S] clusters, not other iron-sulfur cluster types. One cluster is the radical-SAM cluster (coordinated with 3 cysteines and exchangeable SAM), and the other is the auxiliary cluster that is consumed during catalysis as the sulfur source. Both are [4Fe-4S] clusters (Lee et al. 2008; Cronan 2024). Supporting Evidence: UniProt:O32129 Binds 2 [4Fe-4S] clusters per subunit. One cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine. |
| GO:0009107 lipoate biosynthetic process | IGI PMID:19820084 A lipA (yutB) mutant, encoding lipoic acid synthase, provide... | MODIFY | Summary: This experimental annotation (IGI - Inferred from Genetic Interaction) assigns involvement in lipoate biosynthesis based on the lipA mutant study by Martin et al. (2009). Disruption of lipA interrupted lipoate-dependent reactions in B. subtilis. Reason: The Martin et al. (2009) study directly demonstrated that disruption of lipA eliminates de novo lipoate biosynthesis in B. subtilis, causing lipoate auxotrophy. The IGI evidence is strong experimental support for this core biological process. GO:0009107 was obsoleted by GO (2026-08-22, replaced_by GO:0009249 protein lipoylation, obsoleted because term usage was inconsistent), so the annotation should move to the replacement term. GOA already carries independent GO:0009249 rows for this gene, so the replacement merges onto an existing annotation rather than asserting a new one. Proposed replacements: protein lipoylation Supporting Evidence: PMID:19820084 We report the characterization of a Bacillus subtilis mutant obtained by disruption of the lipA (yutB) gene, which encodes lipoyl synthase (LipA), the enzyme that catalyzes the final step in the de novo biosynthesis of this cofactor. |
| GO:0009249 protein lipoylation | IGI PMID:19820084 A lipA (yutB) mutant, encoding lipoic acid synthase, provide... | ACCEPT | Summary: This experimental annotation assigns involvement in protein lipoylation based on the lipA mutant study. The loss of LipA function led to interruption of lipoate-dependent reactions, which require lipoylated proteins. Reason: The Martin et al. (2009) study showed that lipA disruption interrupts lipoate-dependent reactions, which implies loss of protein lipoylation. LipA acts directly on protein-bound octanoyl substrates to generate protein-bound lipoyl cofactors. Supporting Evidence: PMID:19820084 Interrupting lipoate-dependent reactions strongly inhibits growth in minimal medium |
| GO:0016992 lipoate synthase activity | IGI PMID:19820084 A lipA (yutB) mutant, encoding lipoic acid synthase, provide... | ACCEPT | Summary: This experimental annotation assigns lipoate synthase activity based on the lipA mutant study. The gene was identified as encoding the lipoyl synthase responsible for the final step in lipoate biosynthesis. Reason: The Martin et al. (2009) study identified lipA (yutB) as encoding lipoyl synthase and demonstrated through mutant analysis that the gene product is required for lipoate biosynthesis, consistent with lipoate synthase activity. Supporting Evidence: PMID:19820084 the lipA (yutB) gene, which encodes lipoyl synthase (LipA), the enzyme that catalyzes the final step in the de novo biosynthesis of this cofactor |
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Q: What is the order of sulfur insertion (C6 first or C8 first) for B. subtilis LipA?
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