Bio2p is the mitochondrial biotin synthase (BioB; EC 2.8.1.6) of Saccharomyces cerevisiae, a radical SAM enzyme that catalyses the final step of biotin biosynthesis, inserting a sulfur atom between C6 and C9 of dethiobiotin to close the thiophane ring of biotin. By similarity to bacterial BioB it binds a [4Fe-4S] cluster that reductively cleaves S-adenosylmethionine to generate 5'-deoxyadenosyl radicals, and a [2Fe-2S] cluster that serves as the sulfur source; reducing equivalents come from ferredoxin. The protein carries an N-terminal mitochondrial transit peptide and localizes to mitochondria. Disruption of BIO2 blocks conversion of dethiobiotin to biotin.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO from the generic radical SAM signatures (IPR006638, IPR007197). True but uninformative; Bio2 is a biotin synthase. Reason: Root-level MF; the specific activity is known. Proposed replacements: biotin synthase activity Supporting Evidence: PMID:10525840 The gene BIO2, encoding a biotin synthase, is shown to be interrupted in this mutant. |
| GO:0004076 biotin synthase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN000540961, seeded by E. coli BioB (P12996), M. tuberculosis BioB, S. pombe bio2 and S. cerevisiae Bio2 itself. Bio2 has the complete BioB architecture (radical SAM core plus BATS domain), so inheritance is sound. Supporting Evidence: PMID:10525840 The gene BIO2, encoding a biotin synthase, is shown to be interrupted in this mutant. |
| GO:0004076 biotin synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA from InterPro IPR024177 (biotin synthase) with RHEA:22060 / EC 2.8.1.6. Correct for this protein. Supporting Evidence: file:yeast/BIO2/BIO2-uniprot.txt biotin + 2 5'-deoxyadenosine + 2 L-methionine + 2 oxidized [2Fe-2S]- |
| GO:0004076 biotin synthase activity | IMP PMID:10525840 Cloning of Schizosaccharomyces pombe bio2 by heterologous co... | ACCEPT | Summary: IMP from Phalip et al. 1999 (abstract only); a transposon insertion in BIO2 blocks the last step of biotin synthesis (dethiobiotin to biotin), and S. pombe bio2 complements. Defer to SGD curator who read the full text. Supporting Evidence: PMID:10525840 The gene BIO2, encoding a biotin synthase, is shown to be interrupted in this mutant. PMID:10525840 A Saccharomyces cerevisiae mutant affected in the last step of the biotin biosynthesis pathway was isolated by using a transposon mutagenesis method. |
| GO:0004076 biotin synthase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways BIOTIN-SYNTHESIS-PWY assigns Bio2 to EC 2.8.1.6 (dethiobiotin + sulfur -> biotin). Correct. Supporting Evidence: file:yeast/BIO2/BIO2-uniprot.txt biotin + 2 5'-deoxyadenosine + 2 L-methionine + 2 oxidized [2Fe-2S]- |
| GO:0005739 mitochondrion | HDA PMID:14562095 Global analysis of protein localization in budding yeast. | ACCEPT | Summary: HDA from the genome-wide GFP localization study (Huh et al. 2003); Bio2 carries a predicted N-terminal mitochondrial transit peptide. Supporting Evidence: file:yeast/BIO2/BIO2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000269|PubMed:14562095}. |
| GO:0005739 mitochondrion | HDA PMID:24769239 Quantitative variations of the mitochondrial proteome and ph... | ACCEPT | Summary: HDA from quantitative mitochondrial proteomics of isolated mitochondria (Renvoise et al. 2014; abstract only). Agrees with the GFP data and the transit peptide. Supporting Evidence: PMID:24769239 we performed an overall quantitative proteomic and phosphoproteomic study of isolated mitochondria file:yeast/BIO2/BIO2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000269|PubMed:14562095}. |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: SubCell mapping from the UniProt 'Mitochondrion' location (from Huh et al. 2003). Correct. Supporting Evidence: file:yeast/BIO2/BIO2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000269|PubMed:14562095}. |
| GO:0005829 cytosol | RCA GO_REF:0000123 | REMOVE | Summary: YeastPathways default compartment for BIOTIN-SYNTHESIS-PWY. Bio2 is a transit-peptide-bearing protein localized to mitochondria by GFP and by mitochondrial proteomics; there is no evidence of cytosolic activity. Reason: Pathway-default compartment contradicted by experimental mitochondrial localization of this enzyme. Supporting Evidence: file:yeast/BIO2/BIO2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000269|PubMed:14562095}. |
| GO:0009102 biotin biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN000540961 (E. coli BioB, S. pombe bio2, Aspergillus BioB, Bio2). Correct; Bio2 performs the final step. Supporting Evidence: PMID:10525840 A Saccharomyces cerevisiae mutant affected in the last step of the biotin biosynthesis pathway was isolated by using a transposon mutagenesis method. |
| GO:0009102 biotin biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (ARBA, IPR024177, UniPathway UPA00078). Correct. Supporting Evidence: file:yeast/BIO2/BIO2-uniprot.txt PATHWAY: Cofactor biosynthesis; biotin biosynthesis; biotin from 7,8- |
| GO:0009102 biotin biosynthetic process | IMP PMID:10525840 Cloning of Schizosaccharomyces pombe bio2 by heterologous co... | ACCEPT | Summary: IMP from Phalip et al. 1999; bio2 insertion mutant is blocked in the last step of the biotin pathway. Supporting Evidence: PMID:10525840 A Saccharomyces cerevisiae mutant affected in the last step of the biotin biosynthesis pathway was isolated by using a transposon mutagenesis method. |
| GO:0009102 biotin biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways BIOTIN-SYNTHESIS-PWY. Correct. Supporting Evidence: PMID:10525840 A Saccharomyces cerevisiae mutant affected in the last step of the biotin biosynthesis pathway was isolated by using a transposon mutagenesis method. |
| GO:0051536 iron-sulfur cluster binding | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO from radical SAM signatures. Bio2 binds a [4Fe-4S] cluster (radical SAM) and a [2Fe-2S] cluster (sulfur donor) by similarity to E. coli BioB; correct but general. Reason: Following the RADICAL_SAM project rule for the generic domain-derived rows (projects/RADICAL_SAM.md): correct but general, and TOO_GENERAL does not apply because no more specific cluster term is asserted elsewhere in this review for the radical SAM cluster itself. UniProt records both a [4Fe-4S] radical SAM cluster and an auxiliary [2Fe-2S] cluster, so both descendants are given; this matches ECOLI/bioB and PSEPK/bioB. Proposed replacements: 4 iron, 4 sulfur cluster binding 2 iron, 2 sulfur cluster binding Supporting Evidence: file:yeast/BIO2/BIO2-uniprot.txt Note=Binds 1 [4Fe-4S] cluster. The cluster is coordinated with 3 file:yeast/BIO2/BIO2-uniprot.txt Note=Binds 1 [2Fe-2S] cluster. The cluster is coordinated with 3 |
| GO:0051537 2 iron, 2 sulfur cluster binding | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN000540961 seeded by E. coli BioB, whose [2Fe-2S] cluster is the sacrificial sulfur source for biotin. The coordinating Cys/Arg residues are annotated in Bio2 by similarity, supporting inheritance. Supporting Evidence: file:yeast/BIO2/BIO2-uniprot.txt Note=Binds 1 [2Fe-2S] cluster. The cluster is coordinated with 3 |
| GO:1904047 S-adenosyl-L-methionine binding | IC file:yeast/BIO2/BIO2-uniprot.txt | NEW | Summary: BIO2 binds S-adenosyl-L-methionine at the unique iron of its radical SAM [4Fe-4S] cluster and cleaves it to the 5'-deoxyadenosyl radical; two SAM are consumed per biotin formed. Reason: Not in GOA. Added under the RADICAL_SAM treatment rule, which treats GO:1904047 as a core cosubstrate-binding function of every radical SAM enzyme whose catalysis is established. This is a molecular function the protein itself performs, so the participation test is met directly: BIO2 binds SAM and cleaves it, rather than merely being required for a process that consumes it. UniProt's curated cofactor note records the exchangeable S-adenosyl-L-methionine on the radical SAM cluster and the entry's binding features name the 4Fe-4S-S-AdoMet ligand, so the claim rests on curated record content rather than on an electronic GO line. Coded IC because the inference is the reviewer's, drawn from that curated content and the established biotin synthase activity rather than from a SAM-binding assay on this protein. Comparator check, against GOA rather than against this project's own proposals: GOA does annotate GO:1904047 to radical SAM enzymes in exactly this role, by UniRule -- ECOLI/queE (UR000100349), ECOLI/moaA and PSEPK/moaA (UR000101305), METEA/pqqE and PSEPK/pqqE (UR000098303). So the absence here is patchy UniRule coverage, which rules happen to carry the term, not a GO convention against annotating a radical SAM enzyme's own cosubstrate. That is also why those five genes have an existing row to ACCEPT or MODIFY while this one needs a NEW row. Supporting Evidence: file:yeast/BIO2/BIO2-uniprot.txt Note=Binds 1 [4Fe-4S] cluster. The cluster is coordinated with 3 file:yeast/BIO2/BIO2-uniprot.txt cysteines and an exchangeable S-adenosyl-L-methionine file:yeast/BIO2/BIO2-uniprot.txt /ligand_note="4Fe-4S-S-AdoMet" |
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Download this section (compressed HTML)Q: Which mitochondrial Fe-S assembly factors and ferredoxin (Yah1) reductant supply Bio2, and is Bio2 single-turnover in vivo like E. coli BioB?
Experiment: Purify Bio2 and measure dethiobiotin-to-biotin conversion with Yah1/Arh1 as reductant; test biotin production in yah1 or isu-depleted strains fed dethiobiotin.
Biotin synthase; catalyzes the conversion of dethiobiotin to biotin, which is the last step of the biotin biosynthesis pathway; complements E. coli bioB mutant
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