Acetohydroxyacid synthase (acetolactate synthase, EC 2.2.1.6) catalytic subunit of Schizosaccharomyces pombe (SPBP35G2.07, PomBase ilv1), the ortholog of S. cerevisiae Ilv2 (not of S. cerevisiae Ilv1). This thiamine diphosphate-, Mg2+- and FAD-dependent enzyme condenses two pyruvates to 2-acetolactate (valine and leucine branch) or pyruvate and 2-oxobutanoate to 2-aceto-2-hydroxybutanoate (isoleucine branch), the first shared step of branched-chain amino acid synthesis. S. pombe ilv1 complements a S. cerevisiae ilv2 deletion, and the S. pombe enzyme is feedback-inhibited by valine. It has a mitochondrial transit peptide and acts in the mitochondrial matrix.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000287 magnesium ion binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro2GO (TPP enzyme / AHAS large-subunit signatures) to magnesium ion binding; AHAS binds one Mg2+ per subunit to anchor thiamine diphosphate. Correct, non-core. Reason: Cofactor binding. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt Note=Binds 1 Mg(2+) ion per subunit. |
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO (IPR011766, TPP enzyme TPP-binding domain) to generic 'catalytic activity'. True but uninformative; the specific activity is acetolactate synthase. Proposed replacements: acetolactate synthase activity Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt Reaction=2 pyruvate + H(+) = (2S)-2-acetolactate + CO2; |
| GO:0003984 acetolactate synthase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA (PTN000438682) for acetolactate synthase, with S. pombe ilv1 itself among the sources (its own IDA/IGI, expected rather than circular) together with S. cerevisiae Ilv2, E. coli and plant AHAS. Correct. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt Reaction=2 pyruvate + H(+) = (2S)-2-acetolactate + CO2; PMID:8299177 The putative ilv1 isolated from S. pombe was shown to encode a functional subunit of acetolactate synthase by complementation of an S. cerevisiae strain deleted for the ILV2 locus. |
| GO:0003984 acetolactate synthase activity | IDA PMID:4698210 Biosynthesis of branched-chain amino acids in Schizosaccharo... | ACCEPT | Summary: AHAS activity partially purified from S. pombe extracts and characterised kinetically (pH optimum 6.5, valine feedback inhibition). The gene attribution is the curator's; ilv1 is the AHAS catalytic subunit. Accept. Supporting Evidence: PMID:4698210 the first enzyme in the biosynthetic pathway to valine and the second in the isoleucine pathway PMID:4698210 high sensitivity to feedback inhibition by valine at this pH |
| GO:0003984 acetolactate synthase activity | IDA PMID:4821071 Biosynthesis of branched-chain amino acids in Schizosaccharo... | ACCEPT | Summary: McDonald et al. (1974) studied regulation of the S. pombe isoleucine/valine/leucine enzymes; the cached record has no abstract, so the assay cannot be checked here. The companion paper (PMID:4698210) shows AHAS activity in S. pombe extracts. Deferring to the PomBase curator. Supporting Evidence: PMID:4698210 the first enzyme in the biosynthetic pathway to valine and the second in the isoleucine pathway file:SCHPO/ilv1/ilv1-uniprot.txt Reaction=2 pyruvate + H(+) = (2S)-2-acetolactate + CO2; |
| GO:0003984 acetolactate synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (ARBA, InterPro IPR012846 acetolactate synthase large subunit, RHEA:25249, EC 2.2.1.6). Correct. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt Reaction=2 pyruvate + H(+) = (2S)-2-acetolactate + CO2; |
| GO:0003984 acetolactate synthase activity | IGI PMID:8299177 Isolation and structure of an acetolactate synthase gene fro... | ACCEPT | Summary: S. pombe ilv1 complements a S. cerevisiae ilv2 deletion, showing it encodes a functional AHAS subunit. Accept. Supporting Evidence: PMID:8299177 The putative ilv1 isolated from S. pombe was shown to encode a functional subunit of acetolactate synthase by complementation of an S. cerevisiae strain deleted for the ILV2 locus. |
| GO:0005739 mitochondrion | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: Mitochondrial YFP signal in the ORFeome screen; agrees with the transit peptide. Accept. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (SL-0173 Mitochondrion); ilv1 has a 140-residue N-terminal transit peptide. Correct. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion. file:SCHPO/ilv1/ilv1-uniprot.txt FT TRANSIT 1..140 |
| GO:0005759 mitochondrial matrix | IC GO_REF:0000111 | ACCEPT | Summary: PomBase IC (from GO:0003984) for mitochondrial matrix; the PomBase GO-CAM gomodel:6690711d00002706 places both ilv1 activities in the matrix. Consistent with the transit peptide. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt FT TRANSIT 1..140 file:SCHPO/ilv1/ilv1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion. |
| GO:0005948 acetolactate synthase complex | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA (PTN000438758) for the acetolactate synthase complex, seeded by S. cerevisiae Ilv2 (SGD:S000004714) and E. coli AHAS large subunits. AHAS catalytic subunits act with a small regulatory subunit (Ilv6 in budding yeast); no S. pombe complex data were found, but the inherited assignment is reasonable. Supporting Evidence: PMID:8299177 The putative ilv1 isolated from S. pombe was shown to encode a functional subunit of acetolactate synthase by complementation of an S. cerevisiae strain deleted for the ILV2 locus. file:SCHPO/ilv1/ilv1-uniprot.txt Reaction=2 pyruvate + H(+) = (2S)-2-acetolactate + CO2; |
| GO:0009082 branched-chain amino acid biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: ARBA/InterPro mapping to branched-chain amino acid biosynthesis. Correct: AHAS supplies precursors of valine, leucine and isoleucine. Parent of the more specific valine/isoleucine terms, but an accurate summary of the shared step. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-isoleucine biosynthesis; L- file:SCHPO/ilv1/ilv1-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-valine biosynthesis; L-valine from |
| GO:0009098 L-leucine biosynthetic process | IC PMID:8299177 Isolation and structure of an acetolactate synthase gene fro... | ACCEPT | Summary: PomBase IC (from acetolactate synthase activity) for L-leucine biosynthesis. Acetolactate is converted to 2-oxoisovalerate, the branch point for valine and leucine, so AHAS catalyses the first step of the shared valine/leucine trunk; this matches the PomBase GO-CAM, which models one ilv1 activity part_of leucine biosynthesis. Accept. Supporting Evidence: PMID:8299177 The putative ilv1 isolated from S. pombe was shown to encode a functional subunit of acetolactate synthase by complementation of an S. cerevisiae strain deleted for the ILV2 locus. file:SCHPO/ilv1/ilv1-uniprot.txt Reaction=2 pyruvate + H(+) = (2S)-2-acetolactate + CO2; |
| GO:0009099 L-valine biosynthetic process | EXP PMID:4698210 Biosynthesis of branched-chain amino acids in Schizosaccharo... | ACCEPT | Summary: The paper identifies AHAS as the first enzyme of the valine pathway and shows strong valine feedback inhibition. Accept. Supporting Evidence: PMID:4698210 the first enzyme in the biosynthetic pathway to valine and the second in the isoleucine pathway PMID:4698210 high sensitivity to feedback inhibition by valine at this pH |
| GO:0009099 L-valine biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for L-valine biosynthesis; AHAS is the first enzyme of the valine pathway. Correct. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-valine biosynthesis; L-valine from PMID:4698210 the first enzyme in the biosynthetic pathway to valine and the second in the isoleucine pathway |
| GO:0009099 L-valine biosynthetic process | IDA PMID:4821071 Biosynthesis of branched-chain amino acids in Schizosaccharo... | ACCEPT | Summary: Same 1974 study, cited for valine biosynthesis; text unavailable. Valine feedback inhibition of S. pombe AHAS (PMID:4698210) supports involvement in valine synthesis. Deferring to the curator. Supporting Evidence: PMID:4698210 high sensitivity to feedback inhibition by valine at this pH file:SCHPO/ilv1/ilv1-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-valine biosynthesis; L-valine from |
| GO:0009099 L-valine biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: UniPathway UPA00049 mapping; AHAS is step 1/4 of L-valine synthesis from pyruvate. Correct. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-valine biosynthesis; L-valine from |
| GO:0030976 thiamine pyrophosphate binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro2GO (TPP enzyme signatures) to thiamine pyrophosphate binding; ilv1 binds one ThDP per subunit (by similarity). Correct cofactor binding, non-core. Reason: Catalytic cofactor binding. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt Note=Binds 1 thiamine pyrophosphate per subunit. |
| GO:0050660 flavin adenine dinucleotide binding | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PAINT IBA for FAD binding (seeded by S. cerevisiae Ilv2 and E. coli). AHAS requires FAD as a non-redox structural cofactor. Correct cofactor binding, non-core (as for S. cerevisiae ILV2). Reason: By similarity and family membership: UniProt places three FAD-binding regions on ilv1 by similarity (ECO:0000250), and ilv1 is in the acetolactate synthase large-subunit family (InterPro IPR012846; NCBIfam acolac_lg), whose members bind FAD; it descends from the PAINT node seeded by S. cerevisiae Ilv2 and E. coli IlvB. No S. pombe FAD assay. FAD is a structural, non-redox cofactor of AHAS, so non-core. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt BINDING 351..372 FT /ligand="FAD" file:SCHPO/ilv1/ilv1-uniprot.txt IPR012846; Acetolactate_synth_lsu. file:SCHPO/ilv1/ilv1-uniprot.txt TIGR00118; acolac_lg |
| GO:0050660 flavin adenine dinucleotide binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro2GO (IPR012846) to FAD binding; consistent with the by-similarity FAD-binding sites. Non-core. Reason: Family membership: ilv1 matches the acetolactate synthase large-subunit signature (IPR012846) behind this mapping, and UniProt places FAD-binding regions on it by similarity (ECO:0000250). No S. pombe assay. FAD is a structural cofactor of AHAS, so non-core, consistent with the IBA row. Supporting Evidence: file:SCHPO/ilv1/ilv1-uniprot.txt IPR012846; Acetolactate_synth_lsu. file:SCHPO/ilv1/ilv1-uniprot.txt BINDING 403..422 FT /ligand="FAD" |
| GO:1901705 L-isoleucine biosynthetic process | EXP PMID:4698210 Biosynthesis of branched-chain amino acids in Schizosaccharo... | ACCEPT | Summary: AHAS is the second enzyme of the isoleucine pathway (condensing pyruvate with 2-oxobutanoate). Accept. Supporting Evidence: PMID:4698210 the first enzyme in the biosynthetic pathway to valine and the second in the isoleucine pathway file:SCHPO/ilv1/ilv1-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-isoleucine biosynthesis; L- |
| GO:1901705 L-isoleucine biosynthetic process | IGI PMID:8299177 Isolation and structure of an acetolactate synthase gene fro... | ACCEPT | Summary: Complementation of the ilv2 deletion (which requires isoleucine and valine) shows ilv1 can supply the AHAS step of isoleucine synthesis. Accept. Supporting Evidence: PMID:8299177 The putative ilv1 isolated from S. pombe was shown to encode a functional subunit of acetolactate synthase by complementation of an S. cerevisiae strain deleted for the ILV2 locus. file:SCHPO/ilv1/ilv1-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-isoleucine biosynthesis; L- |
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Download this section (compressed HTML)Q: Does S. pombe have an Ilv6-like regulatory small subunit that confers the valine feedback sensitivity measured in extracts, and does ilv1 form a complex with it?
Q: Does the valine feedback inhibition seen in S. pombe extracts reside in ilv1 alone or require a small subunit?
Experiment: Co-purify tagged ilv1 from mitochondria to identify a regulatory subunit; reconstitute AHAS activity and valine inhibition with recombinant proteins.
Type: biochemistry
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