Ketol-acid reductoisomerase (acetohydroxy-acid reductoisomerase, KARI; EC 1.1.1.86) of fission yeast, encoded by SPBC56F2.12 and orthologous to S. cerevisiae ILV5 and bacterial IlvC. Using NADPH and Mg2+, it isomerises and reduces 2-acetolactate to 2,3-dihydroxy-3-methylbutanoate (valine and leucine precursor) and 2-aceto-2-hydroxybutanoate to 2,3-dihydroxy-3-methylpentanoate (isoleucine precursor). This is the second step of the shared branched-chain amino acid trunk. The protein carries an N-terminal mitochondrial presequence and localises to mitochondria, where it acts in the matrix with acetohydroxy-acid synthase (ilv1/ilv6) and dihydroxy-acid dehydratase (ilv3). The mtDNA nucleoid-stabilising role described for S. cerevisiae Ilv5 has not been investigated in S. pombe.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004455 ketol-acid reductoisomerase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN000483120 (seeded by E. coli IlvC, S. cerevisiae ILV5 and other KARIs). ilv5 is a canonical fungal KARI (IPR016207, TIGR00465) and the predicted S. pombe acetohydroxy-acid reductoisomerase. Core MF. Supporting Evidence: file:SCHPO/ilv5/ilv5-uniprot.txt Reaction=(2R)-2,3-dihydroxy-3-methylbutanoate + NADP(+) = (2S)-2- file:SCHPO/ilv5/ilv5-uniprot.txt SIMILARITY: Belongs to the ketol-acid reductoisomerase family. PMID:35325114 by acetohydroxyacid reductoisomerase, which is predicted to be encoded by ilv5+ |
| GO:0004455 ketol-acid reductoisomerase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (InterPro KARI signatures, RHEA:22068, EC 1.1.1.86) for ketol-acid reductoisomerase activity; correct. Supporting Evidence: file:SCHPO/ilv5/ilv5-uniprot.txt Reaction=(2R)-2,3-dihydroxy-3-methylbutanoate + NADP(+) = (2S)-2- |
| GO:0005739 mitochondrion | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: ORFeome-wide YFP localisation placed ilv5 in mitochondria, consistent with its N-terminal presequence and the mitochondrial KARI of S. cerevisiae. Supporting Evidence: PMID:35325114 Like ALS, the protein encoded by ilv5+ is localized in the mitochondria (Matsuyama et al. 2006). |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA (PTN001085749, seeded by S. cerevisiae ILV5) for mitochondrial location; agrees with the S. pombe HDA. Supporting Evidence: PMID:35325114 Like ALS, the protein encoded by ilv5+ is localized in the mitochondria (Matsuyama et al. 2006). file:SCHPO/ilv5/ilv5-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000250}. |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (Mitochondrion, by similarity); consistent with the HDA. Supporting Evidence: file:SCHPO/ilv5/ilv5-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000250}. |
| GO:0005759 mitochondrial matrix | IC GO_REF:0000111 | ACCEPT | Summary: PomBase curator inference (from GO:0004455) that KARI acts in the mitochondrial matrix, where the soluble BCAA trunk enzymes reside in fungi; this is the location used in the PomBase GO-CAM. Supporting Evidence: PMID:35325114 Like ALS, the protein encoded by ilv5+ is localized in the mitochondria (Matsuyama et al. 2006). |
| GO:0005759 mitochondrial matrix | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA rule for mitochondrial matrix; consistent with the curator IC and with the matrix location of fungal KARI. Supporting Evidence: file:SCHPO/ilv5/ilv5-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000250}. |
| GO:0006551 L-leucine metabolic process | ISS GO_REF:0000024 | MODIFY | Summary: ISS from S. cerevisiae ILV5 (P06168) to L-leucine metabolic process. KARI produces 2,3-dihydroxy-3-methylbutanoate, the precursor of 2-oxoisovalerate, which is the start of the leucine branch; the relevant process is leucine biosynthesis, not generic leucine metabolism. The PomBase GO-CAM uses this same term on its leucine-branch ilv5 activity. Reason: Direction is biosynthetic; replace with the more specific L-leucine biosynthetic process. Proposed replacements: L-leucine biosynthetic process Supporting Evidence: PMID:35325114 Because all the enzymes that act in Ile and Val biosynthesis are also required for Leu biosynthesis, there are Leu auxotrophic strains but not auxotrophic strains that require only Ile or Val. PMID:35325114 by acetohydroxyacid reductoisomerase, which is predicted to be encoded by ilv5+ |
| GO:0009082 branched-chain amino acid biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro KARI mapping to branched-chain amino acid biosynthesis; correct. Supporting Evidence: file:SCHPO/ilv5/ilv5-uniprot.txt SIMILARITY: Belongs to the ketol-acid reductoisomerase family. PMID:35325114 by acetohydroxyacid reductoisomerase, which is predicted to be encoded by ilv5+ |
| GO:0009099 L-valine biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA (PTN000483120) for L-valine biosynthesis; ilv5 catalyses step 2/4 of valine synthesis. Supporting Evidence: file:SCHPO/ilv5/ilv5-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-valine biosynthesis; L-valine from PMID:35325114 by acetohydroxyacid reductoisomerase, which is predicted to be encoded by ilv5+ |
| GO:0009099 L-valine biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: UniPathway mapping (L-valine biosynthesis step 2/4); correct. Supporting Evidence: file:SCHPO/ilv5/ilv5-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-valine biosynthesis; L-valine from |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro (IPR013023, KARI) mapping to the generic oxidoreductase activity; true (NADPH-dependent reduction) but uninformative. Reason: Replace with the specific activity, as done for S. cerevisiae ILV5. Proposed replacements: ketol-acid reductoisomerase activity Supporting Evidence: file:SCHPO/ilv5/ilv5-uniprot.txt Reaction=(2R)-2,3-dihydroxy-3-methylbutanoate + NADP(+) = (2S)-2- |
| GO:1901705 L-isoleucine biosynthetic process | TAS PMID:35325114 Response to leucine in Schizosaccharomyces pombe (fission ye... | NEW | Summary: KARI also converts (S)-2-aceto-2-hydroxybutanoate to (2R,3R)-2,3-dihydroxy-3-methylpentanoate, step 2/4 of isoleucine synthesis (UniProt pathway; second Rhea reaction). GOA has valine but no isoleucine process for ilv5, although the PomBase GO-CAM places ilv5 activity part_of GO:1901705. ilv5 itself catalyses this step, so this is participation. Reason: ilv5 performs the reductoisomerase step of the isoleucine branch. Supporting Evidence: PMID:35325114 by acetohydroxyacid reductoisomerase, which is predicted to be encoded by ilv5+ file:SCHPO/ilv5/ilv5-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-isoleucine biosynthesis; L- PMID:35325114 it has been confirmed that at least the reaction using (S)-2-aceto-2-hydroxybutanoate as a substrate requires Mg2+ in S. pombe |
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Download this section (compressed HTML)Q: Does S. pombe ilv5, like S. cerevisiae Ilv5, associate with mitochondrial nucleoids and contribute to mtDNA stability, or is that moonlighting role specific to budding yeast?
Experiment: Delete ilv5 and test branched-chain amino acid auxotrophy and mtDNA maintenance (rho0 frequency, nucleoid imaging), and measure NADPH-dependent KARI activity of recombinant ilv5 on both acetohydroxy-acid substrates.
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