5-Aminolevulinate (ALA) synthase (EC 2.3.1.37) of Saccharomyces cerevisiae, a homodimeric pyridoxal 5'-phosphate-dependent enzyme of the class-II aminotransferase fold that condenses glycine with succinyl-CoA to form 5-aminolevulinate, CO2 and CoA. This is the first committed step of tetrapyrrole biosynthesis, supplying ALA for both heme and siroheme; hem1 mutants are heme-deficient (lacking cytochromes, catalase and sterol synthesis) and methionine-requiring (lacking siroheme-containing sulfite reductase), and are rescued by exogenous ALA. Hem1 is nuclear-encoded, synthesized as a precursor with an N-terminal presequence, and imported into the mitochondrial matrix where it is processed. The purified enzyme is inhibited by hemin. Loading of its pyridoxal 5'-phosphate cofactor is stimulated by the mitochondrial AAA+ unfoldase ClpX (Mcx1), and cells lacking Mcx1 have reduced ALA and heme. HEM1 transcription is constitutive but is activated by the Hap2-Hap3 complex and shaped by further positive and negative control sites.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003870 5-aminolevulinate synthase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for 5-aminolevulinate synthase activity from ancestral node PTN000343737 (PTHR13693), whose IBD seeds include mouse ALAS1/2, S. pombe hem1, Candida HEM1 and Hem1 itself. Hem1 is in the ALAS clade (UniProt also places it in the ALAS-specific NCBIfam TIGR01821 family; its PTHR13693:SF102 subfamily name refers to a paralog and does not affect the node used here) and has its own direct biochemical evidence, so the inherited activity is correct. Supporting Evidence: file:yeast/HEM1/HEM1-uniprot.txt PANTHER; PTHR13693; CLASS II AMINOTRANSFERASE/8-AMINO-7-OXONONANOATE SYNTHASE; 1. file:yeast/HEM1/HEM1-uniprot.txt NCBIfam; TIGR01821; 5aminolev_synth; 1. file:yeast/HEM1/HEM1-uniprot.txt Reaction=succinyl-CoA + glycine + H(+) = 5-aminolevulinate + CO2 + CoA; PMID:6381051 5-Aminolevulinate synthase from yeast mitochondria has been purified to homogeneity for the first time. |
| GO:0003870 5-aminolevulinate synthase activity | IDA PMID:6381051 Isolation and properties of 5-aminolevulinate synthase from ... | ACCEPT | Summary: IDA from Volland & Felix 1984: ALA synthase purified to homogeneity from yeast mitochondria, PLP-dependent and inhibited by hemin. Defines the core activity. Supporting Evidence: PMID:6381051 5-Aminolevulinate synthase from yeast mitochondria has been purified to homogeneity for the first time. PMID:6381051 Pyridoxal 5'-phosphate has been shown to be an essential cofactor. |
| GO:0003870 5-aminolevulinate synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (IPR010961 ALAS, RHEA:12921, EC 2.3.1.37). Correct. Supporting Evidence: file:yeast/HEM1/HEM1-uniprot.txt Reaction=succinyl-CoA + glycine + H(+) = 5-aminolevulinate + CO2 + CoA; |
| GO:0003870 5-aminolevulinate synthase activity | IMP PMID:24173275 Cloning of the Ξ΄-aminolevulinic acid synthase structural gen... | ACCEPT | Summary: IMP from Arrese et al.: HEM1 cloned by complementation of a hem1 mutant; multicopy HEM1 raised ALA synthase activity 24-28-fold, showing that the gene encodes catalytically active ALAS. Accepted. Supporting Evidence: PMID:24173275 The yeast transformants, bearing the HEM1-containing plasmids pYe(HEM1), showed a 24-28 fold increase in Ξ΄-aminolevulinic acid synthase activity and in the intracellular content of Ξ΄-aminolevulinic acid (5-8 fold) as compared to wild type strains |
| GO:0003870 5-aminolevulinate synthase activity | IMP PMID:323256 Yeast mutants deficient in heme biosynthesis and a heme muta... | ACCEPT | Summary: IMP from Gollub et al. 1977: hem1 mutants lack ALA synthase activity and grow on ALA. Supporting Evidence: PMID:323256 hem1 mutants grew on delta-aminolevulinate and lacked delta-aminolevulinate synthase activity |
| GO:0003870 5-aminolevulinate synthase activity | IMP PMID:7035824 Genetic and biochemical characterization of mutants of Sacch... | ACCEPT | Summary: IMP from Urban-Grimal & Labbe-Bois 1981: one complementation group of heme-deficient mutants is specifically blocked in ALA synthase activity. Supporting Evidence: PMID:7035824 Six of the seven mutants were blocked in a different enzyme activity: 5-aminolevulinate synthase, porphobilinogen synthase, uroporphyrinogen I synthase, uroporphyrinogen decarboxylase, coproporphyrinogen III oxidase and ferrochelatase. |
| GO:0003870 5-aminolevulinate synthase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PWY3O-50, tetrapyrrole biosynthesis) for the glycine + succinyl-CoA -> ALA step. Correct and consistent with experimental data. Supporting Evidence: file:yeast/HEM1/HEM1-uniprot.txt Reaction=succinyl-CoA + glycine + H(+) = 5-aminolevulinate + CO2 + CoA; |
| GO:0003870 5-aminolevulinate synthase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PWY3O-69, superpathway of heme and siroheme biosynthesis). Correct; Hem1 supplies ALA for both heme and siroheme. Supporting Evidence: file:yeast/HEM1/HEM1-uniprot.txt Reaction=succinyl-CoA + glycine + H(+) = 5-aminolevulinate + CO2 + CoA; PMID:323256 Mutants in hem1, hem2, and hem3 had an additional requirement for methionine on synthetic medium supplemented with either heme or ergosterol and Tween 80, owing to a lack of sulfite reductase which contains siroheme |
| GO:0005739 mitochondrion | HDA PMID:16823961 Toward the complete yeast mitochondrial proteome: multidimen... | ACCEPT | Summary: HDA from the PROMITO mitochondrial proteome (Reinders et al. 2006). Organelle proteomics cannot resolve the sub-compartment, so under the organelle policy the root mitochondrion row is accepted; the matrix location is captured by the separate GO:0005759 rows. Supporting Evidence: PMID:16823961 A total of 851 different proteins (PROMITO dataset) were identified by use of multidimensional LC-MS/MS file:yeast/HEM1/HEM1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005739 mitochondrion | HDA PMID:24769239 Quantitative variations of the mitochondrial proteome and ph... | ACCEPT | Summary: HDA from the quantitative mitochondrial proteome of Renvoise et al. 2014. Whole-organelle proteomics; accepted at the organelle level, with the matrix captured by the GO:0005759 rows. Supporting Evidence: PMID:24769239 we performed an overall quantitative proteomic and phosphoproteomic study of isolated mitochondria |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA is_active_in mitochondrion from PTN000343737 (PTHR13693). Checked the IBD seeds: mammalian ALAS1/ALAS2, S. pombe hem1 and Hem1 itself are all mitochondrial enzymes, and Hem1 is imported into the matrix (PMID:3023841). The organelle claim holds; the matrix sub-compartment is captured by the GO:0005759 rows. Supporting Evidence: file:yeast/HEM1/HEM1-uniprot.txt PANTHER; PTHR13693; CLASS II AMINOTRANSFERASE/8-AMINO-7-OXONONANOATE SYNTHASE; 1. file:yeast/HEM1/HEM1-uniprot.txt NCBIfam; TIGR01821; 5aminolev_synth; 1. PMID:3023841 The enzyme is synthesized as a precursor in the cytoplasm and imported into the matrix of the mitochondria, where it is processed to its mature form. file:yeast/HEM1/HEM1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005759 mitochondrial matrix | EXP PMID:6381051 Isolation and properties of 5-aminolevulinate synthase from ... | ACCEPT | Summary: EXP from Volland & Felix 1984: ALAS purified from yeast mitochondria. The matrix assignment is consistent with the import and processing study (PMID:3023841). Accepted; the curator had the full text, which is not cached here. Supporting Evidence: PMID:6381051 5-Aminolevulinate synthase from yeast mitochondria has been purified to homogeneity for the first time. PMID:3023841 The enzyme is synthesized as a precursor in the cytoplasm and imported into the matrix of the mitochondria, where it is processed to its mature form. |
| GO:0005759 mitochondrial matrix | IDA PMID:3023841 The nine amino-terminal residues of delta-aminolevulinate sy... | ACCEPT | Summary: IDA from Keng et al. 1986: protease protection and subfractionation place Hem1 N-terminal fusions, and the processed enzyme, in the mitochondrial matrix. Supporting Evidence: PMID:3023841 The enzyme is synthesized as a precursor in the cytoplasm and imported into the matrix of the mitochondria, where it is processed to its mature form. |
| GO:0005759 mitochondrial matrix | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell mapping (SL-0170) for mitochondrial matrix, derived from the same experimental data. Correct. Supporting Evidence: file:yeast/HEM1/HEM1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005829 cytosol | RCA GO_REF:0000123 | REMOVE | Summary: Cytosol asserted by the YeastPathways-to-GO-CAM conversion for PWY3O-50 (tetrapyrrole biosynthesis). This is wrong for Hem1: ALA synthase is synthesized as a precursor in the cytoplasm but imported into and processed in the mitochondrial matrix, where it acts on mitochondrial succinyl-CoA. The cytosol 'is_active_in' assertion reflects a default compartment in the pathway model, not the enzyme's location. Reason: Hem1 is a mitochondrial matrix enzyme; cytosol is a pathway-model default contradicted by fractionation data. Supporting Evidence: PMID:3023841 The enzyme is synthesized as a precursor in the cytoplasm and imported into the matrix of the mitochondria, where it is processed to its mature form. file:yeast/HEM1/HEM1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005829 cytosol | RCA GO_REF:0000123 | REMOVE | Summary: Cytosol asserted by the YeastPathways-to-GO-CAM conversion for PWY3O-69 (superpathway of heme and siroheme biosynthesis). This is wrong for Hem1: ALA synthase is synthesized as a precursor in the cytoplasm but imported into and processed in the mitochondrial matrix, where it acts on mitochondrial succinyl-CoA. The cytosol 'is_active_in' assertion reflects a default compartment in the pathway model, not the enzyme's location. Reason: Hem1 is a mitochondrial matrix enzyme; cytosol is a pathway-model default contradicted by fractionation data. Supporting Evidence: PMID:3023841 The enzyme is synthesized as a precursor in the cytoplasm and imported into the matrix of the mitochondria, where it is processed to its mature form. file:yeast/HEM1/HEM1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0006783 heme biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for heme biosynthetic process (PTN000343737). Correct: ALA synthase catalyses the first committed step. Supporting Evidence: file:yeast/HEM1/HEM1-uniprot.txt PANTHER; PTHR13693; CLASS II AMINOTRANSFERASE/8-AMINO-7-OXONONANOATE SYNTHASE; 1. file:yeast/HEM1/HEM1-uniprot.txt NCBIfam; TIGR01821; 5aminolev_synth; 1. PMID:3023841 delta-Aminolevulinate synthase, the first enzyme in the heme biosynthetic pathway, is encoded by the nuclear gene HEM1. |
| GO:0006783 heme biosynthetic process | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA IEA for heme biosynthetic process. Correct for Hem1. Supporting Evidence: PMID:3023841 delta-Aminolevulinate synthase, the first enzyme in the heme biosynthetic pathway, is encoded by the nuclear gene HEM1. |
| GO:0006783 heme biosynthetic process | IMP PMID:323256 Yeast mutants deficient in heme biosynthesis and a heme muta... | ACCEPT | Summary: IMP from Gollub 1977: hem1 mutants are heme-deficient, lacking cytochromes and catalase unless supplied with heme or ALA. Supporting Evidence: PMID:323256 hem1 mutants grew on delta-aminolevulinate and lacked delta-aminolevulinate synthase activity |
| GO:0006783 heme biosynthetic process | IMP PMID:7035824 Genetic and biochemical characterization of mutants of Sacch... | ACCEPT | Summary: IMP from Urban-Grimal & Labbe-Bois 1981: hem1-class mutants blocked at ALA synthase are heme-deficient. Supporting Evidence: PMID:7035824 Six of the seven mutants were blocked in a different enzyme activity: 5-aminolevulinate synthase, porphobilinogen synthase, uroporphyrinogen I synthase, uroporphyrinogen decarboxylase, coproporphyrinogen III oxidase and ferrochelatase. |
| GO:0006783 heme biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PWY3O-69) for heme biosynthetic process. Correct. Supporting Evidence: PMID:3023841 delta-Aminolevulinate synthase, the first enzyme in the heme biosynthetic pathway, is encoded by the nuclear gene HEM1. |
| GO:0016740 transferase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro (IPR001917 aminotransferase class-II, PLP-binding site) mapping to the root 'transferase activity'. Correct but uninformative. Reason: Correct but too general: the specific reaction, 5-aminolevulinate synthase activity (GO:0003870), is an is_a descendant already carried by this gene. Proposed replacements: 5-aminolevulinate synthase activity Supporting Evidence: file:yeast/HEM1/HEM1-uniprot.txt Reaction=succinyl-CoA + glycine + H(+) = 5-aminolevulinate + CO2 + CoA; |
| GO:0030170 pyridoxal phosphate binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro IEA for pyridoxal phosphate binding. PLP is an experimentally demonstrated essential cofactor of yeast ALA synthase. Supporting Evidence: PMID:6381051 Pyridoxal 5'-phosphate has been shown to be an essential cofactor. file:yeast/HEM1/HEM1-uniprot.txt Name=pyridoxal 5'-phosphate |
| GO:0033014 tetrapyrrole biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro IEA (IPR010961) for tetrapyrrole biosynthetic process. Appropriate: ALA made by Hem1 is the precursor of both heme and siroheme, and hem1 mutants lack siroheme-dependent sulfite reductase (methionine auxotrophy). Supporting Evidence: PMID:323256 Mutants in hem1, hem2, and hem3 had an additional requirement for methionine on synthetic medium supplemented with either heme or ergosterol and Tween 80, owing to a lack of sulfite reductase which contains siroheme |
| GO:0033014 tetrapyrrole biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PWY3O-50 tetrapyrrole biosynthesis). Correct for the same reason; covers the siroheme branch that the heme term does not. Supporting Evidence: PMID:323256 Mutants in hem1, hem2, and hem3 had an additional requirement for methionine on synthetic medium supplemented with either heme or ergosterol and Tween 80, owing to a lack of sulfite reductase which contains siroheme |
| GO:1902117 positive regulation of organelle assembly | IMP PMID:32075909 "Labile" heme critically regulates mitochondrial biogenesis ... | MARK AS OVER ANNOTATED | Summary: IMP from Bouchez et al. 2020, who used a heme-deficient (hem1) strain as a tool to titrate cellular 'labile' heme with exogenous ALA and showed that heme controls mitochondrial biogenesis by stabilising the Hap4 co-activator. The regulatory agent is heme acting through the HAP complex; Hem1's contribution is to make the precursor of that signal. The effect on organelle assembly is a downstream, pleiotropic consequence of loss of heme rather than a regulatory activity of Hem1. Reason: Indirect consequence of heme deficiency; Hem1 performs no regulatory step in organelle assembly. Supporting Evidence: PMID:32075909 Taking advantage of a yeast strain deficient for heme production that enabled controlled modulation and monitoring of labile heme levels PMID:32075909 cellular labile heme is critical for the post-translational regulation of HAP complex activity |
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Download this section (compressed HTML)Q: Is the hemin inhibition of purified Hem1 physiologically relevant, given that yeast (unlike mammals) is thought to regulate heme synthesis mainly downstream of ALA (e.g. at Hem2/Hem3)?
Experiment: Measure ALA and heme flux in strains expressing hemin-insensitive Hem1 variants to test whether feedback inhibition of Hem1 contributes to heme homeostasis in vivo.
5-aminolevulinate synthase; catalyzes the first step in the heme biosynthetic pathway; an N-terminal signal sequence is required for localization to the mitochondrial matrix; expression is regulated by Hap2p-Hap3p; has a pyridoxal phosphate cofactor whose insertion is mediated by Mcx1p
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