FAU1 (YER183C) encodes 5,10-methenyltetrahydrofolate synthetase (MTHFS; 5-formyltetrahydrofolate cyclo-ligase, EC 6.3.3.2), a 211-residue member of the 5-formyltetrahydrofolate cyclo-ligase family. It catalyses the ATP-dependent, irreversible cyclisation of 5-formyltetrahydrofolate (folinic acid) to 5,10-methenyltetrahydrofolate, the only known enzymatic route by which 5-formyl-THF re-enters the one-carbon folate pool. 5-Formyl-THF is generated in vivo by a side reaction of serine hydroxymethyltransferase and acts as a storage form and inhibitor of folate-dependent enzymes; fau1 disruptants accumulate it ~4-fold, and FAU1 is required for folinic acid to satisfy the folate requirement of strains lacking de novo folate synthesis. The protein is detected in purified mitochondria by proteomics and homologues are cytosolic and mitochondrial, so it probably acts in both compartments.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT places cytoplasmic activity at the MTHFS family node (human MTHFS P49914 and plant/bacterial orthologues are cytosolic). Yeast-specific localisation evidence is mitochondrial (proteomics), but a cytosolic pool is plausible given the cytosolic folate cycle and no N-terminal targeting signal is annotated. Accept as inherited, consistent with homologues. Supporting Evidence: file:yeast/FAU1/FAU1-uniprot.txt Reaction=(6S)-5-formyl-5,6,7,8-tetrahydrofolate + ATP = (6R)-5,10- |
| GO:0005739 mitochondrion | HDA PMID:14576278 The proteome of Saccharomyces cerevisiae mitochondria. | ACCEPT | Summary: Fau1 was identified in the high-coverage mass-spectrometry proteome of highly purified yeast mitochondria (Sickmann et al. 2003); UniProt uses this as its location evidence. Supporting Evidence: PMID:14576278 The proteins of highly pure yeast mitochondria were separated by several independent methods and analyzed by tandem MS. file:yeast/FAU1/FAU1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000269|PubMed:14576278}. |
| GO:0005739 mitochondrion | HDA PMID:16823961 Toward the complete yeast mitochondrial proteome: multidimen... | ACCEPT | Summary: Independent mitochondrial proteomics dataset (PROMITO, Reinders et al. 2006) also contains Fau1, corroborating mitochondrial association. Supporting Evidence: PMID:16823961 The most complete overview was achieved by a combination of such orthogonal techniques as shown by the analysis of the yeast mitochondrial proteome. |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT mitochondrial node (PTN000601269) including human MTHFS, which has a mitochondrial pool; consistent with yeast proteomic detection of Fau1 in mitochondria. Supporting Evidence: file:yeast/FAU1/FAU1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000269|PubMed:14576278}. |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (SL-0173) derived from the mitochondrial proteome evidence; correct and redundant with the HDA rows. Supporting Evidence: file:yeast/FAU1/FAU1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000269|PubMed:14576278}. |
| GO:0005829 cytosol | RCA GO_REF:0000123 | KEEP AS NON CORE | Summary: YeastPathways (PWY-2201 folate transformations) defaults the enzyme to the cytosol. There is no yeast experimental evidence for a cytosolic pool (the only localisation data are mitochondrial proteomics), although orthologues are cytosolic. Retain as plausible but not established. Reason: Pathway-default compartment without yeast-specific localisation evidence; mitochondrion is the experimentally supported location. Supporting Evidence: file:yeast/FAU1/FAU1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000269|PubMed:14576278}. |
| GO:0009396 folic acid-containing compound biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: Inherited from the MTHFS family node with yeast FAU1 itself as the experimental source. MTHFS converts 5-formyl-THF to 5,10-methenyl-THF, regenerating an active folate cofactor; this is formally within folate-derivative biosynthesis (the more precise parent concept is tetrahydrofolate interconversion, also annotated). Supporting Evidence: PMID:11923304 when the MTHFS gene was disrupted in a strain lacking the de novo folate biosynthesis pathway, folinic acid (5-CHO-THF) could no longer support the folate requirement |
| GO:0009396 folic acid-containing compound biosynthetic process | IDA PMID:11923304 Cloning and characterization of methenyltetrahydrofolate syn... | ACCEPT | Summary: Holmes & Appling 2002 purified recombinant Fau1 with MTHFS kinetics and showed FAU1 is required for folinic acid to support growth of folate-auxotrophic yeast, i.e. Fau1 produces active folate from 5-CHO-THF. Correct, though GO:0035999 tetrahydrofolate interconversion captures the step more precisely. Supporting Evidence: PMID:11923304 when the MTHFS gene was disrupted in a strain lacking the de novo folate biosynthesis pathway, folinic acid (5-CHO-THF) could no longer support the folate requirement PMID:11923304 The yeast enzyme was expressed in Escherichia coli, and the purified recombinant enzyme exhibited kinetics similar to previously purified MTHFS. |
| GO:0030272 5-formyltetrahydrofolate cyclo-ligase activity | IBA GO_REF:0000033 | ACCEPT | Summary: MTHFS activity is conserved across the family (human, E. coli YgfA P0AC28, Arabidopsis) and yeast Fau1 has direct biochemical evidence. Core MF. Supporting Evidence: PMID:11923304 The yeast enzyme was expressed in Escherichia coli, and the purified recombinant enzyme exhibited kinetics similar to previously purified MTHFS. file:yeast/FAU1/FAU1-uniprot.txt Reaction=(6S)-5-formyl-5,6,7,8-tetrahydrofolate + ATP = (6R)-5,10- |
| GO:0030272 5-formyltetrahydrofolate cyclo-ligase activity | IDA PMID:11923304 Cloning and characterization of methenyltetrahydrofolate syn... | ACCEPT | Summary: Purified recombinant Fau1 catalysed 5-formyl-THF cyclo-ligation with kinetics similar to mammalian MTHFS (Km 33 uM 5-CHO-THF, 43 uM ATP per UniProt). Core MF. Supporting Evidence: PMID:11923304 The yeast enzyme was expressed in Escherichia coli, and the purified recombinant enzyme exhibited kinetics similar to previously purified MTHFS. file:yeast/FAU1/FAU1-uniprot.txt Reaction=(6S)-5-formyl-5,6,7,8-tetrahydrofolate + ATP = (6R)-5,10- |
| GO:0030272 5-formyltetrahydrofolate cyclo-ligase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA from RHEA:10488 / EC 6.3.3.2; mapping is correct for Fau1 and redundant with IDA. Supporting Evidence: file:yeast/FAU1/FAU1-uniprot.txt Reaction=(6S)-5-formyl-5,6,7,8-tetrahydrofolate + ATP = (6R)-5,10- |
| GO:0030272 5-formyltetrahydrofolate cyclo-ligase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways PWY-2201 assigns the 5-formyl-THF -> 5,10-methenyl-THF step (EC 6.3.3.2) to Fau1, which is correct. Supporting Evidence: PMID:11923304 The yeast enzyme was expressed in Escherichia coli, and the purified recombinant enzyme exhibited kinetics similar to previously purified MTHFS. |
| GO:0035999 folate cycle | IBA GO_REF:0000033 | ACCEPT | Summary: Tetrahydrofolate interconversion (GOA label 'folate cycle'): MTHFS returns 5-formyl-THF to the interconverting one-carbon THF pool as 5,10-methenyl-THF. Appropriate core process. Supporting Evidence: PMID:11923304 when the MTHFS gene was disrupted in a strain lacking the de novo folate biosynthesis pathway, folinic acid (5-CHO-THF) could no longer support the folate requirement PMID:11923304 In fau1 disruptants, 5-CHO-THF was elevated 4-fold over wild-type yeast. |
| GO:0035999 folate cycle | RCA GO_REF:0000123 | ACCEPT | Summary: Same process from YeastPathways PWY-2201 (folate transformations); correct for Fau1. Supporting Evidence: PMID:11923304 In fau1 disruptants, 5-CHO-THF was elevated 4-fold over wild-type yeast. |
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Download this section (compressed HTML)Q: Does Fau1 have a cytosolic pool in addition to the mitochondrial pool detected by proteomics, and how is dual targeting achieved without an annotated presequence?
Q: Is the AICAR-dependent methionine deficiency of fau1 ade16 ade17 strains caused by 5-formyl-THF inhibition of a specific folate-dependent enzyme (e.g. Met13/Met6)?
Experiment: Fluorescent-protein tagging at the endogenous FAU1 locus plus subcellular fractionation to quantify cytosolic vs mitochondrial Fau1.
5,10-methenyltetrahydrofolate synthetase; involved in folic acid biosynthesis
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