erg-4 (NCU03006) encodes the Neurospora crassa sterol C-24 methyltransferase of the Erg6/SMT family. It is a class I-like S-adenosyl-L-methionine-dependent methyltransferase required for ergosterol biosynthesis; Neurospora erg-4 mutants are blocked at the C-24 methylation step and fail to make ergosterol. Erg-4 transfers a methyl group from S-adenosyl-L-methionine to lanosterol to form eburicol, placing the enzyme early in the filamentous-fungal route from lanosterol to ergosterol and distinguishing it from budding-yeast Erg6, whose curated substrate is zymosterol.
Definition: Catalysis of the reaction: lanosterol + S-adenosyl-L-methionine = eburicol + S-adenosyl-L-homocysteine + H(+).
Justification: Neurospora Erg-4 catalyzes the RHEA:52652 lanosterol-to-eburicol reaction. GO:0003838 sterol 24-C-methyltransferase activity is the right parent but is currently defined as the budding-yeast zymosterol-to-fecosterol reaction RHEA:21128.
Parent term: sterol 24-C-methyltransferase activity
Mappings:
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003838 sterol 24-C-methyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PTN002226525 is the eukaryotic sterol C-24 methyltransferase node containing fungal ERG6/erg-4 and plant SMT enzymes, and Q9P3R1 is a PTHR44068:SF1 member. The inherited activity is correct at the family level; Neurospora appears to use lanosterol rather than zymosterol, so a child term for the exact lanosterol-to-eburicol reaction would add useful substrate resolution. Reason: PAINT places the activity at the correct ancestral node: Q9P3R1 is in the same PTHR44068:SF1 sterol C-24 methyltransferase subfamily as S. cerevisiae Erg6, S. pombe erg6, C. albicans Erg6, Aspergillus fumigatus erg6, and Arabidopsis SMT1. GO:0003838 is currently defined as the RHEA:21128 zymosterol-to-fecosterol reaction, but PAINT uses it for the broader inherited sterol C-24 methyltransferase activity class. Retain the class-level term while proposing a lanosterol-specific child term for the Neurospora RHEA:52652 reaction. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002226525 SUPPORTS TRANSFER PTN002226525 supports conserved sterol C-24 methyltransferase activity across fungal and plant SMT enzymes. Supporting Evidence: PMID:154056 erg-4 has an inactive C-24 methyl transferase file:genes/NEUCR/erg-4/erg-4-uniprot.txt Reaction=lanosterol + S-adenosyl-L-methionine = eburicol + S-adenosyl- file:genes/NEUCR/erg-4/erg-4-uniprot.txt superfamily. Erg6/SMT family. file:interpro/panther/PTHR44068/PTHR44068-paint.tsv PTHR44068 PTN002226525 GO:0003838 F IBD false AGI_LocusCode:AT5G13710|CGD:CAL0000189580|SGD:S000004467 taxon:2759 20181004 file:interpro/panther/PTHR44068/PTHR44068-review.yaml PAINT places sterol 24-C-methyltransferase activity on the sterol SMT node that contains fungal Erg6 proteins and plant SMT1 |
| GO:0003838 sterol 24-C-methyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined automated annotation from a budding-yeast Erg6 source and an ARBA rule. It detects the correct Erg6/SMT activity class. Reason: The source yeast enzyme and the Neurospora target are both sterol C-24 methyltransferases. Budding-yeast Erg6 catalyzes zymosterol to fecosterol, whereas Neurospora Erg-4 catalyzes lanosterol to eburicol, but both reactions are sterol C-24 methyl transfers and the exact lanosterol term should be added as a GO:0003838 child when GO has one. Propagation Review Root cause: NO FAILURE CORE Sources checked: UniProtKB:P25087 Β· ERG6 SUPPORTS TRANSFER Yeast Erg6 supports sterol C-24 methyltransferase activity. ARBA:ARBA00088937 SUPPORTS TRANSFER The ARBA rule supports the conserved Erg6/SMT activity class. Supporting Evidence: file:genes/NEUCR/erg-4/erg-4-uniprot.txt Reaction=lanosterol + S-adenosyl-L-methionine = eburicol + S-adenosyl- PMID:154056 erg-4 has an inactive C-24 methyl transferase |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: IBA ER localization from PTN002226525. Sterol C-24 methyltransferases act in the endomembrane sterol pathway, and the ER is the conserved site for the downstream demethylation and desaturation steps that convert methylated sterol intermediates to ergosterol. Reason: No Neurospora-specific localization paper was found, but the PAINT placement is appropriately conservative: it asserts ER activity rather than the more lineage-variable lipid-droplet pool reported in budding yeast. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002226525 SUPPORTS TRANSFER The ER node covers Q9P3R1 and is consistent with fungal sterol biosynthesis. Supporting Evidence: file:genes/NEUCR/erg-4/erg-4-uniprot.txt PATHWAY: Steroid metabolism; ergosterol biosynthesis. file:interpro/panther/PTHR44068/PTHR44068-paint.tsv PTHR44068 PTN002226525 GO:0005783 C IBD false SGD:S000004467|UniProtKB:Q4FKJ2|dictyBase:DDB_G0288907 taxon:2759 20250904 file:interpro/panther/PTHR44068/PTHR44068-review.yaml ER localization is sound on the sterol SMT branch |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000107 | ACCEPT | Summary: Ensembl Compara transfer of the budding-yeast ER annotation. The location agrees with the PAINT ER annotation and with the expected site of fungal sterol biosynthesis. Reason: The same ER assertion is made by PAINT for the Q9P3R1-containing node. Supporting Evidence: file:genes/NEUCR/erg-4/erg-4-uniprot.txt PATHWAY: Steroid metabolism; ergosterol biosynthesis. |
| GO:0005811 lipid droplet | IEA GO_REF:0000107 | UNDECIDED | Summary: Ensembl Compara transfer of the S. cerevisiae lipid-droplet annotation. Budding yeast Erg6 is lipid-droplet enriched, but the fission-yeast review did not find equivalent evidence and no Neurospora Erg-4 localization study was found. Reason: A lipid-droplet pool is plausible for a neutral-lipid-associated sterol enzyme, but direct evidence is missing for Neurospora and the PAINT localization remains at ER rather than propagating budding-yeast lipid-droplet localization. Propagation Review Root cause: UNRESOLVED Sources checked: UniProtKB:P25087 Β· ERG6 UNRESOLVED Budding yeast supports the source location; conservation to Neurospora is untested. Supporting Evidence: file:genes/yeast/ERG6/ERG6-ai-review.yaml active on lipid droplets and in the ER |
| GO:0006694 steroid biosynthetic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the sterol methyltransferase C-terminal domain to the broad steroid biosynthetic process parent. Correct, but ergosterol biosynthetic process is the specific fungal sterol pathway for Erg-4. Reason: Erg-4 directly catalyzes sterol C-24 methylation on the route to ergosterol; replace the broad steroid-biosynthesis parent with the fungal ergosterol biosynthetic process. Proposed replacements: ergosterol biosynthetic process Supporting Evidence: file:genes/NEUCR/erg-4/erg-4-uniprot.txt PATHWAY: Steroid metabolism; ergosterol biosynthesis. |
| GO:0006696 ergosterol biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA ergosterol-biosynthesis annotation from fungal PTN000802684, seeded by Candida, S. pombe, and S. cerevisiae ERG6 genes. Neurospora erg-4 is the same fungal sterol C-24 methyltransferase step and erg-4 mutants are blocked in ergosterol production. Reason: This IBA is correctly placed within the fungal sterol C-24 methyltransferase clade and the direct Neurospora mutant evidence supports the pathway assignment. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000802684 SUPPORTS TRANSFER The fungal node transfers ergosterol biosynthesis to Q9P3R1 appropriately. Supporting Evidence: PMID:154056 None of the mutants was able to synthesize ergosterol PMID:41341311 Disruption of erg5 and erg6 or both yielded sterol-deficient mutants with ERG reductions of 77.8-79.5% compared to wild-type file:genes/NEUCR/erg-4/erg-4-uniprot.txt PATHWAY: Steroid metabolism; ergosterol biosynthesis. file:interpro/panther/PTHR44068/PTHR44068-paint.tsv PTHR44068 PTN000802684 GO:0006696 P IBD false CGD:CAL0000189580|PomBase:SPBC16E9.05|SGD:S000004467 taxon:4751 20181004 file:interpro/panther/PTHR44068/PTHR44068-review.yaml The fungal Erg6 branch produces C-24 methylated sterols on the route to ergosterol |
| GO:0006696 ergosterol biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: Combined automated ergosterol-biosynthesis annotation from ARBA and yeast and fission-yeast Erg6 sources. Correct for Neurospora erg-4. Reason: Although the route from lanosterol to ergosterol differs between budding yeast and Neurospora, C-24 methylation is a genuine step in the Neurospora ergosterol pathway. Supporting Evidence: PMID:154056 None of the mutants was able to synthesize ergosterol PMID:41341311 Disruption of erg5 and erg6 or both yielded sterol-deficient mutants with ERG reductions of 77.8-79.5% compared to wild-type file:genes/NEUCR/erg-4/erg-4-uniprot.txt PATHWAY: Steroid metabolism; ergosterol biosynthesis. |
| GO:0008168 methyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping to generic methyltransferase activity from Erg6/SMT signatures. True but much less specific than the sterol C-24 methyltransferase activity supported by the same family signatures. Reason: Replace this generic methyltransferase term with sterol 24-C-methyltransferase activity. Proposed replacements: sterol 24-C-methyltransferase activity Supporting Evidence: file:genes/NEUCR/erg-4/erg-4-uniprot.txt Reaction=lanosterol + S-adenosyl-L-methionine = eburicol + S-adenosyl- |
| GO:0008757 S-adenosylmethionine-dependent methyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the Methyltransf_11 SAM-dependent methyltransferase domain. Correct as the parent class, but too general for a core SMT enzyme. Reason: Replace this generic SAM-dependent methyltransferase parent with sterol 24-C-methyltransferase activity. Proposed replacements: sterol 24-C-methyltransferase activity Supporting Evidence: file:genes/NEUCR/erg-4/erg-4-uniprot.txt Reaction=lanosterol + S-adenosyl-L-methionine = eburicol + S-adenosyl- |
| GO:0016126 sterol biosynthetic process | IEA GO_REF:0000041 | MODIFY | Summary: UniPathway UPA00768 mapping to sterol biosynthesis. Ergosterol biosynthesis is the specific fungal sterol pathway, but the parent term is true and matches the broader PTN002226525 PAINT assertion for sterol C-24 methyltransferases. Reason: Erg-4 catalyzes a sterol methylation step in ergosterol biosynthesis; replace the broad sterol-biosynthesis parent with the specific fungal ergosterol biosynthetic process. Proposed replacements: ergosterol biosynthetic process Supporting Evidence: file:genes/NEUCR/erg-4/erg-4-uniprot.txt PATHWAY: Steroid metabolism; ergosterol biosynthesis. |
| GO:0042802 identical protein binding | IEA GO_REF:0000107 | UNDECIDED | Summary: Ensembl Compara transfer of the budding-yeast Erg6 self-interaction. The Neurospora enzyme may self-associate, but no Neurospora-specific interaction evidence or SMT oligomerization evidence for Q9P3R1 was found. Reason: Homomerization was experimentally observed for S. cerevisiae Erg6, but the functional relevance and conservation of identical protein binding to Neurospora Erg-4 are uncertain. Propagation Review Root cause: UNRESOLVED Sources checked: UniProtKB:P25087 Β· ERG6 UNRESOLVED The source self-interaction is accepted for yeast but has not been tested in Neurospora. Supporting Evidence: file:genes/yeast/ERG6/ERG6-ai-review.yaml detected an Erg6 homomer in vivo |
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Download this section (compressed HTML)Q: Does Neurospora Erg-4 methylate only lanosterol in vivo, or can it also use zymosterol or other C-24-unmethylated sterols under perturbed pathway conditions?
Q: Is Neurospora Erg-4 restricted to the ER, or does it also partition to lipid droplets as budding-yeast Erg6 does?
Experiment: Express Q9P3R1 and measure SAM-dependent methyl transfer to lanosterol, zymosterol, and related sterol acceptors, identifying products by GC-MS or LC-MS/MS.
Hypothesis: Neurospora Erg-4 directly catalyzes RHEA:52652, the methylation of lanosterol to eburicol.
Type: enzyme kinetics
Experiment: Tag erg-4 at the native locus and compare Erg-4 localization with ER and lipid-droplet markers under vegetative growth and azole-induced sterol stress.
Hypothesis: The ER is the principal site of Neurospora Erg-4 activity.
Type: fluorescence microscopy
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