erg31 (SPAC1687.16c; synonym erg3) encodes one of two Delta7-sterol C-5 desaturases of Schizosaccharomyces pombe, a non-heme di-iron enzyme of the sterol desaturase family with histidine boxes and several transmembrane segments, homologous to budding-yeast Erg3 and animal SC5D. Using O2 and electrons from cytochrome b5 it introduces the C5=C6 double bond into episterol to form 5-dehydroepisterol in the ER membrane. erg31 and its paralog erg32 are functionally redundant: either single deletion still allows ergosterol synthesis, whereas the double deletion abolishes it. erg31 expression is induced under anaerobic conditions by the SREBP Sre1.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000248 C-5 sterol desaturase activity | IBA GO_REF:0000033 | MODIFY | Summary: IBA from the sterol C5-desaturase node PTN000221192 (human SC5D, rat Sc5d, C. albicans and S. cerevisiae ERG3). The inherited biology (Delta7-sterol C-5 desaturation) is correct for erg31, which with its paralog erg32 supplies the redundant C-5 desaturase of S. pombe. However GO:0000248 "C-5 sterol desaturase activity" has a text definition (5,7,24(28)-ergostatrienol + O2 + NADPH -> 5,7,22,24(28)-ergostatetraenol) that describes the C-22 desaturation catalysed by erg5 (cf. GO:0000249), not the C-5 reaction. GO:0050046 delta7-sterol 5(6)-desaturase activity (Rhea:54320, EC 1.14.19.20) matches the reaction UniProt assigns and is already annotated by IBA/IEA. Same decision as for S. cerevisiae ERG3. Reason: Intended activity is correct but the GO:0000248 definition describes the C-22 desaturase reaction; use the term whose definition matches the C-5 reaction. Propagation Review Root cause: TERM SCOPING PROBLEM Sources checked: PANTHER:PTN000221192 Β· PTN000221192 SUPPORTS TRANSFER Node placement (sterol C5-desaturase clade incl. human SC5D, S. cerevisiae ERG3) is sound; the problem is that the GO:0000248 definition describes the C-22 desaturase reaction. Proposed replacements: delta7-sterol 5(6)-desaturase activity Supporting Evidence: file:SCHPO/erg31/erg31-uniprot.txt Reaction=episterol + 2 Fe(II)-[cytochrome b5] + O2 + 2 H(+) = 5- |
| GO:0005506 iron ion binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro2GO iron ion binding from the fatty acid hydroxylase/sterol desaturase domain (His-box di-iron centre); UniProt lists Fe cation as cofactor by similarity. Correct cofactor statement, not the function. Reason: Cofactor binding; non-core. Supporting Evidence: file:SCHPO/erg31/erg31-uniprot.txt Name=Fe cation; Xref=ChEBI:CHEBI:24875; |
| GO:0005783 endoplasmic reticulum | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: ORFeome YFP localisation (Matsuyama et al. 2006) detected erg31 in the ER; consistent with an ER-membrane sterol desaturase. Supporting Evidence: PMID:16823372 Next, we determined the localization of 4,431 proteins, corresponding to |
| GO:0005789 endoplasmic reticulum membrane | IBA GO_REF:0000033 | ACCEPT | Summary: IBA ER membrane from the sterol desaturase family; S. cerevisiae Erg3 is an ER-membrane glycoprotein and PomBase models erg31/erg32 activity in the ER membrane. Supporting Evidence: PMID:16823372 Next, we determined the localization of 4,431 proteins, corresponding to |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell mapping (ER membrane, multi-pass); correct and most specific location. Supporting Evidence: file:SCHPO/erg31/erg31-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005794 Golgi apparatus | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | KEEP AS NON CORE | Summary: The ORFeome screen also scored a Golgi signal for erg31-YFP. Proteins of the late sterol pathway act in the ER; a Golgi pool could reflect overexpression, ER-Golgi trafficking or punctate ER exit sites. The high-throughput call cannot be checked from the abstract, so it is retained as non-core rather than removed. Reason: High-throughput secondary location; catalytic site is the ER membrane. Supporting Evidence: PMID:16823372 Next, we determined the localization of 4,431 proteins, corresponding to |
| GO:0006696 ergosterol biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA ergosterol biosynthetic process from the sterol C5-desaturase clade; supported for erg31 by the erg31 erg32 double-deletion phenotype. Supporting Evidence: PMID:18310029 Disruption of erg31(+) or erg32(+) did not cause ergosterol deficiency or tolerance to polyene drugs, indicating that the two C-5 sterol desaturases have overlapping functions. PMID:23145048 On the other hand, in Ξerg6 cells, Ξerg31Ξerg32 cells, and Ξerg5 cells, the ergosterol levels were extremely lower than that in wild-type cells |
| GO:0006696 ergosterol biosynthetic process | IGI PMID:18310029 Multiple functions of ergosterol in the fission yeast Schizo... | ACCEPT | Summary: Iwaki et al. 2008: single erg31 or erg32 disruptions still make ergosterol, but the two C-5 desaturases have overlapping functions and the double disruptant lacks ergosterol (UniProt disruption phenotype). The genetic-interaction evidence directly supports erg31 in ergosterol synthesis. Supporting Evidence: PMID:18310029 Disruption of erg31(+) or erg32(+) did not cause ergosterol deficiency or tolerance to polyene drugs, indicating that the two C-5 sterol desaturases have overlapping functions. file:SCHPO/erg31/erg31-uniprot.txt DISRUPTION PHENOTYPE: Abolishes the production of ergosterol when erg32 |
| GO:0006696 ergosterol biosynthetic process | IGI PMID:23145048 A genetic and pharmacological analysis of isoprenoid pathway... | ACCEPT | Summary: Nakamura et al. 2012 measured very low ergosterol in erg31 erg32 double-deleted cells by LC-MS/MS, confirming that the paralog pair supplies the C-5 desaturation required for ergosterol. Supporting Evidence: PMID:23145048 On the other hand, in Ξerg6 cells, Ξerg31Ξerg32 cells, and Ξerg5 cells, the ergosterol levels were extremely lower than that in wild-type cells |
| GO:0008610 lipid biosynthetic process | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO lipid biosynthetic process from the sterol desaturase family signature; correct but very broad (the same InterPro entry also covers fatty acid hydroxylases). Reason: Correct but uninformative grouping term; GO:0006696 is the specific process. Supporting Evidence: file:SCHPO/erg31/erg31-uniprot.txt PATHWAY: Steroid metabolism; ergosterol biosynthesis. |
| GO:0016126 sterol biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: UniPathway ergosterol biosynthesis mapping to sterol biosynthetic process; correct parent of GO:0006696. Supporting Evidence: file:SCHPO/erg31/erg31-uniprot.txt PATHWAY: Steroid metabolism; ergosterol biosynthesis. |
| GO:0050046 delta7-sterol 5(6)-desaturase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA delta7-sterol 5(6)-desaturase activity from PTN000221192. This term's definition (Delta7-sterol + 2 ferrocytochrome b5 + O2 -> Delta5,7-sterol) is exactly the episterol -> 5-dehydroepisterol reaction assigned to erg31; it is the correct MF for the C-5 desaturase. Supporting Evidence: file:SCHPO/erg31/erg31-uniprot.txt Reaction=episterol + 2 Fe(II)-[cytochrome b5] + O2 + 2 H(+) = 5- |
| GO:0050046 delta7-sterol 5(6)-desaturase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined automated annotation from the UniProt EC 1.14.19.20 / Rhea:46560 assignment; matches GO:0050046. Supporting Evidence: file:SCHPO/erg31/erg31-uniprot.txt Reaction=episterol + 2 Fe(II)-[cytochrome b5] + O2 + 2 H(+) = 5- |
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Download this section (compressed HTML)Q: The text definition of GO:0000248 "C-5 sterol desaturase activity" describes the C-22 desaturation of 5,7,24(28)-ergostatrienol (the erg5/GO:0000249 reaction). Should GO correct the definition or obsolete GO:0000248 in favour of GO:0050046? PomBase's ergosterol GO-CAM (66c7d41500002088) types both erg31 and erg32 with GO:0000248.
Q: Do erg31 and erg32 differ in expression (e.g. Sre1/hypoxia induction), substrate preference or localisation, or are they fully redundant?
Experiment: Sterol GC-MS of single and double deletants for episterol accumulation, and complementation of S. cerevisiae erg3 by each S. pombe gene.
Hypothesis: erg31 and erg32 encode redundant cytochrome b5-dependent Delta7-sterol C-5 desaturases.
Type: genetics / sterol profiling
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