erg26

UniProt ID: O43050
Organism: Schizosaccharomyces pombe 972h-
Review Status: COMPLETE
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Gene Description

erg26 (SPBC3F6.02c) encodes the C-3 sterol dehydrogenase/C-4 decarboxylase (sterol-4alpha-carboxylate 3-dehydrogenase, decarboxylating; EC 1.1.1.170) of Schizosaccharomyces pombe, an extended short-chain dehydrogenase/reductase of the 3-beta-HSD family. Using NAD(P)+, it oxidises the 3beta-hydroxyl of 4alpha-carboxy sterols and decarboxylates them to 3-keto sterols, the second reaction of each C-4 demethylation round between Erg25 (oxidase) and Erg27 (3-ketoreductase). It is a peripheral protein of the ER membrane and, by homology, part of the Erg25-Erg26-Erg27-Erg28 C-4 demethylation complex.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0000252 3-beta-hydroxysteroid dehydrogenase [NAD(P)+]/C4-decarboxylase activity
IBA
GO_REF:0000033 		ACCEPT
Summary: IBA C-3 sterol dehydrogenase/C-4 decarboxylase activity (PTN000820972; S. cerevisiae ERG26, Candida ERG26). Correct for the S. pombe ortholog.
Supporting Evidence:
file:SCHPO/erg26/erg26-uniprot.txt
the C-4 demethylation complex that catalyzes the oxidative
file:SCHPO/erg26/erg26-uniprot.txt
Reaction=4beta-methylzymosterol-4alpha-carboxylate + NADP(+) = 3-
GO:0000252 3-beta-hydroxysteroid dehydrogenase [NAD(P)+]/C4-decarboxylase activity
IEA
GO_REF:0000120 		ACCEPT
Summary: Combined IEA (ARBA, RHEA:33447, EC 1.1.1.170); correct.
Supporting Evidence:
file:SCHPO/erg26/erg26-uniprot.txt
Reaction=4beta-methylzymosterol-4alpha-carboxylate + NADP(+) = 3-
GO:0000252 3-beta-hydroxysteroid dehydrogenase [NAD(P)+]/C4-decarboxylase activity
ISO
GO_REF:0000024 		ACCEPT
Summary: PomBase ISO from S. cerevisiae Erg26; the core activity, used in the PomBase GO-CAM.
Supporting Evidence:
file:SCHPO/erg26/erg26-uniprot.txt
the C-4 demethylation complex that catalyzes the oxidative
GO:0005783 endoplasmic reticulum
HDA
PMID:16823372
ORFeome cloning and global analysis of protein localization ... 		ACCEPT
Summary: ORFeome HDA ER localisation; correct.
Supporting Evidence:
PMID:16823372
Next, we determined the localization of 4,431 proteins, corresponding to
GO:0005783 endoplasmic reticulum
IBA
GO_REF:0000033 		ACCEPT
Summary: IBA is_active_in ER (PTN000820972); correct.
Supporting Evidence:
file:SCHPO/erg26/erg26-uniprot.txt
SUBCELLULAR LOCATION: Endoplasmic reticulum membrane
GO:0005789 endoplasmic reticulum membrane
IEA
GO_REF:0000044 		ACCEPT
Summary: UniProt SubCell ER membrane (peripheral, from the ORFeome); correct.
Supporting Evidence:
file:SCHPO/erg26/erg26-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: ORFeome HDA Golgi apparatus. The overexpressed YFP fusion was scored with a Golgi component; not verifiable from the abstract and not overruled, but no functional role of Erg26 at the Golgi is known and the C-4 demethylation partners are ER-resident.
Reason: Unverifiable high-throughput call; not the site of the core activity.
Supporting Evidence:
PMID:16823372
Next, we determined the localization of 4,431 proteins, corresponding to
GO:0006694 steroid biosynthetic process
IEA
GO_REF:0000002 		ACCEPT
Summary: InterPro2GO (IPR002225, 3-beta-HSD) steroid biosynthetic process; correct though general.
Supporting Evidence:
file:SCHPO/erg26/erg26-uniprot.txt
SIMILARITY: Belongs to the 3-beta-HSD family. {ECO:0000305}.
GO:0006696 ergosterol biosynthetic process
IBA
GO_REF:0000033 		ACCEPT
Summary: IBA ergosterol biosynthetic process (PTN000820973); C-4 decarboxylation is required for ergosterol.
Supporting Evidence:
file:SCHPO/erg26/erg26-uniprot.txt
the C-4 demethylation complex that catalyzes the oxidative
GO:0006696 ergosterol biosynthetic process
IEA
GO_REF:0000117 		ACCEPT
Summary: ARBA ergosterol biosynthetic process; correct.
Supporting Evidence:
file:SCHPO/erg26/erg26-uniprot.txt
the C-4 demethylation complex that catalyzes the oxidative
GO:0016126 sterol biosynthetic process
IEA
GO_REF:0000041 		ACCEPT
Summary: UniPathway sterol biosynthetic process; correct.
Supporting Evidence:
file:SCHPO/erg26/erg26-uniprot.txt
the C-4 demethylation complex that catalyzes the oxidative
GO:0016616 oxidoreductase activity, acting on the CH-OH group of donors, NAD or NADP as acceptor
IEA
GO_REF:0000002 		MODIFY
Summary: InterPro2GO oxidoreductase acting on CH-OH with NAD(P); the specific bifunctional dehydrogenase/decarboxylase activity is known.
Reason: Generic parent; specific activity applies.
Supporting Evidence:
file:SCHPO/erg26/erg26-uniprot.txt
Reaction=4beta-methylzymosterol-4alpha-carboxylate + NADP(+) = 3-

Core Functions

C-3 sterol dehydrogenase/C-4 decarboxylase: NAD(P)+-dependent oxidative decarboxylation of 4alpha-carboxy sterols to 3-keto sterols, the second reaction of each C-4 demethylation round; ER membrane-associated.

Molecular Function:
3-beta-hydroxysteroid dehydrogenase [NAD(P)+]/C4-decarboxylase activity
Directly Involved In:
ergosterol biosynthetic process zymosterol biosynthetic process
Cellular Locations:
endoplasmic reticulum membrane
Supporting Evidence:
  • file:SCHPO/erg26/erg26-uniprot.txt
    the C-4 demethylation complex that catalyzes the oxidative
  • file:SCHPO/erg26/erg26-uniprot.txt
    Reaction=4beta-methylzymosterol-4alpha-carboxylate + NADP(+) = 3-
  • file:SCHPO/erg26/erg26-uniprot.txt
    SUBCELLULAR LOCATION: Endoplasmic reticulum membrane

References

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Suggested Questions for Experts

Q: Is the ORFeome Golgi signal for Erg26-YFP reproducible at endogenous expression, or an overexpression artefact?

📚 Additional Documentation

Notes

(erg26-notes.md)

erg26 (SPBC3F6.02c, UniProt O43050) notes

Module: ergosterol_biosynthesis (C-3 sterol dehydrogenase/C-4 decarboxylase); S. cerevisiae ortholog ERG26 (P53199). Fetch verified: O43050.

Evidence

  • 3-beta-HSD family; reaction [UniProt:O43050 "Reaction=4beta-methylzymosterol-4alpha-carboxylate + NADP(+) = 3-"]; ER membrane peripheral (ORFeome) PMID:16823372.
  • All activity evidence is by similarity/phylogeny; no S. pombe biochemistry.

Curation decisions

  • Golgi HDA (ORFeome) kept non-core; generic CH-OH oxidoreductase IEA MODIFY -> GO:0000252.
  • PomBase GO-CAM uses GO:0005783 ER (not ER membrane) for erg26.
  • UniProt PANTHER xref is PTHR43245 (BIFUNCTIONAL POLYMYXIN RESISTANCE PROTEIN ARNA) / SF51 (SDR42E2) - surprising family names for the NSDHL/ERG26 descriptor in the module.

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