ERG28 (YER044C) encodes a small, multi-pass endoplasmic reticulum membrane protein of the conserved ERG28 family that has no catalytic activity of its own. It acts as a transmembrane scaffold that tethers the sterol C-4 demethylation enzymes Erg25 (C-4 methylsterol oxidase), Erg26 (C-3 sterol dehydrogenase/C-4 decarboxylase) and Erg27 (3-ketosteroid reductase) into an ER-membrane complex, and bridges this complex to the downstream C-24 sterol methyltransferase Erg6 and to other ergosterol enzymes (Erg11, Erg1). Loss of ERG28 causes slow growth and accumulation of 3-keto and carboxylic acid sterol intermediates of C-4 demethylation, without full ergosterol auxotrophy. Orthologues occur in fission yeast, plants and humans.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:12119386 Protein-protein interactions among C-4 demethylation enzymes... | MODIFY | Summary: Co-immunoprecipitation of Erg28 with the C-4 demethylation enzymes Erg25, Erg26 and Erg27 (PMID:12119386). These interactions are real and are the basis of the scaffold function, but "protein binding" is uninformative; the scaffold role is captured by protein-macromolecule adaptor activity. Reason: Replace uninformative protein binding with the adaptor term that describes what the Erg28-Erg25/26/27 interaction does (tethering the demethylation enzymes in the ER membrane). Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:12119386 Erg28p works as a transmembrane scaffold to tether Erg27p and possibly other C-4 demethylation proteins (Erg25p, Erg26p), forming a demethylation complex in the endoplasmic reticulum |
| GO:0005515 protein binding | IPI PMID:12119386 Protein-protein interactions among C-4 demethylation enzymes... | MODIFY | Summary: Co-immunoprecipitation of Erg28 with the C-4 demethylation enzymes Erg25, Erg26 and Erg27 (PMID:12119386). These interactions are real and are the basis of the scaffold function, but "protein binding" is uninformative; the scaffold role is captured by protein-macromolecule adaptor activity. Reason: Replace uninformative protein binding with the adaptor term that describes what the Erg28-Erg25/26/27 interaction does (tethering the demethylation enzymes in the ER membrane). Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:12119386 Erg28p works as a transmembrane scaffold to tether Erg27p and possibly other C-4 demethylation proteins (Erg25p, Erg26p), forming a demethylation complex in the endoplasmic reticulum |
| GO:0005515 protein binding | IPI PMID:12119386 Protein-protein interactions among C-4 demethylation enzymes... | MODIFY | Summary: Co-immunoprecipitation of Erg28 with the C-4 demethylation enzymes Erg25, Erg26 and Erg27 (PMID:12119386). These interactions are real and are the basis of the scaffold function, but "protein binding" is uninformative; the scaffold role is captured by protein-macromolecule adaptor activity. Reason: Replace uninformative protein binding with the adaptor term that describes what the Erg28-Erg25/26/27 interaction does (tethering the demethylation enzymes in the ER membrane). Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:12119386 Erg28p works as a transmembrane scaffold to tether Erg27p and possibly other C-4 demethylation proteins (Erg25p, Erg26p), forming a demethylation complex in the endoplasmic reticulum |
| GO:0005515 protein binding | IPI PMID:16300994 A systematic study of yeast sterol biosynthetic protein-prot... | MODIFY | Summary: Split-ubiquitin membrane two-hybrid interactions of Erg28 with Erg25, Erg26 and Erg27 (PMID:16300994), placing Erg28 in the core of the sterol enzyme assembly. Correct interactions, but protein binding adds nothing beyond the adaptor annotation. Reason: The interaction data support the scaffold/adaptor function; use GO:0030674 rather than protein binding. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:16300994 Erg11p, Erg25p, Erg27p, and Erg28p appear to form a core center that can interact with other enzymes in the pathway |
| GO:0005515 protein binding | IPI PMID:16300994 A systematic study of yeast sterol biosynthetic protein-prot... | MODIFY | Summary: Split-ubiquitin membrane two-hybrid interactions of Erg28 with Erg25, Erg26 and Erg27 (PMID:16300994), placing Erg28 in the core of the sterol enzyme assembly. Correct interactions, but protein binding adds nothing beyond the adaptor annotation. Reason: The interaction data support the scaffold/adaptor function; use GO:0030674 rather than protein binding. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:16300994 Erg11p, Erg25p, Erg27p, and Erg28p appear to form a core center that can interact with other enzymes in the pathway |
| GO:0005515 protein binding | IPI PMID:16300994 A systematic study of yeast sterol biosynthetic protein-prot... | MODIFY | Summary: Split-ubiquitin membrane two-hybrid interactions of Erg28 with Erg25, Erg26 and Erg27 (PMID:16300994), placing Erg28 in the core of the sterol enzyme assembly. Correct interactions, but protein binding adds nothing beyond the adaptor annotation. Reason: The interaction data support the scaffold/adaptor function; use GO:0030674 rather than protein binding. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:16300994 Erg11p, Erg25p, Erg27p, and Erg28p appear to form a core center that can interact with other enzymes in the pathway |
| GO:0005515 protein binding | IPI PMID:23831759 Mapping the functional yeast ABC transporter interactome. | REMOVE | Summary: Interaction with the ABC transporter Pdr10 from a high-throughput membrane yeast two-hybrid screen of ABC transporter interactors (PMID:23831759). ERG28 is not discussed in the paper text and no functional consequence is shown; protein binding is uninformative here. Reason: Single high-throughput screen hit of no demonstrated relevance to Erg28 function; protein binding is not an informative MF and the paper supports no more specific activity. Removal does not imply the interaction is false. Supporting Evidence: PMID:23831759 Mapping the functional yeast ABC transporter interactome |
| GO:0005783 endoplasmic reticulum | HDA PMID:26928762 One library to make them all: streamlining the creation of y... | ACCEPT | Summary: Genome-wide GFP localisation (SWAT library, PMID:26928762) placing Erg28 in the ER. Consistent with the targeted GFP localisation in PMID:12119386; the more precise ER membrane term is also annotated. Reason: Correct, though less specific than ER membrane. Supporting Evidence: PMID:12119386 Green fluorescent protein-fusion protein localization studies showed that Erg26p, Erg27p, and Erg28p are all located in the endoplasmic reticulum |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA (PTN000397028, with Arabidopsis and yeast members) for ER as the site of activity. Consistent with experimental ER membrane localisation of yeast Erg28. Reason: Phylogenetically sound and supported by direct localisation of the yeast protein. Supporting Evidence: PMID:12119386 Green fluorescent protein-fusion protein localization studies showed that Erg26p, Erg27p, and Erg28p are all located in the endoplasmic reticulum |
| GO:0005789 endoplasmic reticulum membrane | IDA PMID:12119386 Protein-protein interactions among C-4 demethylation enzymes... | ACCEPT | Summary: Erg28 is membrane-associated by differential centrifugation and ER-localised by GFP fusion (PMID:12119386). This is the core location of the scaffold. Reason: Direct experimental evidence for ER membrane localisation. Supporting Evidence: PMID:12119386 Differential centrifugation showed that Erg26p, Erg27p, and Erg28p are all membrane-associated proteins |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (SL-0097, ER membrane) for this multi-pass ER membrane protein; agrees with the IDA annotation. Reason: Correct mapping, redundant with the IDA annotation. Supporting Evidence: file:yeast/ERG28/ERG28-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0006696 ergosterol biosynthetic process | IDA PMID:11160377 A novel gene conserved from yeast to humans is involved in s... | ACCEPT | Summary: erg28 deletion strains accumulate C-4 demethylation intermediates (3-keto and carboxylic acid sterols), placing Erg28 in ergosterol biosynthesis (PMID:11160377). Erg28 does work in the process by organising the C-4 demethylation enzymes, so involved_in is appropriate. Reason: Core BP; supported by sterol profiling of the deletion. Supporting Evidence: PMID:11160377 Sterol profiles indicate accumulation of 3-keto and carboxylic acid sterol intermediates |
| GO:0006696 ergosterol biosynthetic process | IDA PMID:12119386 Protein-protein interactions among C-4 demethylation enzymes... | ACCEPT | Summary: Erg28 forms a complex with Erg25/26/27 and is required for normal C-4 demethylation (PMID:12119386). Supports participation in ergosterol biosynthesis as a structural scaffold of the demethylation complex. Reason: Core BP. Supporting Evidence: PMID:12119386 a complex containing Erg25p/Erg26p/Erg27p/Erg28p was identified |
| GO:0006696 ergosterol biosynthetic process | IMP PMID:10929718 Functional discovery via a compendium of expression profiles... | ACCEPT | Summary: Expression-profile compendium study that identified YER044C as a sterol pathway gene and confirmed a sterol defect in the deletion (PMID:10929718). Consistent with later direct work. Reason: Experimental mutant phenotype supporting the core BP; curator saw full text. Supporting Evidence: PMID:10929718 we identify and experimentally confirm that eight uncharacterized open reading frames encode proteins required for sterol metabolism |
| GO:0006696 ergosterol biosynthetic process | IMP PMID:29319811 Identification of a consensus motif in Erg28p required for C... | ACCEPT | Summary: Truncation/deletion mutants of Erg28 (including loss of a conserved motif) accumulate C-4 demethylation intermediates and reduce ergosterol (PMID:29319811). Reason: Mutational evidence supporting the core BP. Supporting Evidence: PMID:29319811 resulted both in a significant growth inhibition and a reduction of ergosterol biosynthesis |
| GO:0016020 membrane | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro (IPR005352, Erg28 family) to membrane. Correct but much less informative than the experimentally supported ER membrane term. Reason: True but general; ER membrane is the informative location. Supporting Evidence: PMID:12119386 Differential centrifugation showed that Erg26p, Erg27p, and Erg28p are all membrane-associated proteins |
| GO:0030674 protein-macromolecule adaptor activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA placing protein-macromolecule adaptor activity at the ERG28 family node (PTN000397028), with yeast ERG28 itself among the experimentally annotated descendants. Matches the scaffold role. Reason: Core MF; phylogenetic inference grounded in experimental data for yeast Erg28. Supporting Evidence: PMID:12119386 Erg28p works as a transmembrane scaffold to tether Erg27p and possibly other C-4 demethylation proteins (Erg25p, Erg26p), forming a demethylation complex in the endoplasmic reticulum |
| GO:0030674 protein-macromolecule adaptor activity | IPI PMID:12119386 Protein-protein interactions among C-4 demethylation enzymes... | ACCEPT | Summary: Adaptor activity with Erg25 (SGD:S000004090) as partner, based on co-immunoprecipitation and complex purification (PMID:12119386). This is the defining activity of Erg28. Reason: Core MF with direct experimental support. Supporting Evidence: PMID:12119386 Erg25p coimmunoprecipitates with both Erg27p and Erg28p |
| GO:0030674 protein-macromolecule adaptor activity | IPI PMID:15522820 The ERG28-encoded protein, Erg28p, interacts with both the s... | ACCEPT | Summary: Adaptor activity bridging the C-4 demethylation complex to Erg6 (SGD:S000004467); Erg28 and Erg6 reciprocally co-immunoprecipitate and Erg6 ER levels drop in erg28 cells (PMID:15522820). Reason: Experimental support for the bridging/scaffold activity. Supporting Evidence: PMID:15522820 Erg28p may not only anchor the C-4 demethylation enzyme complex to the ER but also acts as a protein bridge to the Erg6p enzyme required for the next ergosterol biosynthetic step |
| GO:0060090 molecular adaptor activity | IDA PMID:12119386 Protein-protein interactions among C-4 demethylation enzymes... | MODIFY | Summary: Generic molecular adaptor activity from the same complex data (PMID:12119386). Correct but the parent of the more specific protein-macromolecule adaptor activity, which is already annotated. Reason: Erg28 adapts protein partners specifically; GO:0030674 is the more precise child term and is already supported. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:12119386 Erg28p works as a transmembrane scaffold to tether Erg27p and possibly other C-4 demethylation proteins (Erg25p, Erg26p), forming a demethylation complex in the endoplasmic reticulum |
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Download this section (compressed HTML)Q: Does Erg28 only position Erg25/26/27 or does it also channel the C-4 oxidised sterol intermediates between active sites, and why is the erg28 null not an ergosterol auxotroph?
Experiment: Reconstitute Erg25, Erg26 and Erg27 in proteoliposomes with and without Erg28 and compare C-4 demethylation flux and intermediate release, to test whether the scaffold increases catalytic efficiency or substrate channelling.
Endoplasmic reticulum membrane protein; may facilitate protein-protein interactions between the Erg26p dehydrogenase and the Erg27p 3-ketoreductase and/or tether these enzymes to the ER, also interacts with Erg6p
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