DFG10 (YIL049W) encodes polyprenal reductase (EC 1.3.1.94), a multi-pass endoplasmic-reticulum membrane enzyme of the steroid 5-alpha-reductase family (SRD5A3 subfamily) and the ortholog of human SRD5A3. It catalyses the NADPH-dependent saturation of the alpha-isoprene unit of polyprenal to give dolichal, the middle step of the three-step detour that converts polyprenol to dolichol: the SDR enzyme Tda5 (DHRSX) oxidises polyprenol to polyprenal beforehand and reduces dolichal to dolichol afterwards. Dfg10 expressed in mammalian cell membranes reduces polyprenal but has no detectable activity on polyprenol, correcting the earlier view that it was the polyprenol reductase. dfg10 cells have strongly reduced dolichol with large increases in polyprenol and polyprenal, accumulate squalene, underglycosylate carboxypeptidase Y and grow slowly; SRD5A3 complements them. Dolichol is then phosphorylated by Sec59 to dolichyl phosphate, the lipid carrier for N-glycosylation, O-mannosylation and GPI-anchor synthesis. DFG10 was first identified as required for diploid filamentous (pseudohyphal) growth, a downstream consequence of its glycosylation defect.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003865 3-oxo-5-alpha-steroid 4-dehydrogenase activity | ISS PMID:20637498 SRD5A3 is required for converting polyprenol to dolichol and... | MODIFY | Summary: ISS from human SRD5A3 for 3-oxo-5-alpha-steroid 4-dehydrogenase (steroid 5-alpha-reductase). The steroid activity rested on an early report that SRD5A3 over-expression reduces testosterone; no steroid activity has been shown for Dfg10, Cantagrel et al. emphasised that the domain reduces a non-steroid lipid, and Wilson et al. 2024 showed Dfg10 and SRD5A3 are polyprenal reductases. Reason: Family-name-driven activity; the demonstrated activity of the same ortholog pair is polyprenal reductase. Proposed replacements: polyprenal reductase activity Supporting Evidence: PMID:20637498 This study also illustrates that the predicted steroid 5-alpha reductase domain is involved in the reduction of a non-steroid lipid PMID:38821050 SRD5A3 and its yeast orthologue Dfg10 produce dolichal from polyprenal (reaction 2) but have undetectable activity on polyprenol |
| GO:0005783 endoplasmic reticulum | HDA PMID:26928762 One library to make them all: streamlining the creation of y... | ACCEPT | Summary: Yofe et al. 2016 SWAT-GFP library: ER. Reason: Consistent with the ER membrane enzyme. Supporting Evidence: file:yeast/DFG10/DFG10-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: IBA (is_active_in ER) from PTN000379006 with SRD5A3 and plant/rat sources. Reason: Correct. Supporting Evidence: file:yeast/DFG10/DFG10-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell 'Endoplasmic reticulum membrane' (by similarity to SRD5A3); four TM segments. Reason: Correct; site of action. Supporting Evidence: file:yeast/DFG10/DFG10-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005789 endoplasmic reticulum membrane | ISS GO_REF:0000024 | ACCEPT | Summary: ISS from human SRD5A3 (ER membrane). Reason: Correct. Supporting Evidence: file:yeast/DFG10/DFG10-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA from PTN000379006. Dfg10 makes the dolichol moiety that, after phosphorylation, becomes the carrier on which the LLO is built; it does not take part in oligosaccharide assembly itself. Reason: Upstream supplier of the lipid carrier; dolichyl monophosphate biosynthesis is the precise process. Supporting Evidence: file:yeast/DFG10/DFG10-uniprot.txt reductase that mediates the reduction of polyprenal into dolichal in a PMID:20637498 In contrast with wt strain (L5366), the dfg10–100 mutants (diploid and homozygous at the DFG10 locus) produced hypoglycosylated CPY |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IMP PMID:20637498 SRD5A3 is required for converting polyprenol to dolichol and... | KEEP AS NON CORE | Summary: Cantagrel et al. 2010: dfg10 mutants produce hypoglycosylated CPY. Reason: Glycosylation defect is a downstream consequence of reduced dolichol; non-core. Supporting Evidence: PMID:20637498 In contrast with wt strain (L5366), the dfg10–100 mutants (diploid and homozygous at the DFG10 locus) produced hypoglycosylated CPY |
| GO:0006629 lipid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro IPR001104 (3-oxo-5-alpha-steroid 4-dehydrogenase C-terminal domain) mapping to lipid metabolic process. True but very general. Reason: Specific process is dolichyl monophosphate (dolichol) biosynthesis. Proposed replacements: dolichyl monophosphate biosynthetic process Supporting Evidence: PMID:38821050 We first measured polyisoprenoid levels from Dfg10-deficient yeast, and noted a 4-fold decrease in dolichol, accompanied by a 36-fold increase in polyprenol and a 45-fold increase in polyprenal |
| GO:0007124 pseudohyphal growth | IMP PMID:9055077 Dissection of filamentous growth by transposon mutagenesis i... | KEEP AS NON CORE | Summary: Mosch and Fink 1997 transposon screen: dfg10 mutations block filamentous growth. Reason: Indirect phenotype downstream of the glycosylation defect; non-core. Supporting Evidence: PMID:9055077 DFG5, DFG9, DFG10, BUD8 and DFG16, mutations that block filamentous growth |
| GO:0016627 oxidoreductase activity, acting on the CH-CH group of donors | IEA GO_REF:0000002 | MODIFY | Summary: InterPro IPR001104/IPR039698 (DFG10/SRD5A3 family) mapping to 'oxidoreductase activity, acting on the CH-CH group of donors'. Correct class (polyprenal reductase saturates a C=C bond) but general. Reason: Specific activity demonstrated. Proposed replacements: polyprenal reductase activity Supporting Evidence: PMID:38821050 SRD5A3 and its yeast orthologue Dfg10 produce dolichal from polyprenal (reaction 2) but have undetectable activity on polyprenol |
| GO:0043048 dolichyl monophosphate biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN000379006 (DFG10/SGD:S000001311 and SRD5A3 are sources). Reason: Core process. Supporting Evidence: file:yeast/DFG10/DFG10-uniprot.txt reductase that mediates the reduction of polyprenal into dolichal in a |
| GO:0043048 dolichyl monophosphate biosynthetic process | IDA PMID:38821050 A pseudoautosomal glycosylation disorder prompts the revisio... | ACCEPT | Summary: Wilson et al. 2024: Dfg10 reduces polyprenal to dolichal, a step in dolichol (and thus Dol-P) synthesis; dfg10 yeast shows decreased dolichol and increased polyprenol/polyprenal. Reason: Direct evidence; core. Supporting Evidence: PMID:38821050 The SRD5A3 yeast orthologue Dfg10 also shows activity on polyprenal but not on polyprenol. PMID:38821050 We first measured polyisoprenoid levels from Dfg10-deficient yeast, and noted a 4-fold decrease in dolichol, accompanied by a 36-fold increase in polyprenol and a 45-fold increase in polyprenal |
| GO:0043048 dolichyl monophosphate biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro IPR039698 (polyprenal reductase family) mapping. Correct. Reason: Correct. Supporting Evidence: file:yeast/DFG10/DFG10-uniprot.txt reductase that mediates the reduction of polyprenal into dolichal in a |
| GO:0043048 dolichyl monophosphate biosynthetic process | IMP PMID:20637498 SRD5A3 is required for converting polyprenol to dolichol and... | ACCEPT | Summary: Cantagrel et al. 2010: dfg10 mutant has 70% less dolichol. Reason: Core process (the 'polyprenol reductase' interpretation was later refined to polyprenal reduction). Supporting Evidence: PMID:20637498 we detected a 70% decrease in dolichol in the dfg10–100 mutant compared to the wt yeast from the same background |
| GO:0160198 polyprenal reductase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN000379006 (polyprenal reductase node). Reason: Core activity. Supporting Evidence: file:yeast/DFG10/DFG10-uniprot.txt reductase that mediates the reduction of polyprenal into dolichal in a |
| GO:0160198 polyprenal reductase activity | IDA PMID:38821050 A pseudoautosomal glycosylation disorder prompts the revisio... | ACCEPT | Summary: Wilson et al. 2024: membranes from HEK293T cells expressing Dfg10 reduce polyprenal to dolichal (NADPH) with no activity on polyprenol. Reason: Direct enzymatic evidence; core. Supporting Evidence: PMID:38821050 The SRD5A3 yeast orthologue Dfg10 also shows activity on polyprenal but not on polyprenol. PMID:38821050 SRD5A3 and its yeast orthologue Dfg10 produce dolichal from polyprenal (reaction 2) but have undetectable activity on polyprenol |
| GO:0160198 polyprenal reductase activity | IEA GO_REF:0000120 | ACCEPT | Summary: RHEA:80727 / EC 1.3.1.94 mapping. Correct. Reason: Correct. Supporting Evidence: file:yeast/DFG10/DFG10-uniprot.txt reductase that mediates the reduction of polyprenal into dolichal in a |
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Download this section (compressed HTML)Q: Why do tda5 dfg10 double mutants retain dolichol, and does Dfg10 also regulate isoprenoid flux upstream (squalene accumulation in dfg10)?
Experiment: Co-immunoprecipitation / proximity labelling of tagged Dfg10 and Tda5 in ER membranes and measurement of polyprenal leakage in strains with forced separation.
Hypothesis: Dfg10 and Tda5 form a channelling complex for the polyprenal intermediate
Type: biochemistry / lipidomics
Probable polyprenol reductase; catalyzes conversion of polyprenol to dolichol, the precursor for N-glycosylation; involved in filamentous growth; mutations in human homolog SRD5A3 confer CDG (Congenital Disorders of Glycosylation); human SRD5A3 can complement yeast null mutant
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