Tsc10 (YBR265W) is the 3-ketosphinganine (3-ketodihydrosphingosine) reductase of Saccharomyces cerevisiae, a short-chain dehydrogenase/reductase (SDR) family enzyme that catalyses the second step of de novo sphingolipid synthesis: NADPH-dependent reduction of 3-ketosphinganine, produced by serine palmitoyltransferase, to sphinganine (dihydrosphingosine) (EC 1.1.1.102). Tsc10 is an integral endoplasmic reticulum membrane protein with two C-terminal transmembrane segments and an N-terminal catalytic domain facing the cytoplasm. TSC10 is essential unless cells are supplied with dihydrosphingosine or phytosphingosine. The enzyme is functionally replaced by the topologically distinct human ortholog KDSR (FVT1). Tsc10 has also been detected on lipid droplets.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | HDA PMID:11914276 Subcellular localization of the yeast proteome. | KEEP AS NON CORE | Summary: HDA from the Kumar et al. 2002 immunolocalization survey. Tsc10 is an integral ER membrane protein whose catalytic domain faces the cytoplasm, so a cytoplasmic signal is not wrong but is less precise than the ER membrane annotations. Supporting Evidence: PMID:19141869 In contrast, protease digestion studies showed that the N terminus of Tsc10p is cytoplasmic. |
| GO:0005741 mitochondrial outer membrane | HDA PMID:16407407 Proteomic analysis of the yeast mitochondrial outer membrane... | KEEP AS NON CORE | Summary: HDA from the mitochondrial outer membrane proteome (Zahedi et al. 2006). Not supported by low-throughput work, which places Tsc10 in the ER; could reflect ER-mitochondria contact material in the preparation. Retained as a non-core observation. Supporting Evidence: PMID:16407407 Proteomic analysis of the yeast mitochondrial outer membrane reveals accumulation of a subclass of preproteins. |
| GO:0005783 endoplasmic reticulum | HDA PMID:11914276 Subcellular localization of the yeast proteome. | ACCEPT | Summary: HDA (Kumar et al. 2002) placing Tsc10 in the ER; consistent with the low-throughput ER membrane localization. Supporting Evidence: PMID:19141869 Nevertheless, both Tsc10p and the residual fragment of FVT1 produced by removal of the N-terminal domain with factor Xa protease behave as integral membrane proteins. |
| GO:0005783 endoplasmic reticulum | HDA PMID:14562095 Global analysis of protein localization in budding yeast. | ACCEPT | Summary: HDA from the Huh et al. 2003 GFP localization survey; ER, consistent with the experimentally defined ER membrane location. Supporting Evidence: PMID:19141869 Nevertheless, both Tsc10p and the residual fragment of FVT1 produced by removal of the N-terminal domain with factor Xa protease behave as integral membrane proteins. |
| GO:0005783 endoplasmic reticulum | HDA PMID:26928762 One library to make them all: streamlining the creation of y... | ACCEPT | Summary: HDA from the SWAp-Tag GFP library (Yofe et al. 2016); ER, consistent with other data. Supporting Evidence: PMID:19141869 Nevertheless, both Tsc10p and the residual fragment of FVT1 produced by removal of the N-terminal domain with factor Xa protease behave as integral membrane proteins. |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA rule (ARBA00028672) IEA for ER; correct. Supporting Evidence: file:yeast/TSC10/TSC10-uniprot.txt -!- SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005789 endoplasmic reticulum membrane | EXP PMID:19141869 Tsc10p and FVT1: topologically distinct short-chain reductas... | ACCEPT | Summary: EXP from Gupta et al. 2009 (topology and membrane-association studies): Tsc10 is an integral membrane protein of the ER with a cytoplasmic catalytic domain. Supporting Evidence: PMID:19141869 Nevertheless, both Tsc10p and the residual fragment of FVT1 produced by removal of the N-terminal domain with factor Xa protease behave as integral membrane proteins. PMID:19141869 In contrast, protease digestion studies showed that the N terminus of Tsc10p is cytoplasmic. |
| GO:0005789 endoplasmic reticulum membrane | IBA GO_REF:0000033 | ACCEPT | Summary: IBA (PTN000673031) for ER membrane; consistent with experimental data on Tsc10 and KDSR. Supporting Evidence: PMID:19141869 Nevertheless, both Tsc10p and the residual fragment of FVT1 produced by removal of the N-terminal domain with factor Xa protease behave as integral membrane proteins. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (SL-0097) IEA; correct. Supporting Evidence: file:yeast/TSC10/TSC10-uniprot.txt -!- SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005811 lipid droplet | IDA PMID:24868093 High confidence proteomic analysis of yeast LDs identifies a... | KEEP AS NON CORE | Summary: IDA from Currie et al. 2014 (high-confidence lipid droplet proteome), which newly identified Tsc10 as an LD-localized protein. Plausible secondary location for an ER membrane enzyme; the core activity is assigned to the ER. Supporting Evidence: PMID:24868093 However, we newly identified six proteins (Cab5, Rer2, Say1, Tsc10, YKL047W, and YPR147C) as localizing to LDs |
| GO:0005829 cytosol | RCA GO_REF:0000123 | MODIFY | Summary: YeastPathways RCA (SPHINGOLIPID-SYN-PWY-1) default cytosol placement. Tsc10 is an integral ER membrane protein; although its catalytic domain faces the cytoplasm, the protein is not in the cytosol proper. Reason: Pathway default compartment conflicts with experimental ER membrane localization. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:19141869 Nevertheless, both Tsc10p and the residual fragment of FVT1 produced by removal of the N-terminal domain with factor Xa protease behave as integral membrane proteins. |
| GO:0006665 sphingolipid metabolic process | IEA GO_REF:0000041 | TOO GENERAL | Summary: UniPathway (UPA00222) IEA for sphingolipid metabolic process. Correct but general. Supporting Evidence: PMID:9804843 These data indicate that Tsc10p is necessary and sufficient for catalyzing the NADPH-dependent reduction of 3-ketosphinganine to dihydrosphingosine. |
| GO:0030148 sphingolipid biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA (PTN000673031) for sphingolipid biosynthetic process, with Tsc10, human KDSR, Candida and Aspergillus orthologs as experimental members. Correct. Supporting Evidence: PMID:9804843 These data indicate that Tsc10p is necessary and sufficient for catalyzing the NADPH-dependent reduction of 3-ketosphinganine to dihydrosphingosine. |
| GO:0030148 sphingolipid biosynthetic process | IDA PMID:16431155 Sphingolipid biosynthesis in pathogenic fungi: identificatio... | ACCEPT | Summary: IDA from Fornarotto et al. 2006. The abstract centres on the C. albicans and A. fumigatus orthologs but restates that Tsc10 catalyses this step in S. cerevisiae; the full text is not cached, so the assay on Tsc10 cannot be checked here. The function is well established; deferring to the curator. Supporting Evidence: PMID:16431155 An early step in sphingolipid biosynthesis, the reduction of 3-ketosphinganine, is catalyzed in the yeast Saccharomyces cerevisiae by Tsc10p (TSC10 (YBR265W)). |
| GO:0030148 sphingolipid biosynthetic process | IDA PMID:35667415 Identification and characterization of 3-ketosphinganine red... | ACCEPT | Summary: IDA from Lee et al. 2022 (Bacteroides 3-KDSR study), in which yeast TSC10 was expressed in E. coli as the positive control and converted 3-ketosphinganine to sphinganine. Supporting Evidence: PMID:35667415 3-KDSR (TSC10) and confirmed the conversion of 3-KDS to SA |
| GO:0030148 sphingolipid biosynthetic process | IDA PMID:9804843 The Saccharomyces cerevisiae TSC10/YBR265w gene encoding 3-k... | ACCEPT | Summary: IDA from Beeler et al. 1998: recombinant Tsc10 reduces 3-ketosphinganine, the second step of the long-chain base pathway. Supporting Evidence: PMID:9804843 The recombinant protein catalyzes the NADPH-dependent reduction of 3-ketosphinganine. |
| GO:0030148 sphingolipid biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (ARBA00027455; InterPro IPR045022 KDSR-like). Correct. Supporting Evidence: PMID:9804843 These data indicate that Tsc10p is necessary and sufficient for catalyzing the NADPH-dependent reduction of 3-ketosphinganine to dihydrosphingosine. |
| GO:0030148 sphingolipid biosynthetic process | IMP PMID:9804843 The Saccharomyces cerevisiae TSC10/YBR265w gene encoding 3-k... | ACCEPT | Summary: IMP from Beeler et al. 1998: tsc10 mutants accumulate 3-ketosphinganine, have low microsomal reductase activity, and need exogenous long-chain base to grow. Supporting Evidence: PMID:9804843 The tsc10 mutants accumulate 3-ketosphinganine and microsomal membranes isolated from tsc10 mutants have low 3-ketosphinganine reductase activity. |
| GO:0030148 sphingolipid biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA placing the 3-dehydrosphinganine reductase step in sphingolipid biosynthesis; correct for Tsc10. Supporting Evidence: PMID:9804843 These data indicate that Tsc10p is necessary and sufficient for catalyzing the NADPH-dependent reduction of 3-ketosphinganine to dihydrosphingosine. |
| GO:0047560 3-dehydrosphinganine reductase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA (PTN000673031) for 3-dehydrosphinganine reductase activity; Tsc10 is among the experimentally characterized members, as expected. Supporting Evidence: PMID:9804843 The recombinant protein catalyzes the NADPH-dependent reduction of 3-ketosphinganine. |
| GO:0047560 3-dehydrosphinganine reductase activity | IDA PMID:16431155 Sphingolipid biosynthesis in pathogenic fungi: identificatio... | ACCEPT | Summary: IDA from Fornarotto et al. 2006; the abstract reports NADPH-dependent 3-ketosphinganine reduction by the fungal orthologs, and UniProt cites this paper for Tsc10's EC 1.1.1.102 activity. Full text not cached; deferring to the curator. Supporting Evidence: file:yeast/TSC10/TSC10-uniprot.txt EC=1.1.1.102 {ECO:0000269|PubMed:16431155, ECO:0000269|PubMed:9804843, ECO:0000305|PubMed:35667415}; |
| GO:0047560 3-dehydrosphinganine reductase activity | IDA PMID:35667415 Identification and characterization of 3-ketosphinganine red... | ACCEPT | Summary: IDA from the 2022 Bacteroides 3-KDSR study using Tsc10 as the reference enzyme in E. coli; confirmed reduction of 3-ketosphinganine to sphinganine. Supporting Evidence: PMID:35667415 3-KDSR (TSC10) and confirmed the conversion of 3-KDS to SA |
| GO:0047560 3-dehydrosphinganine reductase activity | IDA PMID:9804843 The Saccharomyces cerevisiae TSC10/YBR265w gene encoding 3-k... | ACCEPT | Summary: IDA from Beeler et al. 1998: purified His6-Tsc10 catalyses NADPH-dependent reduction of 3-ketosphinganine. Core activity. Supporting Evidence: PMID:9804843 The recombinant protein catalyzes the NADPH-dependent reduction of 3-ketosphinganine. PMID:9804843 These data indicate that Tsc10p is necessary and sufficient for catalyzing the NADPH-dependent reduction of 3-ketosphinganine to dihydrosphingosine. |
| GO:0047560 3-dehydrosphinganine reductase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (RHEA:22640 / EC 1.1.1.102); matches the experimentally established activity. Supporting Evidence: file:yeast/TSC10/TSC10-uniprot.txt Reaction=sphinganine + NADP(+) = 3-oxosphinganine + NADPH + H(+); |
| GO:0047560 3-dehydrosphinganine reductase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA for the 3-dehydrosphinganine -> sphinganine step (EC 1.1.1.102); correct. Supporting Evidence: PMID:9804843 The recombinant protein catalyzes the NADPH-dependent reduction of 3-ketosphinganine. |
| GO:0070402 NADPH binding | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS from the C. albicans ortholog (P0CR36) for NADPH binding. Tsc10 is an NADPH-dependent SDR with a GXSXG cofactor motif, so NADPH binding is correct but is a cofactor-level aspect of the reductase activity. Supporting Evidence: PMID:9804843 The recombinant protein catalyzes the NADPH-dependent reduction of 3-ketosphinganine. |
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Download this section (compressed HTML)Q: Is the lipid droplet pool of Tsc10 catalytically active, and does it contribute to long-chain base synthesis under conditions of high neutral-lipid storage?
Experiment: Compare 3-ketosphinganine reductase activity in purified ER and lipid droplet fractions from cells expressing endogenously tagged Tsc10.
3-ketosphinganine reductase; catalyzes the second step in phytosphingosine synthesis; essential for growth in the absence of exogenous dihydrosphingosine or phytosphingosine; localized to lipid droplets; member of short chain dehydrogenase/reductase protein family; mutations in human homolog KDSR cause recessive progressive symmetric erythrokeratoderma
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