Fatty acid elongase 2 (Elo2/Fen1/Gns1/Vbm2) is a multi-pass endoplasmic reticulum membrane 3-keto-acyl-CoA synthase of the ELO family that catalyses the rate-limiting condensation of an acyl-CoA with malonyl-CoA, the first of the four reactions of the ER fatty acid elongation cycle. Elo2 forms elongase II, which extends C16-C18 acyl-CoAs to C20-C24 species; the downstream reduction, dehydration and second reduction are carried out by Ifa38, Phs1 and Tsc13, with which Elo2 co-immunoprecipitates. Its active site faces the cytosol and product length is set by a lysine near the luminal end of transmembrane helix 6. Elo2 is partially redundant with Elo3 (the elo2 elo3 double mutant is inviable); the VLCFAs produced are the amide-linked acyl chains of ceramide and inositol sphingolipids, and loss of Elo2 lowers all sphingolipid classes, raises long-chain bases and causes pleiotropic membrane phenotypes (1,3-beta-glucan synthesis, secretion, endosomal traffic).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005783 endoplasmic reticulum | IDA PMID:12087109 The Saccharomyces cerevisiae YBR159w gene encodes the 3-keto... | ACCEPT | Summary: Han et al. 2002 showed GFP-tagged ELO2 co-localising with the ER elongase components (Ybr159p/Ifa38 co-localises with Elo3p and Tsc13p); ELO2 is an integral ER membrane condensing enzyme. Correct but less specific than ER membrane. Supporting Evidence: PMID:12087109 Green fluorescent protein-tagged Ybr159p co-localizes and co-immunoprecipitates with other elongating enzymes, Elo3p and Tsc13p file:yeast/ELO2/ELO2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA machine-learning rule assigns ER to ELO-family proteins; correct for ELO2, a polytopic ER membrane elongase. Supporting Evidence: file:yeast/ELO2/ELO2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005789 endoplasmic reticulum membrane | EXP PMID:12087109 The Saccharomyces cerevisiae YBR159w gene encodes the 3-keto... | ACCEPT | Summary: UniProt-curated EXP location citing Han et al. 2002 (co-localisation with ER elongase components). ELO2 is a multi-pass ER membrane protein whose active site faces the cytosol. Supporting Evidence: PMID:12087109 Green fluorescent protein-tagged Ybr159p co-localizes and co-immunoprecipitates with other elongating enzymes, Elo3p and Tsc13p file:yeast/ELO2/ELO2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane PMID:17719544 Mutational analysis revealed that the Elop active site faces the cytosol, whereas VLCFA length is determined by a lysine near the luminal end of an Elop transmembrane helix |
| GO:0005789 endoplasmic reticulum membrane | EXP PMID:14562095 Global analysis of protein localization in budding yeast. | ACCEPT | Summary: Huh et al. 2003 genome-wide GFP survey scored ELO2-GFP at the ER; consistent with all dedicated localisation studies. Supporting Evidence: PMID:14562095 We classify these proteins, representing 75% of the yeast proteome, into 22 distinct subcellular localization categories file:yeast/ELO2/ELO2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005789 endoplasmic reticulum membrane | EXP PMID:9832547 Involvement of long chain fatty acid elongation in the traff... | ACCEPT | Summary: David et al. 1998 (where ELO2 was isolated as VBM2) fractionated HA-tagged protein with resident ER/early Golgi markers, not with secretory vesicles, and described the Vbm proteins as ER-localised membrane proteins. Supporting Evidence: PMID:9832547 Recessive mutations in either VBM1 or VBM2, which encode related ER-localized membrane proteins, allow yeast to grow normally and secrete in the absence of Snc v-SNAREs PMID:9832547 The results from these complimentary strategies suggest a probable ER and, perhaps, early Golgi localization for the Vbm proteins. |
| GO:0005789 endoplasmic reticulum membrane | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from the ELO/ELOVL family node PTN000125390; all characterised members (yeast Elo1-3, mammalian ELOVL1-7) are ER membrane condensing enzymes, and ELO2 has its own experimental support for this location. Supporting Evidence: file:yeast/ELO2/ELO2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane PMID:11113186 Even at very low expression levels, Elo2p-GFP distribution in the ER was indistinguishable from the wild-type pattern |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location keyword mapping (SL-0097 Endoplasmic reticulum membrane), itself based on the experimental UniProt statement for ELO2. Supporting Evidence: file:yeast/ELO2/ELO2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005829 cytosol | RCA GO_REF:0000123 | REMOVE | Summary: YeastPathways-to-GO-CAM conversion of PWY-5080-1 (very long chain fatty acid biosynthesis I) placed the condensation step 'is_active_in cytosol', apparently a compartment default of the conversion. ELO2 is a multi-pass integral ER membrane protein; only its active site faces the cytosolic side of the membrane. Reason: Computational location default contradicted by direct localisation data; the enzyme is an integral ER membrane protein, not a soluble cytosolic protein, and the ER membrane is already annotated. Supporting Evidence: PMID:17719544 Mutational analysis revealed that the Elop active site faces the cytosol, whereas VLCFA length is determined by a lysine near the luminal end of an Elop transmembrane helix file:yeast/ELO2/ELO2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0009922 fatty acid elongase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from ELO/ELOVL family node PTN000125390. 3-keto-acyl-CoA synthase (condensing) activity is the defining activity of the family and ELO2 has direct biochemical support (elongase activity lost in the mutant; reconstitution with purified components). Supporting Evidence: PMID:12684876 Elongases I, II and III are specifically inactivated in, respectively, elo1, elo2 and elo3 mutants PMID:17719544 Proteoliposomes reconstituted here from purified membrane components-an elongase protein (Elop), a novel dehydratase, and two reductases-catalyzed repeated rounds of two-carbon addition |
| GO:0009922 fatty acid elongase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (InterPro IPR002076 ELO family, RHEA:32727, EC 2.3.1.199) for the VLC 3-oxoacyl-CoA synthase reaction; matches the UniProt-curated catalytic activity of ELO2. Supporting Evidence: file:yeast/ELO2/ELO2-uniprot.txt Reaction=a very-long-chain acyl-CoA + malonyl-CoA + H(+) = a very-long- |
| GO:0009922 fatty acid elongase activity | IMP PMID:12684876 Functional differentiation and selective inactivation of mul... | ACCEPT | Summary: Rossler et al. 2003 defined three microsomal elongase activities by primer specificity in vitro and showed elongase II is specifically lost in the elo2 mutant. Elo2 (elongase II) preferentially elongates C16-C18 acyl-CoAs to C20-C22/C24. Supporting Evidence: PMID:12684876 Elongases I, II and III are specifically inactivated in, respectively, elo1, elo2 and elo3 mutants PMID:12684876 Elongase II elongates palmitoyl-CoA and stearoyl-CoA up to C22 fatty acids, and elongase III synthesizes 20-26-carbon fatty acids from C18-CoA primers |
| GO:0009922 fatty acid elongase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways PWY-5080-1 assigns the condensation step (long-chain acyl-CoA + malonyl-CoA -> 3-oxoacyl-CoA + CO2 + CoA) to ELO2; this assignment is correct and matches the experimental data. Supporting Evidence: PMID:12684876 Elongases I, II and III are specifically inactivated in, respectively, elo1, elo2 and elo3 mutants file:yeast/ELO2/ELO2-uniprot.txt Reaction=a very-long-chain acyl-CoA + malonyl-CoA + H(+) = a very-long- |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from IPR002076 (ELO family) to 'membrane'; correct but uninformative given the experimentally established ER membrane location. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: file:yeast/ELO2/ELO2-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0016192 vesicle-mediated transport | IMP PMID:9832547 Involvement of long chain fatty acid elongation in the traff... | MARK AS OVER ANNOTATED | Summary: David et al. 1998 isolated elo2/vbm2 mutations as suppressors bypassing the Snc v-SNARE requirement in secretion. The authors attribute this to altered lipid synthesis in the ER; Elo2 is not on secretory vesicles and does none of the transport work. Reason: Indirect consequence of VLCFA/sphingolipid composition, not participation in vesicle-mediated transport. Kept as over-annotation (IMP) rather than removed. Supporting Evidence: PMID:9832547 Recessive mutations in either VBM1 or VBM2, which encode related ER-localized membrane proteins, allow yeast to grow normally and secrete in the absence of Snc v-SNAREs PMID:9832547 act at the level of lipid synthesis to affect the ability of secretory vesicles to sort and deliver protein cargo PMID:9832547 The results from these complimentary strategies suggest a probable ER and, perhaps, early Golgi localization for the Vbm proteins. |
| GO:0019367 fatty acid elongation, saturated fatty acid | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA (PTN000125390) for elongation of saturated fatty acids. Yeast VLCFAs (C20-C26, sphingolipid C26:0) are saturated, and ELO2 elongates saturated C16:0/C18:0 primers, so this term is appropriate. Supporting Evidence: PMID:12684876 Elongase II elongates palmitoyl-CoA and stearoyl-CoA up to C22 fatty acids, and elongase III synthesizes 20-26-carbon fatty acids from C18-CoA primers PMID:9211877 produce the 26-carbon very long chain fatty acids that are precursors for ceramide and sphingolipids |
| GO:0030148 sphingolipid biosynthetic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PAINT IBA for sphingolipid biosynthesis. ELO2 supplies the VLCFA acyl-CoA that ceramide synthase amide-links to the long-chain base; it does not catalyse a sphingolipid-forming step itself. Supporting Evidence: PMID:9211877 produce the 26-carbon very long chain fatty acids that are precursors for ceramide and sphingolipids PMID:9211877 Disruption of either gene reduces cellular sphingolipid levels and results in the accumulation of the long chain base, phytosphingosine |
| GO:0030148 sphingolipid biosynthetic process | IMP PMID:9211877 ELO2 and ELO3, homologues of the Saccharomyces cerevisiae EL... | KEEP AS NON CORE | Summary: Oh et al. 1997: disruption of ELO2 reduces sphingolipid levels and causes phytosphingosine accumulation. Consistent with an upstream precursor-supply role. Supporting Evidence: PMID:9211877 Disruption of either gene reduces cellular sphingolipid levels and results in the accumulation of the long chain base, phytosphingosine PMID:9211877 produce the 26-carbon very long chain fatty acids that are precursors for ceramide and sphingolipids |
| GO:0030497 fatty acid elongation | IMP PMID:9211877 ELO2 and ELO3, homologues of the Saccharomyces cerevisiae EL... | TOO GENERAL | Summary: Oh et al. 1997: ELO2 null mutants are defective in VLCFA formation; ELO2 encodes a component of the membrane-bound fatty acid elongation system. Correct process; VLCFA biosynthesis is the more specific term. Supporting Evidence: PMID:9211877 null mutations of ELO2 and ELO3 produce defects in the formation of very long chain fatty acids PMID:9211877 Elo2p appears to be involved in the elongation of fatty acids up to 24 carbons |
| GO:0032511 late endosome to vacuole transport via multivesicular body sorting pathway | IGI PMID:23325927 Effects on vesicular transport pathways at the late endosome... | MARK AS OVER ANNOTATED | Summary: Obara et al. 2013: fen1 deletion is synthetically sick with vps21 (Rab5) and impairs endosomal trafficking (CPY, endocytosis) in the double mutant. This reflects a requirement of the endosomal membrane for VLCFAs rather than a transport function of the elongase. Reason: Genetic-interaction phenotype downstream of lipid composition; the ER-resident elongase does not participate in late endosome to vacuole transport. Kept as over-annotation (IGI) rather than removed. Supporting Evidence: PMID:23325927 These results suggest that, of all the intracellular trafficking pathways, requirement of VLCFAs is especially high in the endosomal pathways. |
| GO:0034625 fatty acid elongation, monounsaturated fatty acid | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: PAINT IBA (PTN000125390) for monounsaturated fatty acid elongation, propagated from mammalian ELOVLs (e.g. ELOVL1/3/7). Yeast VLCFAs used in sphingolipids are saturated and no experiment shows ELO2 elongating C16:1/C18:1 in vivo. Reason: Plausible as a minor in vitro capability of the condensing enzyme but not shown for yeast; the physiological substrates are saturated acyl-CoAs. Propagation Review Root cause: PROPAGATION BAD Failure modes: FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN000125390 SUPPORTS SOURCE BUT NOT TARGET Node spans all ELO/ELOVL condensing enzymes; MUFA elongation is documented for vertebrate/insect/amoebozoan members but no yeast Elo has been shown to elongate monounsaturated acyl-CoAs in vivo. Supporting Evidence: PMID:12684876 Elongase II elongates palmitoyl-CoA and stearoyl-CoA up to C22 fatty acids, and elongase III synthesizes 20-26-carbon fatty acids from C18-CoA primers PMID:9211877 produce the 26-carbon very long chain fatty acids that are precursors for ceramide and sphingolipids |
| GO:0034626 fatty acid elongation, polyunsaturated fatty acid | IBA GO_REF:0000033 | REMOVE | Summary: PAINT IBA (PTN000125390) for polyunsaturated fatty acid elongation, propagated from PUFA-elongating ELOVL2/4/5 orthologues. S. cerevisiae makes no polyunsaturated fatty acids (it has only the Ole1 delta-9 desaturase), so there is no PUFA substrate for ELO2 in vivo. Reason: Biologically inapplicable in this organism: no PUFA synthesis in S. cerevisiae; the IBA node spans PUFA-specific ELOVL subfamilies whose specificity is not inherited by the yeast saturated-VLCFA elongases. Propagation Review Root cause: PROPAGATION BAD Failure modes: LINEAGE OR TAXON MISMATCH Sources checked: PANTHER:PTN000125390 SUPPORTS SOURCE BUT NOT TARGET PUFA elongation is grounded in animal ELOVL PUFA elongases; S. cerevisiae synthesises no polyunsaturated fatty acids, so the process does not occur in the target lineage. Supporting Evidence: PMID:12684876 Elongase II elongates palmitoyl-CoA and stearoyl-CoA up to C22 fatty acids, and elongase III synthesizes 20-26-carbon fatty acids from C18-CoA primers PMID:9211877 produce the 26-carbon very long chain fatty acids that are precursors for ceramide and sphingolipids |
| GO:0042761 very long-chain fatty acid biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA (PTN000125390) for VLCFA biosynthesis; the core process of the ELO family and directly supported for ELO2 by mutant fatty-acid profiles and in vitro elongation. Supporting Evidence: PMID:9211877 null mutations of ELO2 and ELO3 produce defects in the formation of very long chain fatty acids PMID:12684876 Elongase II elongates palmitoyl-CoA and stearoyl-CoA up to C22 fatty acids, and elongase III synthesizes 20-26-carbon fatty acids from C18-CoA primers |
| GO:0042761 very long-chain fatty acid biosynthetic process | IMP PMID:23325927 Effects on vesicular transport pathways at the late endosome... | ACCEPT | Summary: Obara et al. 2013 assayed microsomal FA elongation: fen1 deletion membranes were impaired in elongation beyond C18-CoA. Direct IMP support for the core process. Supporting Evidence: PMID:23325927 However, elongations beyond C18-CoA and C22-CoA were largely impaired in fen1 Ξ and sur4 Ξ cells, respectively. |
| GO:0042761 very long-chain fatty acid biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways PWY-5080-1 (very long chain fatty acid biosynthesis I) assignment of the condensation step to Elo2; correct. Supporting Evidence: PMID:9211877 null mutations of ELO2 and ELO3 produce defects in the formation of very long chain fatty acids PMID:12684876 Elongase II elongates palmitoyl-CoA and stearoyl-CoA up to C22 fatty acids, and elongase III synthesizes 20-26-carbon fatty acids from C18-CoA primers |
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Download this section (compressed HTML)Q: Does Elo2 physically associate with Elo3 in the same Ifa38-Phs1-Tsc13 complex, or do elongase II and III assemble as separate complexes in the ER membrane?
Q: What fraction of the reported vesicle-trafficking and 1,3-beta-glucan phenotypes of elo2/fen1 mutants is explained by altered ceramide acyl-chain length versus long-chain base accumulation?
Experiment: Reconstitute purified Elo2 with Ifa38, Phs1 and Tsc13 in proteoliposomes and test saturated versus monounsaturated C16-C20 acyl-CoA primers by LC-MS.
Hypothesis: Elo2 substrate range in vivo is restricted to saturated C16-C22 acyl-CoAs.
Fatty acid elongase, involved in sphingolipid biosynthesis; acts on fatty acids of up to 24 carbons in length; mutations have regulatory effects on 1,3-beta-glucan synthase, vacuolar ATPase, and the secretory pathway; ELO2 has a paralog, ELO1, that arose from the whole genome duplication; lethality of the elo2 elo3 double null mutation is functionally complemented by human ELOVL1 and weakly complemented by human ELOVL3 or ELOV7
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Download this section (compressed HTML)Loading supporting contentβ¦
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