Lag1 (longevity assurance gene 1) is a multi-pass integral membrane protein of the endoplasmic reticulum and one of two redundant catalytic subunits (with its paralog Lac1) of the acyl-CoA dependent, fumonisin B1-sensitive ceramide synthase of Saccharomyces cerevisiae. The enzyme transfers very long chain (mainly C26) fatty acyl groups from acyl-CoA onto the sphingoid bases phytosphingosine and dihydrosphingosine, producing the phytoceramide/dihydroceramide backbone of all yeast complex sphingolipids (IPC, MIPC, M(IP)2C). Lag1 and Lac1 co-purify with the small single-span subunit Lip1 in a heterotetrameric ceramide synthase complex. Lag1 belongs to the TLC-domain ceramide synthase (CerS) family conserved to human CERS1-6. Lag1 prefers phytosphingosine and is enriched in the nuclear and cortical ER; it is phosphorylated by Ypk1 downstream of TORC2 to stimulate sphingolipid synthesis. Loss of both LAG1 and LAC1 abolishes acyl-CoA dependent ceramide synthesis, causing severe growth defects, slowed ER-to-Golgi transport of GPI-anchored proteins and defective GPI-anchor lipid remodelling; LAG1 deletion alone extends replicative lifespan.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:15692566 Lip1p: a novel subunit of acyl-CoA ceramide synthase. | REMOVE | Summary: IPI with Lac1 (P28496) from Vallee & Riezman 2005: tagged Lag1p and Lac1p co-purify as subunits of the ceramide synthase. 'Protein binding' is uninformative; the biologically meaningful content (membership of the Lag1/Lac1/Lip1 acyl-CoA ceramide synthase complex) is captured by GO:0061576. Removed per the protein-binding policy; the interaction itself is not disputed. Supporting Evidence: PMID:15692566 They copurified with ceramide synthase activity, giving unequivocal evidence that they are subunits of the enzyme. |
| GO:0005515 protein binding | IPI PMID:15692566 Lip1p: a novel subunit of acyl-CoA ceramide synthase. | REMOVE | Summary: IPI with Lip1 (Q03579) from Vallee & Riezman 2005, who identified Lip1p as a co-purifying third subunit of purified ceramide synthase. 'Protein binding' is uninformative; the biologically meaningful content (membership of the Lag1/Lac1/Lip1 acyl-CoA ceramide synthase complex) is captured by GO:0061576. Removed per the protein-binding policy; the interaction itself is not disputed. Supporting Evidence: PMID:15692566 SDS-PAGE analysis of purified ceramide synthase revealed the presence of a novel subunit of the enzyme, Lip1p. |
| GO:0005515 protein binding | IPI PMID:16093310 Large-scale identification of yeast integral membrane protei... | REMOVE | Summary: IPI with Lac1 (P28496) from the Miller et al. 2005 split-ubiquitin screen of integral membrane proteins; consistent with the Lag1-Lac1 paralog pair in one complex. 'Protein binding' is uninformative; the biologically meaningful content (membership of the Lag1/Lac1/Lip1 acyl-CoA ceramide synthase complex) is captured by GO:0061576. Removed per the protein-binding policy; the interaction itself is not disputed. Supporting Evidence: PMID:16093310 We carried out a large-scale screen to identify interactions between integral membrane proteins of Saccharomyces cerevisiae by using a modified split-ubiquitin technique. |
| GO:0005515 protein binding | IPI PMID:18467557 An in vivo map of the yeast protein interactome. | REMOVE | Summary: IPI with Lac1 (P28496) from the Tarassov et al. 2008 DHFR protein-fragment complementation screen. 'Protein binding' is uninformative; the biologically meaningful content (membership of the Lag1/Lac1/Lip1 acyl-CoA ceramide synthase complex) is captured by GO:0061576. Removed per the protein-binding policy; the interaction itself is not disputed. Supporting Evidence: PMID:18467557 We have performed a genome-wide in vivo screen for protein-protein interactions in Saccharomyces cerevisiae by means of a protein-fragment complementation assay (PCA). |
| GO:0005515 protein binding | IPI PMID:18719252 High-quality binary protein interaction map of the yeast int... | REMOVE | Summary: IPI with Lip1 (Q03579) from the Yu et al. 2008 high-throughput yeast two-hybrid map. 'Protein binding' is uninformative; the biologically meaningful content (membership of the Lag1/Lac1/Lip1 acyl-CoA ceramide synthase complex) is captured by GO:0061576. Removed per the protein-binding policy; the interaction itself is not disputed. Supporting Evidence: PMID:18719252 high-throughput Y2H data set covering approximately 20% of all yeast binary interactions |
| GO:0005515 protein binding | IPI PMID:37968396 The social and structural architecture of the yeast protein ... | REMOVE | Summary: IPI with Lac1 (P28496) from the Michaelis et al. 2023 proteome-wide affinity-enrichment MS interactome. 'Protein binding' is uninformative; the biologically meaningful content (membership of the Lag1/Lac1/Lip1 acyl-CoA ceramide synthase complex) is captured by GO:0061576. Removed per the protein-binding policy; the interaction itself is not disputed. Supporting Evidence: PMID:37968396 Here we develop a sensitive high-throughput method using highly reproducible affinity enrichment coupled to mass spectrometry |
| GO:0005783 endoplasmic reticulum | HDA PMID:11914276 Subcellular localization of the yeast proteome. | ACCEPT | Summary: ER localisation from the Kumar et al. 2002 genome-wide immunolocalisation screen. Consistent with Lag1 being a multi-pass ER membrane protein. Supporting Evidence: PMID:11914276 By high-throughput immunolocalization of tagged gene products, we have determined the subcellular localization of 2744 yeast proteins. PMID:11694577 Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. |
| GO:0005783 endoplasmic reticulum | HDA PMID:14562095 Global analysis of protein localization in budding yeast. | ACCEPT | Summary: ER localisation from the Huh et al. 2003 GFP-fusion collection. Consistent with the known ER membrane location of Lag1. Supporting Evidence: PMID:14562095 Here we describe the construction and analysis of a collection of yeast strains expressing full-length, chromosomally tagged green fluorescent protein fusion PMID:11694577 Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. |
| GO:0005783 endoplasmic reticulum | HDA PMID:22842922 Dissecting DNA damage response pathways by analysing protein... | ACCEPT | Summary: ER localisation recorded in the Tkach et al. 2012 GFP-collection imaging screen (DNA replication stress). Matches the established ER location of Lag1. Supporting Evidence: PMID:22842922 We use high-throughput microscopic screening of the yeast GFP fusion collection PMID:11694577 Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. |
| GO:0005783 endoplasmic reticulum | HDA PMID:26928762 One library to make them all: streamlining the creation of y... | ACCEPT | Summary: ER localisation from the SWAT N-terminal GFP library of endomembrane proteins (Yofe et al. 2016). Matches the established ER location of Lag1. Supporting Evidence: PMID:26928762 we constructed and investigated a library of βΌ1,800 strains carrying SWAT-GFP modules at the amino termini of endomembrane proteins PMID:11694577 Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: PANTHER IBA (PTN000285423, ceramide synthase/TLC family including human CERS1-6, S. pombe Lac1/Lag1 and S. cerevisiae Lag1/Lac1). ER is the conserved site of acyl-CoA dependent ceramide synthesis; correct for Lag1. Supporting Evidence: PMID:11694577 Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell mapping (SL-0097). Lag1 is a multi-pass integral ER membrane protein; this is the most precise location term. Supporting Evidence: file:yeast/LAG1/LAG1-uniprot.txt Endoplasmic reticulum membrane PMID:11694577 Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. |
| GO:0006665 sphingolipid metabolic process | IEA GO_REF:0000041 | TOO GENERAL | Summary: UniPathway mapping (UPA00222 sphingolipid metabolism). Correct but broad; the specific process (ceramide biosynthetic process) is also annotated. Supporting Evidence: file:yeast/LAG1/LAG1-uniprot.txt Component of the ceramide synthase complex that catalyzes the |
| GO:0016020 membrane | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro TLC-domain (IPR006634) mapping to membrane. Correct but less specific than ER membrane, which is also annotated. Supporting Evidence: PMID:11694577 Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. |
| GO:0046513 ceramide biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PANTHER IBA for ceramide biosynthesis across the CerS family. Lag1 (with Lac1) is the acyl-CoA dependent ceramide synthase of yeast; it does the N-acylation step itself, so this is a core process. Supporting Evidence: PMID:11694577 lag1 Ξ lac1 Ξ cells have reduced sphingolipid levels due to a block of the fumonisin B1-sensitive and acyl-CoAβdependent ceramide synthase reaction. PMID:11387200 Here we show that microsomes or detergent extracts from lag1Ξ lac1Ξ double mutants lack an activity transferring C26 fatty acids from C26-coenzyme A onto dihydrosphingosine or phytosphingosine. |
| GO:0046513 ceramide biosynthetic process | IDA PMID:15692566 Lip1p: a novel subunit of acyl-CoA ceramide synthase. | ACCEPT | Summary: Vallee & Riezman 2005 purified tagged Lag1p/Lac1p to near homogeneity and showed they copurify with ceramide synthase activity. Direct biochemical evidence that Lag1 makes ceramide. Supporting Evidence: PMID:15692566 They copurified with ceramide synthase activity, giving unequivocal evidence that they are subunits of the enzyme. PMID:15692566 In purified form, the acyl-CoA dependence, fatty acyl-CoA chain length specificity, and Fumonisin B1/Australifungin sensitivity of the ceramide synthase were the same as in cells |
| GO:0046513 ceramide biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro Lag1/Lac1-like family (IPR016439) mapping. Correct for this experimentally characterised ceramide synthase. Supporting Evidence: PMID:11694577 lag1 Ξ lac1 Ξ cells have reduced sphingolipid levels due to a block of the fumonisin B1-sensitive and acyl-CoAβdependent ceramide synthase reaction. |
| GO:0046513 ceramide biosynthetic process | IMP PMID:11694577 Lag1p and Lac1p are essential for the Acyl-CoA-dependent cer... | ACCEPT | Summary: Schorling et al. 2001: lag1 lac1 double deletion blocks the fumonisin B1-sensitive acyl-CoA dependent ceramide synthase reaction and lowers sphingolipid levels; LAG1 alone complements. Supporting Evidence: PMID:11694577 lag1 Ξ lac1 Ξ cells have reduced sphingolipid levels due to a block of the fumonisin B1-sensitive and acyl-CoAβdependent ceramide synthase reaction. PMID:11694577 underlines the redundant functions of Lag1p and Lac1p. |
| GO:0050291 sphingosine N-acyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PANTHER IBA for ceramide synthase activity (EC 2.3.1.24 family node PTN000285423). GO:0050291 is the only GO term for acyl-CoA ceramide synthase; its sphingosine-specific wording is broader in practice and yeast Lag1 acylates phytosphingosine and dihydrosphingosine with C26-CoA. Core activity. Supporting Evidence: PMID:11387200 Here we show that microsomes or detergent extracts from lag1Ξ lac1Ξ double mutants lack an activity transferring C26 fatty acids from C26-coenzyme A onto dihydrosphingosine or phytosphingosine. file:yeast/LAG1/LAG1-uniprot.txt Reaction=a very long-chain fatty acyl-CoA + a sphingoid base = an N- |
| GO:0050291 sphingosine N-acyltransferase activity | IDA PMID:15692566 Lip1p: a novel subunit of acyl-CoA ceramide synthase. | ACCEPT | Summary: Purified Lag1p/Lac1p preparations carry ceramide synthase activity with the same acyl-CoA specificity and fumonisin B1 sensitivity as in cells (Vallee & Riezman 2005). Supporting Evidence: PMID:15692566 They copurified with ceramide synthase activity, giving unequivocal evidence that they are subunits of the enzyme. PMID:15692566 In purified form, the acyl-CoA dependence, fatty acyl-CoA chain length specificity, and Fumonisin B1/Australifungin sensitivity of the ceramide synthase were the same as in cells |
| GO:0050291 sphingosine N-acyltransferase activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro IPR016439 (Lag1/Lac1-like) mapping to sphingosine N-acyltransferase activity. Correct for Lag1. Supporting Evidence: PMID:11387200 Here we show that microsomes or detergent extracts from lag1Ξ lac1Ξ double mutants lack an activity transferring C26 fatty acids from C26-coenzyme A onto dihydrosphingosine or phytosphingosine. |
| GO:0050291 sphingosine N-acyltransferase activity | IMP PMID:11387200 C26-CoA-dependent ceramide synthesis of Saccharomyces cerevi... | ACCEPT | Summary: Guillas et al. 2001: microsomes/detergent extracts of lag1 lac1 mutants lack transfer of C26 fatty acid from C26-CoA onto dihydrosphingosine or phytosphingosine. Supporting Evidence: PMID:11387200 Here we show that microsomes or detergent extracts from lag1Ξ lac1Ξ double mutants lack an activity transferring C26 fatty acids from C26-coenzyme A onto dihydrosphingosine or phytosphingosine. |
| GO:0050291 sphingosine N-acyltransferase activity | IMP PMID:11694577 Lag1p and Lac1p are essential for the Acyl-CoA-dependent cer... | ACCEPT | Summary: Schorling et al. 2001: lag1 lac1 cells lack the acyl-CoA dependent, fumonisin B1-sensitive ceramide synthase activity. Supporting Evidence: PMID:11694577 lag1 Ξ lac1 Ξ cells have reduced sphingolipid levels due to a block of the fumonisin B1-sensitive and acyl-CoAβdependent ceramide synthase reaction. |
| GO:0061576 acyl-CoA ceramide synthase complex | IDA PMID:15692566 Lip1p: a novel subunit of acyl-CoA ceramide synthase. | ACCEPT | Summary: Lag1 copurifies with Lac1 and Lip1 as the acyl-CoA ceramide synthase complex (Vallee & Riezman 2005); GO:0061576 was defined from this paper. Supporting Evidence: PMID:15692566 They copurified with ceramide synthase activity, giving unequivocal evidence that they are subunits of the enzyme. PMID:15692566 SDS-PAGE analysis of purified ceramide synthase revealed the presence of a novel subunit of the enzyme, Lip1p. |
| GO:0061576 acyl-CoA ceramide synthase complex | IPI PMID:15692566 Lip1p: a novel subunit of acyl-CoA ceramide synthase. | ACCEPT | Summary: Same complex membership supported by co-purification (IPI) in Vallee & Riezman 2005. Supporting Evidence: PMID:15692566 SDS-PAGE analysis of purified ceramide synthase revealed the presence of a novel subunit of the enzyme, Lip1p. |
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Download this section (compressed HTML)Q: Lag1 and Lac1 are redundant for viability but differ in sphingoid-base preference and ER subdomain localisation; does Lag1-specific phytoceramide synthesis have a distinct physiological output (e.g. ER diffusion barriers, lifespan) separable from bulk sphingolipid synthesis?
Experiment: Purify Lag1-only and Lac1-only complexes (with Lip1) and compare kinetic parameters for PHS versus DHS and C24/C26-CoA, to quantify paralog specialisation.
Ceramide synthase component; involved in synthesis of ceramide from C26(acyl)-coenzyme A and dihydrosphingosine or phytosphingosine, functionally equivalent to Lac1p; forms ER foci upon DNA replication stress; homolog of human CERS2, a tumor metastasis suppressor gene whose silencing enhances invasion/metastasis of prostate cancer cells; LAG1 has a paralog, LAC1, that arose from the whole genome duplication
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