imt1 (SPAC2F3.01; imt1; UniProt O14084) encodes one of three redundant Golgi inositol phosphoceramide mannosyltransferases (imt1-imt3; SUR1/CSH1 homologues) that mannosylate IPC to MIPC, the terminal and most abundant complex sphingolipid of fission yeast. Single imt mutants are viable, but the triple disruptant lacks MIPC and accumulates IPC. It then shows defects in cell and vacuole morphology, ergosterol distribution and endocytic sorting of a plasma-membrane amino acid transporter.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000030 mannosyltransferase activity | IBA GO_REF:0000033 | TOO GENERAL | Summary: PAINT inference of generic mannosyltransferase activity; the specific IPC mannosyltransferase activity, which entails it, is annotated elsewhere in this review. Reason: The IBA is sound (imt1 is in the PANTHER mannosyl phosphorylinositol ceramide synthase family, PTHR32385), but the term is a broad parent. Inositol phosphorylceramide mannosyltransferase activity (GO:0103064), already on the gene, is_a mannosyltransferase activity. It rests on UniProt's curated function from the S. pombe triple-disruptant study (ECO:0000269|PubMed:20388730). Supporting Evidence: file:SCHPO/imt1/imt1-uniprot.txt Catalyzes the addition of mannosyl to phosphorylinositol ceramide (IPC). PMID:20388730 MIPC was not detected and IPC levels were increased in the triple disruptant, indicating that the three SUR1 homologues are involved in the synthesis of MIPC. |
| GO:0005794 Golgi apparatus | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: ORFeome screen: Golgi. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins |
| GO:0005794 Golgi apparatus | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping to Golgi apparatus. Reason: The root organelle term is sound. UniProt records cis- and trans-Golgi network membrane locations, and GFP-Imt1p localises to Golgi membranes in S. pombe (PMID:20388730); the sub-compartment rows (cis-/trans-Golgi network membrane, IDA) sit beside this one. Supporting Evidence: file:SCHPO/imt1/imt1-uniprot.txt SUBCELLULAR LOCATION: Golgi apparatus, cis-Golgi network membrane; PMID:20388730 GFP-tagged Imt1p, Imt2p and Imt3p localized to Golgi apparatus membranes. |
| GO:0005802 trans-Golgi network | IDA PMID:20388730 Mannosylinositol phosphorylceramide is a major sphingolipid ... | ACCEPT | Summary: GFP-Imt proteins localise to Golgi membranes. Supporting Evidence: PMID:20388730 GFP-tagged Imt1p, Imt2p and Imt3p localized to Golgi apparatus membranes. |
| GO:0006673 inositol phosphoceramide metabolic process | IEA GO_REF:0000117 | MODIFY | Summary: IPC metabolism (ARBA mapping); true, since Imt1 mannosylates IPC, but a parent of the MIPC biosynthesis term the gene already carries. Reason: GO:0051999 mannosyl-inositol phosphorylceramide biosynthetic process is an is_a descendant (via GO:0006675) of inositol phosphoceramide metabolic process and is supported for imt1 by IGI/IMP (PMID:20388730), where the triple disruptant lacks MIPC and accumulates IPC. Proposed replacements: mannosyl-inositol phosphorylceramide biosynthetic process Supporting Evidence: PMID:20388730 MIPC was not detected and IPC levels were increased in the triple disruptant, indicating that the three SUR1 homologues are involved in the synthesis of MIPC. file:SCHPO/imt1/imt1-uniprot.txt Catalyzes the addition of mannosyl to phosphorylinositol ceramide (IPC). |
| GO:0006688 glycosphingolipid biosynthetic process | IEA GO_REF:0000117 | MODIFY | Summary: Glycosphingolipid biosynthesis (MIPC is a mannosylated sphingolipid); true but a parent of the MIPC biosynthesis term the gene already carries. Reason: GO:0051999 mannosyl-inositol phosphorylceramide biosynthetic process is a descendant of glycosphingolipid biosynthetic process and is supported for imt1 by IGI/IMP (PMID:20388730). Proposed replacements: mannosyl-inositol phosphorylceramide biosynthetic process Supporting Evidence: PMID:20388730 MIPC was not detected and IPC levels were increased in the triple disruptant, indicating that the three SUR1 homologues are involved in the synthesis of MIPC. |
| GO:0032588 trans-Golgi network membrane | IDA PMID:20388730 Mannosylinositol phosphorylceramide is a major sphingolipid ... | ACCEPT | Summary: Golgi membrane localisation of GFP-Imt. Supporting Evidence: PMID:20388730 GFP-tagged Imt1p, Imt2p and Imt3p localized to Golgi apparatus membranes. |
| GO:0033106 cis-Golgi network membrane | IDA PMID:20388730 Mannosylinositol phosphorylceramide is a major sphingolipid ... | ACCEPT | Summary: Golgi membrane localisation of GFP-Imt. Supporting Evidence: PMID:20388730 GFP-tagged Imt1p, Imt2p and Imt3p localized to Golgi apparatus membranes. |
| GO:0051999 mannosyl-inositol phosphorylceramide biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference of MIPC biosynthesis for the SUR1/CSH1 family; confirmed by S. pombe genetics. Reason: Corroborated by the S. pombe triple-disruptant lipid analysis (PMID:20388730); that evidence is collective for imt1-imt3, which act redundantly. Supporting Evidence: PMID:20388730 MIPC was not detected and IPC levels were increased in the triple disruptant, indicating that the three SUR1 homologues are involved in the synthesis of MIPC. |
| GO:0051999 mannosyl-inositol phosphorylceramide biosynthetic process | IGI PMID:20388730 Mannosylinositol phosphorylceramide is a major sphingolipid ... | ACCEPT | Summary: The imt1 imt2 imt3 triple disruptant lacks MIPC and accumulates IPC. Supporting Evidence: PMID:20388730 MIPC was not detected and IPC levels were increased in the triple disruptant, indicating that the three SUR1 homologues are involved in the synthesis of MIPC. |
| GO:0051999 mannosyl-inositol phosphorylceramide biosynthetic process | IMP PMID:20388730 Mannosylinositol phosphorylceramide is a major sphingolipid ... | ACCEPT | Summary: As above. Supporting Evidence: PMID:20388730 MIPC was not detected and IPC levels were increased in the triple disruptant, indicating that the three SUR1 homologues are involved in the synthesis of MIPC. |
| GO:0103064 inositol phosphorylceramide mannosyltransferase activity | ISO GO_REF:0000024 | ACCEPT | Summary: Transfer from S. cerevisiae Sur1/Csh1: IPC mannosyltransferase activity. Reason: UniProt's curated function statement (ECO:0000269, PubMed:20388730) assigns IPC mannosylation to imt1; the S. pombe evidence behind it is genetic (loss of MIPC in the triple disruptant), not an in vitro assay of Imt1 alone, so the activity call also rests on the S. cerevisiae Sur1/Csh1 orthologs that are the ISO source. Supporting Evidence: file:SCHPO/imt1/imt1-uniprot.txt Catalyzes the addition of mannosyl to phosphorylinositol ceramide (IPC). PMID:20388730 MIPC was not detected and IPC levels were increased in the triple disruptant, indicating that the three SUR1 homologues are involved in the synthesis of MIPC. |
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