title: Csg1p and newly identified Csh1p function in mannosylinositol phosphorylceramide synthesis by interacting with Csg2p.
abstract: Csg1p and Csg2p have been shown to be involved in the synthesis of mannosylinositol phosphorylceramide (MIPC) from inositol phosphorylceramide. YBR161w, termed CSH1 here, encodes a protein that exhibits a strong similarity to Csg1p. To examine whether Csh1p also functions in MIPC synthesis, we performed a [3H]dihydrosphingosine labeling experiment. Deltacsg1 cells exhibited only a reduction in the synthesis of mannosylated sphingolipids compared with wild-type cells, whereas the Deltacsg1 Deltacsh1 double deletion mutant exhibited a total loss. These results indicated that Csg1p and Csh1p have redundant functions in MIPC synthesis. Analyses using Deltacsg1 and Deltacsh1 cells in the Deltaipt1, Deltasur2, or Deltascs7 genetic background demonstrated that Csh1p has a different substrate specificity from Csg1p. We also revealed that Csg2p interacts with both Csg1p and Csh1p. Deletion of the CSG2 gene reduced the Csg1p activity and abolished the Csh1p activity. These results suggested that two distinct inositol phosphorylceramide mannosyltransferase complexes, Csg1p-Csg2p and Csh1p-Csg2p, exist.
authors.affiliation: Department of Biomembrane and Biofunctional Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita 12-jo, Nishi 6-choume, Kita-ku, Sapporo 060-0812, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Uemura
authors.forename: Akio
authors.initials: A
authors.lastname: Kihara
authors.forename: Jin-Ichi
authors.initials: J
authors.lastname: Inokuchi
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Igarashi
mesh_terms: D000595:Amino Acid Sequence; D002518:Ceramides / Q000096:biosynthesis*; D005656:Fungal Proteins / Q000378:metabolism / Q000502:physiology*; D017353:Gene Deletion; D005838:Genotype; D006028:Glycosphingolipids / Q000096:biosynthesis* / Q000737:chemistry*; D016695:Glycosyltransferases; D015151:Immunoblotting; D008358:Mannose / Q000737:chemistry; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism / Q000502:physiology*; D013107:Sphingolipids / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: C430064:CSH1 protein, Candida albicans; D002518:Ceramides; D005656:Fungal Proteins; D006028:Glycosphingolipids; D008565:Membrane Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D013107:Sphingolipids; C479822:mannosylinositol phosphoylceramide; D016695:Glycosyltransferases; C092031:SUR1 protein, S cerevisiae; D008358:Mannose