Protein sorting in the late Golgi of Saccharomyces cerevisiae does not require mannosylated sphingolipids.
Glycosphingolipids are widely viewed as integral components of the Golgi-based machinery by which membrane proteins are targeted to compartments of the endosomal/lysosomal system and to the surface domains of polarized cells. The yeast Saccharomyces cerevisiae creates glycosphingolipids by transferring mannose to the head group of inositol phosphorylceramide (IPC), yielding mannosyl-IPC (MIPC). Addition of an extra phosphoinositol group onto MIPC generates mannosyldi-IPC (M(IP)2C), the final and most abundant sphingolipid in yeast. Mannosylation of IPC is partially dependent on CSG1, a gene encoding a putative sphingolipidmannosyltransferase. Here we show that open reading frame YBR161w, renamed CSH1, is functionally homologous to CSG1 and that deletion of both genes abolishes MIPC and M(IP)2C synthesis without affecting protein mannosylation. Csg1p and Csh1p are closely related polytopic membrane proteins that co-localize with IPC synthase in the medial-Golgi. Loss of Csg1p and Csh1p has no effect on clathrin- or AP-3 adaptor-mediated protein transport from the Golgi to the vacuole. Moreover, segregation of the periplasmic enzyme invertase, the plasma membrane ATPase Pma1p and the glycosylphosphatidylinositol-anchored protein Gas1p into distinct classes of secretory vesicles occurs independently of Csg1p and Csh1p. Our results indicate that protein sorting in the late Golgi of yeast does not require production of mannosylated sphingolipids.
Department of Membrane Enzymology, Utrecht University Faculty of Chemistry, 3584 CH Utrecht, The Netherlands.
Quirine
Q
Lisman
Thomas
T
Pomorski
Chantal
C
Vogelzangs
Dorothy
D
Urli-Stam
William
W
de Cocq van Delwijnen
Joost C M
JC
Holthuis
D000251:Adenosine Triphosphatases / Q000737:chemistry; D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry; D006028:Glycosphingolipids / Q000737:chemistry; D016695:Glycosyltransferases; D006056:Golgi Apparatus / Q000378:metabolism*; D015151:Immunoblotting; D008055:Lipids / Q000737:chemistry; D008358:Mannose / Q000737:chemistry*; D008364:Mannosyltransferases / Q000737:chemistry; D008562:Membrane Glycoproteins / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D006180:Proton-Translocating ATPases / Q000737:chemistry; D012097:Repressor Proteins / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013107:Sphingolipids / Q000737:chemistry* / Q000378:metabolism; D013347:Subcellular Fractions
C430064:CSH1 protein, Candida albicans; D005656:Fungal Proteins; D006028:Glycosphingolipids; D008055:Lipids; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C075636:OCH1 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D013107:Sphingolipids; C477937:inositolphosphorylceramide; D016695:Glycosyltransferases; C092031:SUR1 protein, S cerevisiae; D008364:Mannosyltransferases; D000251:Adenosine Triphosphatases; C092477:PMA1 protein, S cerevisiae; D006180:Proton-Translocating ATPases; D008358:Mannose