title: Gpi19, the Saccharomyces cerevisiae homologue of mammalian PIG-P, is a subunit of the initial enzyme for glycosylphosphatidylinositol anchor biosynthesis.
abstract: Glycosylphosphatidylinositols (GPIs) are attached to the C termini of some glycosylated secretory proteins, serving as membrane anchors for many of those on the cell surface. Biosynthesis of GPIs is initiated by the transfer of N-acetylglucosamine (GlcNAc) from UDP-GlcNAc to phosphatidylinositol. This reaction is carried out at the endoplasmic reticulum (ER) by an enzyme complex called GPI-N-acetylglucosaminyltransferase (GPI-GlcNAc transferase). The human enzyme has six known subunits, at least four of which, GPI1, PIG-A, PIG-C, and PIG-H, have functional homologs in the budding yeast Saccharomyces cerevisiae. The uncharacterized yeast gene YDR437w encodes a protein with some sequence similarity to human PIG-P, a fifth subunit of the GPI-GlcNAc transferase. Here we show that Ydr437w is a small but essential subunit of the yeast GPI-GlcNAc transferase, and we designate its gene GPI19. Similar to other mutants in the yeast enzyme, temperature-sensitive gpi19 mutants display cell wall defects and hyperactive Ras phenotypes. The Gpi19 protein associates with the yeast GPI-GlcNAc transferase in vivo, as judged by coimmuneprecipitation with the Gpi2 subunit. Moreover, conditional gpi19 mutants are defective for GPI-GlcNAc transferase activity in vitro. Finally, we present evidence for the topology of Gpi19 within the ER membrane.
authors.affiliation: Department of Biochemistry & Molecular Biology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, MD 21205-2179, USA.
authors.forename: Heather A
authors.initials: HA
authors.lastname: Newman
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Romeo
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Lewis
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Yan
authors.forename: Peter
authors.initials: P
authors.lastname: Orlean
authors.forename: David E
authors.initials: DE
authors.lastname: Levin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols / Q000096:biosynthesis* / Q000378:metabolism*; D006602:Hexosyltransferases; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D015815:Cell Adhesion Molecules; D017261:Glycosylphosphatidylinositols; D008565:Membrane Proteins; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; D005964:Glucosyltransferases; D006602:Hexosyltransferases; D017351:N-Acetylglucosaminyltransferases; C508482:Gpi19 protein, S cerevisiae; C414441:PIGP protein, human; D018631:ras Proteins