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Eukaryotic Cell, November 2005, p. 1801-1807, Vol. 4, No. 11
1535-9778/05/$08.00+0     doi:10.1128/EC.4.11.1801-1807.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Gpi19, the Saccharomyces cerevisiae Homologue of Mammalian PIG-P, Is a Subunit of the Initial Enzyme for Glycosylphosphatidylinositol Anchor Biosynthesis

Heather A. Newman,1 Martin J. Romeo,1,{dagger} Sarah E. Lewis,1 Benjamin C. Yan,2 Peter Orlean,2 and David E. Levin1*

Department of Biochemistry & Molecular Biology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, Maryland 21205,1 Department of Microbiology, University of Illinois, Urbana-Champaign, Urbana, Illinois 618012

Received 30 August 2005/ Accepted 7 September 2005

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.

* Corresponding author. Mailing address: Department of Biochemistry & Molecular Biology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, MD 21205-2179. Phone: (410) 955-9825. Fax: (410) 955-2926. E-mail: levin{at}jhmi.edu.

{dagger} Present address: Laboratory of Pathology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.

Eukaryotic Cell, November 2005, p. 1801-1807, Vol. 4, No. 11
1535-9778/05/$08.00+0     doi:10.1128/EC.4.11.1801-1807.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Orlean, P., Menon, A. K. (2007). Thematic review series: Lipid Posttranslational Modifications. GPI anchoring of protein in yeast and mammalian cells, or: how we learned to stop worrying and love glycophospholipids. J. Lipid Res. 48: 993-1011 [Abstract] [Full Text]  


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