STRUCTURES OF GLYCOSYLPHOSPHATIDYLINOSITOL MEMBRANE ANCHORS FROM SACCHAROMYCES-CEREVISIAE

Metabolic labeling studies suggest that Saccharomyces cerevisiae conta ins many glycoproteins that are anchored in the lipid bilayer by glyco sylphosphatidylinositol membrane anchors. Membrane anchors were purifi ed from a crude yeast membrane protein fraction and analyzed by two-di mensional H-1-H-1 NMR, fast atom bombardment-mass spectrometry, compos itional and methylation linkage analyses, as well as chemical and enzy matic modifications. The yeast glycosylphosphatidylinositol anchors co nsist of the following structures: analpha1-4Glc-NH2alpha1-6myo-inosit ol-1-PO4-lipid, where R is mainly Manalpha1- (80%) with some Manalpha1 -2Manalpha1- (15%) and Manalpha1-3Manalpha1- (5%). The core region of the yeast anchors pha1-6Manalpha1-4GlcNH2alpha1-6myo-inositol-1-PO4) i s identical to the conserved core region found in glycosylphosphatidyl inositol anchors from protozoa and mammals. The lipid moieties of the total yeast glycosylphosphatidylinositol anchors are mainly ceramides, consisting mostly of C18:0 phytosphingosine and C26:0 fatty acid. How ever, the lipid moiety of the glycosylphosphatidylinositol anchor of t he purified ggp125 protein is a lyso- or diacylglycerol, containing C2 6:0 fatty acids. This suggests that yeast adds different lipid compone nts to the glycosylphosphatidylinositol anchors of different proteins.