tailieunhanh - Báo cáo khoa học: Saccharomyces cerevisiae Ybr004c and its human homologue are required for addition of the second mannose during glycosylphosphatidylinositol precursor assembly

Addition of the second mannose is the only obvious step in glycosylphos-phatidylinositol (GPI) precursor assembly for which a responsible gene has not been discovered. A bioinformatics-based strategy identified the essential Saccharomyces cerevisiaeYbr004c protein as a candidate for the second GPIa-mannosyltransferase (GPI-MT-II). S. cerevisiae cells depleted of Ybr004cp have weakened cell walls and abnormal morphology, are unable to incorporate [ 3 H]inositol into proteins, and accumulate a GPI intermedi-ate having a single mannose that is likely modified with ethanolamine phosphate. . | iFEBS Journal Saccharomyces cerevisiae Ybr004c and its human homologue are required for addition of the second mannose during glycosylphosphatidylinositol precursor assembly Anne-Lise Fabre1 Peter Orlean2 and Christopher H. Taron1 1 New England Biolabs Beverly MA USA 2 Department of Microbiology University of Illinois Urbana IL USA Keywords cell wall glycosylphosphatidylinositol mannosyltransferase Saccharomyces cerevisiae Correspondence Christopher H. Taron New England Biolabs 32 Tozer Road Beverly MA 01915 USA Fax 978 9211350 Tel 978 9275054 E-mail taron@ Received 28 October 2004 revised 21 December 2004 accepted 4 January 2005 doi Addition of the second mannose is the only obvious step in glycosylphosphatidylinositol GPI precursor assembly for which a responsible gene has not been discovered. A bioinformatics-based strategy identified the essential Saccharomyces cerevisiae Ybr004c protein as a candidate for the second GPI a-mannosyltransferase GPI-MT-II . S. cerevisiae cells depleted of Ybr004cp have weakened cell walls and abnormal morphology are unable to incorporate 3H inositol into proteins and accumulate a GPI intermediate having a single mannose that is likely modified with ethanolamine phosphate. These data indicate that Ybr004cp-depleted yeast cells are defective in second mannose addition to GPIs and suggest that Ybr004cp is GPI-MT-II or an essential subunit of that enzyme. Ybr004cp homologues are encoded in all sequenced eukaryotic genomes and are predicted to have 8 transmembrane domains but show no obvious resemblance to members of established glycosyltransferase families. The human Ybr004cp homologue can substitute for its S. cerevisiae counterpart in vivo. Glycosylphosphatidylinositols GPIs are key glycolipids produced by all eukaryotes. GPIs become covalently attached to the C-termini of certain secretory proteins and act as anchors to attach such proteins to the outer face of the plasma membrane 1 2 . .