Involvement
of Cwh8p in the sphigolipids biosynthesis in yeast S. cervisiae.
Martine Pittet,
Andreas Conzelmann
Institute for Biochemistry, University of Fribourg, Ch. du Musée 5, Fribourg,
1700, Switzerland (martine.pittet2@unifr.ch)
In the yeast Saccharomyces cervisiae Cwh8p (encoded by the gene YGR036c) is now known to be involved in the dolichol metabolism as a phosphatase for dolichol pyrophosphate. This allows to recycle the dolichol carriers used for the formation of the core oligosaccharide that is then transferred onto proteins for glycosylation (Fernandez F. et al, JBC 2001, 276 (44) : 41455-64). In this mutant the glycoproteins are underglycosylated but oligosaccharides have a normal structures (vanBerkel M.A.A., et al, Glycobiology, 1999, 9 (3) : 243-253). We found that cwh8 mutant present another particularity in that they have a defect in sphingolipid biosynthesis. After labeling with [3H]-inositol, the strain presents a decreased level of IPC compared to isogenic wild type and an accumulation of PI. Complementation of the mutant with a plasmid containing CWH8 can rescue this defect. The link between the function of Cwh8p and this defect in sphingolipid biosynthesis remains to be identified. Defects in ceramide synthase or in IPC synthase have been excluded. This strain presents a slight unfolded protein response (UPR) induction and an overproduction of inositol (opi-phenotype) but none of these particularities has any influence on the sphingolipid biosynthesis pathway and do not decrease the level of IPCs. Data indicate that N-glycosylation may be involved in this curious phenotype in other genetic background.