Cdc1 removes the ethanolamine phosphate of the first mannose of GPI anchors and thereby facilitates the integration of GPI proteins into the yeast cell wall.
Bottom Line: Cdc1-314(ts) mutants do not accumulate GPI proteins in the ER but have a partial secretion block later in the secretory pathway.Osmotic support restores GPI protein secretion and actin polarization but not growth.This suggests that the presumed transglycosidases Dfg5 and Dcw1 of cdc1-314(ts) transfer GPI proteins to cell wall β1,6-glucans inefficiently.
Affiliation: Department of Biology, University of Fribourg, CH-1700 Fribourg, Switzerland.Show MeSH
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Mentions: The activity transferring GPI proteins from the plasma membrane onto β-glucans may reside with Dfg5 and Dcw1, two highly homologous GPI proteins (54% identity; Kitagaki et al., 2002). During the transfer of GPI-CWPs to cell wall glucans, the glucosamine–inositol–phospholipid moiety of the anchor is lost, whereas four to five mannoses (Man), the phosphodiester bond, and the bridging ethanolamine (EtN) remain attached to the protein (Figure 1). Therefore Dfg5 and Dcw1, having homology with bacterial endomannosidases, are proposed to cleave the Manα1,4glucosamine linkage of the GPI anchor and to reattach the liberated Man residue with the attached GPI protein to β1,6-glucans of the cell wall (Kollar et al., 1997; Fujii et al., 1999; Kitagaki et al., 2002). Simultaneous deletion of DFG5 and DCW1 is lethal, suggesting that the covalent attachment of GPI-CWPs to glucans is essential, and this remains true even if cells receive osmotic support (Kitagaki et al., 2002).
Affiliation: Department of Biology, University of Fribourg, CH-1700 Fribourg, Switzerland.