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: To investigate whether Cdc1 may be involved in the removal of EtN-P from Man1, we produced a cdc1∆/mcd4∆ haploid strain harboring two different plasmids carrying yeast CDC1 and TbGPI10. MCD4 is an essential gene, because Gpi10, the mannosyltransferase adding Man3, does not work on GPI lipid intermediates lacking EtN-P on Man1, but MCD4 becomes nonessential if yeast harbors the GPI10 orthologue from Trypanosoma brucei, a species that does not add EtN-P onto Man1 (Zhu et al., 2006). Mcd4∆ cells have dividing times three times longer than WT in liquid media and also grow badly on plates (Zhu et al., 2006). As shown in Figure 2, cdc1∆ harboring TbGpi10 is unable to grow but mcd4∆/cdc1∆ harboring TbGpi10 grows as fast as mcd4∆ harboring TbGpi10. This indicates that deletion of CDC1 in a mcd4∆ background has no negative growth effect and our data (see Figure 6A, rows mcd4∆ and mcd4∆/cdc1, later in this article) show that it does not aggravate the cell wall defect of mcd4∆. Thus, whatever the problem caused by the deletion of the essential CDC1 gene may be, it is fully compensated by not adding EtN-P to Man1 during the biosynthesis of the GPI lipid precursor. This constellation strongly suggests that Cdc1 has specialized in removing EtN-P from Man1.
Affiliation: Department of Biology, University of Fribourg, CH-1700 Fribourg, Switzerland.