Cell wall integrity phenotype of Saccharomyces cerevisae with erd1 and gda1 double Mutations

We studied the roles of glycosylation in the cell wall structure of yeast. The yeast cell wall is composed of glucan and mannoproteins. Mannoproteins are primarily glycolylated in the Golgi apparatus. The substrate for mannosylation is GDP‐mannose which is transported to the Golgi from the cytoplasm. Transfer of mannose to protein releases free GDP in the Golgi. A functional GDPase, a gene product of GDA1 , hydrolyses this GDP to GMP, which in turn, exits the Golgi in a transport mechanism coupled to the entry of GDP‐Mannose. It is well known that defects in GDPase result in defects in O ‐glycosylation and N ‐glycosylation of mannoproteins. Such defects in glycosylation have been shown to compromise the integrity of the cell wall, as measured by susceptibility to lysis. The ERD1 gene plays a role in retention of proteins in the ER. Consequently, the erd1 mutation causes resident ER proteins to be secreted. We have found that erd1 negatively affects O ‐glycosylation, and the integrity of cell wall, although the effects were less than that of gda1 mutation. It was consequently expected that the erd1gda1 double mutant would have a susceptibility to lysis greater than that of gda1 . Our result, surprisingly, indicated that erd1 partially rescued the gda1 mutation with respect to cell wall phenotype. The gda1erd1 double mutant was more resistant to Zymolyase spheroplasting than the gda1single mutant.