Possible involvement of GDI1 protein, a GDP dissociation inhibitor related to vesicle transport, in an amelioration of zinc toxicity in Saccharomyces cerevisiae

The GDI1 protein related vesicle transport system was studied to investigate the possibility that an exclusion of toxic zinc (Zn) from the cytoplasm ameliorates Zn toxicity in Saccharomyces cerevisiae (yeast). A temperature-sensitive gdi1 mutant (originally called sec19), in which the GDP dissociation inhibitor becomes inactive at the non-permissive temperature (37°C), was more sensitive to Zn than its parental GDI1 strain at 32°C (a moderately non-permissive temperature). The relative efflux of cytoplasmic Zn in the gdi1 mutant was lower than that in the control strain. Treatment with a vesicle transport-specific inhibitor, Brefeldin A, caused an increase of Zn sensitivity and a decrease of Zn efflux in these strains. It is therefore suggested that the GDI1-related vesicle transport system contributes to Zn tolerance in yeast. Furthermore, changes in the number of Zn-specific fluorescent granules (zincosomes) were observed by zinquin staining in the mutant cells under Zn treatment at 32°C and 37°C. We concluded that the GDI1 protein is implicated in control of vesicle numbers. Collectively, the results suggest that the GDI1protein is involved in Zn efflux via small vesicle trafficking and contributes to the control of cytoplasmic Zn content, allowing yeast to survive in the presence of toxic Zn.