Saccharomyces cerevisiae Vacuole in Zinc Storage and Intracellular Zinc Distribution

Abstract

Previous studies of the yeast Saccharomyces cerevisiae indicated that the vacuole is a major site of zinc storage in the cell. However, these studies did not address the absolute level of zinc that was stored in the vacuole nor did they examine the abundances of stored zinc in other compartments of the cell. In this report, we describe an analysis of the cellular distribution of zinc by use of both an organellar fractionation method and an electron probe X-ray microanalysis. With these methods, we determined that zinc levels in the vacuole vary with zinc status and can rise to almost 100 mM zinc (i.e., 7 ؋ 10 8 atoms of vacuolar zinc per cell). Moreover, this zinc can be mobilized effectively to supply the needs of as many as eight generations of progeny cells under zinc starvation conditions. While the Zrc1 and Cot1 zinc transporters are essential for zinc uptake into the vacuole under steady-state growth conditions, additional transporters help mediate zinc uptake into the vacuole during "zinc shock," when zinc-limited cells are resupplied with zinc. In addition, we found that other compartments of the cell do not provide significant stores of zinc. In particular, zinc accumulation in mitochondria is low and is homeostatically regulated independently of vacuolar zinc storage. Finally, we observed a strong correlation between zinc status and the levels of magnesium and phosphorus accumulated in cells. Our results implicate zinc as a major determinant of the ability of the cell to store these other important nutrients.

MNR2 Regulates Intracellular Magnesium Storage in Saccharomyces cerevisiae

“…Subcellular location of Mnr2: Studies of the distribution of Mg in yeast cells revealed a predominantly vacuolar location (Simm et al 2007), implicating this All strains were generated during this study except for DY1514 (obtained from David Eide), DBY747, mrs2D-2, and lpe10D-1 (obtained from Anton Graschopf). All strains are isogenic to DY1514 except for those isogenic to DBY747 (lpe10D-1, mrs2D-2, NP103, NP107, and NP112).…”

“…In part, this model proposes that, in Mg-replete conditions, an intracellular compartment (most probably the vacuole) provides a storage site for excess Mg. Consistent with this idea, the vacuolar Mg concentration is approximately fourfold higher than the cytoplasmic concentration in Mg-replete yeast cells (Simm et al 2007). The accumulation of excess Mg in the vacuole would require active transport to overcome the charge gradient generated by V-ATPase activity.…”

“…In both wild-type and mnr2 strains, variation in Mg content was associated with altered phosphate content. Previous reports have also noted a close relationship between Mg supply and phosphate accumulation by yeast (Weimberg 1975;Beeler et al 1997;Simm et al 2007). The basis for this correlation is still unclear, however, and further work is required to understand the relationship.…”

“…/H 1 exchanger activity, as this phenotype could result from the inhibition of other processes that may influence Mg accumulation in this compartment, such as polyphosphate synthesis (Beeler et al 1997;Simm et al 2007).…”

“…Previous work (Beeler et al 1997) as well as our observations (Figure 3) show that the initial Mg content of wild-type yeast cells affects the rate of growth upon transfer to Mg-free medium and that Mg content rapidly decreases under these conditions. Because $80% of the Mg content of replete cells is vacuolar (Simm et al 2007), these observations suggest that, when replete cells are transferred to deficient conditions, vacuolar Mg is redistributed to maintain the required concentration in other critical cellular compartments. The effect of the tfp1 mutation on Mg content and the severe growth defect displayed by tfp1 cells transferred to Mg-deficient conditions ( Figure 4B) provide support for this view.…”