Biochemical Properties of Vacuolar Zinc Transport Systems ofSaccharomyces cerevisiae

Abstract

The yeast vacuole plays an important role in zinc homeostasis by storing zinc for later use under deficient conditions, sequestering excess zinc for its detoxification, and buffering rapid changes in intracellular zinc levels. The mechanisms involved in vacuolar zinc sequestration are only poorly characterized. Here we describe the properties of zinc transport systems in yeast vacuolar membrane vesicles. The major zinc transport activities in these vesicles were ATP-dependent, requiring a H ؉ gradient generated by the V-ATPase for function. One system we identified was dependent on the ZRC1 gene, which encodes a member of the cation diffusion facilitator family of metal transporters. These data are consistent with the proposed role of Zrc1 as a vacuolar zinc transporter. Zrc1-independent activity was also observed that was not dependent on the closely related vacuolar Cot1 protein. Both Zrc1-dependent and independent activities showed a high specificity for Zn 2؉ over other physiologically relevant substrates such as Ca 2؉ , Fe 2؉ , and Mn 2؉ . Moreover, these systems had high affinities for zinc with apparent K m values in the 100 -200 nM range. These results provide biochemical insight into the important role of Zrc1 and related proteins in eukaryotic zinc homeostasis.

Influence of Zinc on Distiller's Yeast: Cellular Accumulation of Zinc and Impact on Spirit Congeners

“…Despite the fact that alcohol dehydrogenase ADH (the terminal enzyme in ethanol fermentation) is a zinc metalloenzyme 20 , yeast cells with high zinc content produced low concentrations of ethanol. This could be related to zinc accumulation in vacuoles 18,19,22,8 not made available to ADH or to the presence in the studied strains of other zinc enzymes with higher affinities for Zn.…”

“…The difference in zinc concentration did not depend on cell competition for zinc as the final cell number was similar in the wine and distiller's strain population (10 8 cells/mL). Since zinc translocates primarily to the yeast vacuole 8,18,19,22 , it is conceivable that yeast with larger cell volumes, and consequently bigger vacuoles, are able to accumulate more zinc than smaller cells. However, the capability to accumulate zinc at higher concentrations could also depend on other factors such as the presence of Zn-binding intra-vacuolar components (e.g., polyphosphate bodies) 17 .…”

“…Zinc is then subsequently translocated to the yeast vacuole 8,18,19,22 . Temperature, pH and metabolic inhibitors all influence zinc sequestration by yeast cells 11,12,24,28,35 .…”

OmZnT1 and OmFET, two metal transporters from the metal-tolerant strain Zn of the ericoid mycorrhizal fungus Oidiodendron maius, confer zinc tolerance in yeast

“…CDF transporters were first described in S. cerevisiae (Zrc1p) ( Kamizono et al, 1989) and in the Gram-negative bacteria Ralstonia metallidurans (CzcD) ( Nies, 1992), but they were later also found in plants and animals (see in Montanini et al, 2007). The key feature of the CDF transporters is that they export zinc and/or other metal ions out of the cells, or they sequester them into intracellular compartments ( Eide, 2006and Peiter et al, 2007, thus reducing cytosolic metal concentrations ( Anton et al, 1999 andMacDiarmid et al, 2002).…”

“…Similarly, FETD, the FET4 ortholog of Aspergillus fumigatus, was involved in the accumulation of zinc during iron starvation ( Yasmin et al, 2009). The CDF transporters Zrc1p and Cot1p are the major determinants of zinc tolerance in yeast (Gaither and Eide, 2001), and they are responsible for the vacuolar delivery and sequestration of zinc ( MacDiarmid et al, 2000 andMacDiarmid et al, 2002). Two other CDF members, Msc2p and Zrg17p, form a heteromeric zinc transport complex in the ER membranes, and have been implicated in the homeostatic maintenance of ER function (Ellis et al, 2004 andEllis et al, 2005).…”