Department of Membrane Transport, Institute of Physiology Academy of Sciences of the Czech Republic, Prague, Czech Republic.
Curr Genet. 2012 Dec;58(5-6):255-64. doi: 10.1007/s00294-012-0381-7. Epub 2012 Sep 5.
Three different transport systems exist to accumulate a sufficient amount of potassium cations in yeasts. The most common of these are Trk-type transporters, which are used by all yeast species. Though most yeast species employ two different types of transporters, we only identified one gene encoding a potassium uptake system (Trk-type) in the genome of the highly osmotolerant yeast Zygosaccharomyces rouxii, and our results showed that ZrTrk1 is its major (and probably only) specific potassium uptake system. When expressed in Saccharomyces cerevisiae, the product of the ZrTRK1 gene is localized to the plasma membrane and its presence efficiently complements the phenotypes of S. cerevisiae trk1∆ trk2∆ cells. Deletion of the ZrTRK1 gene resulted in Z. rouxii cells being almost incapable of growth at low K(+) concentrations and it changed some cell physiological parameters in a way that differs from S. cerevisiae. In contrast to S. cerevisiae, Z. rouxii cells without the TRK1 gene contained less potassium than the control cells and their plasma membrane was significantly hyperpolarized compared with those of the parental strain when grown in the presence of 100 mM KCl. On the other hand, subsequent potassium starvation led to a substantial depolarization which is again different from S. cerevisiae. Plasma-membrane hyperpolarization did not prevent the efflux of potassium from Z. rouxii trk1Δ cells during potassium starvation, and the activity of ZrPma1 is less affected by the absence of ZrTRK1 than in S. cerevisiae. The use of a newly constructed Z. rouxii-specific plasmid for the expression of pHluorin showed that the intracellular pH of the Z. rouxii wild type and the trk1∆ mutant is not significantly different. Together with the fact that Z. rouxii cells contain a significantly lower amount of intracellular potassium than identically grown S. cerevisiae cells, our results suggest that this highly osmotolerant yeast species maintain its intracellular pH and potassium homeostasis in way(s) partially distinct from S. cerevisiae.
三种不同的转运系统存在于酵母中，用于积累足够数量的钾阳离子。其中最常见的是 Trk 型转运蛋白，所有酵母物种都使用这种转运蛋白。尽管大多数酵母物种使用两种不同类型的转运蛋白，但我们只在高度耐渗酵母 Zygosaccharomyces rouxii 的基因组中鉴定出一个编码钾摄取系统（Trk 型）的基因，并且我们的结果表明 ZrTrk1 是其主要（可能是唯一）特定的钾摄取系统。当在酿酒酵母中表达时，ZrTRK1 基因的产物定位于质膜上，其存在有效地补充了 S. cerevisiae trk1∆ trk2∆ 细胞的表型。ZrTRK1 基因的缺失导致 Z. rouxii 细胞几乎无法在低 K+浓度下生长，并且它以不同于 S. cerevisiae 的方式改变了一些细胞生理参数。与 S. cerevisiae 不同，没有 TRK1 基因的 Z. rouxii 细胞比对照细胞含有更少的钾，并且当在 100 mM KCl 存在下生长时，它们的质膜比亲本菌株明显超极化。另一方面，随后的钾饥饿导致显著去极化，这与 S. cerevisiae 再次不同。质膜超极化并没有阻止 Z. rouxii trk1Δ 细胞在钾饥饿期间钾的外流，并且 ZrPma1 的活性受 ZrTRK1 缺失的影响小于 S. cerevisiae。使用新构建的 Z. rouxii 特异性质粒表达 pHluorin 表明，Z. rouxii 野生型和 trk1∆ 突变体的细胞内 pH 没有显著差异。再加上 Z. rouxii 细胞比相同生长的 S. cerevisiae 细胞含有显著更少的细胞内钾的事实，我们的结果表明，这种高度耐渗的酵母物种以部分不同于 S. cerevisiae 的方式维持其细胞内 pH 和钾稳态。
