Potassium Starvation in Yeast: Mechanisms of Homeostasis Revealed by Mathematical Modeling (original) (raw)
Related papers
2012
Saccharomyces cerevisiae wild-type (BY4741) and the corresponding mutant lacking the plasma membrane main potassium uptake systems (trk1,trk2) were used to analyze the consequences of K + starvation following a proteomic approach. In order to trigger high-affinity mode of potassium transport, cells were transferred to potassium-free medium. Protein profile was followed by two-dimensional (2-D) gels in samples taken at 0, 30, 60, 120, 180, and 300 min during starvation. We observed a general decrease of protein content during starvation that was especially drastic in the mutant strain as it was the case of an important number of proteins involved in glycolysis. On the contrary, we identified proteins related to stress response and alternative energetic metabolism that remained clearly present. Neural networkbased analysis indicated that wild type was able to adapt much faster than the mutant to the stress process. We conclude that complete potassium starvation is a stressful process for yeast cells, especially for potassium transport mutants, and we propose that less stressing conditions should be used in order to study potassium homeostasis in yeast.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2014
Saccharomyces cerevisiae cells are able to grow at very different potassium concentrations adapting its intracellular cation levels to changes in the external milieu. Potassium homeostasis in wild type cells resuspended in media with low potassium is an example of non-perfect adaptation since the same intracellular concentration is not approached irrespective of the extracellular levels of the cation. By using yeasts lacking the Trk1,2 system or expressing different versions of the mutated main plasma membrane potassium transporter (Trk1), we show that Trk1 is not essential for adaptation to potassium changes but the dynamics of potassium loss is very different in the wild type and in trk1,2 mutant or in yeasts expressing Trk1 versions with highly impaired transport characteristics. We also show that the pattern here described can be also fulfilled by heterologous expression of NcHAK1, a potassium transporter not belonging to the TRK family. Hyperpolarization and cationic drugs sensitivity in mutants with defective transport capacity provide additional support to the hypothesis of connections between the activity of the Trk system and the plasma membrane H + ATPase (Pma1) in the adaptive process.
Dual System for Potassium Transport In Saccharomyces Cerevisiae
Journal of bacteriology, 1984
Like all other organisms, Saccharomyces cerevisiae accu-mulates K+ from the external medium to fulfill cellular requirements. The transport of K+ in yeasts has been the subject of very extensive studies (2) that have clarified many kinetic aspects of the process. All of the alkali cations ...
The short-term response of yeast to potassium starvation
Environmental Microbiology, 2012
Potassium is the major intracellular cation in most living cells, including yeasts. Although K + has been demonstrated to be necessary for diverse cellular functions, such as enzyme activation, additional, still uncharacterized cellular targets may exist. We show here that in Saccharomyces cerevisiae short-term potassium deprivation impacts in the mRNA level of over one thousand genes. Lack of potassium drastically alters sulfur metabolism (mainly Met and Cys metabolism), triggers an oxidative stress response and activates the retrograde pathway, possibly due to the ammonium accumulation that occurs through the Trk1 potassium transporter. We also observe a remarkable halt in the expression of genes required for ribosome biogenesis and translation, a decrease in expression of diverse components (cyclins, protein kinases) required for progression through the cell cycle and a blockage in septins assembly. Only specific subsets of these changes were observed in a strain deleted for the TRK1 and TRK2 genes growing in the presence of sufficient potassium (50 mM). Therefore, a shortage of potassium in the environment triggers an acute transcriptional response, which covers different aspects of the cell biology so far unexplored, and whose investigation will likely reveal novel functional roles for this cation.
FEMS Yeast Research, 2010
A new YNB medium containing very low concentrations of alkali metal cations has been developed to carry out experiments to study potassium homoeostasis. Physiological characterization of Saccharomyces cerevisiae BY4741 strain and the corresponding mutant lacking the main potassium uptake systems (trk1 trk2) under potassium nonlimiting and limiting concentrations was performed, and novel important differences between both strains were found. At nonlimiting concentrations of KCl, the two strains had a comparable cell size and potassium content. Nevertheless, mutants were hyperpolarized, had lower pH and extruded fewer protons compared with the BY4741 strain. Upon transfer to K 1-limiting conditions, cells of both strains became hyperpolarized and their cell volume and K 1 content diminished; however, the decrease was more relevant in BY4741. In low potassium, trk1 trk2 cells were not able to accomplish the cell cycle to the same extent as in BY4741. Moreover, K 1 limitation triggered a high-affinity K 1 /Rb 1 uptake process only in BY4741, with the highest affinity being reached as soon as 30 min after transfer to potassium-limiting conditions. By establishing basic cellular parameters under standard growth conditions, this work aims to establish a basis for the investigation of potassium homoeostasis at the system level.
Regulation of potassium fluxes in Saccharomyces cerevisiae
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1990
To investigate the regulation of K + fluxes in Saccharomyces cerevisiae the dependence of K + efflux and Rb + influx on [K+]i, pHi, [Na+h, membrane potential, cell volume, and turgor pressure were studied in cells with different K + contents. By decreasing the cell volume with osmotic shocks and the cellular pH with butyric acid the following was found. (1) The K ÷ efflux induced by uncouplers decreases simultaneously with the decrease of the K + content of the ceil, but the process was insensitive to [K +]i, pHi, cell volume and turgor pressure. The internal presence of Na + inhibited this K + efflux. (2) The increase of the Vmax of Rb ÷ influx observed in low-K + cells is due to the decrease of the pH i and probably mediated by the increase of the activity of the plasma membrane ATPase. The Vmx is independent of [K+]i, [Na+]i, cell volume and turgor pressure. (3) The decrease in the K m of Rb + influx observed in iow-K + cells does not depend directly on [K+]i, pHi, cell volume or turgor pressure. If Na + is present, [Na+]i might be directly involved in the regulation of the K m.
Potassium uptake system Trk2 is crucial for yeast cell viability during anhydrobiosis
FEMS Microbiology Letters, 2014
Yeasts grow at very different potassium concentrations, adapting their intracellular cation levels to changes in the external environment. Potassium homeostasis is maintained with the help of several transporters mediating the uptake and efflux of potassium with various affinities and mechanisms. In the model yeast Saccharomyces cerevisiae, two uptake systems, Trk1 and Trk2, are responsible for the accumulation of a relatively high intracellular potassium content (200-300 mM) and the efflux of surplus potassium is mediated by the Tok1 channel and active exporters Ena ATPase and Nha1 cation/proton antiporter. Using a series of deletion mutants, we studied the role of individual potassium transporters in yeast cell resistance to dehydration. The Trk2 transporter (whose role in S. cerevisiae physiology was not clear) is important for cell viability in the stationary phase of growth and, moreover, it plays a crucial role in the yeast survival of dehydration/rehydration treatments. Mutants lacking the TRK2 gene accumulated significantly lower amounts of potassium ions in the stationary culture growth phase, and these lower amounts correlated with decreased resistance to dehydration/rehydration stress. Our results showed Trk2 to be the major potassium uptake system in stationary cells, and potassium content to be a crucial parameter for desiccation survival.
FEBS Letters, 1999
Ionic currents related to the major potassium uptake systems in Saccharomyces cerevisiae were examined by whole cell patch-clamping, under K + replete conditions. Those currents have the following properties. They (1) are inward under all conditions investigated, (2) arise instantaneously with appropriate voltage steps, (3) depend solely upon the moderate affinity transporter Trk2p, not upon the high affinity transporter Trk1p. They (4) appear to be independent of the extracellular K + concentration, (5) are also independent of extracellular Ca 2+ , Mg 2+ and Cl 3 but (6) are strongly dependent on extracellular pH, being large at low pH (up to several hundred pA at 3200 mV and pH 4) and near zero at high pH (above 7.5). They increase in proportion to log[H + ] o , rather than directly in proportion to the proton concentration and behave kinetically as if each transporter cycle moved one proton plus one (high pH) or two (low pH) other ions, as yet unidentified. In view of background knowledge on K + transport related to Trk2p, the new results suggest that the K + status of yeast cells modulates both the kinetics of Trk2p-mediated transport and the identity of ions involved. That modulation could act either on the Trk2 protein itself or on interactions of Trk2 with other proteins in a hypothetical transporter complex. Structural considerations suggest a strong analogy to the KtrAB system in Vibrio alginolyticus and/or the TrkH system in Escherichia coli.
Characterization of potassium, sodium and their interactions effects in yeasts
Biotechnology requires efficient microbial cell factories. The budding yeast Saccharomyces cerevisiae is an important cell factory but for a sustainable use of natural resources more diverse cellular attributes are essential. Here, we benchmarked non-conventional yeasts Kluyveromyces marxianus (KM) and Rhodotorula toruloides (RT) against the extensively characterized strains of S. cerevisiae, CEN.PK and W303. We developed a computational method for the characterization of cell/vacuole volumes and observed an inverse relationship between the maximal growth rate and the median cell volume that was responsive to monovalent cations. We found that the supplementation of certain K+ concentrations to CEN.PK cultures containing 1.0 M Na+ increased the specific growth rate by four-fold with a parabolic shift in the median cell/vacuole volumes. The impairment of ethanol and acetate utilization in CEN.PK, acetate in W303, at the higher K+/Na+ concentrations implied an interference in the metab...
Yeast, 2006
In S. cerevisiae, K + transport relies principally on two structurally related membrane proteins, known as Trk1p and Trk2p. Direct involvement in cation movements has been demonstrated for Trk1p, which is a high-affinity K + transporter. Initially described as a low-affinity K + transporter, Trk2p seems to play a minor role in K + transport, since its activity is only apparent under very specific conditions, such as in a ∆sin3 background. Here we show that growth of a ∆trk1∆sin3 double mutant, under K + -limiting conditions or at low pH, is Trk2p-dependent, and by Northern blot analysis we demonstrate that deletion of SIN3 results in transcriptional derepression of TRK2. In addition, we show that heterologous overexpression of TRK2 with the inducible GAL1 promoter bypasses Sin3p repression in a ∆trk1∆trk2 double mutant and fully restores growth under non-permissive conditions. Furthermore, kinetic experiments in a ∆trk1∆sin3 double mutant revealed a K + transporter with an apparent high affinity and a moderate capacity. Taken together, these results indicate that TRK2 encodes a functional K + transporter that, under our experimental conditions, displays distinctive kinetic characteristics.