Physiological effects of calcium shortage on Saccharomyces cerevisiae: proteomic and metabolomic profiling

Calcium has long been recognized a highly versatile intracellular messenger able to regulate many different cellular functions and processes in all biological systems, from prokaryotes to higher eukaryotes. New Ca2+ functions added one by one over the years generated a very complex picture, in which Ca2+ orchestrates a wide set of processes in a very fine tuned way. In the present study, the physiological remodelling of the budding yeast Saccharomyces cerevisiae, has been observed following depletion of calcium, in order to better define the complex web of processes orchestrates by calcium. The physiological response of S. cerevisiae system has been observed under a perturbed environmental condition primarily characterized by Ca2+ shortage and analyzed at three different levels. In particular, a first observation of macroscopic phenotypes induced by Ca2+ shortage has been followed by the analysis of changes triggered by this perturbation both on the global protein expression and on the metabolite profile. At first glance, Ca2+ shortage triggered growth rate slowdown, decreased cell volume and anomalous DNA distribution in cells growing on complete synthetic medium (SC) supplied with non limiting glucose concentration. While changes in cell volume were demonstrated to be the result of an affected vacuole morphology, the anomalous DNA distribution have been suggested to derive from damages affecting cells to increasing extent as cell genealogical age increased. Comparative proteomic profiling provided a better insight into the effects generated from Ca2+ shortage, as expression of proteins belonging to particular functional pathways and active in common cellular processes, has been shown to change because of Ca2+ shortage. Strikingly, one of the major effects of Ca2+ shortage was the choral increase in expression of proteins typically active in response to a boost in oxidative stress. This specific stress condition was further elucidated, determining that under Ca2+ shortage cells are affected by high oxidative stress levels. Interestingly, Ca2+ shortage effects, in terms of growth rate slowdown, cell volume decrease and anomalous DNA profile (macroscopic phenotypes), were detectable only in the presence of particular nutrient condition, depending on the presence of specific sugars and aminoacids. These findings defined a tight connection between the role played by Ca2+ and the cellular metabolic state, which was further investigated through metabolite profile analysis. This study shows how, even though Ca2+ plays an overall important role in modulating an ensemble of yeast cellular functions, its importance may depend upon the general environmental condition in which yeast is growing. In particular, our results suggest that S.cerevisiae requires Ca2+ to different extents, depending on the precise yeast cellular metabolic state.