Interaction of the GTS1 gene product with glyceraldehyde- 3-phosphate dehydrogenase 1 required for the maintenance of the metabolic oscillations of the yeast Saccharomyces cerevisiae

Progress of Molecular Display Technology Using Saccharomyces cerevisiae to Achieve Sustainable Development Goals

In the long history of microorganism use, yeasts have been developed as hosts for producing biologically active compounds or for conventional fermentation. Since the introduction of genetic engineering, recombinant proteins have been designed and produced using yeast or bacterial cells. Yeasts have the unique property of expressing genes derived from both prokaryotes and eukaryotes. Saccharomyces cerevisiae is one of the well-studied yeasts in genetic engineering. Recently, molecular display technology, which involves a protein-producing system on the yeast cell surface, has been established. Using this technology, designed proteins can be displayed on the cell surface, and novel abilities are endowed to the host yeast strain. This review summarizes various molecular yeast display technologies and their principles and applications. Moreover, S. cerevisiae laboratory strains generated using molecular display technology for sustainable development are described. Each application of a molecular displayed yeast cell is also associated with the corresponding Sustainable Development Goals of the United Nations.

A Peptide Derived from GAPDH Enhances Resistance to DNA Damage in Saccharomyces cerevisiae Cells

Social behaviors do not exist only in higher organisms but are also present in microbes that interact for the common good. Here, we report that budding yeast cells interact with their neighboring cells after exposure to DNA damage. Yeast cells irradiated with DNA-damaging UV light secrete signal peptides that can increase the survival of yeast cells exposed to DNA-damaging stress. The secreted peptide is derived from glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and it induced cell death of a fraction of yeast cells in the group. The data suggest that the GAPDH-derived peptide serves in budding yeast's social interaction in response to DNA-damaging stress. IMPORTANCE Many studies have shown that microorganisms, including bacteria and yeast, display increased tolerance to stress after exposure to the same stressor. However, the mechanism remains unknown. In this study, we report a striking finding that Saccharomyces cerevisiae cells respond to DNA damage by secreting a peptide that facilitates resistance to DNA-damaging stress. Although it has been shown that GAPDH possesses many key functions in cells aside from its well-established role in glycolysis, this study demonstrated that GAPDH is also involved in the social behaviors response to DNA-damaging stress. The study opens the gate to an interesting research field about microbial social activity for adaptation to a harsh environment.

Hap4 is not essential for activation of respiration at low specific growth rates in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, the heme-activated protein complex Hap2/3/4/5 plays a major role in the transcription of genes involved in respiration. Thus, overexpression of HAP4 has been shown to result in a 10% increase in the respiratory capacity. Here the physiology of a HAP4-deleted S. cerevisiae strain was investigated, and we found that the hap4delta S. cerevisiae exhibited poor growth on ethanol, although the growth rate on glucose was indifferent from the wild type in aerobic as well as anaerobic cultures. Moreover, it exhibited a large (75%) reduction in the critical glucose uptake rate at which fermentative metabolism is onset, indicating a substantial reduction in respiratory capacity. We also performed whole genome transcription analysis for the hap4delta and the wild type, grown in carbon-limited chemostat cultures operated at a dilution rate of 0.05 h(-1). Although both strains exhibited respiratory metabolism, there was significant change in expression of many genes in the hap4delta strain. These genes are involved in several different parts of the metabolism, including oxidative stress response, peroxisomal functions, and energy generation. This study strongly indicates that Hap4 activation only occurs at intermediate specific growth rates, below which the transcription of genes responsible for respiration is dependent on the Hap2/3/5 complex and above which the Hap4 protein augments the transcription. Furthermore, statistical analysis of the transcription data and integration of the data with a genome scale metabolic network provided new insight and evidence for the role of Hap4 in transcriptional regulation of mitochondrial respiration.

Gts1p stabilizes oscillations in energy metabolism by activating the transcription of TPS1 encoding trehalose-6-phosphate synthase 1 in the yeast Saccharomyces cerevisiae

We reported previously that Gts1p regulates oscillations of heat resistance in concert with those of energy metabolism in continuous cultures of the yeast Saccharomyces cerevisiae by inducing fluctuations in the levels of trehalose, but not in those of Hsp104 (heat shock protein 104). Further, the expression of TPS1, encoding trehalose-6-phosphate synthase 1, and HSP104 was activated by Gts1p in combination with Snf1 kinase, a transcriptional activator of glucose-repressible genes, in batch cultures under derepressed conditions. Here we show that, in continuous cultures, the mRNA level of TPS1 increased 6-fold in the early respiro-fermentative phase, while that of HSP104 did not change. The expression of SUC2, a representative glucose-repressible gene encoding invertase, also fluctuated, suggesting the involvement of the Snf1 kinase in the periodic activation of these genes. However, this possibility was proven to be unlikely, since the oscillations in both TPS1 and SUC2 mRNA expression were reduced by approx. 3-fold during the transient oscillation in gts1Delta (GTS1-deleted) cells, in which the energy state determined by extracellular glucose and intracellular adenine nucleotide levels was comparable with that in wild-type cells. Furthermore, neither the mRNA level nor the phosphorylation status of Snf1p changed significantly during the oscillation. Thus we suggest that Gts1p plays a major role in the oscillatory expression of TPS1 and SUC2 in continuous cultures of Saccharomyces cerevisiae, and hypothesized that Gts1p stabilizes oscillations in energy metabolism by activating trehalose synthesis to facilitate glycolysis at the shift from the respiratory to the respiro-fermentative phase.

NADH-reductive stress in Saccharomyces cerevisiae induces the expression of the minor isoform of glyceraldehyde-3-phosphate dehydrogenase (TDH1)

A strain of Saccharomyces cerevisiae lacking the GPD2 gene, encoding one of the glycerol-3-phosphate dehydrogenases, grows slowly under anaerobic conditions, due to reductive stress caused by the accumulation of cytoplasmic NADH. We used 2D-PAGE to study the effect on global protein expression of reductive stress in the anaerobically grown gpd2Delta strain. The most striking response was a strongly elevated expression of Tdh1p, the minor isoform of glyceraldehyde-3-phosphate dehydrogenase. This increased expression could be reversed by the addition of acetoin, a NADH-specific redox sink, which furthermore largely restored anaerobic growth of the gpd2Delta strain. Additional deletion of the TDH1 gene (but not of TDH2 or TDH3) improved anaerobic growth of the gpd2Delta strain. We therefore propose that TDH1 has properties not displayed by the other TDH isogenes and that its expression is regulated by reductive stress caused by an excess of cytoplasmic NADH.

The rhythm of yeast

Although yeast are unicellular and comparatively simple organisms, they have a sense of time which is not related to reproduction cycles. The glycolytic pathway exhibits oscillatory behaviour, i.e. the metabolite concentrations oscillate around phosphofructokinase. The frequency of these oscillations is about 1 min when using intact cells. Also a yeast cell extract can oscillate, though with a lower frequency. With intact cells the macroscopic oscillations can only be observed when most of the cells oscillate in concert. Transient oscillations can be observed upon simultaneous induction; sustained oscillations require an active synchronisation mechanism. Such an active synchronisation mechanism, which involves acetaldehyde as a signalling compound, operates under certain conditions. How common these oscillations are in the absence of a synchronisation mechanism is an open question. Under aerobic conditions an oscillatory metabolism can also be observed, but with a much lower frequency than the glycolytic oscillations. The frequency is between one and several hours. These oscillations are partly related to the reproductive cycle, i.e. the budding index also oscillates; however, under some conditions they are unrelated to the reproductive cycle, i.e. the budding index is constant. These oscillations also have an active synchronisation mechanism, which involves hydrogen sulfide as a synchronising agent. Oscillations with a frequency of days can be observed with yeast colonies on plates. Here the oscillations have a synchronisation mechanism which uses ammonia as a synchronising agent.

Gts1p activates SNF1-dependent derepression of HSP104 and TPS1 in the stationary phase of yeast growth

We previously reported that the GTS1 product, Gts1p, plays an important role in the regulation of heat tolerance of yeast under glucose-limited conditions in either batch or continuous culture. Here we show that heat tolerance was decreased in GTS1-deleted and increased in GTS1-overexpressing cells under glucose-derepressed conditions during the batch culture and that the disruption of SNF1, a transcriptional activator of glucose-repressible genes, diminished this effect of GTS1. Intracellular levels of Hsp104 and trehalose, which were reportedly required for the acquisition of heat tolerance in the stationary phase of cell growth, were affected in both GTS1 mutants roughly in proportion to the gene dosage of GTS1, whereas those of other Hsps were less affected. The mRNA levels of genes for Hsp104 and trehalose-6-phosphate synthase 1 changed as a function of GTS1 gene dosage. The Q-rich domain of Gts1p fused with the DNA-binding domain of LexA activated the transcription of the reporter gene LacZ, and Gts1p lacking the Q-rich domain lost the activation activity of HSP104 and TPS1. Furthermore, Gts1p bound to subunits of Snf1 kinase, whereas it did not bind to DNA. Therefore, we suggested that GTS1 increases heat tolerance by mainly activating Snf1 kinase-dependent derepression of HSP104 and TPS1 in the stationary phase of yeast growth.

The Gts1 protein stabilizes the autonomous oscillator in yeast

Continuous cultures of Saccharomyces cerevisiae show a robust autonomous temperature compensated oscillation in many metabolic functions. Respiratory activity, a convenient output to measure, oscillates with a period of 40 min. Deletion of GTS1, whose protein product has homology to the circadian per protein, has been implicated in temporal events within yeast, causes a reduction in periodicity to 18 min (wild-type period 40-60 min). The dilution rate was steadily increased from 0.04/h to 0.085/h and the oscillation stabilized after four to six dilutions. However, Gts1p's involvement in the maintenance and generation of metabolic synchrony, and in the central oscillating loop, appear to be minimal, as the mutant oscillation was robust and autonomous. Deletion of GTS1 did cause decreased temperature compensation of the period of the oscillation from Q(10) = 1.07 for the wild-type to Q(10) = 1.6 for the mutant. Also the degree of nutrient compensation observed for the wild-type was not observed in the GTS1-null mutant strain. It is postulated that Gts1p is involved in the mechanism that communicates external conditions, such as temperature, to the central oscillating loop.