HSP12, a new small heat shock gene of Saccharomyces cerevisiae: analysis of structure, regulation and function

Insight into the biochemical and cell biological function of an intrinsically unstructured heat shock protein, Hsp12 of Ustilago maydis

Small heat shock proteins (sHsps) play diverse roles in the stress response and maintenance of cellular functions. The Ustilago maydis genome codes for few sHsps. Among these, Hsp12 has previously been demonstrated to be involved in the pathogenesis of the fungus by our group. In the present study we further investigated the biological function of the protein in the pathogenic development of U. maydis. Analysis of the primary amino acid sequence of Hsp12 in combination with spectroscopic methods to analyse secondary protein structures revealed an intrinsically disordered nature of the protein. We also carried out detailed analysis on the protein aggregation prevention activity associated with Hsp12. Our data suggest Hsp12 has trehalose-dependent protein aggregation prevention activity. Through assaying the interaction of Hsp12 with lipid membranes in vitro we also showed the ability of U. maydis Hsp12 to induce stability in lipid vesicles. U. maydis hsp12 deletion mutants exhibited defects in the endocytosis process and delayed completion of the pathogenic life cycle. Therefore, U. maydis Hsp12 contributes to the pathogenic development of the fungus through its ability to relieve proteotoxic stress during infection as well as its membrane-stabilizing function.

Enabling growth-decoupled Komagataella phaffii recombinant protein production based on the methanol-free PDH promoter

The current transition towards the circular bioeconomy requires a rational development of biorefineries to sustainably fulfill the present demands. The use of Komagataella phaffii (Pichia pastoris) can meet this challenge, since it has the capability to use crude glycerol as a carbon-source, a by-product from the biodiesel industry, while producing high- and low-added value products. Recombinant protein production (RPP) using K. phaffii has often been driven either by the methanol induced AOX1 promoter (P_AOX1) and/or the constitutive GAP promoter (P_GAP). In the last years, strong efforts have been focused on developing novel expression systems that expand the toolbox variety of K. phaffii to efficiently produce diverse proteins that requires different strategies. In this work, a study was conducted towards the development of methanol-free expression system based on a heat-shock gene promoter (P_DH) using glycerol as sole carbon source. Using this promoter, the recombinant expression is strongly induced in carbon-starving conditions. The classical P_GAP was used as a benchmark, taking for both strains the lipase B from Candida antarctica (CalB) as model protein. Titer of CalB expressed under P_DH outperformed P_GAP controlled expression in shake-flask cultivations when using a slow-release continuous feeding technology, confirming that P_DH is induced under pseudo-starving conditions. This increase was also confirmed in fed-batch cultivations. Several optimization rounds were carried out for P_DH under different feeding and osmolarity conditions. In all of them the P_DH controlled process outperformed the P_GAP one in regard to CalB titer. The best P_DH approach reached 3.6-fold more specific productivity than P_GAP fed-batch at low μ. Compared to the optimum approach for P_GAP-based process, the best P_DH fed-batch strategy resulted in 2.3-fold higher titer, while the specific productivity was very similar. To summarize, P_DH is an inducible promoter that exhibited a non-coupled growth regulation showing high performance, which provides a methanol-free additional solution to the usual growth-coupled systems for RPP. Thus, this novel system emerges as a potential alternative for K. phaffii RPP bioprocess and for revaluing crude glycerol, promoting the transition towards a circular economy.

The small heat shock protein Hsp12.1 has a major role in the stress response and virulence of Cryptococcus gattii

Cryptococcus gattii is one of the etiological agents of cryptococcosis. To achieve a successful infection, C. gattii cells must overcome the inhospitable host environment and deal with the highly specialized immune system and poor nutrients availability. Inside the host, C. gattii uses a diversified set of tools to maintain homeostasis and establish infection, such as the expression of remarkable and diverse heat shock proteins (Hsps). Grouped by molecular weight, little is known about the Hsp12 subset in pathogenic fungi. In this study, the function of the C. gattii HSP12.1 and HSP12.2 genes was characterized. Both genes were upregulated during murine infection and heat shock. The hsp12.1 Δ null mutant cells were sensitive to plasma membrane and oxidative stressors. Moreover, HSP12 deletion induced C. gattii reactive oxygen species (ROS) accumulation associated with a differential expression pattern of oxidative stress-responsive genes compared to the wild type strain. Apart from these findings, the deletion of the paralog gene HSP12.2 did not lead to any detectable phenotype. Additionally, the double-deletion mutant strain hsp12.1 Δ /hsp12.2 Δ presented a similar phenotype to the single-deletion mutant hsp12.1 Δ, suggesting a minor participation of Hsp12.2 in these processes. Furthermore, HSP12.1 disruption remarkably affected C. gattii virulence and phagocytosis by macrophages in an invertebrate model of infection, demonstrating its importance for C. gattii pathogenicity.

Developing a Temperature-Inducible Transcriptional Rheostat in Neurospora crassa

Heat shock protein (HSP)-encoding genes (hsp), part of the highly conserved heat shock response (HSR), are known to be induced by thermal stress in several organisms. In Neurospora crassa, three hsp genes, hsp30, hsp70, and hsp80, have been characterized; however, the role of defined cis elements in their responses to discrete changes in temperature remains largely unexplored. To fill this gap, while also aiming to obtain a reliable fungal heat shock-inducible system, we analyzed different sections of each hsp promoter by assessing the expression of real-time transcriptional reporters. Whereas all three promoters and their resected versions were acutely induced by high temperatures, only hsp30 displayed a broad range of expression and high tunability, amply exceeding other inducible promoter systems existing in Neurospora, such as quinic acid- or light-inducible ones. As proof of concept, we employed one of these promoters to control the expression of clr-2, which encodes the master regulator of Neurospora cellulolytic capabilities. The resulting strain fails to grow on cellulose at 25°C, whereas it grows robustly if heat shock pulses are delivered daily. Additionally, we designed two hsp30 synthetic promoters and characterized them, as well as the native promoters, using a gradient of high temperatures, yielding a wide range of responses to thermal stimuli. Thus, Neurospora hsp30-based promoters represent a new set of modular elements that can be used as transcriptional rheostats to adjust the expression of a gene of interest or for the implementation of regulated circuitries for synthetic biology and biotechnological strategies. IMPORTANCE A timely and dynamic response to strong temperature fluctuations is paramount for organismal biology. At the same time, inducible promoters are a powerful tool for fungal biotechnological and synthetic biology endeavors. In this work, we analyzed the activity of several N. crassa heat shock protein (hsp) promoters at a wide range of temperatures, observing that hsp30 exhibits remarkable sensitivity and a dynamic range of expression as we charted the response of this promoter to subtle increases in temperature, and also as we built and analyzed synthetic promoters based on hsp30 cis elements. As proof of concept, we tested the ability of hsp30 to provide tight control of a central process, cellulose degradation. While this study provides an unprecedented description of the regulation of the N. crassa hsp genes, it also contributes a noteworthy addition to the molecular toolset of transcriptional controllers in filamentous fungi.

The Trisubstituted Isoxazole MMV688766 Exerts Broad-Spectrum Activity against Drug-Resistant Fungal Pathogens through Inhibition of Lipid Homeostasis

Candida species are among the most prevalent causes of systemic fungal infection, posing a growing threat to public health. While Candida albicans is the most common etiological agent of systemic candidiasis, the frequency of infections caused by non-albicans Candida species is rising. Among these is Candida auris, which has emerged as a particular concern. Since its initial discovery in 2009, it has been identified worldwide and exhibits resistance to all three principal antifungal classes. Here, we endeavored to identify compounds with novel bioactivity against C. auris from the Medicines for Malaria Venture's Pathogen Box library. Of the five hits identified, the trisubstituted isoxazole MMV688766 emerged as the only compound displaying potent fungicidal activity against C. auris, as well as other evolutionarily divergent fungal pathogens. Chemogenomic profiling, as well as subsequent metabolomic and phenotypic analyses, revealed that MMV688766 disrupts cellular lipid homeostasis, driving a decrease in levels of early sphingolipid intermediates and fatty acids and a concomitant increase in lysophospholipids. Experimental evolution to further probe MMV688766's mode of action in the model fungus Saccharomyces cerevisiae revealed that loss of function of the transcriptional regulator HAL9 confers resistance to MMV688766, in part through the upregulation of the lipid-binding chaperone HSP12, a response that appears to assist in tolerating MMV688766-induced stress. The novel mode of action we have uncovered for MMV688766 against drug-resistant fungal pathogens highlights the broad utility of targeting lipid homeostasis to disrupt fungal growth and how screening structurally-diverse chemical libraries can provide new insights into resistance-conferring stress responses of fungi. IMPORTANCE As widespread antimicrobial resistance threatens to propel the world into a postantibiotic era, there is a pressing need to identify mechanistically distinct antimicrobial agents. This is of particular concern when considering the limited arsenal of drugs available to treat fungal infections, coupled with the emergence of highly drug-resistant fungal pathogens, including Candida auris. In this work, we demonstrate that existing libraries of drug-like chemical matter can be rich resources for antifungal molecular scaffolds. We discovered that the small molecule MMV688766, from the Pathogen Box library, displays previously undescribed broad-spectrum fungicidal activity through perturbation of lipid homeostasis. Characterization of the mode of action of MMV688766 provided new insight into the protective mechanisms fungi use to cope with the disruption of lipid homeostasis. Our findings highlight that elucidating the genetic circuitry required to survive in the presence of cellular stress offers powerful insights into the biological pathways that govern this important phenotype.

PiP2 favors an α-helical structure of non-recombinant Hsp12 of Saccharomyces cerevisiae

Hsp12 is a small heat shock protein of Saccharomyces cerevisiae upregulated in response to various stresses. Non recombinant Hsp12 has been purified and characterized. Using circular dichroism (CD), Isothermal Titration Calorimetry (ITC) and Differential Scanning Calorimetry (DSC), it has been demonstrated that the native Hsp12 is monomeric and intrinsically disordered (IDP). Hsp12 gains in structure in the presence of specific lipids (PiP₂). The helical form binds to liposomes models membrane with high affinity, leading to their rigidification. These results suggest that hydrophobic and ionic interactions are involved. Hsp12 is most likely a membrane chaperone expressed during stresses in Saccharomyces cerevisiae.

Misactivation of multiple starvation responses in yeast by loss of tRNA modifications

Previously, combined loss of different anticodon loop modifications was shown to impair the function of distinct tRNAs in Saccharomyces cerevisiae. Surprisingly, each scenario resulted in shared cellular phenotypes, the basis of which is unclear. Since loss of tRNA modification may evoke transcriptional responses, we characterized global transcription patterns of modification mutants with defects in either tRNAGlnUUG or tRNALysUUU function. We observe that the mutants share inappropriate induction of multiple starvation responses in exponential growth phase, including derepression of glucose and nitrogen catabolite-repressed genes. In addition, autophagy is prematurely and inadequately activated in the mutants. We further demonstrate that improper induction of individual starvation genes as well as the propensity of the tRNA modification mutants to form protein aggregates are diminished upon overexpression of tRNAGlnUUG or tRNALysUUU, the tRNA species that lack the modifications of interest. Hence, our data suggest that global alterations in mRNA translation and proteostasis account for the transcriptional stress signatures that are commonly triggered by loss of anticodon modifications in different tRNAs.

Small but mighty: a functional look at bacterial sHSPs

Small heat shock proteins (sHSPs) are widespread in every kingdom of life, being indispensable for protein quality control networks. Alongside canonical chaperone functions, sHSPs seem to have been a very plastic scaffold for acquiring multiple related functions across evolution. This review aims to summarize what is known about sHSPs functioning in the Bacteria Kingdom.

A class I cytosolic HSP20 of rice enhances heat and salt tolerance in different organisms

Small heat shock proteins (sHSPs) have been thought to function as chaperones, protecting their targets from denaturation and aggregation when organisms are subjected to various biotic and abiotic stresses. We previously reported an sHSP from Oryza sativa (OsHSP20) that homodimerizes and forms granules within the cytoplasm but its function was unclear. We now show that OsHSP20 transcripts were significantly up-regulated by heat shock and high salinity but not by drought. A recombinant protein was purified and shown to inhibit the thermal aggregation of the mitochondrial malate dehydrogenase (MDH) enzyme in vitro, and this molecular chaperone activity suggested that OsHSP20 might be involved in stress resistance. Heterologous expression of OsHSP20 in Escherichia coli or Pichia pastoris cells enhanced heat and salt stress tolerance when compared with the control cultures. Transgenic rice plants constitutively overexpressing OsHSP20 and exposed to heat and salt treatments had longer roots and higher germination rates than those of control plants. A series of assays using its truncated mutants showed that its N-terminal arm plus the ACD domain was crucial for its homodimerization, molecular chaperone activity in vitro, and stress tolerance in vivo. The results supported the viewpoint that OsHSP20 could confer heat and salt tolerance by its molecular chaperone activity in different organisms and also provided a more thorough characterization of HSP20-mediated stress tolerance in O. sativa.

The InsP7 phosphatase Siw14 regulates inositol pyrophosphate levels to control localization of the general stress response transcription factor Msn2

The environmental stress response (ESR) is critical for cell survival. Yeast cells unable to synthesize inositol pyrophosphates (PP-InsPs) are unable to induce the ESR. We recently discovered a diphosphoinositol pentakisphosphate (PP-InsP₅) phosphatase in Saccharomyces cerevisiae encoded by SIW14 Yeast strains deleted for SIW14 have increased levels of PP-InsPs. We hypothesized that strains with high inositol pyrophosphate levels will have an increased stress response. We examined the response of the siw14Δ mutant to heat shock, nutrient limitation, osmotic stress, and oxidative treatment using cell growth assays and found increased resistance to each. Transcriptional responses to oxidative and osmotic stresses were assessed using microarray and reverse transcriptase quantitative PCR. The ESR was partially induced in the siw14Δ mutant strain, consistent with the increased stress resistance, and the mutant strain further induced the ESR in response to oxidative and osmotic stresses. The levels of PP-InsPs increased in WT cells under oxidative stress but not under hyperosmotic stress, and they were high and unchanging in the mutant. Phosphatase activity of Siw14 was inhibited by oxidation that was reversible. To determine how altered PP-InsP levels affect the ESR, we performed epistasis experiments with mutations in rpd3 and msn2/4 combined with siw14Δ. We show that mutations in msn2Δ and msn4Δ, but not rpd3, are epistatic to siw14Δ by assessing growth under oxidative stress conditions and expression of CTT1 Msn2-GFP nuclear localization was increased in the siw14Δ. These data support a model in which the modulation of PP-InsPs influence the ESR through general stress response transcription factors Msn2/4.

Spt6 Is Required for the Fidelity of Promoter Selection

Spt6 is a conserved factor that controls transcription and chromatin structure across the genome. Although Spt6 is viewed as an elongation factor, spt6 mutations in Saccharomyces cerevisiae allow elevated levels of transcripts from within coding regions, suggesting that Spt6 also controls initiation. To address the requirements for Spt6 in transcription and chromatin structure, we have combined four genome-wide approaches. Our results demonstrate that Spt6 represses transcription initiation at thousands of intragenic promoters. We characterize these intragenic promoters and find sequence features conserved with genic promoters. Finally, we show that Spt6 also regulates transcription initiation at most genic promoters and propose a model of initiation site competition to account for this. Together, our results demonstrate that Spt6 controls the fidelity of transcription initiation throughout the genome.

Synergy between the small intrinsically disordered protein Hsp12 and trehalose sustain viability after severe desiccation

Anhydrobiotes are rare microbes, plants and animals that tolerate severe water loss. Understanding the molecular basis for their desiccation tolerance may provide novel insights into stress biology and critical tools for engineering drought-tolerant crops. Using the anhydrobiote, budding yeast, we show that trehalose and Hsp12, a small intrinsically disordered protein (sIDP) of the hydrophilin family, synergize to mitigate completely the inviability caused by the lethal stresses of desiccation. We show that these two molecules help to stabilize the activity and prevent aggregation of model proteins both in vivo and in vitro. We also identify a novel in vitro role for Hsp12 as a membrane remodeler, a protective feature not shared by another yeast hydrophilin, suggesting that sIDPs have distinct biological functions.

Condition-specific promoter activities in Saccharomyces cerevisiae

BACKGROUND

Saccharomyces cerevisiae is widely studied for production of biofuels and biochemicals. To improve production efficiency under industrially relevant conditions, coordinated expression of multiple genes by manipulating promoter strengths is an efficient approach. It is known that gene expression is highly dependent on the practically used environmental conditions and is subject to dynamic changes. Therefore, investigating promoter activities of S. cerevisiae under different culture conditions in different time points, especially under stressful conditions is of great importance.

RESULTS

In this study, the activities of various promoters in S. cerevisiae under stressful conditions and in the presence of xylose were characterized using yeast enhanced green fluorescent protein (yEGFP) as a reporter. The stresses include toxic levels of acetic acid and furfural, and high temperature, which are related to fermentation of lignocellulosic hydrolysates. In addition to investigating eight native promoters, the synthetic hybrid promoter P_3xC-TEF1 was also evaluated. The results revealed that P _TDH3 and the synthetic promoter P_3xC-TEF1 showed the highest strengths under almost all the conditions. Importantly, these two promoters also exhibited high stabilities throughout the cultivation. However, the strengths of P _ADH1 and P _PGK1 , which are generally regarded as 'constitutive' promoters, decreased significantly under certain conditions, suggesting that cautions should be taken to use such constitutive promoters to drive gene expression under stressful conditions. Interestingly, P _HSP12 and P _HSP26 were able to response to both high temperature and acetic acid stress. Moreover, P _HSP12 also led to moderate yEGFP expression when xylose was used as the sole carbon source, indicating that this promoter could be used for inducing proper gene expression for xylose utilization.

CONCLUSION

The results here revealed dynamic changes of promoter activities in S. cerevisiae throughout batch fermentation in the presence of inhibitors as well as using xylose. These results provide insights in selection of promoters to construct S. cerevisiae strains for efficient bioproduction under practical conditions. Our results also encouraged applications of synthetic promoters with high stability for yeast strain development.

Production and Purification of the Native Saccharomyces cerevisiae Hsp12 in Escherichia coli

Hsp12 is a small heat shock protein produced in many organisms, including the yeast Saccharomyces cerevisiae. It has been described as an indicator of yeast stress rate and has also been linked to the sweetness sensation of wine. To obtain a sufficient amount of protein, we produced and purified Hsp12 without tag in Escherichia coli. A simple fast two-step process was developed using a microplate approach and a design of experiments. A capture step on an anion-exchange salt-tolerant resin was followed by size exclusion chromatography for polishing, leading to a purity of 97%. Thereafter, specific anti-Hsp12 antibodies were obtained by rabbit immunization. An ELISA was developed to quantify Hsp12 in various strains of Saccharomyces cerevisiae. The antibodies showed high specificity and allowed the quantitation of Hsp12 in the yeast. The quantities of Hsp12 measured in the strains differed in direct proportion to the level of expression found in previous studies.

The CsHSP17.2 molecular chaperone is essential for thermotolerance in Camellia sinensis

Small heat shock proteins (sHSPs) play important roles in responses to heat stress. However, the functions of sHSPs in tea plants (Camellia sinensis) remain uncharacterized. A novel sHSP gene, designated CsHSP17.2, was isolated from tea plants. Subcellular localization analyses indicated that the CsHSP17.2 protein was present in the cytosol and the nucleus. CsHSP17.2 expression was significantly up-regulated by heat stress but was unaffected by low temperature. The CsHSP17.2 transcript levels increased following salt and polyethylene glycol 6000 treatments but decreased in the presence of abscisic acid. The molecular chaperone activity of CsHSP17.2 was demonstrated in vitro. Transgenic Escherichia coli and Pichia pastoris expressing CsHSP17.2 exhibited enhanced thermotolerance. The transgenic Arabidopsis thaliana exhibited higher maximum photochemical efficiencies, greater soluble protein proline contents, higher germination rates and higher hypocotyl elongation length than the wild-type controls. The expression levels of several HS-responsive genes increased in transgenic A. thaliana plants. Additionally, the CsHSP17.2 promoter is highly responsive to high-temperature stress in A. thaliana. Our results suggest that CsHSP17.2 may act as a molecular chaperone to mediate heat tolerance by maintaining maximum photochemical efficiency and protein synthesis, enhancing the scavenging of reactive oxygen species and inducing the expression of HS-responsive genes.

The widespread occurrence of tRNA-derived fragments in Saccharomyces cerevisiae

Short RNAs derived from the cleavage of tRNA molecules are observed in most organisms. Their occurrence seems to be induced by stress conditions, but still little is known about their biogenesis and functions. We find that the recovery of tRNA fragments depends on the RNA isolation method. Using an optimized RNA extraction protocol and northern blot hybridization technique, we show that the tRNA-derived fragments in yeast are widespread in 12 different growth conditions. We did not observe significant stress-dependent changes in the amounts of tRNA fragments pool. Instead, we show the differential processing of almost all individual tRNAs. We also provide evidence that 3'-part-derived tRNA fragments are as abundant as the 5'- one in Saccharomyces cerevisiae. The resulting set of S. cerevisiae tRNA fragments provides a robust basis for further experimental studies on biological functions of tRFs.

Early transcriptional response to biotic stress in mixed starter fermentations involving Saccharomyces cerevisiae and Torulaspora delbrueckii

Advances in microbial wine biotechnology have led to the recent commercialization of several non-Saccharomyces starter cultures. These are intended to be used in either simultaneous or sequential inoculation with Saccharomyces cerevisiae. The different types of microbial interactions that can be stablished during wine fermentation acquire an increased relevance in the context of these mixed-starter fermentations. We analysed the transcriptional response to co-cultivation of S. cerevisiae and Torulaspora delbrueckii. The study focused in the initial stages of wine fermentation, before S. cerevisiae completely dominates the mixed cultures. Both species showed a clear response to the presence of each other, even though the portion of the genome showing altered transcription levels was relatively small. Changes in the transcription pattern suggested a stimulation of metabolic activity and growth, as a consequence of the presence of competitors in the same medium. The response of S. cerevisiae seems to take place earlier, as compared to T. delbrueckii. Enhanced glycolytic activity of the mixed culture was confirmed by the CO₂ production profile during these early stages of fermentation. Interestingly, HSP12 expression appeared induced by co-cultivation for both of S. cerevisiae and Torulaspora delbrueckii in the two time points studied. This might be related with a recently described role of Hsp12 in intercellular communication in yeast. Expression of S. cerevisiae PAU genes was also stimulated in mixed cultures.

Quantitative proteomic comparison of stationary/G0 phase cells and tetrads in budding yeast

Most of the microbial cells on earth under natural conditions exist in a dormant condition, commonly known as quiescent state. Quiescent cells exhibit low rates of transcription and translation suggesting that cellular abundance of proteins may be similar in quiescent cells. Therefore, this study aim to compare the proteome of budding yeast cells from two quiescent states viz. stationary phase/G0 and tetrads. Using iTRAQ (isobaric tag for relative and absolute quantitation) based quantitative proteomics we identified 289 proteins, among which around 40 proteins exhibited ±1.5 fold change consistently from the four biological replicates. Proteomics data was validated by western blot and denstiometric analysis of Hsp12 and Spg4. Level of budding yeast 14-3-3 proteins was found to be similar in both the quiescent states, whereas Hsp12 and Spg4 expressed only during stress. FACS (fluorescence-activated cell sorting) analysis showed that budding yeast cells were arrested at G1 stages both in tetrads as well as in stationary phase. We also observed that quiescent states did not express Ime1 (inducer of meiosis). Taken together, our present study demonstrates that the cells in quiescent state may have similar proteome, and accumulation of proteins like Hsp12, Hsp26, and Spg4 may play an important role in retaining viability of the cells during dormancy.

Fungal spores for dispersion in space and time

Spores are an integral part of the life cycle of the gross majority of fungi. Their morphology and the mode of formation are both highly variable among the fungi, as is their resistance to stressors. The main aim for spores is to be dispersed, both in space, by various mechanisms or in time, by an extended period of dormancy. Some fungal ascospores belong to the most stress-resistant eukaryotic cells described to date. Stabilization is a process in which biomolecules and complexes thereof are protected by different types of molecules against heat, drought, or other molecules. This review discusses the most important compounds that are known to protect fungal spores and also addresses the biophysics of cell protection. It further covers the phenomena of dormancy, breaking of dormancy, and early germination. Germination is the transition from a dormant cell toward a vegetative cell and includes a number of specific changes. Finally, the applied aspects of spore biology are discussed.

Survey of molecular chaperone requirement for the biosynthesis of hamster polyomavirus VP1 protein in Saccharomyces cerevisiae

A number of viruses utilize molecular chaperones during various stages of their life cycle. It has been shown that members of the heat-shock protein 70 (Hsp70) chaperone family assist polyomavirus capsids during infection. However, the molecular chaperones that assist the formation of recombinant capsid viral protein 1 (VP1)-derived virus-like particles (VLPs) in yeast remain unclear. A panel of yeast strains with single chaperone gene deletions were used to evaluate the chaperones required for biosynthesis of recombinant hamster polyomavirus capsid protein VP1. The impact of deletion or mild overexpression of chaperone genes was determined in live cells by flow cytometry using enhanced green fluorescent protein (EGFP) fused with VP1. Targeted genetic analysis demonstrated that VP1-EGFP fusion protein levels were significantly higher in yeast strains in which the SSZ1 or ZUO1 genes encoding ribosome-associated complex components were deleted. The results confirmed the participation of cytosolic Hsp70 chaperones and suggested the potential involvement of the Ydj1 and Caj1 co-chaperones and the endoplasmic reticulum chaperones in the biosynthesis of VP1 VLPs in yeast. Likewise, the markedly reduced levels of VP1-EGFP in Δhsc82 and Δhsp82 yeast strains indicated that both Hsp70 and Hsp90 chaperones might assist VP1 VLPs during protein biosynthesis.

Hydrophilins in the filamentous fungus Neosartorya fischeri (Aspergillus fischeri) have protective activity against several types of microbial water stress

Hydrophilins are proteins that occur in all domains of life and protect cells and organisms against drought and other stresses. They include most of the late embryogenesis abundant (LEA) proteins and the heat shock protein (HSP) Hsp12. Here, the role of a predicted LEA-like protein (LeamA) and two Hsp12 proteins (Hsp12A and Hsp12B) of Neosartorya fischeri was studied. This filamentous fungus forms ascospores that belong to the most stress-resistant eukaryotic cells described to date. Heterologous expression of LeamA, Hsp12A and Hsp12B resulted in increased tolerance against salt and osmotic stress in Escherichia coli. These proteins were also shown to protect lactate dehydrogenase against dry heat and freeze-thaw cycles in vitro. Deletion of leamA caused diminished viability of sexual ascospores after drought and heat. This is the first report on functionality of Hsp12 and putative LeamA proteins derived from filamentous fungi, and their possible role in N. fischeri ascospore resistance against desiccation, high temperature and osmotic stress is discussed.

Oxygen availability strongly affects chronological lifespan and thermotolerance in batch cultures of Saccharomyces cerevisiae

Stationary-phase (SP) batch cultures of Saccharomyces cerevisiae, in which growth has been arrested by carbon-source depletion, are widely applied to study chronological lifespan, quiescence and SP-associated robustness. Based on this type of experiments, typically performed under aerobic conditions, several roles of oxygen in aging have been proposed. However, SP in anaerobic yeast cultures has not been investigated in detail. Here, we use the unique capability of S. cerevisiae to grow in the complete absence of oxygen to directly compare SP in aerobic and anaerobic bioreactor cultures. This comparison revealed strong positive effects of oxygen availability on adenylate energy charge, longevity and thermotolerance during SP. A low thermotolerance of anaerobic batch cultures was already evident during the exponential growth phase and, in contrast to the situation in aerobic cultures, was not substantially increased during transition into SP. A combination of physiological and transcriptome analysis showed that the slow post-diauxic growth phase on ethanol, which precedes SP in aerobic, but not in anaerobic cultures, endowed cells with the time and resources needed for inducing longevity and thermotolerance. When combined with literature data on acquisition of longevity and thermotolerance in retentostat cultures, the present study indicates that the fast transition from glucose excess to SP in anaerobic cultures precludes acquisition of longevity and thermotolerance. Moreover, this study demonstrates the importance of a preceding, calorie-restricted conditioning phase in the acquisition of longevity and stress tolerance in SP yeast cultures, irrespective of oxygen availability.

Solution NMR studies on the orientation of membrane-bound peptides and proteins by paramagnetic probes

Many peptides and proteins are attached to or immersed in a biological membrane. In order to understand their function not only the structure but also their topology in the membrane is important. Solution NMR spectroscopy is one of the most often used approaches to determine the orientation and localization of membrane-bound peptides and proteins. Here we give an application-oriented overview on the use of paramagnetic probes for the investigation of membrane-bound peptides and proteins. The examples discussed range from the large pool of antimicrobial peptides, bacterial toxins, cell penetrating peptides to domains of larger proteins or the calcium regulating protein phospholamban. Topological information is obtained in all these examples by the use of either attached or freely mobile paramagnetic tags. For some examples information obtained from the paramagnetic probes was included in the structure determination.

Distinct and redundant roles of the two MYST histone acetyltransferases Esa1 and Sas2 in cell growth and morphogenesis of Candida albicans

Candida albicans is associated with humans, as both a harmless commensal organism and a pathogen. Adaption to human body temperature is extremely important for its growth and morphogenesis. Saccharomyces cerevisiae Esa1, a member of the MYST family HATs (histone acetyltransferases) and the catalytic subunit of the NuA4 complex, and its homologues in other eukaryotes have been shown to be essential for cell growth. To investigate the functional roles of two MYST family HATs, Esa1 and Sas2 in C. albicans, we deleted ESA1 and SAS2 in the C. albicans genome and performed cell growth analyses. Our results demonstrated that C. albicans Esa1 is not essential for general growth but is essential for filamentous growth. The esa1/esa1 mutant cells exhibited sensitivity to thermal, genotoxic, and oxidative stresses but tolerance to cold, osmotic, and cell wall stresses. In contrast, the sas2/sas2 mutant adapted to growth at higher temperatures and promoted filament formation at lower temperatures, resembling the phenotype of a C. albicans strain overexpressing ESA1. Cells with deletions of both ESA1 and SAS2 were inviable, reflecting the functional redundancy in cell growth. C. albicans Esa1 and Sas2 have distinct and synergistic effects on histone acetylation at H4K5, H4K12, and H4K16. Esa1 contributes mainly to acetylation of H4K5 and H4K12, whereas Sas2 contributes to acetylation of H4K16. Our findings suggest that C. albicans Esa1 and Sas2 play opposite roles in cell growth and morphogenesis and contribute coordinately to histone acetylation and gene regulation.

Functional characterization of the small heat shock protein Hsp12p from Candida albicans

Hsp12p is considered to be a small heat shock protein and conserved among fungal species. To investigate the expression of this heat shock protein in the fungal pathogen Candida albicans we developed an anti-CaHsp12p antibody. We show that this protein is induced during stationary phase growth and under stress conditions including heat shock, osmotic, oxidative and heavy metal stress. Furthermore, we find that CaHsp12p expression is influenced by the quorum sensing molecule farnesol, the change of CO(2) concentration and pH. Notably we show that the key transcription factor Efg1p acts as a positive regulator of CaHsp12p in response to heat shock and oxidative stress and demonstrate that CaHsp12p expression is additionally modulated by Hog1p and the cAMP-PKA signaling pathway. To study the function of Hsp12p in C. albicans we generated a null mutant, in which all four CaHSP12 genes have been deleted. Phenotypic analysis of the strain shows that CaHSP12 is not essential for stress resistance, morphogenesis or virulence when tested in a Drosophila model of infection. However, when overexpressed, CaHSP12 significantly enhanced cell-cell adhesion, germ tube formation and susceptibility to azole antifungal agents whilst desensitizing C. albicans to the quorum sensing molecule farnesol.

Comparative proteomic analysis of transition of saccharomyces cerevisiae from glucose-deficient medium to glucose-rich medium

Background

When glucose is added to Saccharomyces cerevisiae grown in non-fermentable carbon sources, genes encoding ribosomal, cell-cycle, and glycolytic proteins are induced. By contrast, genes involved in mitochondrial functions, gluconeogenesis, and the utilization of other carbon sources are repressed. Glucose also causes the activation of the plasma membrane ATPase and the inactivation of gluconeogenic enzymes and mitochondrial enzymes. The goals of this study were to use the iTRAQ-labeling mass spectrometry technique to identify proteins whose relative levels change in response to glucose re-feeding and to correlate changes in protein abundance with changes in transcription and enzymatic activities. We used an experimental condition that causes the degradation of gluconeogenic enzymes when glucose starved cells are replenished with glucose. Identification of these enzymes as being down-regulated by glucose served as an internal control. Furthermore, we sought to identify new proteins that were either up-regulated or down-regulated by glucose.

Results

We have identified new and known proteins that change their relative levels in cells that were transferred from medium containing low glucose to medium containing high glucose. Up-regulated proteins included ribosomal subunits, proteins involved in protein translation, and the plasma membrane ATPase. Down-regulated proteins included small heat shock proteins, mitochondrial proteins, glycolytic enzymes, and gluconeogenic enzymes. Ach1p is involved in acetate metabolism and is also down-regulated by glucose.

Conclusions

We have identified known proteins that have previously been reported to be regulated by glucose as well as new glucose-regulated proteins. Up-regulation of ribosomal proteins and proteins involved in translation may lead to an increase in protein synthesis and in nutrient uptake. Down-regulation of glycolytic enzymes, gluconeogenic enzymes, and mitochondrial proteins may result in changes in glycolysis, gluconeogenesis, and mitochondrial functions. These changes may be beneficial for glucose-starved cells to adapt to the addition of glucose.

Functional analysis to identify genes in wine yeast adaptation to low-temperature fermentation

AIMS

  To identify genes and proteins involved in adaptation to low-temperature fermentations in a commercial wine yeast.

METHODS AND RESULTS

  Nine proteins were identified as representing the most significant changes in proteomic maps during the first 24 h of fermentation at low (13°C) and standard temperature (25°C). These proteins were mainly involved in stress response and in glucose and nitrogen metabolism. Transcription analysis of the genes encoding most of these proteins within the same time frame of wine fermentation presented a good correlation with proteomic data. Knockout and overexpressing strains of some of these genes were constructed and tested to evaluate their ability to start the fermentation process. The strain overexpressing ILV5 improved its fermentation activity in the first hours of fermentation. This strain showed a quicker process of mitochondrial degeneration, an altered intracellular amino acid profile and laxer nitrogen catabolite repression regulation.

CONCLUSIONS

  The proteomic and transcriptomic analysis is useful to detect key molecular adaptation mechanisms of biotechnological interest for industrial processes. ILV5 gene seems to be important in wine yeast adaptation to low-temperature fermentation.

SIGNIFICANCE AND IMPACT OF THE STUDY

  This study provides information that might help improve the future performance of wine yeast, either by genetic modification or by adaptation during industrial production.

Modification of the TRX2 gene dose in Saccharomyces cerevisiae affects hexokinase 2 gene regulation during wine yeast biomass production

In the industrial yeast biomass production process, cells undergo an oxidative and other stresses which worsen the quality of the produced biomass. The overexpression of the thioredoxin codifying gene TRX2 in a wine Saccharomyces cerevisiae strain increases resistance to oxidative stress and industrial biomass production yield. We observed that variations in the TRX2 gene dose in wine yeast strains are relevant to determine the fermentative capacity throughout the industrial biomass production process. So, we studied the molecular changes using a transcriptomic approach under these conditions. The results provide an overview of the different metabolic pathways affected during industrial biomass production by TRX2 gene manipulation. The oxidative stress-related genes, like those related with the glutathione metabolism, presented outstanding variations. The data also allowed us to propose new thioredoxin targets in S. cerevisiae, such as hexokinase 2, with relevance for industrial fermentation performance.

System-wide perturbation analysis with nearly complete coverage of the yeast proteome by single-shot ultra HPLC runs on a bench top Orbitrap

Yeast remains an important model for systems biology and for evaluating proteomics strategies. In-depth shotgun proteomics studies have reached nearly comprehensive coverage, and rapid, targeted approaches have been developed for this organism. Recently, we demonstrated that single LC-MS/MS analysis using long columns and gradients coupled to a linear ion trap Orbitrap instrument had an unexpectedly large dynamic range of protein identification (Thakur, S. S., Geiger, T., Chatterjee, B., Bandilla, P., Frohlich, F., Cox, J., and Mann, M. (2011) Deep and highly sensitive proteome coverage by LC-MS/MS without prefractionation. Mol. Cell Proteomics 10, 10.1074/mcp.M110.003699). Here we couple an ultra high pressure liquid chromatography system to a novel bench top Orbitrap mass spectrometer (Q Exactive) with the goal of nearly complete, rapid, and robust analysis of the yeast proteome. Single runs of filter-aided sample preparation (FASP)-prepared and LysC-digested yeast cell lysates identified an average of 3923 proteins. Combined analysis of six single runs improved these values to more than 4000 identified proteins/run, close to the total number of proteins expressed under standard conditions, with median sequence coverage of 23%. Because of the absence of fractionation steps, only minuscule amounts of sample are required. Thus the yeast model proteome can now largely be covered within a few hours of measurement time and at high sensitivity. Median coverage of proteins in Kyoto Encyclopedia of Genes and Genomes pathways with at least 10 members was 88%, and pathways not covered were not expected to be active under the conditions used. To study perturbations of the yeast proteome, we developed an external, heavy lysine-labeled SILAC yeast standard representing different proteome states. This spike-in standard was employed to measure the heat shock response of the yeast proteome. Bioinformatic analysis of the heat shock response revealed that translation-related functions were down-regulated prominently, including nucleolar processes. Conversely, stress-related pathways were up-regulated. The proteomic technology described here is straightforward, rapid, and robust, potentially enabling widespread use in the yeast and other biological research communities.

Structural characterization of Hsp12, the heat shock protein from Saccharomyces cerevisiae, in aqueous solution where it is intrinsically disordered and in detergent micelles where it is locally α-helical

Hsp12 (heat shock protein 12) belongs to the small heat shock protein family, partially characterized as a stress response, stationary phase entry, late embryonic abundant-like protein located at the plasma membrane to protect membrane from desiccation. Here, we report the structural characterization of Hsp12 by NMR and biophysical techniques. The protein was labeled uniformly with nitrogen-15 and carbon-13 so that its conformation could be determined in detail both in aqueous solution and in two membrane-mimetic environments, SDS and dodecylphosphocholine (DPC) micelles. Secondary structural elements determined from assigned chemical shifts indicated that Hsp12 is dynamically disordered in aqueous solution, whereas it gains four helical stretches in the presence of SDS micelles and a single helix in presence of DPC. These conclusions were reinforced by circular dichroism spectra of the protein in all three environments. The lack of long range interactions in NOESY spectra indicated that the helices present in SDS micelles do not pack together. R₁ and R₂, relaxation and heteronuclear NOE measurements showed that the protein is disordered in aqueous solution but becomes more ordered in presence of detergent micelles. NMR spectra collected in presence of paramagnetic spin relaxation agents (5DSA, 16DSA, and Gd(DTPA-BMA)) indicated that the amphipathic α-helices of Hsp12 in SDS micelles lie on the membrane surface. These observations are in agreement with studies suggesting that Hsp12 functions to protect the membrane from desiccation.

Influence of yeast macromolecules on sweetness in dry wines: role of the saccharomyces cerevisiae protein Hsp12

Yeast autolysis during lees contact influences the organoleptic properties of wines especially by increasing their sweet taste. Although observed by winemakers, this phenomenon is poorly explained in enology. Moreover, the compounds responsible for sweetness in wine remain unidentified. This work provides new insights in this way by combining sensorial, biochemical and genetic approaches. First, we verified by sensory analysis that yeast autolysis in red wine has a significant effect on sweetness. Moderate additions of ethanol or glycerol did not have the same effect. Second, a sapid fraction was isolated from lees extracts by successive ultrafiltrations and HPLC purifications. Using nano-LC-MS/MS, peptides released by the yeast heat shock protein Hsp12p were distinctly identified in this sample. Third, we confirmed the sweet contribution of this protein by sensorial comparison of red wines incubated with two kinds of yeast strains: a wild-type strain containing the native Hsp12p and a deletion mutant strain that lacks the Hsp12p protein (Δ°HSP12 strain). Red wines incubated with wild-type strain showed a significantly higher sweetness than control wines incubated with Δ°HSP12 strains. These results demonstrated the contribution of protein Hsp12p in the sweet perception consecutive to yeast autolysis in wine.

G = MAT: linking transcription factor expression and DNA binding data

Transcription factors are proteins that bind to motifs on the DNA and thus affect gene expression regulation. The qualitative description of the corresponding processes is therefore important for a better understanding of essential biological mechanisms. However, wet lab experiments targeted at the discovery of the regulatory interplay between transcription factors and binding sites are expensive. We propose a new, purely computational method for finding putative associations between transcription factors and motifs. This method is based on a linear model that combines sequence information with expression data. We present various methods for model parameter estimation and show, via experiments on simulated data, that these methods are reliable. Finally, we examine the performance of this model on biological data and conclude that it can indeed be used to discover meaningful associations. The developed software is available as a web tool and Scilab source code at http://biit.cs.ut.ee/gmat/.

Late phase of the endoplasmic reticulum stress response pathway is regulated by Hog1 MAP kinase

When unfolded proteins accumulate in the endoplasmic reticulum (ER) causing ER stress, the unfolded protein response (UPR) responds rapidly to induce a transcriptional program that functions to alleviate the stress. However, under extreme conditions, when UPR activation is not sufficient to alleviate ER stress, the stress may persist long term. Very little is known about how the cell responds to persistent ER stress that is not resolved by the immediate activation of the UPR. We show that Hog1 MAP kinase becomes phosphorylated during the late stage of ER stress and helps the ER regain homeostasis. Although Hog1 is well known to function in osmotic stress and cell wall integrity pathways, we show that the activation mechanism for Hog1 during ER stress is distinct from both of these pathways. During late stage ER stress, upon phosphorylation, Hog1 translocates into the nucleus and regulates gene expression. Subsequently, Hog1 returns to the cytoplasm, where its phosphorylation levels remain high. From its cytoplasmic location, Hog1 contributes to the activation of autophagy by enhancing the stability of Atg8, a critical autophagy protein. Thus, Hog1 coordinates a multifaceted response to persistent ER stress.

Comparative transcriptome analysis reveals novel roles of the Ras and cyclic AMP signaling pathways in environmental stress response and antifungal drug sensitivity in Cryptococcus neoformans

The cyclic AMP (cAMP) pathway plays a central role in the growth, differentiation, and virulence of pathogenic fungi, including Cryptococcus neoformans. Three upstream signaling regulators of adenylyl cyclase (Cac1), Ras, Aca1, and Gpa1, have been demonstrated to control the cAMP pathway in C. neoformans, but their functional relationship remains elusive. We performed a genome-wide transcriptome analysis with a DNA microarray using the ras1Delta, gpa1Delta, cac1Delta, aca1Delta, and pka1Delta pka2Delta mutants. The aca1Delta, gpa1Delta, cac1Delta, and pka1Delta pka2Delta mutants displayed similar transcriptome patterns, whereas the ras1Delta mutant exhibited transcriptome patterns distinct from those of the wild type and the cAMP mutants. Interestingly, a number of environmental stress response genes are modulated differentially in the ras1Delta and cAMP mutants. In fact, the Ras signaling pathway was found to be involved in osmotic and genotoxic stress responses and the maintenance of cell wall integrity via the Cdc24-dependent signaling pathway. Notably, the Ras and cAMP mutants exhibited hypersensitivity to a polyene drug, amphotericin B, without showing effects on ergosterol biosynthesis, which suggested a novel method of antifungal combination therapy. Among the cAMP-dependent gene products that we characterized, two small heat shock proteins, Hsp12 and Hsp122, were found to be involved in the polyene antifungal drug susceptibility of C. neoformans.

A cytosolic class I small heat shock protein, RcHSP17.8, of Rosa chinensis confers resistance to a variety of stresses to Escherichia coli, yeast and Arabidopsis thaliana

Among the heat shock proteins (HSPs) of higher plants, those belonging to the small HSP (sHSP) family remain the least characterized in functional terms. To improve our understanding of sHSPs, we have characterized RcHSP17.8 from Rosa chinensis. Sequence alignments and phylogenetic analysis reveal this to be a cytosolic class I sHSP. RcHSP17.8 expression in R. chinensis was induced by heat, cold, salt, drought, osmotic and oxidative stresses. Recombinant RcHSP17.8 was overexpressed in Escherichia coli and yeast to study its possible function under stress conditions. The recombinant E. coli and yeast cells that accumulated RcHSP17.8 showed improved viability under thermal, salt and oxidative stress conditions compared with control cultures. We also produced transgenic Arabidopsis thaliana that constitutively expressed RcHSP17.8. These plants exhibited increased tolerance to heat, salt, osmotic and drought stresses. These results suggest that R. chinensis cytosolic class I sHSP (RcHSP17.8) has the ability to confer stress resistance not only to E. coli and yeast but also to plants grown under a wide variety of unfavorable environmental conditions.

Small heat-shock protein Hsp12 contributes to yeast tolerance to freezing stress

The HSP12 gene encodes one of the two major small heat-shock proteins of Saccharomyces cerevisiae and is induced under different conditions, such as low and high temperatures, osmotic or oxidative stress and high sugar or ethanol concentrations. However, few studies could demonstrate any correlation between HSP12 deletion or overexpression and a phenotype of sensitivity/resistance, making it difficult to attribute a role for Hsp12p under several of these stress conditions. We investigated the possible role of Hsp12p in yeast freezing tolerance. Contrary to what would be expected, the hsp12 null mutant when subjected to prolonged storage at −20 °C showed an increased resistance to freezing when compared with the isogenic wild-type strain. Because the mutant strain displayed a higher intracellular trehalose concentration than the wild-type, which could mask the effect of manipulating HSP12, we overexpressed the HSP12 gene in a trehalose-6-phosphate synthase (TPS1) null mutant. The tps1Δ strain overexpressing HSP12 showed an increase in resistance to freezing storage, indicating that Hsp12p plays a role in freezing tolerance in a way that seems to be interchangeable with trehalose. In addition, we show that overexpression of HSP12 in this tps1Δ strain also increased resistance to heat shock and that absence of HSP12 compromises the ability of yeast cells to accumulate high levels of trehalose in response to a mild heat stress.

Hypersusceptibility to azole antifungals in a clinical isolate of Candida glabrata with reduced aerobic growth

Petite mutations have been described in Saccharomyces cerevisiae and pathogenic yeasts. However, previous studies of the phenotypic traits of these petite mutants reported that they express azole resistance. We describe a clinical isolate of Candida glabrata with a striking association between increased susceptibility to azoles and respiratory deficiency. This isolate was obtained from a urine sample together with a respiration-competent C. glabrata isolate which exhibited azole resistance. The respiratory status of the two isolates was confirmed by cultivation on glycerol-containing agar and oxygraphy. Flow cytometry revealed the normal incorporation of rhodamine 123, and mitochondrial sections with typical cristae were seen by transmission electron microscopy for both isolates. Together, these results suggested a nuclear origin for the reduced respiratory capacity of the hypersusceptible isolate. The sterol contents of these isolates were similar to the sterol content of a reference strain. Sequencing of the ERG11 and PDR1 genes revealed that the sequences were identical in the two isolates, demonstrating their close relatedness. In addition to silent mutations, they carried a nonsense mutation in PDR1 that led to the truncation of transcription factor Pdr1p. They also overexpressed both PDR1 and one of its targets, CDR1, providing a possible explanation for the azole resistance of the respiration-competent isolate. In conclusion, in addition to azole resistance, which is a common feature of C. glabrata mitochondrial petite mutants, the mutation of a nuclear gene affecting aerobic growth may lead to azole hypersusceptibility; however, the mechanisms underlying this phenotype remain to be determined.

Effect of trehalose on protein structure

Trehalose is a ubiquitous molecule that occurs in lower and higher life forms but not in mammals. Till about 40 years ago, trehalose was visualized as a storage molecule, aiding the release of glucose for carrying out cellular functions. This perception has now changed dramatically. The role of trehalose has expanded, and this molecule has now been implicated in a variety of situations. Trehalose is synthesized as a stress-responsive factor when cells are exposed to environmental stresses like heat, cold, oxidation, desiccation, and so forth. When unicellular organisms are exposed to stress, they adapt by synthesizing huge amounts of trehalose, which helps them in retaining cellular integrity. This is thought to occur by prevention of denaturation of proteins by trehalose, which would otherwise degrade under stress. This explanation may be rational, since recently, trehalose has been shown to slow down the rate of polyglutamine-mediated protein aggregation and the resultant pathogenesis by stabilizing an aggregation-prone model protein. In recent years, trehalose has also proved useful in the cryopreservation of sperm and stem cells and in the development of a highly reliable organ preservation solution. This review aims to highlight the changing perception of the role of trehalose over the last 10 years and to propose common mechanisms that may be involved in all the myriad ways in which trehalose stabilizes protein structures. These will take into account the structure of trehalose molecule and its interactions with its environment, and the explanations will focus on the role of trehalose in preventing protein denaturation.

Effects of yeast cell-wall characteristics on 4-ethylphenol sorption capacity in model wine

Saccharomyces cerevisiae is an efficient biosorbant, used in winemaking to reduce the concentration of undesirable molecules such as fatty acids. Volatile phenols such as 4-ethylphenol, which causes a horsy smell in wine, are particular targets of this type of curative process. This study demonstrates that the sorption capacity of 4-ethylphenol by yeasts is greatly influenced by strain nature, methods, and medium used for biomass production and drying after harvesting. S. cerevisiae mutant strains with deletion of genes encoding specific proteins involved in cell-wall structure and composition were studied, and a major role for mannoproteins in 4-ethylphenol sorption was identified. It was confirmed that 4-ethylphenol sorption occurs at the surface of the yeast wall and that not all mannoproteins are determinants of sorption: the sorption capacity of cells with deletion of the Gas1p-encoding gene was 75% lower than that of wild type. Physicochemical properties of yeast cell surface have been also studied.

A compensatory increase in trehalose synthesis in response to desiccation stress in Saccharomyces cerevisiae cells lacking the heat shock protein Hsp12p

The effect of HSP12 deletion on the response of yeast to desiccation was investigated. The Deltahsp12 strain was found to be more desiccation tolerant than the wild-type strain. Furthermore, the increased intracellular trehalose levels in the Deltahsp12 strain suggested that this strain compensated for the lack of Hsp12p synthesis by increasing trehalose synthesis, which facilitated increased desiccation tolerance. Results obtained from flow cytometry using the membrane exclusion dye propidium iodide suggested that Hsp12p helped maintain plasma membrane integrity during desiccation. Analysis of the oxidative loads experienced by the wild-type and Deltahsp12 strains showed that during mid-exponential phase, the increased trehalose levels present in the Deltahsp12 cells resulted in increased protection of these cells against reactive oxygen species compared with wild-type cells. During stationary phase, lower levels of reactive oxygen species reduction by reduced glutathione was enhanced in the wild-type strain, which displayed lower intracellular trehalose concentrations. Comparison of the tolerance of the wild-type and Deltahsp12 strains with applied oxidative stress showed that the Deltahsp12 strain was more tolerant to exogenously applied H2O2, which we attributed to the higher intracellular trehalose concentration. Flow cytometry demonstrated that Hsp12p played a role in maintaining plasma membrane integrity during applied oxidative stress.

Multiway real-time PCR gene expression profiling in yeast Saccharomyces cerevisiae reveals altered transcriptional response of ADH-genes to glucose stimuli

BACKGROUND

The large sensitivity, high reproducibility and essentially unlimited dynamic range of real-time PCR to measure gene expression in complex samples provides the opportunity for powerful multivariate and multiway studies of biological phenomena. In multiway studies samples are characterized by their expression profiles to monitor changes over time, effect of treatment, drug dosage etc. Here we perform a multiway study of the temporal response of four yeast Saccharomyces cerevisiae strains with different glucose uptake rates upon altered metabolic conditions.

RESULTS

We measured the expression of 18 genes as function of time after addition of glucose to four strains of yeast grown in ethanol. The data are analyzed by matrix-augmented PCA, which is a generalization of PCA for 3-way data, and the results are confirmed by hierarchical clustering and clustering by Kohonen self-organizing map. Our approach identifies gene groups that respond similarly to the change of nutrient, and genes that behave differently in mutant strains. Of particular interest is our finding that ADH4 and ADH6 show a behavior typical of glucose-induced genes, while ADH3 and ADH5 are repressed after glucose addition.

CONCLUSION

Multiway real-time PCR gene expression profiling is a powerful technique which can be utilized to characterize functions of new genes by, for example, comparing their temporal response after perturbation in different genetic variants of the studied subject. The technique also identifies genes that show perturbed expression in specific strains.

Modulation of Congo-red-induced aberrations in the yeast Saccharomyces cerevisiae by the general stress response protein Hsp12p

Previous studies have shown that in Saccharomyces cerevisiae HSP12, which codes for the small cell wall heat shock protein Hsp12p, was induced upon exposure to cell-wall-damaging agents such as Congo red. Here, we demonstrate that Hsp12p decreases the interaction between Congo red and chitin. A Δhsp12 mutant strain displayed decreased viability, increased aggregation and sedimentation, as well as an altered morphology when grown in the presence of Congo red dye. The presence of Hsp12p was also necessary for the Congo-red-mediated invasion of agar plates.

Genome-wide transcriptional profiling of the cyclic AMP-dependent signaling pathway during morphogenic transitions of Candida albicans

Candida albicans is an opportunistic human fungal pathogen that causes systemic candidiasis as well as superficial mucosal candidiasis. In response to the host environment, C. albicans transitions between yeast and hyphal forms. In particular, hyphal growth is important in facilitating adhesion and invasion of host tissues, concomitant with the expression of various hypha-specific virulence factors. In previous work, we showed that the cyclic AMP (cAMP) signaling pathway plays a crucial role in morphogenic transitions and virulence of C. albicans by studying genes encoding adenylate cyclase-associated protein (CAP1) and high-affinity phosphodiesterase (PDE2) (Y. S. Bahn, J. Staab, and P. Sundstrom, Mol. Microbiol. 50:391-409, 2003; and Y. S. Bahn and P. Sundstrom, J. Bacteriol. 183:3211-3223, 2001). However, little is known about the downstream targets of the cAMP signaling pathway that are responsible for morphological transitions and the expression of virulence factors. Here, microarrays were probed with RNA from strains with hypoactive (cap1/cap1 null mutant), hyperactive (pde2/pde2 null mutant), and wild-type cAMP signaling pathways to provide insight into the molecular mechanisms of virulence that are regulated by cAMP and that are related to the morphogenesis of C. albicans. Genes controlling metabolic specialization, cell wall structure, ergosterol/lipid biosynthesis, and stress responses were modulated by cAMP during hypha formation. Phenotypic traits predicted to be regulated by cAMP from the profiling results correlated with the relative strengths of the mutants when tested for resistance to azoles and subjected to heat shock stress and oxidative/nitrosative stress. The results from this study provide important insights into the role of the cAMP signaling pathway not only in morphogenic transitions of C. albicans but also for adaptation to stress and for survival during host infections.

The stress response protein Hsp12p increases the flexibility of the yeast Saccharomyces cerevisiae cell wall

The yeast S. cerevisiae cell wall comprising a 10 nm thick layer of polysaccharides, predominantly beta(1,3)-glucan and proteins, is the interface between the cell and the neighbouring environment. As such it is not a static entity but rather one that is dynamically remodelled in response to changes in the environmental conditions. We have recently proposed from studies using yeast cells lacking the gene encoding Hsp12p (Deltahsp12 yeast) and from incorporation of Hsp12p into agarose, used as a model system for the beta-glucan layer of the cell wall, that the hydrophilic stress response cell wall protein Hsp12p acts as a cell wall plasticizer. In this report we have used force spectroscopy to confirm that Deltahsp12 yeast are indeed less flexible than the wild type strain. The spring constant of the cell wall of Deltahsp12 yeast, kcw was determined to be 72+/-3 mN m-1 as compared to 17+/-5 mN m-1 obtained for the wild type strain. A similar result was found on the basis of a quantitative analysis of the electrophoretic mobilities measured for the two yeast strains. Those indicated that the hydrodynamic permeability quantified through the softness parameter of the external layer of Deltahsp12 cells was smaller than the one of wild type cells. We proposed from surface infrared spectroscopy measurements that yeast compensate for the lack of Hsp12p by reducing the carbohydrate/proteins ratio of the cell wall or increasing the cell wall chitin content.