Thermotolerance in Saccharomyces cerevisiae: the Yin and Yang of trehalose

Role of reserve carbohydrates in the growth dynamics of Saccharomyces cerevisiae

The purpose of this study was to explore the role of glycogen and trehalose in the ability of Saccharomyces cerevisiae to respond to a sudden rise of the carbon flux. To this end, aerobic glucose-limited continuous cultures were challenged with a sudden increase of the dilution rate from 0.05 to 0.15 h(-1). Under this condition, a rapid mobilization of glycogen and trehalose was observed which coincided with a transient burst of budding and a decrease of cell biomass. Experiments carried out with mutants defective in storage carbohydrates indicated a predominant role of glycogen in the adaptation to this perturbation. However, the real importance of trehalose in this response was veiled by the unexpected phenotypes harboured by the tps1 mutant, chosen for its inability to synthesize trehalose. First, the biomass yield of this mutant was 25% lower than that of the isogenic wild-type strain at dilution rate of 0.05 h(-1), and this difference was annulled when cultures were run at a higher dilution rate of 0.15 h(-1). Second, the tps1 mutant was more effective to sustain the dilution rate shift-up, apparently because it had a faster glycolytic rate and an apparent higher capacity to consume glucose with oxidative phosphorylation than the wild type. Consequently, a tps1gsy1gsy2 mutant was able to adapt to the dilution rate shift-up after a long delay, likely because the detrimental effects from the absence of glycogen was compensated for by the tps1 mutation. Third, a glg1Deltaglg2Delta strain, defective in glycogen synthesis because of the lack of the glycogen initiation protein, recovered glycogen accumulation upon further deletion of TPS1. This recovery, however, required glycogen synthase. Finally, we demonstrated that the rapid breakdown of reserve carbohydrates triggered by the shift-up is merely due to changes in the concentrations of hexose-6-phosphate and UDPglucose, which are the main metabolic effectors of the rate-limiting enzymes of glycogen and trehalose pathways.

Loss of function of KRE5 suppresses temperature sensitivity of mutants lacking mitochondrial anionic lipids

Disruption of PGS1, which encodes the enzyme that catalyzes the committed step of cardiolipin (CL) synthesis, results in loss of the mitochondrial anionic phospholipids phosphatidylglycerol (PG) and CL. The pgs1Delta mutant exhibits severe growth defects at 37 degrees C. To understand the essential functions of mitochondrial anionic lipids at elevated temperatures, we isolated suppressors of pgs1Delta that grew at 37 degrees C. One of the suppressors has a loss of function mutation in KRE5, which is involved in cell wall biogenesis. The cell wall of pgs1Delta contained markedly reduced beta-1,3-glucan, which was restored in the suppressor. Stabilization of the cell wall with osmotic support alleviated the cell wall defects of pgs1Delta and suppressed the temperature sensitivity of all CL-deficient mutants. Evidence is presented suggesting that the previously reported inability of pgs1Delta to grow in the presence of ethidium bromide was due to defective cell wall integrity, not from "petite lethality." These findings demonstrated that mitochondrial anionic lipids are required for cellular functions that are essential in cell wall biogenesis, the maintenance of cell integrity, and survival at elevated temperature.

Inhibition of yeast glutathione reductase by trehalose: possible implications in yeast survival and recovery from stress

Accumulation of trehalose has been implicated in the tolerance of yeast cells to several forms of stress, including heat-shock and high ethanol levels. However, yeast lacking trehalase, the enzyme that degrades trehalose, exhibit poor survival after exposure to stress conditions. This suggests that optimal cell viability also depends on the capacity to rapidly degrade the high levels of trehalose that build up under stress. Here, we initially examined the effects of trehalose on the activity of an important antioxidant enzyme, glutathione reductase (GR), from Saccharomyces cerevisiae. At 25 degrees C, GR was inhibited by trehalose in a dose-dependent manner, with 70% inhibition at 1.5M trehalose. The inhibition was practically abolished at 40 degrees C, a temperature that induces a physiological response of trehalose accumulation in yeast. The inhibition of GR by trehalose was additive to the inhibition caused by ethanol, indicating that enzyme function is drastically affected upon ethanol-induced stress. Moreover, two other yeast enzymes, cytosolic pyrophosphatase and glucose 6-phosphate dehydrogenase, showed temperature dependences on inhibition by trehalose that were similar to the temperature dependence of GR inhibition. These results are discussed in terms of the apparent paradox represented by the induction of enzymes involved in both synthesis and degradation of trehalose under stress, and suggest that the persistence of high levels of trehalose after recovery from stress could lead to the inactivation of important yeast enzymes.

Effect of nitrogen limitation and surplus upon trehalose metabolism in wine yeast

Trehalose metabolism in yeast has been related to stress and could be used as a stress indicator. Winemaking conditions are stressful for yeast and understanding trehalose metabolism under these conditions could be useful for controlling alcoholic fermentation. In this study, we analysed trehalose metabolism of a commercial wine yeast strain during alcoholic fermentation by varying the nitrogen levels from low (below adequate) to high (excess). We determined trehalose, nitrogen, sugar consumption and expression of NTH1, NTH2 and TPS1. Our results show that trehalose metabolism is slightly affected by nitrogen availability and that the main consumption of nitrogen occurs in the first 24 h. After this period, nitrogen is hardly taken up by the yeast cells. Although nitrogen and sugar are still available, no further growth is observed in high concentrations of nitrogen. Increased expression of genes involved in trehalose metabolism occurs mainly at the end of the growth period. This could be related to an adaptive mechanism for fine tuning of glycolysis during alcoholic tumultuous fermentation, as both anabolic and catabolic pathways are affected by such expression.

Biotechnology to improve health in developing countries -- a review

The growing health disparities between the developing and the developed world call for urgent action from the scientific community. Science and technology have in the past played a vital role in improving public health. Today, with the tremendous potential of genomics and other advances in the life sciences, the contribution of science to improve public health and reduce global health disparities is more pertinent than ever before. Yet the benefits of modern medicine still have not reached millions of people in developing countries. It is crucial to recognize that science and technology can be used very effectively in partnership with public health practices in developing countries and can enhance their efficacy. The fight to improve global health needs, in addition to effective public health measures, requires rapid and efficient diagnostic tools; new vaccines and drugs, efficient delivery methods and novel approaches to therapeutics; and low-cost restoration of water, soil and other natural resources. In 2002, the University of Toronto published a report on the "Top 10 Biotechnologies for Improving Health in Developing Countries". Here we review these new and emerging biotechnologies and explore how they can be used to support the goals of developing countries in improving health.

Two distinct pathways for trehalose assimilation in the yeast Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae can synthesize trehalose and also use this disaccharide as a carbon source for growth. However, the molecular mechanism by which extracellular trehalose can be transported to the vacuole and degraded by the acid trehalase Ath1p is not clear. By using an adaptation of the assay of invertase on whole cells with NaF, we showed that more than 90% of the activity of Ath1p is extracellular, splitting of the disaccharide into glucose. We also found that Agt1p-mediated trehalose transport and the hydrolysis of the disaccharide by the cytosolic neutral trehalase Nth1p are coupled and represent a second, independent pathway, although there are several constraints on this alternative route. First, the AGT1/MAL11 gene is controlled by the MAL system, and Agt1p was active in neither non-maltose-fermenting nor maltose-inducible strains. Second, Agt1p rapidly lost activity during growth on trehalose, by a mechanism similar to the sugar-induced inactivation of the maltose permease. Finally, both pathways are highly pH sensitive and effective growth on trehalose occurred only when the medium was buffered at around pH 5.0. The catabolism of trehalose was purely oxidative, and since levels of Ath1p limit the glucose flux in the cells, batch cultures on trehalose may provide a useful alternative to glucose-limited chemostat cultures for investigation of metabolic responses in yeast.

Trehalose mediated growth inhibition of Arabidopsis seedlings is due to trehalose-6-phosphate accumulation

Trehalose-6-phosphate (T6P) is required for carbon utilization during Arabidopsis development, and its absence is embryo lethal. Here we show that T6P accumulation inhibits seedling growth. Wild-type seedlings grown on 100 mm trehalose rapidly accumulate T6P and stop growing, but seedlings expressing Escherichia coli trehalose phosphate hydrolase develop normally on such medium. T6P accumulation likely results from much-reduced T6P dephosphorylation when trehalose levels are high. Metabolizable sugars added to trehalose medium rescue T6P inhibition of growth. In addition, Suc feeding leads to a progressive increase in T6P concentrations, suggesting that T6P control over carbon utilization is related to available carbon for growth. Expression analysis of genes from the Arabidopsis trehalose metabolism further supports this: Suc rapidly induces expression of trehalose phosphate synthase homolog AtTPS5 to high levels. In contrast, T6P accumulation after feeding trehalose in the absence of available carbon induces repression of genes encoding T6P synthases and expression of T6P phosphatases. To identify processes controlled by T6P, we clustered expression profile data from seedlings with altered T6P content. T6P levels correlate with expression of a specific set of genes, including the S6 ribosomal kinase ATPK19, independently of carbon status. Interestingly, Suc addition represses 15 of these genes, one of which is AtKIN11, encoding a Sucrose Non Fermenting 1 (SNF1)-related kinase known to play a role in Suc utilization.

Characterization of the trehalosyl dextrin-forming enzyme from the thermophilic archaeon Sulfolobus solfataricus ATCC 35092

The trehalosyl dextrin-forming enzyme (TDFE) mainly catalyzes an intramolecular transglycosyl reaction to form trehalosyl dextrins from dextrins by converting the alpha-1,4-glucosidic linkage at the reducing end to an alpha-1,1-glucosidic linkage. In this study, the treY gene encoding TDFE was PCR cloned from the genomic DNA of Sulfolobus solfataricus ATCC 35092 to an expression vector with a T7 lac promoter and then expressed in Escherichia coli. The recombinant TDFE was purified sequentially by using heat treatment, ultrafiltration, and gel filtration. The obtained recombinant TDFE showed an apparent optimal pH of 5 and an optimal temperature of 75 degrees C. The enzyme was stable in a pH range of 4.5-11, and the activity remained unchanged after a 2-h incubation at 80 degrees C. The transglycosylation activity of TDFE was higher when using maltoheptaose as substrate than maltooligosaccharides with a low degree of polymerization (DP). However, the hydrolysis activity of TDFE became stronger when low DP maltooligosaccharides, such as maltotriose, were used as substrate. The ratios of hydrolysis activity to transglycosylation activity were in the range of 0.2-14% and increased when the DP of substrate decreased. The recombinant TDFE was found to exhibit different substrate specificity, such as its preferred substrates for the transglycosylation reaction and the ratio of hydrolysis to transglycosylation of the enzyme reacting with maltotriose, when compared with other natural or recombinant TDFEs from Sulfolobus.

Enhancement of trehalose production in dairy propionibacteria through manipulation of environmental conditions

We have shown that the ability to produce trehalose is widespread within the genus Propionibacterium. Eighteen strains isolated from dairy sources were screened for trehalose synthesis; the effect of environmental conditions on trehalose production was evaluated in Propionibacterium freudenreichii ssp. shermanii NIZO B365, a strain that accumulated high amounts of this disaccharide. Lactose was the best carbohydrate source for trehalose production, whereas lactate, the substrate that led to the highest specific growth rate, was a poor precursor. Trehalose was consumed after exhaustion of the carbon source in the medium, suggesting its role as a reserve compound. The production of trehalose was not affected by lowering the growth temperature from 30 to 20 degrees C. On the other hand, the maximum trehalose accumulation increased from about 200 to 400 mg of trehalose/g of cell protein upon decreasing the pH from 7.0 to 4.7, by increasing the concentration of NaCl to 2% (w/v), or during growth under aerobic conditions (50% air saturation, 24 microM O(2), pH 7.0). In the absence of NaCl, trehalose accumulated concomitantly with growth, but an increase in salinity triggered a high trehalose production already in the early exponential growth phase. The data provide evidence for a dual function of trehalose as a reserve compound and as a stress-response metabolite. Moreover, P. freudenreichii ssp. shermanii NIZO B365 was able to produce high levels of trehalose in skim milk, which is promising for the implementation of fermented dairy products.

Yeast activator proteins and stress response: an overview

Yeast, and especially Saccharomyces cerevisiae, are continuously exposed to rapid and drastic changes in their external milieu. Therefore, cells must maintain their homeostasis, which is achieved through a highly coordinated gene expression involving a plethora of transcription factors, each of them performing specific functions. Here, we discuss recent advances in our understanding of the function of the yeast activator protein family of eight basic-leucine zipper trans-activators that have been implicated in various forms of stress response.

The osmoprotectants glycine and its methyl derivatives prevent the thermal inactivation of protective antigen of Bacillus anthracis

Protective antigen (PA) is the main immunogenic constituent of all vaccines against anthrax. It is known to lose its biological activity even at 37 degrees C. Its thermolabile nature has, thus, remained a cause of concern as even transient exposure of the vaccine to higher temperature could compromise its efficacy. Various types of cosolvent excipients have been used to stabilize a number of proteins with variable success. However, no comprehensive and systematic study to stabilize anthrax PA molecule using this approach has ever been undertaken. We have carried out a systematic study on the effect of osmoprotectants like glycine and its methyl derivatives, sarcosine, dimethylglycine, and betaine, on the thermostability of PA. The thermal stability of PA was found to be highly sensitive to pH with maxima at pH 7.9. All the cosolvent additives used were able to enhance the thermal stability of PA as inferred from an increase in T(1/2) values, the temperature at which 50% activity was retained during short-term incubation. Glycine was found to be the best stabilizer, while the ability of its methyl derivatives to stabilize PA decreased with an increase in the number of substituted methyl groups suggesting perturbation of hydrophobic interactions. On extended incubation at 40 degrees C the half-life of PA thermal inactivation increased more than four times in the presence of glycine. Thus, glycine could be used as an effective stabilizer to enhance the shelf life of recombinant vaccine against anthrax.

Trehalose is required for growth of Mycobacterium smegmatis

Mycobacteria contain high levels of the disaccharide trehalose in free form as well as within various immunologically relevant glycolipids such as cord factor and sulfolipid-1. By contrast, most bacteria use trehalose solely as a general osmoprotectant or thermoprotectant. Mycobacterium tuberculosis and Mycobacterium smegmatis possess three pathways for the synthesis of trehalose. Most bacteria possess only one trehalose biosynthesis pathway and do not elaborate the disaccharide into more complex metabolites, suggesting a distinct role for trehalose in mycobacteria. We disabled key enzymes required for each of the three pathways in M. smegmatis by allelic replacement. The resulting trehalose biosynthesis mutant was unable to proliferate and enter stationary phase unless supplemented with trehalose. At elevated temperatures, however, the mutant was unable to proliferate even in the presence of trehalose. Genetic complementation experiments showed that each of the three pathways was able to recover the mutant in the absence of trehalose, even at elevated temperatures. From a panel of trehalose analogs, only those with the native alpha,alpha-(1,1) anomeric stereochemistry rescued the mutant, whereas alternate stereoisomers and general osmo- and thermoprotectants were inactive. These findings suggest a dual role for trehalose as both a thermoprotectant and a precursor of critical cell wall metabolites.

Interaction of the disaccharide trehalose with a phospholipid bilayer: a molecular dynamics study

The disaccharide trehalose is well known for its bioprotective properties. Produced in large amounts during stress periods in the life of organisms able to survive potentially damaging conditions, trehalose plays its protective role by stabilizing biostructures such as proteins and lipid membranes. In this study, molecular dynamics simulations are used to investigate the interaction of trehalose with a phospholipid bilayer at atomistic resolution. Simulations of the bilayer in the absence and in the presence of trehalose at two different concentrations (1 or 2 molal) are carried out at 325 K and 475 K. The results show that trehalose is able to minimize the disruptive effect of the elevated temperature and stabilize the bilayer structure. At both temperature, trehalose is found to interact directly with the bilayer through hydrogen bonds. However, the water molecules at the bilayer surface are not completely replaced. At high temperature, the protective effect of trehalose is correlated with a significant increase in the number of trehalose-bilayer hydrogen bonds, predominantly through an increase in the number of trehalose molecules bridging three or more lipid molecules.

The importance of a functional trehalose biosynthetic pathway for the life of yeasts and fungi

The view of the role of trehalose in yeast has changed in the last few years. For a long time considered a reserve carbohydrate, it gained new importance when its function in the acquisition of thermotolerance was demonstrated. More recently the cellular processes in which the trehalose biosynthetic pathway has been implicated range from the control of glycolysis to sporulation and infectivity by certain fungal pathogens. There is now enough experimental evidence to conclude that trehalose 6-phosphate, an intermediate of trehalose biosynthesis, is an important metabolic regulator in such different organisms as yeasts or plants. Its inhibition of hexokinase plays a key role in the control of the glycolytic flux in Saccharomyces cerevisiae but other, likely important, sites of action are still unknown. We present examples of the phenotypes produced by mutations in the two steps of the trehalose biosynthetic pathway in different yeasts and fungi, and whenever possible examine the molecular explanations advanced to interpret them.

Yeast Adapt to Near-Freezing Temperatures by STRE/Msn2,4-Dependent Induction of Trehalose Synthesis and Certain Molecular Chaperones

Virtually nothing is known about the biochemical adaptations in eukaryotic cells that may enhance survival at low temperatures or upon freezing. Here we demonstrate an adaptive response in yeast that is activated below 10 degrees C and increases tolerance to low temperatures and freezing. This response involves a dramatic accumulation of the chemical chaperone trehalose and induction of trehalose-synthesizing enzymes (Tps1, Tps2) and certain heat shock proteins (Hsp104, Hsp42, Hsp12, Ssa4). mRNAs for these proteins increase dramatically below 10 degrees C and even at 0 degrees C. Their expression requires Msn2,4 transcription factors but also involves marked mRNA stabilization. Upon return to 30 degrees C, TPS1, TPS2, and HSP104 mRNAs, trehalose levels and tolerance to freezing fall dramatically within minutes. Mutants lacking trehalose or Msn2,4 die more rapidly at 0 degrees C and upon freezing. Thus, below 10 degrees C, yeast show an adaptive response that sustains viability at low or freezing temperatures, which are commonly encountered in natural environments and laboratory refrigerators.

Trehalose metabolism genes in Caenorhabditis elegans and filarial nematodes

The sugar trehalose is claimed to be important in the physiology of nematodes where it may function in sugar transport, energy storage and protection against environmental stresses. In this study we investigated the role of trehalose metabolism in nematodes, using Caenorhabditis elegans as a model, and also identified complementary DNA clones putatively encoding genes involved in trehalose pathways in filarial nematodes. In C. elegans two putative trehalose-6-phosphate synthase (tps) genes encode the enzymes that catalyse trehalose synthesis and five putative trehalase (tre) genes encode enzymes catalysing hydrolysis of the sugar. We showed by RT-PCR or Northern analysis that each of these genes is expressed as mRNA at all stages of the C. elegans life cycle. Database searches and sequencing of expressed sequence tag clones revealed that at least one tps gene and two tre genes are expressed in the filarial nematode Brugia malayi, while one tps gene and at least one tre gene were identified for Onchocerca volvulus. We used the feeding method of RNA interference in C. elegans to knock down temporarily the expression of each of the tps and tre genes. Semiquantitative RT-PCR analysis confirmed that expression of each gene was silenced by RNA interference. We did not observe an obvious phenotype for any of the genes silenced individually but gas-chromatographic analysis showed >90% decline in trehalose levels when both tps genes were targeted simultaneously. This decline in trehalose content did not affect viability or development of the nematodes.

Compatible and counteracting solutes: protecting cells from the Dead Sea to the deep sea

Cells of many organisms accumulate certain small organic molecules--called compatible and counteracting solutes, compensatory solutes, or chemical chaperones--in response to certain physical stresses. These solutes include certain carbohydrates, amino acids, methylamine and methylsulphonium zwitterions, and urea. In osmotic dehydrating stress, these solutes serve as cellular osmolytes. Unlike common salt ions and urea (which inhibit proteins), some organic osmolytes are compatible; i.e., they do not perturb macromolecules such as proteins. In addition, some may protect cells through metabolic processes such as antioxidation reactions and sulphide detoxification. Other osmolytes, and identical or similar solutes accumulated in anhydrobiotic, heat and pressure stresses, are termed counteracting solutes or chemical chaperones because they stabilise proteins and counteract protein-destabilising factors such as urea, temperature, salt, and hydrostatic pressure. Stabilisation of proteins, not necessarily beneficial in the absence of a perturbant, may result indirectly from effects on water structure. Osmotic shrinkage of cells activates genes for chaperone proteins and osmolytes by mechanisms still being elucidated. These solutes have applications in agriculture, medicine and biotechnology.

Overproduction of trehalose: heterologous expression of Escherichia coli trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase in Corynebacterium glutamicum

Trehalose is a disaccharide with potential applications in the biotechnology and food industries. We propose a method for industrial production of trehalose, based on improved strains of Corynebacterium glutamicum. This paper describes the heterologous expression of Escherichia coli trehalose-synthesizing enzymes trehalose-6-phosphate synthase (OtsA) and trehalose-6-phosphate phosphatase (OtsB) in C. glutamicum, as well as its impact on the trehalose biosynthetic rate and metabolic-flux distributions, during growth in a defined culture medium. The new recombinant strain showed a five- to sixfold increase in the activity of OtsAB pathway enzymes, compared to a control strain, as well as an almost fourfold increase in the trehalose excretion rate during the exponential growth phase and a twofold increase in the final titer of trehalose. The heterologous expression described resulted in a reduced specific glucose uptake rate and Krebs cycle flux, as well as reduced pentose pathway flux, a consequence of downregulated glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. The results proved the suitability of using the heterologous expression of Ots proteins in C. glutamicum to increase the trehalose biosynthetic rate and yield and suggest critical points for further improvement of trehalose overproduction in C. glutamicum.

Expression of Drosophila trehalose-phosphate synthase in HEK-293 cells increases hypoxia tolerance

Increasing hypoxia tolerance in mammalian cells is potentially of major importance, but it has not been feasible thus far. The disaccharide trehalose, which accumulates dramatically during heat shock, enhances thermotolerance and reduces aggregation of denatured proteins. Previous studies from our laboratory showed that over-expression of Drosophila trehalose-phosphate synthase (dtps1) increases the trehalose level and anoxia tolerance in flies. To determine whether trehalose can protect against anoxic injury in mammalian cells, we transfected the dtps1 gene into human HEK-293 cells using the recombinant plasmid pcDNA3.1(-)-dtps1 and obtained more than 20 stable cell strains. Glucose starvation in culture showed that HEK-293 cells transfected with pcDNA3.1(-)-dtps1 (HEK-dtps1) do not metabolize intracellular trehalose, and, interestingly, these cells accumulated intracellular trehalose during hypoxic exposure. In contrast to HEK-293 cells transfected with pcDNA3.1(-) (HEK-v), cells with trehalose were more resistant to low oxygen stress (1% O2). To elucidate how trehalose protects cells from anoxic injury, we assayed protein solubility and the amount of ubiquitinated proteins. There was three times more insoluble protein in HEK-v than in HEK-dtps1 after 3 days of exposure to low O2. The amount of Na+-K+ ATPase present in the insoluble proteins dramatically increased in HEK-v cells after 2 and 3 days of exposure, whereas there was no significant change in HEK-dtps1 cells. Ubiquitinated proteins increased dramatically in HEK-v cells after 2 and 3 days of exposure but not in HEK-dtps1 cells over the same period. Our results indicate that increased trehalose in mammalian cells following transfection by the Drosophila tps1 gene protects cells from hypoxic injury. The mechanism of this protection is likely related to a decrease in protein denaturation, through protein-trehalose interactions, resulting in enhanced cellular recovery from hypoxic stress.

Perturbation of folding and reassociation of lactate dehydrogenase by proline and trimethylamine oxide

Investigations of protein-solute interactions typically show that osmolytes favor native conformations. In this study, the effects of representative compatible and counteracting osmolytes on the reactivation of lactate dehydrogenase from two different conformational states were explored. Contrary to expectations, proline and trimethylamine oxide inhibited both the initial time course and the extent of reactivation of lactate dehydrogenase from bovine heart following denaturation in guanidine hydrochloride, as well as following inactivation at pH 2.3. Reactivation of acid-dissociated porcine heart lactate dehydrogenase was inhibited by both proline and trimethylamine oxide (2 M). In all instances, trimethylamine oxide was the more effective inhibitor of reactivation. Analysis of the catalytic properties of the reactivating enzyme provided evidence that the molecular species that was enzymatically active during the initial stages of reactivation of acid-inactivated porcine heart lactate dehydrogenase reflects a non-native conformation. Proline and trimethylamine oxide stabilize polypeptides through exclusion from the polypeptide backbone; the inhibition of renaturation/reassociation described here is probably due to attenuation of this stabilizing influence through favorable interactions of the osmolytes with sidechains of residues that lie at the interfaces of the monomers and dimers that associate to form the active tetramer. In addition, these osmolytes may stabilize non-native intermediates in the folding pathway. The high viscosity of solutions containing more than 3 m proline was a major factor in the inhibition of reassociation of acid-dissociated porcine heart lactate dehydrogenase as well as other viscosity-dependent transformations that may occur during reactivation following unfolding in guanidine hydrochloride.

The donor subsite of trehalose-6-phosphate synthase: binary complexes with UDP-glucose and UDP-2-deoxy-2-fluoro-glucose at 2 A resolution

Trehalose is an unusual non-reducing disaccharide that plays a variety of biological roles, from food storage to cellular protection from environmental stresses such as desiccation, pressure, heat-shock, extreme cold, and oxygen radicals. It is also an integral component of the cell-wall glycolipids of mycobacteria. The primary enzymatic route to trehalose first involves the transfer of glucose from a UDP-glucose donor to glucose-6-phosphate to form alpha,alpha-1,1 trehalose-6-phosphate. This reaction, in which the configurations of two glycosidic bonds are set simultaneously, is catalyzed by the glycosyltransferase trehalose-6-phosphate synthase (OtsA), which acts with retention of the anomeric configuration of the UDP-sugar donor. The classification of activated sugar-dependent glycosyltransferases into approximately 70 distinct families based upon amino acid sequence similarities places OtsA in glycosyltransferase family 20 (see afmb.cnrs-mrs.fr/CAZY/). The recent 2.4 A structure of Escherichia coli OtsA revealed a two-domain enzyme with catalysis occurring at the interface of the twin beta/alpha/beta domains. Here we present the 2.0 A structures of the E. coli OtsA in complex with either UDP-Glc or the non-transferable analogue UDP-2-deoxy-2-fluoroglucose. Both complexes unveil the donor subsite interactions, confirming a strong similarity to glycogen phosphorylases, and reveal substantial conformational differences to the previously reported complex with UDP and glucose 6-phosphate. Both the relative orientation of the two domains and substantial (up to 10 A) movements of an N-terminal loop (residues 9-22) characterize the more open "relaxed" conformation of the binary UDP-sugar complexes reported here.

NMR and Quantum Chemical Study on the OH···π and CH···O Interactions between Trehalose and Unsaturated Fatty Acids: Implication for the Mechanism of Antioxidant Function of Trehalose

Trehalose is a disaccharide that attracts much attention as a stress protectant. In this study, we investigated the mechanism of the antioxidant function of trehalose. The spin-lattice relaxation times (T(1)) of (1)H and (13)C NMR spectra were measured to investigate the interaction between trehalose and unsaturated fatty acid (UFA). We selected several kinds of UFA that differ in the number of double bonds and in their configurations (cis or trans). Several other disaccharides (sucrose, maltose, neotrehalose, maltitol, and sorbitol) were also analyzed by NMR. The T(1) values for the (1)H and (13)C signals assigned to the olefin double bonds in UFA decrease with increasing concentration of trehalose and the changes reaches plateaus at integer ratios of trehalose to UFA. The characteristic T(1) change is observed only for the combination of trehalose and UFA with cis double bond(s). On the other hand, from the (13)C-T(1) measurements for trehalose, the T(1) values of the C-3 (C-3') and C-6' (C-6) are found to change remarkably by addition of UFA. (1)H[bond](1)H NOESY measurements provide direct evidence for complexation of trehalose with linoleic acid. These results indicate that one trehalose molecule stoichiometrically interacts with one cis-olefin double bond of UFA. Computer modeling study indicates that trehalose forms a stable complex with an olefin double bond through OH...pi and CH...O types of hydrogen bonding. Furthermore, a significant increase in the activation energy is found for hydrogen abstraction reaction from the methylene group located between the double bonds that are both interacting with the trehalose molecules. Therefore, trehalose has a significant depression effect on the oxidation of UFA through the weak interaction with the double bond(s). This is the first study to elucidate the antioxidant function of trehalose.

Ethanol and thermotolerance in the bioconversion of xylose by yeasts

The mechanisms underlying ethanol and heat tolerance are complex. Many different genes are involved, and the exact basis is not fully understood. The integrity of cytoplasmic and mitochondrial membranes is critical to maintain proton gradients for metabolic energy and nutrient uptake. Heat and ethanol stress adversely affect membrane integrity. These factors are particularly detrimental to xylose-fermenting yeasts because they require oxygen for biosynthesis of essential cell membrane and nucleic acid constituents, and they depend on respiration for the generation of ATP. Physiological responses to ethanol and heat shock have been studied most extensively in S. cerevisiae. However, comparative biochemical studies with other organisms suggest that similar mechanisms will be important in xylose-fermenting yeasts. The composition of a cell's membrane lipids shifts with temperature, ethanol concentration, and stage of cultivation. Levels of unsaturated fatty acids and ergosterol increase in response to temperature and ethanol stress. Inositol is involved in phospholipid biosynthesis, and it can increase ethanol tolerance when provided as a supplement. Membrane integrity determines the cell's ability to maintain proton gradients for nutrient uptake. Plasma membrane ATPase generates the proton gradient, and the biochemical characteristics of this enzyme contribute to ethanol tolerance. Organisms with higher ethanol tolerance have ATPase activities with low pH optima and high affinity for ATP. Likewise, organisms with ATPase activities that resist ethanol inhibition also function better at high ethanol concentrations. ATPase consumes a significant fraction of the total cellular ATP, and under stress conditions when membrane gradients are compromised the activity of ATPase is regulated. In xylose-fermenting yeasts, the carbon source used for growth affects both ATPase activity and ethanol tolerance. Cells can adapt to heat and ethanol stress by synthesizing trehalose and heat-shock proteins, which stabilize and repair denatured proteins. The capacity of cells to produce trehalose and induce HSPs correlate with their thermotolerance. Both heat and ethanol increase the frequency of petite mutations and kill cells. This might be attributable to membrane effects, but it could also arise from oxidative damage. Cytoplasmic and mitochondrial superoxide dismutases can destroy oxidative radicals and thereby maintain cell viability. Improved knowledge of the mechanisms underlying ethanol and thermotolerance in S. cerevisiae should enable the genetic engineering of these traits in xylose-fermenting yeasts.

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.

Cloning and characterization of a gene encoding trehalose phosphorylase (TP) from Pleurotus sajor-caju

Complementary DNA for a gene encoding trehalose phosphorylase (TP) that reversibly catalyzes trehalose synthesis and degradation from alpha-glucose-1-phosphate (alpha-Glc-1-P) and glucose was cloned from Pleurotus sajor-caju. The cDNA of P. sajor-caju TP (designated PsTP, GenBank Accession No. AF149777) encodes a polypeptide of 751 amino acids with a deduced molecular mass of 83.7 kDa. The PsTP gene is expressed in mycelia, pilei, and stipes of fruiting bodies. Trehalose phosphorylase PsTP was purified from PsTP-transformed Escherichia coli. The enzyme catalyzes both the phosphorolysis of trehalose to produce alpha-Glc-1-P and glucose, and the synthesis of trehalose. The apparent K(m) values for trehalose and Pi in phosphorolytic reaction at pH 7.0 were 74.8 and 5.4 mM, respectively. The PsTP gene complemented Saccharomyces cerevisiae Deltatps1, Deltatps2 double-mutant cells, allowing their growth on glucose medium. Furthermore, yeast transformed with PsTP produced 2-2.5-fold more trehalose than non-transformants or cells transformed with empty vector only.

Why is trehalose an exceptional protein stabilizer? An analysis of the thermal stability of proteins in the presence of the compatible osmolyte trehalose

Trehalose, a naturally occurring osmolyte, is known to be an exceptional stabilizer of proteins and helps retain the activity of enzymes in solution as well as in the freeze-dried state. To understand the mechanism of action of trehalose in detail, we have conducted a thorough investigation of its effect on the thermal stability in aqueous solutions of five well characterized proteins differing in their various physico-chemical properties. Among them, RNase A has been used as a model enzyme to investigate the effect of trehalose on the retention of enzymatic activity upon incubation at high temperatures. 2 m trehalose was observed to raise the transition temperature, Tm of RNase A by as much as 18 degrees C and Gibbs free energy by 4.8 kcal mol-1 at pH 2.5. There is a decrease in the heat capacity of protein denaturation (DeltaCp) in trehalose solutions for all the studied proteins. An increase in the DeltaG and a decrease in the DeltaCp values for all the proteins points toward a general mechanism of stabilization due to the elevation and broadening of the stability curve (DeltaG versus T). A direct correlation of the surface tension of trehalose solutions and the thermal stability of various proteins has been observed. Wyman linkage analysis indicates that at 1.5 m concentration 4-7 molecules of trehalose are excluded from the vicinity of protein molecules upon denaturation. We further show that an increase in the stability of proteins in the presence of trehalose depends upon the length of the polypeptide chain. The pH dependence data suggest that even though the charge status of a protein contributes significantly, trehalose can be expected to work as a universal stabilizer of protein conformation due to its exceptional effect on the structure and properties of solvent water compared with other sugars and polyols.

Principles of low temperature cell preservation

Cell transplantation is becoming an important technique for treatment of heart failure. Preservation is an integral step in any procedure using cells. There are two primary modes of cell preservation at low temperature, hypothermic preservation at temperatures above freezing and cryogenic preservation at temperatures below freezing. Optimal preservation protocols require a fundamental understanding of the principles involved. This review briefly describes the basic mechanisms of damage during hypothermic and cryogenic preservation and the basic principles for developing optimal protocols for preservation of cells.

Acclimation of entomopathogenic nematodes to novel temperatures: trehalose accumulation and the acquisition of thermotolerance

The effect of thermal acclimation on trehalose accumulation and the acquisition of thermotolerance was studied in three species of entomopathogenic nematodes adapted to either cold or warm temperatures. All three Steinernema species accumulated trehalose when acclimated at either 5 or 35 degrees C, but the amount of trehalose accumulation differed by species and temperature. The trehalose content of the cold adapted Steinernema feltiae increased by 350 and 182%, of intermediate Steinernema carpocapsae by 146 and 122% and of warm adapted Steinernema riobrave by 30 and 87% over the initial level (18.25, 27.24 and 23.97 microg trehalose/mg dry weight, respectively) during acclimation at 5 and 35 degrees C, respectively. Warm and cold acclimation enhanced heat (40 degrees C for 8h) and freezing (-20 degrees C for 4h) tolerance of S. carpocapsae and the enhanced tolerance was positively correlated with the increased trehalose levels. Warm and cold acclimation also enhanced heat but not freezing tolerance of S. feltiae and the enhanced heat tolerance was positively correlated with the increased trehalose levels. In contrast, warm and cold acclimation enhanced the freezing but not heat tolerance of S. riobrave, and increased freezing tolerance of only warm acclimated S. riobrave was positively correlated with the increased trehalose levels. The effect of acclimation on maintenance of original virulence by either heat or freeze stressed nematodes against the wax moth Galleria mellonella larvae was temperature dependent and differed among species. During freezing stress, both cold and warm acclimated S. carpocapsae (84%) and during heat stress, only warm acclimated S. carpocapsae (95%) maintained significantly higher original virulence than the non-acclimated (36 and 47%, respectively) nematodes. Both cold and warm acclimated S. feltiae maintained significantly higher original virulence (69%) than the non-acclimated S. feltiae (0%) during heat but not freezing stress. In contrast, both warm and cold acclimated S. riobrave maintained significantly higher virulence (41%) than the non-acclimated (14%) nematodes during freezing, but not during heat stress. Our data indicate that trehalose accumulation is not only a cold associated phenomenon but is a general response of nematodes to thermal stress. However, the extent of enhanced thermal stress tolerance conferred by the accumulated trehalose differs with nematode species.

Functional genomics approaches for the identification and validation of antifungal drug targets

So far, antifungal drug discovery seems to have benefited little from the enormous advances in the field of genomics in the last decade. Although it has become clear that traditional drug screening is not delivering the long-awaited novel potent antifungals, little has been reported on efforts to use novel genome-based methodologies in the quest for new drugs acting on human pathogenic fungi. Although the market for a novel systemic and even topical broad-spectrum antifungal appears considerable, many large pharmaceutical companies have decided to scale back their activities in antifungal drug discovery. Here we report on some of the recent advances in genomics-based technologies that will allow us not only to identify and validate novel drug targets but hopefully also to discover active therapeutic agents. Novel drug targets have already been found by 'en masse' gene inactivation strategies (e.g. using antisense RNA inhibition). In addition, genome expression profiling using DNA microarrays helps to assign gene function but also to understand better the mechanism of action of known drugs (e.g. itraconazole) and to elucidate how new drug candidates work. No doubt, we have a long way to go just to catch up with the advances made in other therapeutic areas, but all tools are at hand to derive practical benefits from the genomics revolution. The next few years should prove a very exciting time in the history of antifungal drug discovery.

Comprehensive expression analysis of time-dependent genetic responses in yeast cells to low temperature

We performed genome-wide expression analysis to determine genetic responses in Saccharomyces cerevisiae to a low temperature environment using a cDNA microarray. Approximately 25% of the genes in the yeast genome were found to be involved in the response of yeast to low temperature. This finding of a large number of genes being involved in the response to low temperature enabled us to give a functional interpretation to the genetic responses to the stimulus. Functional and clustering analyses of temporal changes in gene expression revealed that global states of the expressions of up-regulated genes could be characterized as having three phases (the early, middle, and late phases). In each phase, genes related to rRNA synthesis, ribosomal proteins, or several stress responses are time-dependently up-regulated, respectively. Through these phases, yeast cells may improve reduced efficiency of translation and enhance cell protection mechanisms to survive under a low temperature condition. Furthermore, these time-dependent regulations of these genes would be controlled by the cAMP-protein kinase A pathway. The results of our study provide a global description of transcriptional response for adaptation to low temperature in yeast cells.

Insights into trehalose synthesis provided by the structure of the retaining glucosyltransferase OtsA

Trehalose is a nonreducing disaccharide that plays a major role in many organisms, most notably in survival and stress responses. In Mycobacterium tuberculosis, it plays a central role as the carbohydrate core of numerous immunogenic glycolipids including "cord factor" (trehalose 6,6'-dimycolate). The classical pathway for trehalose synthesis involves the condensation of UDP-glucose and glucose-6-phosphate to afford trehalose-6-phosphate, catalyzed by the retaining glycosyltransferase OtsA. The configurations of two anomeric positions are set simultaneously, resulting in the formation of a double glycoside. The three-dimensional structure of the Escherichia coli OtsA, in complex with both UDP and glucose-6-phosphate, reveals the active site at the interface of two beta/alpha/beta domains. The overall structure and the intimate details of the catalytic machinery reveal a striking similarity to glycogen phosphorylase, indicating a strong evolutionary link and suggesting a common catalytic mechanism.

Nutraceutical production with food-grade microorganisms

Over the past few years a number of new food ingredients labelled as being nutraceuticals have been launched on the food and pharmaceutical market. These include components that have a proven beneficial effect on human health, such as low-calorie sugars and B vitamins. Lactic acid bacteria, in particular Lactococcus lactis, have been demonstrated to be ideal cell factories for the production of these important nutraceuticals. Developments in the genetic engineering of food-grade microoganisms means that the production of certain nutraceuticals can be enhanced or newly induced through overexpression and/or disruption of relevant metabolic genes.

A second UDP-glucose pyrophosphorylase is required for differentiation and development in Dictyostelium discoideum

Uridine diphosphoglucose pyrophosphorylase (UDPGP) is a developmentally regulated enzyme in Dictyostelium discoideum, which is involved in trehalose, cellulose, and glycogen synthesis. Two independent UDPGP proteins are believed to be responsible for this activity. To determine the relative contributions of each protein, the genes encoding them were disrupted individually. Cells lacking the udpgp1 gene exhibit normal growth and development and make normal levels of cellulose. In agreement with these phenotypes, udpgp1(-) cells still have UDPGP activity, although at a reduced level. This supports the importance of the second UDPGP gene. This newly identified gene, ugpB, encodes an active UDPGP as determined by complementation in Escherichia coli. When this gene is disrupted, cells undergo aberrant differentiation and development ending with small, gnarled fruiting bodies. These cells also have decreased spore viability and decreased levels of glycogen, whose production requires UDPGP activity. These phenotypes suggest that UgpB constitutes the major UDPGP activity produced during development. Sequence analysis of the two UDPGP genes shows that UgpB has higher homology to other eukaryotic UDPGPs than does UDPGP1. This includes the presence of 5 conserved lysine residues. Udpgp1 only has 1 of these lysines.

Trehalose-mediated inhibition of the plasma membrane H+-ATPase from Kluyveromyces lactis: dependence on viscosity and temperature

The effect of increasing trehalose concentrations on the kinetics of the plasma membrane H+-ATPase from Kluyveromyces lactis was studied at different temperatures. At 20 degrees C, increasing concentrations of trehalose (0.2 to 0.8 M) decreased V(max) and increased S(0.5) (substrate concentration when initial velocity equals 0.5 V(max)), mainly at high trehalose concentrations (0.6 to 0.8 M). The quotient V(max)/S(0.5) decreased from 5.76 micromol of ATP mg of protein(-1) x min(-1) x mM(-1) in the absence of trehalose to 1.63 micromol of ATP mg of protein(-1) x min(-1) x mM(-1) in the presence of 0.8 M trehalose. The decrease in V(max) was linearly dependent on solution viscosity (eta), suggesting that inhibition was due to hindering of protein domain diffusional motion during catalysis and in accordance with Kramer's theory for reactions in solution. In this regard, two other viscosity-increasing agents, sucrose and glycerol, behaved similarly, exhibiting the same viscosity-enzyme inhibition correlation predicted. In the absence of trehalose, increasing the temperature up to 40 degrees C resulted in an exponential increase in V(max) and a decrease in enzyme cooperativity (n), while S(0.5) was not modified. As temperature increased, the effect of trehalose on V(max) decreased to become negligible at 40 degrees C, in good correlation with the temperature-mediated decrease in viscosity. The trehalose-mediated increase in S(0.5) was similar at all temperatures tested, and thus, trehalose effects on V(max)/S(0.5) were always observed. Trehalose increased the activation energy for ATP hydrolysis. Trehalose-mediated inhibition of enzymes may explain why yeast rapidly hydrolyzes trehalose when exiting heat shock.

Dynamics of cell wall structure in Saccharomyces cerevisiae

The cell wall of Saccharomyces cerevisiae is an elastic structure that provides osmotic and physical protection and determines the shape of the cell. The inner layer of the wall is largely responsible for the mechanical strength of the wall and also provides the attachment sites for the proteins that form the outer layer of the wall. Here we find among others the sexual agglutinins and the flocculins. The outer protein layer also limits the permeability of the cell wall, thus shielding the plasma membrane from attack by foreign enzymes and membrane-perturbing compounds. The main features of the molecular organization of the yeast cell wall are now known. Importantly, the molecular composition and organization of the cell wall may vary considerably. For example, the incorporation of many cell wall proteins is temporally and spatially controlled and depends strongly on environmental conditions. Similarly, the formation of specific cell wall protein-polysaccharide complexes is strongly affected by external conditions. This points to a tight regulation of cell wall construction. Indeed, all five mitogen-activated protein kinase pathways in bakers' yeast affect the cell wall, and additional cell wall-related signaling routes have been identified. Finally, some potential targets for new antifungal compounds related to cell wall construction are discussed.

ISC1-encoded inositol phosphosphingolipid phospholipase C is involved in Na+/Li+ halotolerance of Saccharomyces cerevisiae

In Saccharomyces cerevisiae, toxic concentrations of Na+ orLi+ ions induce the expression of the cation-extrusion ATPase gene, ENA1. Several well-studied signal transduction pathways are known correlating high salinity to the transcriptional activation of ENA1. Nevertheless, information on the actual sensing mechanism initiating these pathways is limited. Here, we report that the ISC1-encoded phosphosphingolipid-specific phospholipase C appears to be involved in stimulation of ENA1 expression and, consequently, in mediating Na+ and Li+ tolerance in yeast. Deletion of ISC1 distinctly decreased cellular Na+ and Li+ tolerance as growth of the Deltaisc1::HIS5 mutant, DZY1, was severely impaired by 0.5 m NaCl or 0.01 m LiCl. In contrast,K+ tolerance and general osmostress regulation wereunaffected. Isc1Delta mutant growth with 0.9 m KCl and glycerol accumulation in the presence of 0.9 m NaCl or 1.5 m sorbitol were comparable to that of the wild-type. ENA1-lacZ reporter studies suggested that the increased salt sensitivity of the isc1Delta mutant is related to a significant reduction of Na+/Li+-stimulated ENA1 expression. Correspondingly, Ena1p-dependent extrusion of Na+/Li+ ions was less efficient in the isc1Delta mutant than in wild-type cells. Itis suggested that ISC1-dependent hydrolysis of an unidentified yeast inositol phosphosphingolipid represents an early event in one of the salt-induced signalling pathways of ENA1 transcriptional activation.

Osmotic stress signaling and osmoadaptation in yeasts

The ability to adapt to altered availability of free water is a fundamental property of living cells. The principles underlying osmoadaptation are well conserved. The yeast Saccharomyces cerevisiae is an excellent model system with which to study the molecular biology and physiology of osmoadaptation. Upon a shift to high osmolarity, yeast cells rapidly stimulate a mitogen-activated protein (MAP) kinase cascade, the high-osmolarity glycerol (HOG) pathway, which orchestrates part of the transcriptional response. The dynamic operation of the HOG pathway has been well studied, and similar osmosensing pathways exist in other eukaryotes. Protein kinase A, which seems to mediate a response to diverse stress conditions, is also involved in the transcriptional response program. Expression changes after a shift to high osmolarity aim at adjusting metabolism and the production of cellular protectants. Accumulation of the osmolyte glycerol, which is also controlled by altering transmembrane glycerol transport, is of central importance. Upon a shift from high to low osmolarity, yeast cells stimulate a different MAP kinase cascade, the cell integrity pathway. The transcriptional program upon hypo-osmotic shock seems to aim at adjusting cell surface properties. Rapid export of glycerol is an important event in adaptation to low osmolarity. Osmoadaptation, adjustment of cell surface properties, and the control of cell morphogenesis, growth, and proliferation are highly coordinated processes. The Skn7p response regulator may be involved in coordinating these events. An integrated understanding of osmoadaptation requires not only knowledge of the function of many uncharacterized genes but also further insight into the time line of events, their interdependence, their dynamics, and their spatial organization as well as the importance of subtle effects.

Protein interaction verification and functional annotation by integrated analysis of genome-scale data

Assays capable of determining the properties of thousands of genes in parallel present challenges with regard to accurate data processing and functional annotation. Collections of microarray expression data are applied here to assess the quality of different high-throughput protein interaction data sets. Significant differences are found. Confidence in 973 out of 5342 putative two-hybrid interactions from S. cerevisiae is increased. Besides verification, integration of expression and interaction data is employed to provide functional annotation for over 300 previously uncharacterized genes. The robustness of these approaches is demonstrated by experiments that test the in silico predictions made. This study shows how integration improves the utility of different types of functional genomic data and how well this contributes to functional annotation.

Mutant analysis reveals complex regulation of sphingolipid long chain base phosphates and long chain bases during heat stress in yeast

Sphingolipid long chain bases (LCBs) in Saccharomyces cerevisiae, dihydrosphingosine (DHS) and phytosphingosine (PHS) and their phosphates (DHS-P and PHS-P) are thought to play roles in heat stress. However, quantitative studies of LCBs and LCBPs have been limited by analytical methods. A new analytical procedure allowed us to measure changes in all known LCBPs and LCBs in wild-type and mutant cells during heat shock and to correlate the changes with heat stress resistance. All five molecular species of LCBPs increased rapidly but transiently when log and stationary phase cells were heat-stressed and when log-phase cells were induced for thermotolerance, suggesting that LCBPs play a role in heat stress. In support of this hypothesis, cells lacking the minor LCB kinase, Lcb5p, but not the major kinase, Lcb4p, were two-fold less resistant to killing when log-phase cells were induced for thermotolerance. Thus, LCBPs seem to play a minor role in heat-stress resistance. However, their role may be masked by LCBs, which are elevated in mutant strains, such as one lacking Lcb4p. This elevation demonstrates that one function of Lcb4p is to regulate LCB levels. Two new compounds, C(16) DHS and C(16) DHS-P, were identified, with the latter being degraded by the Dpl1p lyase. Our data provide a basis for determining how the basal and heat-induced levels of individual species of LCBs and LCBPs are governed by the Lcb4p and Lcb5p kinases, the Dpl1p lyase and the Lcb3p phosphatase.

Neurospora clock-controlled gene 9 (ccg-9) encodes trehalose synthase: circadian regulation of stress responses and development

The circadian clock of Neurospora crassa regulates the rhythmic expression of a number of genes encoding diverse functions which, as an ensemble, are adaptive to life in a rhythmic environment of alternating levels of light and dark, warmth and coolness, and dryness and humidity. Previous differential screens have identified a number of such genes based solely on their cycling expression, including clock-controlled gene 9 (ccg-9). Sequence analysis now shows the predicted CCG-9 polypeptide to be homologous to a novel form of trehalose synthase; as such it would catalyze the synthesis of the disaccharide trehalose, which plays an important role in protecting many cells from environmental stresses. Consistent with this, heat, glucose starvation, and osmotic stress induce ccg-9 transcript accumulation. Surprisingly, however, a parallel role in development is suggested by the finding that inactivation of ccg-9 results in altered conidiophore morphology and abolishes the normal circadian rhythm of asexual macroconidial development. Examination of a clock component, FRQ, in the ccg-9-null strain revealed normal cycling, phosphorylation, and light induction, indicating that loss of the conidiation rhythm is not due to changes in either the circadian oscillator or light input into the clock but pointing instead to a defect in circadian output. These data imply an interplay between a role of trehalose in stress protection and an apparent requirement for trehalose in clock regulation of conidiation under constant environmental conditions. This requirement can be bypassed by a daily light signal which drives a light-entrained rhythm in conidiation in the ccg-9-null strain; this bypass suggests that the trehalose requirement is related to clock control of development and not to the developmental process itself. Circadian control of trehalose synthase suggests a link between clock control of stress responses and that of development.

Chemical chaperones regulate molecular chaperones in vitro and in cells under combined salt and heat stresses

Salt and heat stresses, which are often combined in nature, induce complementing defense mechanisms. Organisms adapt to high external salinity by accumulating small organic compounds known as osmolytes, which equilibrate cellular osmotic pressure. Osmolytes can also act as "chemical chaperones" by increasing the stability of native proteins and assisting refolding of unfolded polypeptides. Adaptation to heat stress depends on the expression of heat-shock proteins, many of which are molecular chaperones, that prevent protein aggregation, disassemble protein aggregates, and assist protein refolding. We show here that Escherichia coli cells preadapted to high salinity contain increased levels of glycine betaine that prevent protein aggregation under thermal stress. After heat shock, the aggregated proteins, which escaped protection, were disaggregated in salt-adapted cells as efficiently as in low salt. Here we address the effects of four common osmolytes on chaperone activity in vitro. Systematic dose responses of glycine betaine, glycerol, proline, and trehalose revealed a regulatory effect on the folding activities of individual and combinations of chaperones GroEL, DnaK, and ClpB. With the exception of trehalose, low physiological concentrations of proline, glycerol, and especially glycine betaine activated the molecular chaperones, likely by assisting local folding in chaperone-bound polypeptides and stabilizing the native end product of the reaction. High osmolyte concentrations, especially trehalose, strongly inhibited DnaK-dependent chaperone networks, such as DnaK+GroEL and DnaK+ClpB, likely because high viscosity affects dynamic interactions between chaperones and folding substrates and stabilizes protein aggregates. Thus, during combined salt and heat stresses, cells can specifically control protein stability and chaperone-mediated disaggregation and refolding by modulating the intracellular levels of different osmolytes.

Urea increases tolerance of yeast inorganic pyrophosphatase activity to ethanol: the other side of urea interaction with proteins

Ethanol is the major product of yeast sugar fermentation and yet, at certain concentrations, it is very toxic to yeast cells. The major targets for ethanol's toxicity are the plasma membrane and the cytosolic enzymes: ethanol alters membrane organization and permeability and inactivates and unfolds globular cytosolic enzymes. The effects of ethanol on the plasma membrane are attenuated by the presence of trehalose, a disaccharide of glucose that is accumulated simultaneously with urea. The data presented in this paper show that trehalose is not effective at protecting yeast cytosolic inorganic pyrophosphatase against the inactivation of its catalytic activity promoted by alcohols. In contrast, 1 M trehalose increased the toxicity of alcohols against pyrophosphatase by at least 34%. On the other hand, 1.5 M urea attenuated the inactivation of pyrophosphatase promoted by alcohols by approximately 50%. Here we propose that, in the presence of alcohols, urea functions as a molecular filter, enriching the vicinity of the protein with water and excluding alcohol molecules. Conversely, trehalose tends to increase the interaction of alcohols with protein molecules, by withdrawing water, leading to a stronger inactivation promoted for a given concentration of alcohol in the bulk solution on pyrophosphatase activity.

The trehalose myth revisited: introduction to a symposium on stabilization of cells in the dry state

This essay is an introduction to a series of papers arising from a symposium on stabilization of cells in the dry state. Nearly all of these investigations have utilized the sugar trehalose as a stabilizing molecule. Over the past two decades a myth has grown up about special properties of trehalose for stabilization of biomaterials. We review many of such uses here and show that under ideal conditions for drying and storage trehalose has few, if any, special properties. However, under suboptimal conditions trehalose has some distinct advantages and thus may remain the preferred excipient. We review the available mechanisms for introducing trehalose into the cytoplasm of living cells as an introduction to the papers that follow.

Reversible dehydration of trehalose and anhydrobiosis: from solution state to an exotic crystal?

Physico-chemical properties of the trehalose-water system are reviewed with special reference to the transformations that may shed light on the mechanism of trehalose bio-protection. Critical analysis of solution thermodynamics is made in order to scrutinize trehalose properties often called 'anomalous' and to check the consistency of literature results. Discussion on the conversion between the solid state polymorphic forms is given, with a special emphasis of the transformations involving the newly identified anhydrous crystalline form of alpha,alpha-trehalose, TRE(alpha). This exotic crystal is almost 'isomorphous' with the dihydrate crystal structure, and possesses the unique feature of reversibly absorbing water to produce the dihydrate, without changing the main structural features. The reversible process could play a functional role in the well-known ability of this sugar to protect biological structures from damage during desiccation. The final aim of the paper is to add some new insights into and to reconcile previous hypotheses for the peculiar 'in vivo' action of trehalose.

Acquisition of tolerance against oxidative damage in Saccharomyces cerevisiae

BACKGROUND

Living cells constantly sense and adapt to redox shifts by the induction of genes whose products act to maintain the cellular redox environment. In the eukaryote Saccharomyces cerevisiae, while stationary cells possess a degree of constitutive resistance towards oxidants, treatment of exponential phase cultures with sub-lethal stresses can lead to the transient induction of protection against subsequent lethal oxidant conditions. The sensors of oxidative stress and the corresponding transcription factors that activate gene expression under these conditions have not yet been completely identified.

RESULTS

We report the role of SOD1, SOD2 and TPS1 genes (which encode the cytoplasmic Cu/Zn-superoxide dismutase, the mitochondrial Mn-isoform and trehalose-6-phosphate synthase, respectively) in the development of resistance to oxidative stress. In all experimental conditions, the cultures were divided into two parts, one was immediately submitted to severe stress (namely: exposure to H2O2, heat shock or ethanol stress) while the other was initially adapted to 40 degrees C for 60 min. The deficiency in trehalose synthesis did not impair the acquisition of tolerance to H2O2, but this disaccharide played an essential role in tolerance against heat and ethanol stresses. We also verified that the presence of only one Sodp isoform was sufficient to improve cellular resistance to 5 mM H2O2. On the other hand, while the lack of Sod2p caused high cell sensitivity to ethanol and heat shock, the absence of Sod1p seemed to be beneficial to the process of acquisition of tolerance to these adverse conditions. The increase in oxidation-dependent fluorescence of crude extracts of sod1 mutant cells upon incubation at 40 degrees C was approximately 2-fold higher than in sod2 and control strain extracts. Furthermore, in Western blots, we observed that sod mutants showed a different pattern of Hsp104p and Hsp26p expression also different from that in their control strain.

CONCLUSIONS

Trehalose seemed not to be essential in the acquisition of tolerance to H2O2 stress, but its absence was strongly felt under water stress conditions such as heat and alcoholic stresses. On the other hand, Sod1p could be involved in the control of ROS production; these reactive molecules could signal the induction of genes implicated within cell tolerance to heat and ethanol. The effects of this deletion needs further investigation.

Trehalose accumulation during cellular stress protects cells and cellular proteins from damage by oxygen radicals

The disaccharide trehalose, which accumulates dramatically during heat shock and stationary phase in many organisms, enhances thermotolerance and reduces aggregation of denatured proteins. Here we report a new role for trehalose in protecting cells against oxygen radicals. Exposure of Saccharomyces cerevisiae to a mild heat shock (38 degrees C) or to a proteasome inhibitor (MG132) induced trehalose accumulation and markedly increased the viability of the cells upon exposure to a free radical-generating system (H(2)O(2)/iron). When cells were returned to normal growth temperature (28 degrees C) or MG132 was removed from the medium, the trehalose content and resistance to oxygen radicals decreased rapidly. Furthermore, a mutant unable to synthesize trehalose was much more sensitive to killing by oxygen radicals than wild-type cells. Providing trehalose exogenously enhanced the resistance of mutant cells to H(2)O(2). Exposure of cells to H(2)O(2) caused oxidative damage to amino acids in cellular proteins, and trehalose accumulation was found to reduce such damage. After even brief exposure to H(2)O(2), the trehalose-deficient mutant exhibited a much higher content of oxidatively damaged proteins than wild-type cells. Trehalose accumulation decreased the initial appearance of damaged proteins, presumably by acting as a free radical scavenger. Therefore, trehalose accumulation in stressed cells plays a major role in protecting cellular constituents from oxidative damage.

Fungal trehalose phosphorylase: kinetic mechanism, pH-dependence of the reaction and some structural properties of the enzyme from Schizophyllum commune

Initial-velocity measurements for the phospholysis and synthesis of alpha,alpha-trehalose catalysed by trehalose phosphorylase from Schizophyllum commune and product and dead-end inhibitor studies show that this enzyme has an ordered Bi Bi kinetic mechanism, in which phosphate binds before alpha,alpha-trehalose, and alpha-D-glucose is released before alpha-D-glucose 1-phosphate. The free-energy profile for the enzymic reaction at physiological reactant concentrations displays its largest barriers for steps involved in reverse glucosyl transfer to D-glucose, and reveals the direction of phospholysis to be favoured thermodynamically. The pH dependence of kinetic parameters for all substrates and the dissociation constant of D-glucal, a competitive dead-end inhibitor against D-glucose (K(i)=0.3 mM at pH 6.6 and 30 degrees C), were determined. Maximum velocities and catalytic efficiencies for the forward and reverse reactions decrease at high and low pH, giving apparent pK values of 7.2--7.8 and 5.5--6.0 for two groups whose correct protonation state is required for catalysis. The pH dependences of k(cat)/K are interpreted in terms of monoanionic phosphate and alpha-D-glucose 1-phosphate being the substrates, and of the pK value seen at high pH corresponding to the phosphate group in solution or bound to the enzyme. The K(i) value for the inhibitor decreases outside the optimum pH range for catalysis, indicating that binding of D-glucal is tighter with incorrectly ionized forms of the complex between the enzyme and alpha-D-glucose 1-phosphate. Each molecule of trehalose phosphorylase contains one Mg(2+) that is non-dissociable in the presence of metal chelators. Measurements of the (26)Mg(2+)/(24)Mg(2+) ratio in the solvent and on the enzyme by using inductively coupled plasma MS show that exchange of metal ion between protein and solution does not occur at measurable rates. Tryptic peptide mass mapping reveals close structural similarity between trehalose phosphorylases from basidiomycete fungi.

Influence of trehalose on the molecular chaperone activity of p26, a small heat shock/alpha-crystallin protein

Encysted embryos of the primitive crustacean Artemia franciscana are among the most resistant of all multicellular eukaryotes to environmental stress, in part due to massive amounts of a small heat shock/alpha-crystallin protein (p26) that acts as a molecular chaperone. These embryos also contain very large amounts of the disaccharide trehalose, well known for its ability to protect macromolecules and membranes against damage due to water removal and temperature extremes. Therefore, we looked for potential interactions between trehalose and p26 in the protection of a model substrate, citrate synthase (CS), against heat denaturation and aggregation and in the restoration of activity after heating in vitro. Both trehalose and p26 decreased the aggregation and irreversible inactivation of CS at 43 degrees C. At approximate physiological concentrations (0.4 M), trehalose did not interfere with the ability of p26 to assist in the reactivation of CS after heating, but higher concentrations (0.8 M) were inhibitory. We also showed that CS and p26 interact physically during heating and that trehalose interferes with complex formation and disrupts CS-p26 complexes that form at high temperatures. We suggest from these results that trehalose may act as a "release factor," freeing folding intermediates of CS that p26 can chaperone to the native state. Trehalose and p26 can act synergistically in vitro, during and after thermal stress, suggesting that these interactions also occur in vivo.