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.     

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.     

Regulation of expression of trehalose-6-phosphate synthase during cold shock in Arthrobacter strain A3

Trehalose is a chemical chaperone known to protect a variety of organisms against cold stress. Members of the genus Arthrobacter, which belongs to the Actinomycetales group, exhibit strong resistance to stress conditions, but exactly how trehalose synthesis is regulated in conditions of cold stress is still unknown. Here, we report that Arthrobacter strain A3, which was isolated from the alpine permafrost, has only two trehalose synthesis pathways (OtsA/B and TreS), while other Arthrobacter spp. have three. Mutants and immunoblot analyses indicate that trehalose is mainly synthesized via OtsA at low temperatures in Arthrobacter strain A3. Therefore, we have focused on the regulation of OtsA expression during cold shock. The results indicated that both low temperature and accumulation of trehalose can inhibit OtsA expression. The elongation factor Tu, which binds to OtsA, stabilizes the expression of OtsA in the cold.     

Heat-induced accumulation and futile cycling of trehalose in Saccharomyces cerevisiae.

Heat shock resulted in rapid accumulation of large amounts of trehalose in Saccharomyces cerevisiae. In cultures growing exponentially on glucose, the trehalose content of the cells increased from 0.01 to 1 g/g of protein within 1 h after the incubation temperature was shifted from 27 to 40 degrees C. When the temperature was readjusted to 27 degrees C, the accumulated trehalose was rapidly degraded. In parallel, the activity of the trehalose-phosphate synthase, the key enzyme of trehalose biosynthesis, increased about sixfold during the heat shock and declined to the normal level after readjustment of the temperature. Surprisingly, the activity of neutral trehalase, the key enzyme of trehalose degradation, also increased about threefold during the heat shock and remained almost constant during recovery of the cells at 27 degrees C. In pulse-labeling experiments with [14C]glucose, trehalose was found to be turned over rapidly in heat-shocked cells, indicating that both anabolic and catabolic enzymes of trehalose metabolism were active in vivo. Possible functions of the heat-induced accumulation of trehalose and its rapid turnover in an apparently futile cycle during heat shock are discussed.     

Trehalose effects on alpha-crystallin aggregates

alpha-Crystallin in its native state is a large, heterogeneous, low-molecular weight (LMW) aggregate that under certain conditions may progressively became part of insoluble high-molecular weight (HMW) systems. These systems are supposed to play a relevant role in eye lens opacification and vision impairment. In this paper, we report the effects of trehalose on alpha-crystallin aggregates. The role of trehalose in alpha-crystallin stress tolerance, chaperone activity and thermal stability is studied. The results show that trehalose stabilizes the alpha-crystallin native structure, inhibits alpha-crystallin aggregation, and disaggregates preformed LMW systems not affecting its chaperone activity.     

The function of trehalose biosynthesis in plants

Trehalose (alpha-D-glucopyranosyl-1,1-alpha-D-glucopyranoside) occurs in a large variety of organisms, ranging from bacteria to invertebrate animals, where it serves as an energy source or stress protectant. Until recently, only few plant species, mainly desiccation-tolerant 'resurrection' plants, were considered to synthesise trehalose. Instead of trehalose, most other plants species accumulate sucrose as major transport sugar and during stress. The ability to synthesize sucrose has probably evolved from the cyanobacterial ancestors of plastids and may be linked to photosynthetic function. Although most plant species do not appear to accumulate easily detectable amounts of trehalose, the discovery of genes for trehalose biosynthesis in Arabidopsis and in a range of crop plants suggests that the ability to synthesise trehalose is widely distributed in the plant kingdom. The apparent lack of trehalose accumulation in these plants is probably due to the presence of trehalase activity. After inhibition of trehalase, trehalose synthesis can be detected in Arabidopsis. Since trehalose induces metabolic changes, such as an accumulation of storage carbohydrates, rapid degradation of trehalose may be required to prevent detrimental effects of trehalose on the regulation of plant metabolism. In addition, the precursor of trehalose, trehalose-6-phosphate, is probably involved in the regulation of developmental and metabolic processes in plants.     

Stabilization of cold-adapted protease MCP-01 promoted by trehalose: prevention of the autolysis

Protease MCP-01 is similar to other cold-adapted enzymes in that it is a cold-adapted serine protease having high specific activity and low thermostability at low and moderate temperature. Its thermolability and self-autolysis has resulted in difficulties in its purification, preservation and research on its structure and function. The disaccharide trehalose is known to effectively stabilize proteins. Its prevention effect on the autolysis of cold-adapted protease MCP-01 was monitored by capillary electrophoresis. In the absence of trehalose, protease MCP-01 autolyzed rapidly at 35 degrees C. However, when trehalose was added, autolysis was remarkably prevented and the loss of activity reduced. MCP-01 may be a useful model for basic research on the interaction of protein and trehalose.     

Trehalose synthesis by sequential reactions of recombinant maltooligosyltrehalose synthase and maltooligosyltrehalose trehalohydrolase from Brevibacterium helvolum

A DNA fragment encoding two enzymes leading to trehalose biosynthesis, maltooligosyltrehalose synthase (BvMTS) and maltooligosyltrehalose trehalohydrolase (BvMTH), was cloned from the nonpathogenic bacterium Brevibacterium helvolum. The open reading frames for the two proteins are 2,331 and 1,770 bp long, respectively, and overlap by four nucleotides. Recombinant BvMTS, BvMTH, and fusion gene BvMTSH, constructed by insertion of an adenylate in the overlapping region, were expressed in Escherichia coli. Purified BvMTS protein catalyzed conversion of maltopentaose to maltotriosyltrehalose, which was further hydrolyzed by BvMTH protein to produce trehalose and maltotriose. The enzymes shortened maltooligosaccharides by two glucose units per cycle of sequential reactions and released trehalose. Maltotriose and maltose were not catalyzed further and thus remained in the reaction mixtures depending on whether the substrates had an odd or even number of glucose units. The bifunctional in-frame fusion enzyme, BvMTSH, catalyzed the sequential reactions more efficiently than an equimolar mixture of the two individual enzymes did, presumably due to a proximity effect on the catalytic sites of the enzymes. The recombinant enzymes produced trehalose from soluble starch, an abundant natural source for trehalose production. Addition of alpha-amylase to the enzyme reaction mixture dramatically increased trehalose production by partial hydrolysis of the starch to provide more reducing ends accessible to the BvMTS catalytic sites.     

Opposing effects of two osmolytes--trehalose and glycerol--on thermal inactivation of rabbit muscle 6-phosphofructo-1-kinase

Trehalose and glycerol are known as good stabilizers of function and structure of several macromolecules against stress conditions. We previously reported that they have comparable effectiveness on protecting two yeast cytosolic enzymes against thermal inactivation. However, enzyme protection has always been associated to a decrease in catalytic activity at the stabilizing conditions i.e., the presence of the protective molecule. In the present study we tested trehalose and glycerol on thermal protection of the mammalian cytosolic enzyme phosphofructokinase. Here we found that trehalose was able to protect phosphofructokinase against thermal inactivation as well as to promote an activation of its catalytic activity. The enzyme incubated in the presence of 1 M trehalose did not present any significant inactivation within 2 h of incubation at 50 degrees C, contrasting to control experiments where the enzyme was fully inactivated during the same period exhibiting a t0.5 for thermal inactivation of 56+/-5 min. On the other hand, enzyme incubated in the presence of 37.5% (v/v) glycerol was not protected against incubation at 50 degrees C. Indeed, when phosphofructokinase was incubated for 45 min at 50 degrees C in the presence of lower concentrations of glycerol (7.5-25%, v/v), the remaining activity was 2-4 times lower than control. These data show that the compatibility of effects previously shown for trehalose and glycerol with some yeast cytosolic enzymes can not be extended to all globular enzyme system. In the case of phosphofructokinase, we believe that its property of shifting between several different complex oligomers configurations can be influenced by the physicochemical properties of the stabilizing molecules.     

Trehalose production with a new enzymatic system from Sulfolobus solfataricus KM1

An amylolytic activity that converts soluble starch to α,α-trehalose (trehalose) was found in the cell homogenate of the hyperthermophilic, acidophilic archaeum Sulfolobus solfataricus KM1. Two enzymes, a glycosyltransferase and an α-amylase, which are essential for this activity, were purified to homogeneity. A glycosyltransferase catalyzed the conversion of maltooligosaccharides to glycosyltrehaloses and an α-amylase catalyzed the hydrolysis of glycosyltrehaloses to trehalose. The glycosyltransferase transferred an oligomer segment of maltooligosaccharide to the C1–OH position of glucose, located at the reducing end of the maltooligosaccharide, to produce a glycosyltrehalose having an α-1,1 linkage. The α-amylase hydrolyzed only the α-1,4 glucosidic linkage adjacent to the trehalose unit of the glycosyltrehaloses. Their activities were maximal at 70–80°C and 70–85°C, with high thermostability, respectively. The genes encoding for both enzymes were cloned and expressed in Escherichia coli. The regions highly conserved in α-amylase family exist in the amino acid sequences of these enzymes. A new process for trehalose production from starch was developed using the purified enzymes. The yield of trehalose from starch was 81.5% using these two enzymes. This review describes our efforts to reveal in detail the characters of these enzymes involved in practical trehalose production.     

Trehalose: Protector of antioxidant enzymes or reactive oxygen species scavenger under heat stress?

Trehalose is known to protect membranes and macromolecules. Its accumulation has been implicated in allowing plants to tolerate stress, including heat-shock. However, under heat-shock, it is not clear whether trehalose eliminates reactive oxygen species (ROS) directly or indirectly by protecting antioxidant enzymes. In this study, we initially examined the effects of trehalose on the activities of key antioxidant enzymes, including superoxide dismutases (SODs), ascorbate catalases (CATs), and ascorbate peroxidases (APX) from wheat (Triticum aestivum L.), and then measured the ability of trehalose to scavenge hydrogen peroxide (H₂O₂) and superoxide anions (O₂⁻). Our results indicated that trehalose protected SOD activity slightly. However, it inhibited CAT and APX activities under heat stress, with a little protection of CAT activity (only about 7% promotion) at 22 °C. Moreover, trehalose scavenged H₂O₂ and O₂⁻ greatly in a concentration-dependent manner, reaching the maximal scavenging H₂O₂ rate of 95% and O₂⁻ rate of 78%, respectively, at 50 mM trehalose. These results suggest that trehalose plays a direct role in eliminating H₂O₂ and O₂⁻ in wheat under heat stress.     

Trehalose Synthesis by Sequential Reactions of Recombinant Maltooligosyltrehalose Synthase and Maltooligosyltrehalose Trehalohydrolase from Brevibacterium helvolum

A DNA fragment encoding two enzymes leading to trehalose biosynthesis, maltooligosyltrehalose synthase (BvMTS) and maltooligosyltrehalose trehalohydrolase (BvMTH), was cloned from the nonpathogenic bacterium Brevibacterium helvolum. The open reading frames for the two proteins are 2,331 and 1,770 bp long, respectively, and overlap by four nucleotides. Recombinant BvMTS, BvMTH, and fusion gene BvMTSH, constructed by insertion of an adenylate in the overlapping region, were expressed in Escherichia coli. Purified BvMTS protein catalyzed conversion of maltopentaose to maltotriosyltrehalose, which was further hydrolyzed by BvMTH protein to produce trehalose and maltotriose. The enzymes shortened maltooligosaccharides by two glucose units per cycle of sequential reactions and released trehalose. Maltotriose and maltose were not catalyzed further and thus remained in the reaction mixtures depending on whether the substrates had an odd or even number of glucose units. The bifunctional in-frame fusion enzyme, BvMTSH, catalyzed the sequential reactions more efficiently than an equimolar mixture of the two individual enzymes did, presumably due to a proximity effect on the catalytic sites of the enzymes. The recombinant enzymes produced trehalose from soluble starch, an abundant natural source for trehalose production. Addition of α-amylase to the enzyme reaction mixture dramatically increased trehalose production by partial hydrolysis of the starch to provide more reducing ends accessible to the BvMTS catalytic sites.     

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.     

Regulation of the yeast trehalose–synthase complex by cyclic AMP-dependent phosphorylation

Background

Trehalose is an important protectant in several microorganisms. In Saccharomyces cerevisiae, it is synthesized by a large complex comprising the enzymes Tps1 and Tps2 and the subunits Tps3 and Tsl1, showing an intricate metabolic control.

Methods

To investigate how the trehalose biosynthesis pathway is regulated, we analyzed Tps1 and Tps2 activities as well as trehalose and trehalose-6-phosphate (T6P) contents by mass spectrometry.

Results

Tsl1 deficiency totally abolished the increase in Tps1 activity and accumulation of trehalose in response to a heat stress, whereas absence of Tps3 only reduced Tps1 activity and trehalose synthesis. In extracts of heat stressed cells, Tps1 was inhibited by T6P and by ATP. Mg^2 + in the presence of cAMP. In contrast, cAMP-dependent phosphorylation did not inhibit Tps1 in tps3 cells, which accumulated a higher proportion of T6P after stress. Tps2 activity was not induced in a tps3 mutant.

Conclusion

Taken together these results suggest that Tsl1 is a decisive subunit for activity of the TPS complex since in its absence no trehalose synthesis occurred. On the other hand, Tps3 seems to be an activator of Tps2. To perform this task, Tps3 must be non-phosphorylated. To readily stop trehalose synthesis during stress recovery, Tps3 must be phosphorylated by cAMP-dependent protein kinase, decreasing Tps2 activity and, consequently, increasing the concentration of T6P which would inhibit Tps1.

General significance

A better understanding of TPS complex regulation is essential for understanding how yeast deals with stress situations and how it is able to recover when the stress is over.     

Is trehalose special for preserving dry biomaterials?

Simple sugars, especially disaccharides, stabilize biomaterials of various composition during air-drying or freeze-drying. We and others have provided evidence that direct interaction, an interaction that we believe is essential for the stabilization, between the sugar and polar groups in, for example, proteins and phospholipids occurs in the dry state. Some researchers, however, have suggested that the ability of the sugar to form a glass is the only requirement for stabilization. More recently, we have shown that both glass formation and direct interaction of the sugar and headgroup are often required for stabilization. In the present study, we present a state diagram for trehalose glass and suggest that the efficacy of this sugar for stabilization may be related to its higher glass transition temperatures at all water contents. We also show that trehalose and trehalose:liposome preparations form trehalose dihydrate as well as trehalose glass when rehydrated with water vapor. Formation of the dihydrate sequesters water, which might otherwise participate in lowering the glass transition temperature to below ambient. Because samples remain in the glassy state at ambient temperatures, viscosity is high and fusion between liposomes is prevented.     

Multiple Effects of Viscosity,Water Activity and Glass Transition Temperature on Peroxidase Activity in Binary and Ternary Carbohydrate Solutions

The individual and combined effects of water activity (a_w), bulk viscosity and glass transition temperature (Tg’) on the activity of horseradish peroxidase (HRP) in buffered sugars (glucose, trehalose and maltose) and maltodextrin solutions were investigated. Viscosity was the most important factor in the inhibition of HRP activity; however, when Tg’ was changed by the using solutes with different molecular weight, it became a key factor in the modulation of enzyme activity. Viscosity being equal, the sugar addition to maltodextrin solution lowered a_w and lowered Tg’ causing an increase of the enzymatic activity. Nevertheless, an inhibition of the HRP activity occurred when a_w values of 0.87 were reached due to the addition of glucose, which, among the tested sugars, showed the lowest molecular weight. Among disaccharides, maltose was more effective than trehalose in impairing the enzyme activity both in binary and ternary systems, and this is due to a non competitive biochemical inhibition exerted by this sugar on HRP. When compared to glucose, maltose and trehalose were more effective in reducing HRP activity only in the low viscosity range whilst in the high viscosity range (1–4 10^?6 m² s^?1) glucose, despite its lower Tg’ value, was slightly more efficient than disaccharides due to its a_w lowering effect.