Trehalose phosphorylase from Pichia fermentans and its role in the metabolism of trehalose

Interaction of storage carbohydrates and other cyclic fluxes with central metabolism: A quantitative approach by non-stationary 13C metabolic flux analysis

13C labeling experiments in aerobic glucose limited cultures of Saccharomyces cerevisiae at four different growth rates (0.054; 0.101, 0.207, 0.307 h-1) are used for calculating fluxes that include intracellular cycles (e.g., storage carbohydrate cycles, exchange fluxes with amino acids), which are rearranged depending on the growth rate. At low growth rates the impact of the storage carbohydrate recycle is relatively more significant than at high growth rates due to a higher concentration of these materials in the cell (up to 560-fold) and higher fluxes relative to the glucose uptake rate (up to 16%). Experimental observations suggest that glucose can be exported to the extracellular space, and that its source is related to storage carbohydrates, most likely via the export and subsequent extracellular breakdown of trehalose. This hypothesis is strongly supported by 13C-labeling experimental data, measured extracellular trehalose, and the corresponding flux estimations.

Biochemical properties of an extracellular trehalase from Malbranchea pulchella var. Sulfurea

The thermophilic fungus Malbranchea pulchella var. sulfurea produced good amounts of extracellular trehalase activity when grown for long periods on starch, maltose or glucose as the main carbon source. Studies with young cultures suggested that the main role of the extracellular acid trehalase is utilizing trehalose as a carbon source. The specific activity of the purified enzyme in the presence of manganese (680 U/mg protein) was comparable to that of other thermophilic fungi enzymes, but many times higher than the values reported for trehalases from other microbial sources. The apparent molecular mass of the native enzyme was estimated to be 104 kDa by gel filtration and 52 kDa by SDS-PAGE, suggesting that the enzyme was composed by two subunits. The carbohydrate content of the purified enzyme was estimated to be 19 % and the pi was 3.5. The optimum pH and temperature were 5.0-5.5 and 55° C, respectively. The purified enzyme was stimulated by manganese and inhibited by calcium ions, and insensitive to ATP and ADP, and 1 mM silver ions. The apparent K(M) values for trehalose hydrolysis by the purified enzyme in the absence and presence of manganese chloride were 2.70 ± 0.29 and 2.58 ± 0.13 mM, respectively. Manganese ions affected only the apparent V(max), increasing the catalytic efficiency value by 9.2-fold. The results reported herein indicate that Malbranchea pulchella produces a trehalase with mixed biochemical properties, different from the conventional acid and neutral enzymes and also from trehalases from other thermophilic fungi.

Genetically altering the expression of neutral trehalase gene affects conidiospore thermotolerance of the entomopathogenic fungus Metarhizium acridum

BACKGROUND

The entomopathogenic fungus Metarhizium acridum has been used as an important biocontrol agent instead of insecticides for controlling crop pests throughout the world. However, its virulence varies with environmental factors, especially temperature. Neutral trehalase (Ntl) hydrolyzes trehalose, which plays a role in environmental stress response in many organisms, including M. acridum. Demonstration of a relationship between Ntl and thermotolerance or virulence may offer a new strategy for enhancing conidiospore thermotolerance of entomopathogenic fungi through genetic engineering.

RESULTS

We selected four Ntl over-expression and four Ntl RNA interference (RNAi) transformations in which Ntl expression is different. Compared to the wild-type, Ntl mRNA expression was reduced to 35-66% in the RNAi mutants and increased by 2.5-3.5-fold in the over-expression mutants. The RNAi conidiospores exhibited less trehalase activity, accumulated more trehalose, and were much more tolerant of heat stress than the wild-type. The opposite effects were found in conidiospores of over-expression mutants compared to RNAi mutants. Furthermore, virulence was not altered in the two types of mutants compared to the wild type.

CONCLUSIONS

Ntl controlled trehalose accumulation in M. acridum by degrading trehalose, and thus affected conidiospore thermotolerance. These results offer a new strategy for enhancing conidiospore thermotolerance of entomopathogenic fungi without affecting virulence.

Trehalose accumulation from corn starch by Saccharomycopsis fibuligera A11 during 2-l fermentation and trehalose purification

In this study, corn starch was used as the substrate for cell growth and trehalose accumulation by Saccharomycopsis fibuligera A11. Effect of different aeration rates, agitation speeds, and concentrations of corn starch on direct conversion of corn starch to trehalose by S. fibuligera A11 were examined using a Biostat B2 2-l fermentor. We found that the optimal conditions for direct conversion of corn starch to trehalose by this yeast strain were that agitation speed was 200 rpm, aeration rate was 4.0 l/min, concentration of corn starch was 2.0% (w/v), initial pH was 5.5, fermentation temperature was 30 degrees C. Under these conditions, over 22.9 g of trehalose per 100 g of cell dry weight was accumulated in the yeast cells, cell mass was 15.2 g/l of the fermentation medium, 0.12% (w/v) of reducing sugar, and 0.21% (w/v) of total sugar were left in the fermented medium within 48 h of the fermentation. It was found that trehalose in the yeast cells could be efficiently extracted by the hot distilled water (80 degrees C). After isolation and purification, the crystal trehalose was obtained from the extract of the cells.

Proteomic and metabolomic analyses of the white-rot fungus Phanerochaete chrysosporium exposed to exogenous benzoic acid

Intracellular processes of the white-rot basidiomycete Phanerochaete chrysosporium involved in the metabolism of benzoic acid (BA) were investigated at the proteome and metabolome level. Up-regulation of aryl-alcohol dehydrogenase, arylaldehyde dehydrogenase, and cytochrome P450s was observed upon addition of exogenous BA, suggesting that these enzymes play key roles in its metabolism. Intracellular metabolic shifts from the short-cut TCA/glyoxylate bicycle system to the TCA cycle and an increased flux in the TCA cycle indicated activation of the heme biosynthetic pathway and the production of NAD(P)H. In addition, combined analyses of proteome and metabolome clearly indicated the role of trehalose as a storage disaccharide and that the mannitol cycle plays a role in an alternative energy-producing pathway.

Acid trehalase in yeasts and filamentous fungi: Localization, regulation and physiological function

Yeasts and filamentous fungi are endowed with two different trehalose-hydrolysing activities, termed acid and neutral trehalases according to their optimal pH for enzymatic activity. A wealth of information already exists on fungal neutral trehalases, while data on localization, regulation and function of fungal acid trehalases have remained elusive. The gene encoding the latter enzyme has now been isolated from two yeast species and two filamentous fungi, and sequences encoding putative acid trehalase can be retrieved from available public sequences. Despite weak similarities between amino acids sequences, this type of trehalase potentially harbours either a transmembrane segment or a signal peptide at the N-terminal sequence, as deduced from domain prediction algorithms. This feature, together with the demonstration that acid trehalase from yeasts and filamentous fungi is localized at the cell surface, is consistent with its main role in the utilisation of exogenous trehalose as a carbon source. The growth on this disaccharide is in fact pretty effective in most fungi except in Saccharomyces cerevisiae. This yeast species actually exhibits a "Kluyver effect" on trehalose. Moreover, an oscillatory behaviour reminiscent of what is observed in aerobic glucose-limited continuous cultures at low dilution rate is also observed in batch growth on trehalose. Finally, the S. cerevisiae acid trehalase may also participate in the catabolism of endogenous trehalose by a mechanism that likely requires the export of the disaccharide, its extracellular hydrolysis, and the subsequent uptake of the glucose released. Based on these recent findings, we suggest to rename "acid" and "neutral" trehalases as "extracellular" and "cytosolic" trehalases, which is more adequate to describe their localization and function in the fungal cell.

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.

Enhanced conversion of soluble starch to trehalose by a mutant of Saccharomycopsis fibuligera sdu

In our previous studies, it was found that Saccharomycopsis fibuligera sdu cells could accumulate 18.0% (gg(-1)) trehalose from soluble starch in SSY medium. However, the yeast strain contained high activities of acid and neutral trehalases, which were reported to mobilize trehalose accumulated by the cells during fermentation. In order to enhance the yield of trehalose, it is necessary to remove the trehalase activities from the cells. By mutagenesis of ethylmethanesulfonate, one mutant that assimilated trehalose very slowly, but grew on other carbon sources as fast as its parent strain, was isolated. In Biostat B2 2-1 fermentation, trehalose accumulation of the mutant was much higher than that of the wild type when grown in YPS medium containing starch. The activities of acid and neutral trehalases of this mutant were much lower than those of the wild type, respectively. We think the reduction of acid and neutral trehalase activities is considered to be responsible for the increased yield of trehalose accumulated by the mutant.

Trehalose accumulation from soluble starch by Saccharomycopsis fibuligera sdu

Trehalose accumulation from starch by Saccharomycopsis fibuligera sdu was examined in 300-ml shaken flask culture and Biostat B(2) 2-1 fermentation. In the 300-ml flask, 16.5% (w/w) trehalose accumulated in the yeast cells (cell dry weight) was observed with 100-ml medium shaken at 200 rpm for 50 h at 30 degrees C. We found that 1.0% soluble starch in the medium was most suitable for trehalose accumulation by this yeast strain. In the Biostat B(2) 2-1 fermentor, 18.0% (w/w) trehalose accumulated in the yeast cells (cell dry weight) was observed within 48 h of fermentation when agitation speed was 200 rpm. The trehalose obtained from the yeast cells was identical to standard trehalose from Sigma based on the analysis results of High-Performance Exchange Anionic Chromatography (HPEAC).

The stereochemical course of the reaction mechanism of trehalose phosphorylase from Schizophyllum commune

Phosphorolysis of alpha,alpha-trehalose catalyzed by trehalose phosphorylase from the basidiomycete Schizophyllum commune proceeds via net retention of anomeric configuration and yields alpha-D-glucose 1-phosphate and alpha-D-glucose as the products. In reverse reaction, only the alpha-anomers of D-glucose 1-phosphate and D-glucose are utilized as glucosyl donor and acceptor, respectively, and give exclusively the alpha,alpha-product. Trehalose phosphorylase converts alpha-D-glucose 1-fluoride and phosphate into alpha-D-glucose 1-phosphate, a reaction requiring the stereospecific protonation of the glucosyl fluoride by a Brønsted acid. The results are discussed with regard to a plausible reaction mechanism of fungal trehalose phosphorylase.

Purification and characterization of a trehalose synthase from the basidiomycete grifola frondosa

A trehalose synthase (TSase) that catalyzes the synthesis of trehalose from D-glucose and alpha-D-glucose 1-phosphate (alpha-D-glucose 1-P) was detected in a basidiomycete, Grifola frondosa. TSase was purified 106-fold to homogeneity with 36% recovery by ammonium sulfate precipitation and several steps of column chromatography. The native enzyme appears to be a dimer since it has apparent molecular masses of 120 kDa, as determined by gel filtration column chromatography, and 60 kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Although TSase catalyzed the phosphorolysis of trehalose to D-glucose and alpha-D-glucose 1-P, in addition to the synthesis of trehalose from the two substrates, the TSase equilibrium strongly favors trehalose synthesis. The optimum temperatures for phosphorolysis and synthesis of trehalose were 32.5 to 35 degreesC and 35 to 37.5 degreesC, respectively. The optimum pHs for these reactions were 6.5 and 6.5 to 6.8, respectively. The substrate specificity of TSase was very strict: among eight disaccharides examined, only trehalose was phosphorolyzed, and only alpha-D-glucose 1-P served as a donor substrate with D-glucose as the acceptor in trehalose synthesis. Two efficient enzymatic systems for the synthesis of trehalose from sucrose were identified. In system I, the alpha-D-glucose 1-P liberated by 1.05 U of sucrose phosphorylase was linked with D-glucose by 1.05 U of TSase, generating trehalose at the initial synthesis rate of 18 mmol/h in a final yield of 90 mol% under optimum conditions (300 mM each sucrose and glucose, 20 mM inorganic phosphate, 37.5 degreesC, and pH 6.5). In system II, we added 1.05 U of glucose isomerase and 20 mM MgSO4 to the reaction mixture of system I to convert fructose, a by-product of the sucrose phosphorylase reaction, into glucose. This system generated trehalose at the synthesis rate of 4.5 mmol/h in the same final yield.

Purification and characterization of trehalose phosphorylase from the commercial mushroom Agaricus bisporus

Trehalose phosphorylase (EC 2.4.1.64) from Agaricus bisporus was purified for the first time from a fungus. This enzyme appears to play a key role in trehalose metabolism in A. bisporus since no trehalase or trehalose synthase activities could be detected in this fungus. Trehalose phosphorylase catalyzes the reversible reaction of degradation (phosphorolysis) and synthesis of trehalose. The native enzyme has a molecular weight of 240 kDa and consists of four identical 61-kDa subunits. The isoelectric point of the enzyme was pH 4.8. The optimum temperature for both enzyme reactions was 30 degrees C. The optimum pH ranges for trehalose degradation and synthesis were 6.0-7.5 and 6.0-7.0, respectively. Trehalose degradation was inhibited by ATP and trehalose analogs, whereas the synthetic activity was inhibited by P(i) (K(i)=2.0 mM). The enzyme was highly specific towards trehalose, P(i), glucose and alpha-glucose-1-phosphate. The stoichiometry of the reaction between trehalose, P(i), glucose and alpha-glucose-1-phosphate was 1:1:1:1 (molar ratio). The K(m) values were 61, 4.7, 24 and 6.3 mM for trehalose, P(i), glucose and alpha-glucose-1-phosphate, respectively. Under physiological conditions, A. bisporus trehalose phosphorylase probably performs both synthesis and degradation of trehalose.

Sensing trehalose biosynthesis in plants

A most unexpected finding in research on plant carbohydrate metabolism is the recent discovery that angiosperms encode genes whose products are involved in trehalose metabolism. The presence and functionality of such genes has been elegantly shown by expressing Arabidopsis-derived trehalose phosphate synthase and trehalose phosphate phosphatase genes in yeast mutants lacking these enzymatic activities. Homologue sequences have now been cloned from a number of different plant species suggesting that the capacity to synthesise trehalose is ubiquitous in angiosperms. Except for Myrothamnus flabellifolius, trehalose biosynthesis has never been observed in tissues of higher plants, probably due to the presence of high levels of trehalase activity. The function of trehalose metabolism in plants is still a mystery. One of the postulated functions of trehalose metabolism in yeast is in the control of glucose repression and a similar function in sugar sensing can be proposed for plants as well.

Trehalases and trehalose hydrolysis in fungi

The simultaneous presence of two different trehalose-hydrolysing activities has been recognised in several fungal species. While these enzymes, known as acid and neutral trehalases, share a strict specificity for trehalose, they are nevertheless rather different in subcellular localisation and in several biochemical and regulatory properties. The function of these apparently redundant activities in the same cell was not completely understood until recently. Biochemical and genetic studies now suggest that these enzymes may have specialised and exclusive roles in fungal cells. It is thought that neutral trehalases mobilise cytosolic trehalose, under the control of developmental programs, chemical and nutrient signals, or stress responses. On the other hand, acid trehalases appear not to mobilise cytosolic trehalose, but to act as 'carbon scavenger' hydrolases enabling cells to utilise exogenous trehalose as a carbon source, under the control of carbon catabolic regulatory circuits. Although much needs to be learned about the molecular identity of trehalases, it seems that in fungi at least one class of acid trehalases evolved independently from the other trehalases.