Intracellular trehalase of a hybrid yeast

Role of individual phosphorylation sites for the 14-3-3-protein-dependent activation of yeast neutral trehalase Nth1

Trehalases are important highly conserved enzymes found in a wide variety of organisms and are responsible for the hydrolysis of trehalose that serves as a carbon and energy source as well as a universal stress protectant. Emerging evidence indicates that the enzymatic activity of the neutral trehalase Nth1 in yeast is enhanced by 14-3-3 protein binding in a phosphorylation-dependent manner through an unknown mechanism. In the present study, we investigated in detail the interaction between Saccharomyces cerevisiae Nth1 and 14-3-3 protein isoforms Bmh1 and Bmh2. We determined four residues that are phosphorylated by PKA (protein kinase A) in vitro within the disordered N-terminal segment of Nth1. Sedimentation analysis and enzyme kinetics measurements show that both yeast 14-3-3 isoforms form a stable complex with phosphorylated Nth1 and significantly enhance its enzymatic activity. The 14-3-3-dependent activation of Nth1 is significantly more potent compared with Ca2+-dependent activation. Limited proteolysis confirmed that the 14-3-3 proteins interact with the N-terminal segment of Nth1 where all phosphorylation sites are located. Site-directed mutagenesis in conjunction with the enzyme activity measurements in vitro and the activation studies of mutant forms in vivo suggest that Ser60 and Ser83 are sites primarily responsible for PKA-dependent and 14-3-3-mediated activation of Nth1.

Degradation of trehalose by rhizobia and characteristics of a trehalose-degrading enzyme isolated from Rhizobium species NGR234

AIMS

This study was designed to examine the breakdown of trehalose by rhizobia and to characterize the trehalose-degrading enzyme isolated from Rhizobium sp. NGR234.

METHODS AND RESULTS

Rhizobium sp. NGR234, Rhizobium fredii USDA257, R. phaseoli RCR3622, R. tropici CIAT899 and R. etli CE3 showed good growth in the presence of carbohydrate. Validamycin A did not prevent the growth of NGR234 on trehalose. The expression of a trehalose-degrading enzyme by NGR234 was intracellular and inducible by trehalose. The isolated enzyme digested other disaccharides, p-nitrophenyl-alpha-d-glucopyranoside and the substrate. The enzyme showed optimum activities at pH 7.0 and 30 degrees C. Its pI was 4.75 and the V(max) of the enzyme occurred at 35.7 micromol s(-1) mg(-1) protein with the K(m) of 23 mmol when trehalose was hydrolysed.

CONCLUSIONS

An enzyme capable of breaking down trehalose was produced. Some of the properties of the trehalose-degrading enzyme are similar to those isolated from other organisms but, this enzyme was validamycin resistant. These rhizobia like other trehalose-degrading microbes use trehalose by enzymatic catabolic action.

SIGNIFICANCE AND IMPACT OF THE STUDY

Trehalose which accumulates during legume-rhizobia symbiosis is toxic to plants. Detoxification by trehalose-degrading enzymes is important for the progress of symbiosis.

Molecular biology of trehalose and the trehalases in the yeast Saccharomyces cerevisiae

The present state of knowledge of the role of trehalose and trehalose hydrolysis catalyzed by trehalase (EC 3.2.1.28) in the yeast Saccharomyces cerevisiae is reviewed. Trehalose is believed to function as a storage carbohydrate because its concentration is high during nutrient limitations and in resting cells. It is also believed to function as a stress metabolite because its concentration increases during certain adverse environmental conditions, such as heat and toxic chemicals. The exact way trehalose may perform the stress function is not understood, and conditions exist under which trehalose accumulation and tolerance to certain stress situations cannot be correlated. Three trehalases have been described in S. cerevisiae: 1) the cytosolic neutral trehalase encoded by the NTH1 gene, and regulated by cAMP-dependent phosphorylation process, nutrients, and temperature; 2) the vacuolar acid trehalase encoded by the ATH1 gene, and regulated by nutrients; and 3) a putative trehalase Nth1p encoded by the NTH2 gene (homolog of the NTH1 gene) and regulated by nutrients and temperature. The neutral trehalase is responsible for intracellular hydrolysis of trehalose, in contrast to the acid trehalase, which is responsible for utilization of extracellular trehalose. The role of the putative trehalase Nth2p in trehalose metabolism is not known. The NTH1 and NTH2 genes are required for recovery of cells after heat shock at 50 degrees C, consistent with their heat inducibility and sequence similarity. Other stressors, such as toxic chemicals, also induce the expression of these genes. We therefore propose that the NTH1 and NTH2 genes have stress-related function and the gene products may be called stress proteins. Whether the stress function of the trehalase genes is linked to trehalose is not clear, and possible mechanisms of stress protective function of the trehalases are discussed.

Enzymes of alpha,alpha-Trehalose Metabolism in Soybean Nodules

Metabolism of trehalose, alpha,d-glucopyranosyl-alpha,d-glucopyranoside, was studied in nodules of Bradyrhizobium japonicum-Glycine max [L.] Merr. cv Beeson 80 symbiosis. The nodule extract was divided into three fractions: bacteroid soluble protein, bacteroid fragments, and cytosol. The bacteroid soluble protein and cytosol fractions were gel-filtered. The key biosynthetic enzyme, trehalose-6-phosphate synthetase, was consistently found only in the bacteroids. Trehalose-6-phosphate phosphatase activity was present both in the bacteroid soluble protein and cytosol fractions. Trehalase, the most abundant catabolic enzyme was present in all three fractions and showed two pH optima: pH 3.8 and 6.6. Two other degradative enzymes, phosphotrehalase, acting on trehalose-6-phosphate forming glucose and glucose-6-phosphate, and trehalose phosphorylase, forming glucose and beta-glucose-1-phosphate, were also detected in the bacteroid soluble protein and cytosol fractions. Trehalase was present in large excess over trehalose-6-phosphate synthetase. Trehalose accumulation in the nodules would appear to be predicated on spatial separation of trehalose and trehalase.

Characterization of two trehalases in baker's yeast

Trehalase activities at pH 5 (not inhibited by EDTA) and pH 7 (inhibited by EDTA) were present in the soluble fraction of disintegrated commercial baker's yeast. The pH 5 activity binds strongly to concanavalin A, is only partially salted out by saturated (NH4)2SO4, has an apparent Mr of 215000 (by gel filtration) and is an acidic protein. It has a Km of 1.4 mM, a broad pH optimum (at 40 mM-trehalose) between pH 4 and 5, and is activated by about 30% by 20-300 mM neutral salts such as KCl, NaNO3 and MnCl2. The enzyme is strongly inhibited by acetic acid/acetate buffers, with a Ki of about 15 mM-acetic acid. The pH 7 activity does not bind to concanavalin A, is salted out at 20-32% (w/v) (NH4)2SO4 and has an Mr of 170000 (by gel filtration). It is absolutely dependent on Ca2+ or Mn2+ ions (Mg2+ is ineffective) and strongly inhibited by neutral salts in the 20-100 mM range. It can be activated by treatment with MgATP in the presence of cyclic AMP. Activation decreases, but does not abolish, the Ca2+ requirement, and does not change the Km for trehalose (5.7 mM) or shift the sharp pH optimum at pH 6.7 (at 40 mM-trehalose).

Trehalase from the cellular slime mold Dictyostelium discoideum: purification and characterization of the homogeneous enzyme from myxamoebae

Trehalase (alpha-alpha'-trehalose 1-D-glucohydrolase, EC 3.2.1.28) was solubilized from myxamoebae of the cellular slime mold Dictyostelium discoideum by a freeze-thaw cycle and was subsequently purified to homogeneity using the techniques of ethanol fractionation, molecular sieve chromatography, DEAE-cellulose ion-exchange chromatography, chromatofocusing, and preparative polyacrylamide disc gel electrophoresis. The 1000-fold purified enzyme had a specific activity of about 104 units/mg, which was accompanied by a net recovery of 5 to 7% of the original activity. The purified enzyme was maximally active at pH 5.5, showed high specificity for trehalose, and exhibited a typical hyperbolic response as a function of trehalose concentration with a Km of 1.2 mM. The enzyme was maximally active at 50 degrees C and had an energy of activation of 12-13 kcal/mol. Thermal stability studies demonstrated that full enzymatic activity was recovered following a 5-min incubation of trehalase at temperatures up to 45-50 degrees C. Analysis of various compounds for inhibitory effects indicated that Tris and urea were slightly effective, reducing enzymatic activity by 28 and 6% at concentrations of 100 and 10 mM, respectively. Of five heavy metals tested, HgCl2 was the most inhibitory, reducing activity by 58% when present at a final concentration of 1.0 mM. Enzymatic activity was not affected by any adenine derivative examined (e.g., ATP, ADP, AMP, cAMP, adenosine, and adenine). The molecular weight of the native enzyme was determined by molecular sieve chromatography, pore gradient electrophoresis, and electrophoresis as a function of acrylamide concentration. All three methods yielded a value of about 10(5) +/- 5 X 10(3). Estimation of the subunit or monomer molecular weight by sodium dodecyl sulfate-gel electrophoresis indicated a value of 95-100 X 10(3). The isoelectric point as determined in 7.5% polyacrylamide gels with pH 3-10 ampholytes was 7.2-7.3. The purified enzyme adsorbed to concanavalin A-Sepharose in the presence of KCl (0.1 M) and was eluted with alpha-methylmannoside, thereby suggesting an association between trehalase and carbohydrate. In agreement with this conclusion was the observation that trehalase could be specifically stained for carbohydrate with the Alcian blue and periodic acid-Schiff's reagents following polyacrylamide disc gel electrophoresis.

Trehalase: stereocomplementary hydrolytic and glucosyl transfer reactions with alpha- and beta-D-glucosyl fluoride

A new understanding has been obtained of the catalytic capabilities of trehalase, an enzyme heretofore held to be strictly specific for hydrolyzing alpha, alpha-trehalose and devoid of transglycosylative ability. Highly purified rabbit renal cortical trehalase and a partly purified Candida tropicalis yeast trehalase were found to utilize both alpha- and beta-D-glucosyl fluoride as substrates. In each case, the reactions were competitively inhibited by alpha, alpha-trehalose. Both enzymes catalyzed rapid hydrolysis of alpha-D-glucosyl fluoride to form beta-D-glucose (also, of alpha, alpha-trehalose to form equimolar alpha- and beta-D-glucose). In addition, digests of beta-D-glucosyl fluoride plus alpha-D-[14C]-glucopyranose with either trehalase (but not controls of enzyme with alpha-D-[14C]glucopyranose alone) yielded small amounts of radioactive trehalose (alpha-D-glucopyranosyl alpha-D-[14C]glucopyranoside) which does not accumulate since it is rapidly hydrolyzed. Trehalase thus catalyzes two stereocomplementary types of glycosylation reactions: (I) alpha-D-glucosyl fluoride (or alpha, alpha-trehalose) + H2O leads to beta-D-glucose + HF (or alpha-D-glucose); (II) beta-D-glucosyl fluoride + alpha-D-glucopyranose leads to alpha, alpha-trehalose + HF. Such behavior shows that the catalytic groups of trehalase, as recently found for other glycosylases, are functionally flexible. The results illustrate the inadequacy of conventional views of carbohydrase specificity and the rigor, as a basic guiding principle, of the concept that glycoside hydrolases and glycosyltransferases form a class of glycosylases effecting glycosyl/proton interchange.

Localization of trehalase in vacuoles and of trehalose in the cytosol of yeast (Saccharomyces cerevisiae)

Protoplasts of Saccharomyces cerevisiae synthesized and degraded trehalose when they were incubated in a medium containing traces of glucose and acetate. Such protoplasts were gently lyzed by the polybase method and a particulate and soluble fraction was prepared. Trehalose was found in the soluble fraction and the trehalase activity mostly in the particulate fraction which also contained the vacuoles besides other cell organelles. Upon purification of the vacuoles, by density gradient centrifugation, the specific activity of trehalase increased parallel to the specific content of vacuolar markers. This indicates that trehalose is located in the cytosol and trehalase in the vacuole. It is suggested that trehalose, in addition to its role as a reserve may also function as a protective agent to maintain the cytosolic structure under conditions of stress.

Carbodiimide-reactive carboxyl groups at the active site of an insect midgut trehalase

Carbodiimide modification of the Rhynchosciara americana midgut trehalase (alpha, alpha-trehalose glucohydrolase, EC 3.2.1.28) at different pH values revealed the existence of two essential groups (pKa 5.28 and pKa 7.74) for the trehalos activity. Those groups must be carboxyl groups since the alternative possibilities (sulfhydryl and phenol groups) have been discarded by selective modification and attempts to reactivate the modified enzyme with hydroxylamine. Furthermore, the increase of the pKa values of carbodiimide-reactive groups in the presence of dioxane supports further evidence that they are carboxyls. The results suggest the pKa 5.28 carboxyl is in the active site, while the pKa 7.74 carboxyl is in its neighborhood buried in the enzyme molecule. The possible role for the carbodiimide-reactive carboxyl groups in catalysis is discussed.

Purification and properties of trehalase from the thermophilic fungus Humicola lanuginosa

Trehalase (alpha,alpha-Trehalose glucohydrolase, EC 3.2.1.28) was partially solubilized from the thermophilic fungus Humicola lanuginosa RM-B, and purified 184-fold. The purified enzyme was optimally active at 50 degrees C in acetate buffer at pH 5.5. It was highly specific for alpha,alpha-trehalose and had an apparent Km = 0.4 mM at 50 degrees C. None of the other disaccharides tested either inhibited or activated the enzyme. The molecular weight of the enzyme was around 170 000. Trehalase from mycelium grown at 40 and 50 degrees C had similar properties. The purified enzyme, in contrast to that in the crude-cell free extract, was less stable. At low concentration, purified trehalase was afforded protection against heat-inactivation by "protection against heat-inactivation by "protective factor(s)" present in mycelial extracts. The "protective factor(s)" was sensitive to proteolytic digestion. It was not diffusible and was stable to boiling for at least 30 min. Bovine serum albumin and casein also protected the enzyme from heat-inactivation.

Physical properties and Tris inhibition of an insect trehalase and a thermodynamic approach to the nature of its active site

The midgut from Rhynchosciara americana larvae display a trehalase (alpha,alpha'-trehalose glucohydrolase, EC 3.2.1.28) which is soluble with a molecular weight of 122 000 and pI 4.6. The optimum pH of the enzyme is 6.0, its apparent Km for trehalose is 0.67 mM and its energy of activation is 16.7 kcal/mol. Sulfhydryl reagents do not inhibit the trehalase. The results suggest the existence of two carboxyl groups in the active site, one of which has a very high (8.3) pK. The increase of the pK values of the essential groups of the free enzyme in the presence of increasing concentrations of dioxane supports the hypothesis that these groups are carboxyls. The purified enzyme hydrolyzes only alpha,alpha'-trehalose and it is competitively inhibited by several compounds.

Carbohydrate metabolism during morphogenesis of Coprinus lagopus (sensu Buller)

The occurrence and properties of enzymes of carbohydrate metabolism were studied during dikaryotic fruiting of the mushroom Coprinus lagopus. Enzymes of hexose monophosphate catabolism, sugar alcohol (polyol) dehydrogenases (DH), and trehalase occurred throughout development. The ratio of xylitol DH to sorbitol DH was greater than unity in both monokaryotic mycelium and dikaryotic fruit body caps, whereas this ratio decreased in the stipe (stalk) tissue. Xylitol DH and sorbitol DH were both dependent upon nicotinamide adenine dinucleotide (NAD) and showed maximal activity at pH 9. Two separate enzymes were suspected on the basis of preferential utilization of the NAD analogue, thionicotinamide-NAD, by xylitol DH, and this feature was consistent throughout development. An appraisal of the carbohydrate pool revealed trehalose and glucose, with the former predominant in the stipe and the latter in excess in the cap of dikaryotic fruit bodies. Trehalase activity in dialyzed enzyme extracts showed pH optima at acid and alkaline pH levels in monokaryotic mycelium, dikaryotic stipes, and cap tissues.

Partial prufication and properties of a trehalase from Streptomyces hygroscopicus

The enzyme alpha,alpha'-glucoside 1-glucohydrolase, which catalyzes the hydrolysis of trehalose, was isolated from Streptomyces hygroscopicus and was purified approximately 80-fold. The enzyme was completely specific for trehalose as substrate. None of the other naturally occurring glucose disaccharides exhibited any significant activity. The pH optimum for enzymatic activity was found to be 6.5 and the K(m) was estimated to be approximately 1.8 x 10(-2)m. The product of the reaction was identified as d-glucose by chemical, chromatographic, and enzymatic methods. The presence of this enzyme was demonstrated in several species of Streptomyces and related organisms.

Purification and physical properties of sweet-almond alpha-galactosidase

1. alpha-Galactosidase from sweet almonds was purified about 2000-fold through eight steps. 2. The enzyme preparation was free from other related enzymes known to occur in sweet almonds, and behaved as a homogeneous protein on filtration through Sephadex G-75. 3. A molecular weight of about 33000 was determined from the gel-filtration data. 4. The ultraviolet-absorption spectrum and thermal inactivation of the enzyme are described. 5. The purified enzyme hydrolysed p-nitrophenyl alpha-d-galactoside at a much faster rate than melibiose. 6. The pH optimum was at 5.5-5.7. 7. Besides hydrolysis, it also catalysed transfer of galactosyl residues, chain elongation of melibiose and the synthesis of oligosaccharides from galactose.