A Thermostable Acid α-Glucosidase from Tetrahymena thermophila: Purification and Characterization

An acid α-glucosidase (EC 3.2.1.20) was purified to homogeneity from the culture medium of Tetrahymena thermophila CU 399. Its general molecular, catalytic and immunological properties were compared to those of the T. pyriformis W enzyme. The enzyme from T. thermophila was a 105-kD monomer and the N-terminus (25 amino acid residues) displayed some homology with that of T. pyriformis enzyme. The purified enzyme was most active at 56° C and showed resistance to thermal inactivation. The acid α-glucosidase appears to have α-1,6-glucosidase as well as α-1,4-glucosidase activity. The Km values determined with p-nitrophenyl-α-glucopyranoside, maltose, isomaltose and glycogen were 0.7 mM, 2.5 mM, 28.5 mM and 18.5 mg/ml, respectively. The enzyme was antigenically distinct from T. pyriformis acid α-glucosidase.     

Purification and characterization of lysosomal alpha-glucosidase secreted by eukaryote Tetrahymena

A large amount of lysosomal acid hydrolases was released into the medium by Tetrahymena pyriformis strain W during growth. An extracellular lysosomal acid alpha-glucosidase has been purified 500-fold with a 41% yield to homogeneity, as judged by polyacrylamide gel electrophoresis. It was found to be a glycoprotein and to consist of a single 110,000-dalton polypeptide chain. The carbohydrate content of the alpha-glucosidase was equivalent to 2.8% of the total protein content, and the oligosaccharide moiety was composed of mannose and N-acetylglucosamine in a molar ratio of 6.7:2. The optimal pHs for hydrolysis of maltose and p-nitrophenyl-alpha-glucopyranoside, maltose, isomaltose, and glycogen were 1.1 mM, 2.5 mM, 33.0 mM, and 18.5 mg/ml, respectively. This purified enzyme appears to have alpha-1,6-glucosidase as well as alpha-1,4-glucosidase activity. Turanose has a noncompetitive inhibitory effect on the hydrolysis of maltose. The antibody raised against Tetrahymena acid alpha-glucosidase inhibited the hydrolysis of all substrates tested. These properties of Tetrahymena acid alpha-glucosidase were found to be similar to those of the human liver lysosomal alpha-glucosidase.     

Species-specific antibodies of Tetrahymena acid alpha-glucosidase.

1. Tetrahymena acid alpha-glucosidases A and B were purified from T. pyriformis W and T. thermophila 399, respectively. The acid alpha-glucosidases A and B were different in immunological properties and thermostability. 2. The acid alpha-glucosidases A and B reflected specific distribution between T. pyriformis and T. thermophila. 3. Type A and B of taurolipid showed a species-specific distribution pattern between T. pyriformis and T. thermophila.     

Hydrolysis of low molecular weight isomaltosaccharides by a p-nitrophenyl-alpha-D-glucopyranoside-hydrolyzing alpha-glucosidase from a thermophile, Bacillus thermoglucosidius KP 1006.

A p-nitrophenyl-alpha-D-glucopyranoside-hydrolyzing alpha-glucosidase of a thermophile, Bacillus thermoglucosidius KP 1006, was purified to an electrophoretically-homogeneous state. Its molecular weight was estimated as 60 000 by gel electrophoresis. The molecular activity (ko) and the Km value at 60 degrees C and pH 6.8 for p-nitrophenyl-alpha-D-glucopyranoside were 233 s-1 and 0.24 mM, respectively. The enzyme cleft the non-reducing terminal alpha-1,6-glucosidic bonds of isomaltose, panose, isomaltotriose, isomaltotetraose, and isomaltopentaose. The ko values were 72.4, 194, 208, 233 and 167 s-1, and the Km values were 3.3, 9.5, 11, 13 and 21 mM, respectively. Each isomaltosaccharide was hydrolyzed to glucose by the cleavage of single glucose units from its nonreducing end. The present study suggests that the enzyme is an oligo-1,6-glucosidase (dextrin 6-alpha-glucanohydrolase, EC 3.2.1.10) and an exo-glucosidase.     

Conserved cis- and trans-acting determinants for replication initiation and regulation of replication fork movement in tetrahymenid species.

The rDNA minichromosomes of Tetrahymena thermophila and Tetrahymena pyriformis share a high degree of sequence similarity and structural organization. The T.thermophila 5' non-transcribed spacer (5' NTS) is sufficient for replication and contains three repeated sequence elements that are conserved in T.pyriformis , including type I elements, the only known determinant for replication control. To assess the role of conserved sequences in replication control, structural and functional studies were performed on T.pyriformis rDNA. Similar to T.thermophila , replication initiates exclusively in the 5' NTS, localizing to a 900 bp segment. Elongating replication forks arrest transiently at one site which bears strong similarity to a tripartite sequence element present at fork arrest sites in T.thermophila rDNA. An in vitro type I element binding activity indistinguishable from the T.thermophila protein, ssA-TIBF, was detected in T.pyriformis extracts. The respective TIBF proteins bind with comparable affinity to type I elements from both species, suggesting that in vivo recognition could cross species boundaries. Despite these similarities, the T.pyriformis 5' NTS failed to support replication in transformed T.thermophila cells, suggesting a more complex genetic organization than previously realized.     

Glycogen debranching enzyme in bovine brain

Glycogen debranching enzyme was partially purified from bovine brain using a substrate for measuring the amylo-1,6-glucosidase activity. Bovine cerebrum was homogenized, followed by cell-fractionation of the resulting homogenate. The enzyme activity was found mainly in the cytosolic fraction. The enzyme was purified 5,000-fold by ammonium sulfate precipitation, anion-exchange chromatography, gel-filtration, anion-exchange HPLC, and gel-permeation HPLC. The enzyme preparation had no alpha-glucosidase or alpha-amylase activities and degraded phosphorylase limit dextrin of glycogen with phosphorylase. The molecular weight of the enzyme was 190,000 and the optimal pH was 6.0. The brain enzyme differed from glycogen debranching enzyme of liver or muscle in its mode of action on dextrins with an alpha-1,6-glucosyl branch, indicating an amino acid sequence different from those of the latter two enzymes. It is likely that the enzyme is involved in the breakdown of brain glycogen in concert with phosphorylase as in the cases of liver and muscle, but that this proceeds in a somewhat different manner. The enzyme activity decreased in the presence of ATP, suggesting that the degradation of brain glycogen is controlled by the modification of the debranching enzyme activity as well as the phosphorylase.     

Studies into hormonal imprinting in a Tetrahymena thermophila mutant incapable of lysosomal enzyme secretion

Reexposure to insulin after primary interaction (hormonal imprinting) was followed by a binding increase in T. pyriformis and by a binding decrease in T. thermophila. The sec. mutant, MS-1 strain of T. thermophila, which is unable of lysosomal enzyme secretion, also showed a binding increase on a second exposure to insulin, from which it follows that alteration of the enzyme secretion, or other factors associated with mutation, accounted for reversion of the trend of imprinting. Thyrotropic hormone (TSH) also gave rise to a negative imprinting in T. thermophila, but did not alter the binding relations of the MS-1 mutant strain.     

High level expression of extracellular secretion of a β-glucosidase gene (PtBglu3) from Paecilomyces thermophila in Pichia pastoris

A novel β-glucosidase gene (designated PtBglu3) from Paecilomyces thermophila was cloned and sequenced. PtBglu3 has an open reading frame of 2,557 bp, encoding 858 amino acids with a calculated molecular mass of 90.9 kDa. The amino acid sequence of the mature polypeptide shared the highest identity (70%) to a glycoside hydrolase (GH) family 3 characterized β-glucosidase from Penicillium purpurogenum. PtBglu3 without the signal peptides was cloned into pPIC9K vector and successfully expressed in Pichia pastoris as an active extracellular β-glucosidase (PtBglu3). High activity of 274.4 U/ml was obtained by high cell-density fermentation, which is by far the highest reported yield for β-glucosidase. The recombinant enzyme was purified to homogeneity with 3.3-fold purification and a recovery of 68.5%. The molecular mass of the enzyme was estimated to be 116 kDa by SDS-PAGE, and 198.2 kDa by gel filtration, indicating that it was a dimer. Optimal activity of the purified enzyme was observed at pH 6.0 and 65 °C, and it was stable up to 60 °C. The enzyme exhibited high specific activity toward pNP-β-D-glucopyranoside, cellooligosaccharides, gentiobiose, amygdalin and salicin, and relatively lower activity against lichenan and laminarin. The present results should contribute to improving industrial production of β-glucosidase.     

Processing and Secretion of Lysosomal Acid α-Glucosidase In Tetrahymena Wild Type and Secretion-Deficient Mutant Cells

ABSTRACT. The proteolytic processing and secretion of a lysosomal enzyme, acid α-glucosidase, was studied by pulse-chase labeling with [³⁵S]methionine in Tetrahymena thermophila CU-399 cells treated with ammonium chloride. This cell secreted a large amount of acid α-glucosidase into the cultured medium during starvation. the secretion was found to be repressed by addition of ammonium chloride (NH₄Cl). Acid α-glucosidase was produced as a precursor form (108 kDa) and then processed to a mature polypeptide (105 kDa) within 60 min. This mature enzyme was secreted into the media within 2-3 h after chase, whereas the precursor form was not secreted by either control cells or NH₄Cl-treated cells. NH₄Cl did not affect the processing of the precursor acid α-glucosidase. Processing profile of this enzyme was apparently indistinguishable from that of the mutant MS-1 defective in lysosomal enzyme secretion. Furthermore, the purified extracellular (CU-399) and intracellular (MS-1) acid a-glucosidases were the same in molecular mass (105 kDa) and enzymatic properties. They contained no mannose 6-phosphate residues in N-linked oligosaccharides. These results suggested that unlike mammalian cells, Tetrahymena acid α-glucosidase may be transferred to lysosomes by a mannose 6-phosphate receptor-independent mechanism, and also that low pH was not essential for the proteolytic processing of precursor polypeptide.     

Replication of the extrachromosomal ribosomal RNA genes of Tetrahymena thermophilia.

Cultures of Tetrahymena thermophila were deprived of nutrients and later refed with enriched medium to obtain partial synchrony of DNA replication. Preferential replication of the extrachromosomal, macronuclear ribosomal RNA genes (rDNA) was found to occur at 40-80 min after refeeding. The rDNA accounted for one half of the label incorporated into cellular DNA during this period. Electron microscopy of the purified rDNA showed 1% replicative intermediates. Their structure was that expected for bidirectional replication of the linear rDNA from an origin or origins located in the central nontranscribed region of the palindromic molecule. Similar forms had previously been observed for the rDNA of a related species, Tetrahymena pyriformis. The electron microscopic data was consistent with an origin of replication located approximatley 600 base pairs from the center of the rDNA of T. thermophila, in contrast to a more central location in the rDNA of T. pyriformis. One implication of an off-center origin of replication is that there are two such sequences per palindromic molecule.     

The effects of supraoptimal temperatures on population growth and cortical patterning in Tetrahymena pyriformis and Tetrahymena thermophila: a comparison

In this investigation, we compare the multiplication rates and morphogenetic responses of the two most studied Tetrahymena species, T. pyriformis and T. thermophila, at supraoptimal temperatures. Although the upper temperature limits differ greatly in the two species, the pattern of growth responses to high temperature is for the most part similar, with some differences in detail. The transient recovery of cell division at the highest temperature that allows cell division, characteristic of T. pyriformis, is observed in a less distinct form in T. thermophila. Moreover, there is a remarkable difference in developmental response, with drastic abnormalities in patterning of oral structures during the transient recovery of cell division in T. pyriformis, and far more limited abnormalities under similar conditions in T. thermophila. The abnormalities result from spatial disorder in the alignment and orientation of basal body pairs within the early oral primordium, followed by failures in the realignment that normally occurs as oral structures (membranelles and undulating membrane) mature. Both the initial spatial disorder and the failures in realignment are far more severe in T. pyriformis than in T. thermophila.     

Purification and partial characterization of glyceraldehyde-3-phosphate dehydrogenase from the ciliate Tetrahymena thermophila

In the present study, we purified the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) which is involved in cellular energy production and has important housekeeping functions, from the ciliate Tetrahymena thermophila using a three-step procedure. The enzyme was purified ~68 folds by ammonium sulfate precipitation, followed by two steps of column chromatography (DEAE-cellulose and Mono-S). The purified enzyme is a homotetramer with a molecular weight of ~120 kDa. Isoelectric focusing analysis showed the presence of only one basic GAPDH isoform with an isoelectric point of 8.8. Western blot analysis showed a single 32-kDa band corresponding to the enzyme subunit using a monospecific polyclonal antibody against the T. thermophila GAPDH. The maximum of enzyme activity occurred at pH 8.0 and at 30-35°C. The apparent K(m) values for both NAD(+) and D-glyceraldehyde-3-phosphate were 0.102 ± 0.012 and 0.360 ± 0.018 mM, respectively. The maximal velocity (V(max)) was 39.40 ± 2.95 U/mg. The T. thermophila GAPDH is inhibited by oxidative and nitrosative stress reagents.     

Properties of purified L-ornithine decarboxylase (EC 4.1.1.17) from Tetrahymena thermophila

Ornithine decarboxylase (ornithine carboxy lyase; EC 4.1.1.17) (ODC) from Tetrahymena thermophila was purified 6,300 fold employing fractionated ammonium sulfate precipitation, gel permeation chromatography on Sephadex G-150, ion exchange chromatography on DEAE-Sepharose CL-6B, and preparative isoelectric focussing. The product obtained in 24% yield was a preparation of the specific activity of 10,200 nmol CO2.h-1.mg-1. The purified enzyme was rather stable at 37 degrees C (14% loss of activity within 1 h). The molecular and catalytic properties of this enzyme were investigated. The isoelectric point was 5.7 and the molecular weight (MW) was estimated to be 68,000 under nondenaturing conditions. The pH optimum was between 6.0 and 7.0, the Km for the substrate L-ornithine was 0.11 mM, and the Km for the cofactor pyridoxal 5-phosphate was 0.12 microM; the product of ODC catalysis, putrescine, was a poor inhibitor with an estimated Ki of about 10 mM. The enzyme was inhibited competitively by D-ornithine with a Ki of 1.6 mM and by alpha-difluoromethylornithine with a Ki of 0.15 mM. The latter one, an enzyme activated irreversible inhibitor of mammalian ODC, inactivated the enzyme from T. thermophila at high concentrations with a half life time of 14 min. Other basic amino acids, e.g. L-lysine, L-arginine, and L-histidine, were neither substrates nor inhibitors of the enzyme, as were the diamines 1,3-diaminopropanol and cadaverine, the polyamines spermidine and spermine and the cosubstrate analogues pyridoxal and pyridoxamine-5-phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular and physiological role of the trehalose-hydrolyzing alpha-glucosidase from Thermus thermophilus HB27

Trehalose supports the growth of Thermus thermophilus strain HB27, but the absence of obvious genes for the hydrolysis of this disaccharide in the genome led us to search for enzymes for such a purpose. We expressed a putative alpha-glucosidase gene (TTC0107), characterized the recombinant enzyme, and found that the preferred substrate was alpha,alpha-1,1-trehalose, a new feature among alpha-glucosidases. The enzyme could also hydrolyze the disaccharides kojibiose and sucrose (alpha-1,2 linkage), nigerose and turanose (alpha-1,3), leucrose (alpha-1,5), isomaltose and palatinose (alpha-1,6), and maltose (alpha-1,4) to a lesser extent. Trehalose was not, however, a substrate for the highly homologous alpha-glucosidase from T. thermophilus strain GK24. The reciprocal replacement of a peptide containing eight amino acids in the alpha-glucosidases from strains HB27 (LGEHNLPP) and GK24 (EPTAYHTL) reduced the ability of the former to hydrolyze trehalose and provided trehalose-hydrolytic activity to the latter, showing that LGEHNLPP is necessary for trehalose recognition. Furthermore, disruption of the alpha-glucosidase gene significantly affected the growth of T. thermophilus HB27 in minimal medium supplemented with trehalose, isomaltose, sucrose, or palatinose, to a lesser extent with maltose, but not with cellobiose (not a substrate for the alpha-glucosidase), indicating that the alpha-glucosidase is important for the assimilation of those four disaccharides but that it is also implicated in maltose catabolism.     

Localization of alpha-glucosidases I, II, and III in organs of European honeybees, Apis mellifera L., and the origin of alpha-glucosidase in honey

Three kinds of alpha-glucosidases, I, II, and III, were purified from European honeybees, Apis mellifera L. In addition, an alpha-glucosidase was also purified from honey. Some properties, including the substrate specificity of honey alpha-glucosidase, were almost the same as those of alpha-glucosidase III. Specific antisera against the alpha-glucosidases were prepared to examine the localization of alpha-glucosidases in the organs of honeybees. It was immunologically confirmed for the first time that alpha-glucosidase I was present in ventriculus, and alpha-glucosidase II, in ventriculus and haemolymph. alpha-Glucosidase III, which became apparent to be honey alpha-glucosidase, was present in the hypopharyngeal gland, from which the enzyme may be secreted into nectar gathered by honeybees. Honey may be finally made up through the process whereby sucrose in nectar, in which glucose and fructose also are naturally contained, is hydrolyzed by secreted alpha-glucosidase III.     

An improved purification procedure for soluble processing alpha-glucosidase I from Saccharomyces cerevisiae overexpressing CWH41

Processing alpha-glucosidase I, which is encoded by CWH41, regulates one of the key steps in asparagine-linked glycoprotein biosynthesis by cleaving the terminal alpha-1,2-linked glucose from Glc(3)Man(9)GlcNAc(2), the common oligosaccharide precursor. This cleavage is essential for further processing of the oligosaccharide to the complex, hybrid, and high mannose type carbohydrate structures found in eukaryotes. A method is described for the purification of the soluble form of the alpha-glucosidase I, from recombinant Saccharomyces cerevisiae overexpressing CWH41. A homogeneous enzyme preparation was obtained in higher yield than previously reported. Cultivation of recombinant S. cerevisiae in a fermenter increased the biomass 1.7 times per liter and enzyme production 2 times per liter compared to cultivation in shake flasks. Ammonium sulfate precipitation with three chromatography steps, including chromatography on an N-(5'-carboxypentyl)-1-deoxynojirimycin column, resulted in highly purified enzyme with no detectable contamination by other alpha- and beta-aryl-glycosidases. The purification procedure reproducibly yielded 40 microg of pure enzyme per gram wet biomass. Enzyme that was purified using an alternative procedure contained minor impurities and was hydrolyzed by an endogenous proteolytic activity to peptides that retained full catalytic activity. Controlled trypsin hydrolysis of the highly purified enzyme released polypeptide(s) containing the alpha-glucosidase I catalytic domain, with no loss of catalytic activity. This suggests that the catalytic domain of yeast alpha-glucosidase I is resistant to trypsin hydrolysis and remains fully functional after cleavage.     

Use of immobilized antibodies in investigating acid alpha-glucosidase in urine in relation to Pompe's disease.

(1) A simple method is described for the isolation of the lysosomal enzyme, acid alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) from normal human liver. Antibodies raised against the purified enzyme were immobilized by covalent coupling to Sepharose 4B. (2) Acid alpha-glucosidase can be quantitatively removed from normal urine by incubating with an excess of immobilized antibody. With p-nitrophenyl-alpha-glucoside as substrate, acid alpha-glucosidase accounts for 91 +/- 3% of the total alpha-glucosidase activity at pH 4.0 IN Normal urine. (3) In urine from a patient with the infantile form of Pompe's disease ('acid maltase deficiency'), no alpha-glucosidase activity could be removed by the immobilized antibody, in agreement with the fact that acid alpha-glucosidase is absent in these patients. (4) In urine from patients with the late-onset form of Pompe's disease, 46 +/- 11% of the alpha-glucosidase activity at pH 4.0 can be removed by incubation with immobilized antibodies, indicating that residual acid alpha-glucosidase activity is present in urine of these patients. The residual acid alpha-glucosidase activity amounts to about 5% of that in the urine of control persons. (5) If acid alpha-glucosidase is adsorbed to immobilized antibodies, the activity can still be measured with p-nitrophenyl-alpha-glucoside as substrate. The Km for p-nitrophenyl-alpha-glucoside is not significantly changed by adsorbing purified acid alpha-glucosidase to immobilized antibodies. (6) The properties of acid alpha-glucosidase from urine of patients with late-onset Pompe's disease were compared with those of acid alpha-glucosidase from normal urine, both adsorbed to immobilized antiserum. The pH-activity profile of the enzyme from urine of patients with late-onset Pompe's disease can not be distinguished from that of the normal urinary enzyme. The Km for p-nitro-phenyl-alpha-glucoside of the two enzymes is identical, both at pH 4 and 3. The titration curves of the two enzymes with immobilized antibodies are identical.