Hiroto Chaen

Cloning and sequencing of a cluster of genes encoding novel enzymes of trehalose biosynthesis from thermophilic archaebacterium Sulfolobus acidocaldarius

Trehalose biosynthesis genes, treZ, treX and treY, encoding maltooligosyltrehalose trehalohydrolase (TreZ), glycogen debranching enzyme (TreX), and maltooligosyltrehalose synthase (TreY) have been cloned from the thermophilic archaebacterium Sulfolobus acidocaldarius ATCC33909. The amino-acid sequences deduced from treZ, treX and treY are composed of 556, 713 and 720 amino-acid residues, respectively. TreZ and TreY are 33-40% homologous to the corresponding enzymes from Arthrobacter sp. Q36. We have proposed that the biosynthesis of trehalose in Sulfolobus occurs via the actions of the three enzymes encoded by treZXY.

Cloning and sequencing of trehalose synthase gene from Pimelobacter sp. R48.

The gene encoding trehalose synthase (catalyzing the conversion of maltose into alpha, alpha-trehalose by intramolecular transglucosylation) was cloned from Pimelobacter sp. R48. Sequence analysis revealed a 1719-bp synthase gene and a 573-residue amino-acid sequence. The 220 N-terminal residues were homologous to those of maltases from Saccharomyces carlsbergensis and Aedes aegypti.

Purification and Characterization of Thermostable Maltooligosyl Trehalose Trehalohydrolase from the Thermoacidophilic Archaebacterium Sulfolobus acidocaldarius

A thermostable maltooligosyl trehalose trehalohydrolase from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius ATCC 33909 was purified from a cell-free extract to an electrophoretically pure state by successive column chromatographies on Sepabeads FP-DA13, Butyl-Toyopearl 650M, DEAE-Toyopearl 650S, Toyopearl HW-55S and Ultrogel AcA44. The enzyme had a molecular mass of 59,000 by SDS-polyacrylamide gel electrophoresis and a pI of 6.1 by gel isoelectrofocusing. The N-terminal amino acid of the enzyme was methionine. The enzyme showed the highest activity from pH 5.5 to 6.0 and at 75 degrees C, and was stable from pH 5.5 to 9.5 and up to 85 degrees C. The activity was inhibited by Hg2+, Cu2+, Fe2+, Pb2+, and Zn2+. The Km values of the enzyme for maltosyl trehalose, maltotriosyl trehalose, maltotetraosyl trehalose, and maltopentaosyl trehalose were 16.7 mM, 2.7 mM, 3.7 mM, and 4.9 mM, respectively.

Bioavailability of glucosyl hesperidin in rats.

Glucosyl hesperidin (G-hesperidin) is a water-soluble derivative of hesperidin. We compared the absorption and metabolism of G-hesperidin with those of hesperidin in rats. After oral administration of G-hesperidin or hesperidin to rats, hesperetin was detected in sera hydrolyzed with β-glucuronidase, but it was not detectable in unhydrolyzed sera. Serum hesperetin was found more rapidly in rats administered G-hesperidin than in those administered hesperidin. The area under the concentration-time curve for hesperetin in the sera of rats administered G-hesperidin was approximately 3.7-fold greater than that of rats administered hesperidin. In the urine of both administration groups, hesperetin and its glucuronide were found. Urinary excretion of metabolites was higher in rats administered G-hesperidin than in those administered hesperidin. These results indicate that G-hesperidin presents the same metabolic profile as hesperidin. Moreover, it was concluded that G-hesperidin is absorbed more rapidly and efficiently than hesperidin, because of its high water solubility.

CLONING AND SEQUENCING OF TREHALOSE SYNTHASE GENE FROM THERMUS AQUATICUS ATCC33923

The gene encoding trehalose synthase (catalyzing the conversion of maltose into alpha, alpha-trehalose by transglucosylation) was cloned from Thermus aquaticus ATCC33923. Sequence analysis revealed a 2892 bp synthase gene and a 963 residue amino-acid sequence. The 547 N-terminal residues were homologous to the full-length synthase from Pimelobacter sp. R48 (53.8% identity).

Purification and Characterization of a Thermostable Trehalose Synthase from Thermus aquaticus

Thermostable trehalose synthase, which catalyzes the conversion of maltose into trehalose by intramolecular transglucosylation, was purified from a cell-free extract of the thermophilic bacterium Thermus aquaticus ATCC 33923 to an electrophoretically homogeneity by successive column chromatographies. The purified enzyme had a molecular weight of 105,000 by SDS-polyacrylamide gel electrophoresis and a pI of 4.6 by gel isoelectrofocusing. The N-terminal amino acid of the enzyme was methionine. The optimum pH and temperature were pH 6.5 and 65°C, respectively. The enzyme was stable from pH 5.5 to 9.5 and up to 80°C for 60min. The trehalose synthase from Thermus aquaticus is more thermoactive and thermostable than that from Pimelobacter sp. R48. The yield of trehalose from maltose by the enzyme was independent of the substrate concentration, and tended to increase at lower temperatures. The maximum yield of trehalose from maltose by the enzyme reached 80-82% at 30-40°C. The activity was inhibited by Cu(2+) , Hg(2+), Zn(2+), and Tris.

Enzymatic synthesis of kojioligosaccharides using kojibiose phosphorylase

We have attempted to synthesize kojioligosaccharides (oligosaccharides having the alpha-1,2 glycosidic linkage at the nonreducing end) using two methods. In the first, mixtures of various proportions of glucose and beta-D-glucose-1-phosphate (beta-G1P) were allowed to react in the presence of kojibiose phosphorylase (KPase). In the second, maltose was allowed to react with KPase and maltose phosphorylase (MPase) simultaneously. In the former method, kojioligosaccharides having only the alpha-1,2 glucosidic linkage were synthesized and the average degree of polymerization (D.P.) of oligosaccharides increased with decreasing proportions of glucose. In the second method, kojioligosaccharides were obtained at approximately 70% yields under optimum conditions. 4-alpha-D-Kojibiosyl-glucose, kojitriose and kojitetraose, the principal kojioligosaccharides synthesized, were not hydrolyzed by salivary amylase, artificial gastric juice, pancreatic amylase, or small intestinal enzymes.

Cloning, Sequencing, and Expression of the Genes Encoding an Isocyclomaltooligosaccharide Glucanotransferase and an α-Amylase from a Bacillus circulans Strain

The gene for a novel glucanotransferase, isocyclomaltooligosaccharide glucanotransferase (IgtY), involved in the synthesis of a cyclomaltopentaose cyclized by an α-1,6-linkage [ICG5; cyclo-{→6)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→}] from starch, was cloned from the genome of B. circulans AM7. The IgtY gene, designated igtY, consisted of 2,985 bp encoding a signal peptide of 35 amino acids and a mature protein of 960 amino acids with a calculated molecular mass of 102,071 Da. The deduced amino-acid sequence showed similarities to 6-α-maltosyltransferase, α-amylase, and cyclomaltodextrin glucanotransferase. The four conserved regions common in the α-amylase family enzymes were also found in this enzyme, indicating that this enzyme should be assigned to this family. The DNA sequence of 8,325-bp analyzed in this study contained two open reading frames (ORFs) downstream of igtY. The first ORF, designated igtZ, formed a gene cluster, igtYZ. The amino-acid sequence deduced from igtZ exhibited no similarity to any proteins with known or unknown functions. IgtZ was expressed in Escherichia coli, and the enzyme was purified. The enzyme acted on maltooligosaccharides that have a degree of polymerization (DP) of 4 or more, amylose, and soluble starch to produce glucose and maltooligosaccharides up to DP5 by a hydrolysis reaction. The enzyme (IgtZ), which has a novel amino-acid sequence, should be assigned to α-amylase. It is notable that both IgtY and IgtZ have a tandem sequence similar to a carbohydrate-binding module belonging to a family 25. These two enzymes jointly acted on raw starch, and efficiently generated ICG5.

Gene Encoding a Trehalose Phosphorylase from Thermoanaerobacter brockii ATCC 35047

A gene encoding a trehalose phosphorylase was cloned from Thermoanaerobacter brockii ATCC 35047. The gene encodes a polypeptide of 774 amino acid residues. The deduced amino acid sequence was homologous to bacterial maltose phosphorylases and a trehalose 6-phosphate phosphorylase catalyzing anomer-inverting reactions. On the other hand, no homology was found between the T. brockii enzyme and an anomer-retaining trehalose phosphorylase from Grifola frondosa.

Effects of Dietary Lactosucrose (4G-β-D-galactosylsucrose) on the IgE Response in Mice

In this study, we examined the effects of dietary lactosucrose (LS, a non-digestible oligosaccharide) on the IgE response in mice immunized with ovalbumin (OVA)/alum. In addition to IgG1 and IgG2a responses, the anti-OVA IgE response in mice fed LS diets was dose-dependently suppressed, as compared with the control mice, while the serum total IgG levels were comparable. Moreover, dietary LS feeding inhibited antigen-specific IgE and IgG1 productions even after a second immunization. Regarding with cytokine production, when stimulated in vitro with OVA, splenocytes obtained from LS-fed mice produced a similar level of IFN-γ, and lower levels of IL-4 and IL-5, as compared with the control mice. But IL-10 production by OVA-stimulated splenocytes was augmented in LS-fed mice, suggesting that IL-10 producing cells are responsible for the immunoregulatory effect of LS. Our findings indicate the further possibility that dietary LS supplementation can be used to prevent IgE-mediated allergic diseases.