6-α-Glucosyltransferase and 3-α-isomaltosyltransferase from Bacillus globisporus N75

Structural insights into starch-metabolizing enzymes and their applications

Starch is a polysaccharide produced exclusively through photosynthesis in plants and algae; however, is utilized as an energy source by most organisms, from microorganisms to higher organisms. In mammals and the germinating seeds of plants, starch is metabolized by simple hydrolysis pathways. Moreover, starch metabolic pathways via unique oligosaccharides have been discovered in some bacteria. Each organism has evolved enzymes responsible for starch metabolism that are diverse in their enzymatic properties. This review, focusing on eukaryotic α-glucosidases and bacterial α-glucoside-hydrolyzing enzymes, summarizes the structural aspects of starch-metabolizing enzymes belonging to glycoside hydrolase families 15, 31, and 77 and their application for oligosaccharide production.

Synthesis of isomaltooligosaccharides using 4-O-α-d-isomaltooligosaccharylmaltooligosaccharide 1,4-α-isomaltooligosaccharohydrolase

Isomaltooligosaccharides (IMOs), including isomaltose, are valuable oligosaccharides, and the development of methods to synthesize high-purity IMOs has long been underway. We recently discovered a novel enzyme, 4-O-α-d-isomaltooligosaccharylmaltooligosaccharide 1,4-α-isomaltooligosaccharohydrolase (IMM-4IH), that showed promise for improving the synthesis process. In this study, we establish methods for synthesizing isomaltose and IMOs consisting of a variety of degrees of polymerization from starch using IMM-4IH. With 5% substrate, by combining IMM-4IH with 1,4-α-glucan 6-α-glucosyltransferase from Bacillus globisporus N75, the yield of isomaltose was 63.0%; incorporating isoamylase and cyclomaltodextrin glucanotransferase increased the yield to 75.3%. On the other hand, by combining IMM-4IH with 1,4-α-glucan 6-α-glucosyltransferase from Paenibacillus sp. PP710, IMOs were synthesized. The inclusion of isoamylase and α-amylase led to the 136 mM IMOs, consisting of oligosaccharides from isomaltose to isomaltodecaose, from 10% starch. The development of these efficient methods will be an important contribution to the industrial production of IMOs.

A subfamily classification to choreograph the diverse activities within glycoside hydrolase family 31

The Carbohydrate-Active Enzyme classification groups enzymes that breakdown, assemble, or decorate glycans into protein families based on sequence similarity. The glycoside hydrolases (GH) are arranged into over 170 enzyme families, with some being very large and exhibiting distinct activities/specificities towards diverse substrates. Family GH31 is a large family that contains more than 20,000 sequences with a wide taxonomic diversity. Less than 1% of GH31 members are biochemically characterized and exhibit many different activities that include glycosidases, lyases, and transglycosidases. This diversity of activities limits our ability to predict the activities and roles of GH31 family members in their host organism and our ability to exploit these enzymes for practical purposes. Here, we established a subfamily classification using sequence similarity networks that was further validated by a structural analysis. While sequence similarity networks provide a sequence-based separation, we obtained good segregation between activities among the subfamilies. Our subclassification consists of 20 subfamilies with sixteen subfamilies containing at least one characterized member and eleven subfamilies that are monofunctional based on the available data. We also report the biochemical characterization of a member of the large subfamily 2 (GH31_2) that lacked any characterized members: RaGH31 from Rhodoferax aquaticus is an α-glucosidase with activity on a range of disaccharides including sucrose, trehalose, maltose, and nigerose. Our subclassification provides improved predictive power for the vast majority of uncharacterized proteins in family GH31 and highlights the remaining sequence space that remains to be functionally explored.

Discovery of a novel glucanohydrolase, 4-α-isomaltooligosylglucose 4-glucanohydrolase, that can be used for efficient production of isomaltose

We discovered a novel enzyme in our pursuit of an improved method for the production of isomaltose. The enzyme, 4-α-isomaltooligosylglucose 4-glucanohydrolase from Sarocladium kiliense U4520, recognizes the panose motif (α-d-Glcp-(1 → 6)-α-d-Glcp-(1 → 4)-d-Glcp) and hydrolyzes the α-1,4-glucosidic bond on the reducing end side with respect to the α-1,6-glucosidic bond. The structure on the non-reducing end of the panose motif is important for the recognition of the substrate by the enzyme, and the substrate specificity is unique and distinguished from previously reported enzymes. The enzyme catalyzes the hydrolysis of panose with a k_cat/K_m of 31.2 s^-1mM^-1, and catalysis results in anomeric inversion. These enzymatic properties suggest that this enzyme will pair well with 1,4-α-glucan 6-α-glucosyltransferase from Bacillus globisporus N75 in the efficient production of isomaltose from starch.

Development of a method for preparing cyclic nigerosylnigerose syrup and investigation of its value as a dietary fiber

Cyclic nigerosylnigerose (CNN) syrup, containing 76% water-soluble dietary fiber, was prepared from starch on an industrial scale, using isoamylase, 6-α-glucosyltransferase, 3-α-isomaltosyltransferase, and cyclodextrin glucanotransferase. CNN syrup has a unique linkage pattern, consisting mainly of α-1,3 and α-1,6 glucoside linkages, and is characterized by its low weight average molecular weight (807) and moderate sweetness (relative sweetness = 25), unlike in well-known dietary fiber materials. The glass transition temperature of CNN is higher than that of the straight chain structures, maltotetraose and maltosyltrehalose. Even when 40% of normally added sucrose was replaced with CNN syrup, sponge cake puffed up sufficiently. The no observed adverse effect level for a single dose of CNN syrup was 0.88 and 0.89 g dry solid/kg body weight for men and women, respectively. The increase in blood glucose and insulin concentrations during consumption of CNN syrup was lower than that of glucose.

Efficient production of isomaltose and isomaltooligosaccharides from starch using 1,4-α-glucan 6-α-glucosyltransferase and isopullulanase

We attempted to develop an efficient method for producing isomaltose, a disaccharide consisting of an α-(1→6)-linkage, from starch by combining enzymes of known activity. We found that the combination of 1,4-α-glucan 6-α-glucosyltransferase from Bacillus globisporus N75 and isopullulanase from Aspergillus brasiliensis ATCC 9642 led to the efficient synthesis of isomaltose. Inclusion of isoamylase and cyclomaltodextrin glucanotransferase resulted in increased efficiency, with production yields exceeding 70%. Furthermore, we considered that isomaltooligosaccharides could be synthesized from starch by combining 1,4-α-glucan 6-α-glucosyltransferase from Paenibacillus sp. PP710 and isopullulanase. In reactions that additionally utilized isoamylase and α-amylase, the total concentration of product, which included a series of isomaltooligosaccharides from isomaltose to isomaltodecaose, was 131 m m, and the ratio of 6-linked glucopyranosyl bonds to all bonds was 91.7% at a substrate concentration of 10%. The development of these manufacturing methods will accelerate the industrial production of isomaltose and isomaltooligosaccharides.

Evaluation of the relative available energy of cyclic nigerosylnigerose using breath hydrogen excretion in healthy humans

Cyclic nigerosylnigerose (CNN) is a cyclic tetrasaccharide with properties distinct from those of other conventional cyclodextrins. We investigated the relative available energy of CNN in healthy humans. CNN digestibility was determined using brush border membrane vesicles from the small intestines of rats. CNN was not hydrolyzed by rat intestinal enzymes. To investigate breath hydrogen excretion, 13 human subjects were included in a double-blind cross-over, randomized, placebo-controlled study. The effects of CNN on hydrogen excretion were compared with those of a typical nondigestible, fermentable fructooligosaccharide (FOS). In the study participants, hydrogen excretion hardly increased upon CNN and was remarkably lower than for FOS. The available energy value was determined using the fermentability based on breath hydrogen excretion and was evaluated as 0 kcal/g for CNN. CNN was hardly metabolized and hence may be used as a low-energy dietary fiber.

A novel dextrin produced by the enzymatic reaction of 6-α-glucosyltransferase. I. The effect of nonreducing ends of glucose with by α-1,6 bonds on the retrogradation inhibition of high molecular weight dextrin

We prepared a high-molecular-weight modified dextrin (MWS-1000) from a partial hydrolysate of waxy corn starch with a weight average molecular weight of 1 × 106 (WS-1000) using Paenibacillus alginolyticus PP710 α-glucosyltransferase. The gel permeation chromatography showed that the weight average molecular weight of MWS-1000 was almost the same as that of WS-1000. The side chain lengths of WS-1000 and MWS-1000 after isomaltodextranase digestion were also shown to be similar to each other by high-performance anion exchange chromatography with pulsed amperometric detection. Since MWS-1000 confirmed the presence of α-1,6 bonds by enzyme digestibility, methylation, and 1H-NMR analyses, it was presumed that the structure of MWS-1000 was based on the introduction of α-1,6 glucosyl residues at the nonreducing ends of the partial hydrolysate of waxy corn starch. Furthermore, the MWS-1000 solution was not retrograded even during refrigerated storage or after repeated freeze–thaw cycles.

Cyclic nigerosylnigerose ameliorates DSS-induced colitis with restoration of goblet cell number and increase in IgA reactivity against gut microbiota in mice

Cyclic nigerosylnigerose (CNN) is a cyclic oligosaccharide. Oral administration of CNN promotes immunoglobulin A (IgA) secretion in the gut. IgA is a major antibody secreted into the gut and plays a crucial role in suppressing gut inflammation due to commensal gut microbiota. To investigate the effect of administration of CNN to promote IgA secretion on gut inflammation, experimental colitis was induced with dextran sulfate sodium (DSS) in Balb/c mice after 6 weeks of CNN pre-feeding. The severity of colitis was evaluated based on a disease activity index (DAI), the gene expression of inflammatory cytokines, and a histological examination. The CNN-treated mice with DSS-induced colitis (CNN-DSS group) showed significantly lower DAI scores and mRNA levels of interleukin-1 compared with the CNN-untreated mice with DSS-induced colitis (DSS group). Histological examination of the colon revealed that the pathological score was significantly lower in the CNN-DSS group compared with the DSS group due to the reduced infiltration of immune cells. The number of goblet cells was significantly higher in the CNN-DSS group compared with the DSS group. The IgA concentration and the ratio of microbiota coated with IgA were evaluated in the cecal content. Although there was no difference in the IgA concentration among groups, a higher proportion of cecal microbiota were coated with IgA in the CNN-DSS group compared with that in the DSS group. These results suggest that CNN might preserve goblet cells in the colon and promote IgA coating of gut microbiota, which synergistically ameliorate gut inflammation in mice with DSS-induced colitis.

Cyclic nigerosyl-1,6-nigerose-based nanosponges: An innovative pH and time-controlled nanocarrier for improving cancer treatment

The design and structural optimisation of a novel polysaccharide-based nanomaterial for the controlled and sustained release of doxorubicin are here reported. A cross-linked polymer was obtained by reacting a tetraglucose, named cyclic nigerosyl-1-6-nigerose (CNN), with pyromellitic dianhydride. The cross-linking reaction formed solid nanoparticles, named nanosponges, able to swell as a function of the pH. Nanoparticle sizes were reduced using High Pressure Homogenization, to obtain uniform nanosuspensions. Doxorubicin was incorporated into the CNN-nanosponges in a good extent. DSC and solid state NMR analyses proved the drug interaction with the polymer matrix. In vitro studies demonstrated pH-dependent slow and prolonged release kinetics of the drug from the nanoformulation. Doxorubicin-loaded CNN-nanosponges were easily internalized in A2780 cell line. They might considered an intracellular doxorubicin reservoir, able to slowly release the drug over time. CNN-nanosponges may be promising biocompatible nanocarriers for the sustained delivery of doxorubicin with potential localised application in cancer treatments.

Effects of a non-cyclodextrin cyclic carbohydrate on mouse melanoma cells: Characterization of a new type of hypopigmenting sugar

Cyclic nigerosyl nigerose (CNN) is a cyclic tetrasaccharide that exhibits properties distinct from other conventional cyclodextrins. Herein, we demonstrate that treatment of B16 melanoma with CNN results in a dose-dependent decrease in melanin synthesis, even under conditions that stimulate melanin synthesis, without significant cytotoxity. The effects of CNN were prolonged for more than 27 days, and were gradually reversed following removal of CNN. Undigested CNN was found to accumulate within B16 cells at relatively high levels. Further, CNN showed a weak but significant direct inhibitory effect on the enzymatic activity of tyrosinase, suggesting one possible mechanism of hypopigmentation. While a slight reduction in tyrosinase expression was observed, tyrosinase expression was maintained at significant levels, processed into a mature form, and transported to late-stage melanosomes. Immunocytochemical analysis demonstrated that CNN treatment induced drastic morphological changes of Pmel17-positive and LAMP-1-positive organelles within B16 cells, suggesting that CNN is a potent organelle modulator. Colocalization of both tyrosinase-positive and LAMP-1-positive regions in CNN-treated cells indicated possible degradation of tyrosinase in LAMP-1-positive organelles; however, that possibility was ruled out by subsequent inhibition experiments. Taken together, this study opens a new paradigm of functional oligosaccharides, and offers CNN as a novel hypopigmenting molecule and organelle modulator.

Carbohydrate-binding architecture of the multi-modular α-1,6-glucosyltransferase from Paenibacillus sp. 598K, which produces α-1,6-glucosyl-α-glucosaccharides from starch

Paenibacillus sp. 598K α-1,6-glucosyltransferase (Ps6TG31A), a member of glycoside hydrolase family 31, catalyzes exo-α-glucohydrolysis and transglucosylation and produces α-1,6-glucosyl-α-glucosaccharides from α-glucan via its disproportionation activity. The crystal structure of Ps6TG31A was determined by an anomalous dispersion method using a terbium derivative. The monomeric Ps6TG31A consisted of one catalytic (β/α)8-barrel domain and six small domains, one on the N-terminal and five on the C-terminal side. The structures of the enzyme complexed with maltohexaose, isomaltohexaose, and acarbose demonstrated that the ligands were observed in the catalytic cleft and the sugar-binding sites of four β-domains. The catalytic site was structured by a glucose-binding pocket and an aglycon-binding cleft built by two sidewalls. The bound acarbose was located with its non-reducing end pseudosugar docked in the pocket, and the other moieties along one sidewall serving three subsites for the α-1,4-glucan. The bound isomaltooligosaccharide was found on the opposite sidewall, which provided the space for the acceptor molecule to be positioned for attack of the catalytic intermediate covalent complex during transglucosylation. The N-terminal domain recognized the α-1,4-glucan in a surface-binding mode. Two of the five C-terminal domains belong to the carbohydrate-binding modules family 35 and one to family 61. The sugar complex structures indicated that the first family 35 module preferred α-1,6-glucan, whereas the second family 35 module and family 61 module preferred α-1,4-glucan. Ps6TG31A appears to have enhanced transglucosylation activity facilitated by its carbohydrate-binding modules and substrate-binding cleft that positions the substrate and acceptor sugar for the transglucosylation.

A glycoside hydrolase family 31 dextranase with high transglucosylation activity from Flavobacterium johnsoniae

Glycoside hydrolase family (GH) 31 enzymes exhibit various substrate specificities, although the majority of members are α-glucosidases. Here, we constructed a heterologous expression system of a GH31 enzyme, Fjoh_4430, from Flavobacterium johnsoniae NBRC 14942, using Escherichia coli, and characterized its enzymatic properties. The enzyme hydrolyzed dextran and pullulan to produce isomaltooligosaccharides and isopanose, respectively. When isomaltose was used as a substrate, the enzyme catalyzed disproportionation to form isomaltooligosaccharides. The enzyme also acted, albeit inefficiently, on p-nitrophenyl α-D-glucopyranoside, and p-nitrophenyl α-isomaltoside was the main product of the reaction. In contrast, Fjoh_4430 did not act on trehalose, kojibiose, nigerose, maltose, maltotriose, or soluble starch. The optimal pH and temperature were pH 6.0 and 60 °C, respectively. Our results indicate that Fjoh_4430 is a novel GH31 dextranase with high transglucosylation activity.

Two Novel Glycoside Hydrolases Responsible for the Catabolism of Cyclobis-(1→6)-α-nigerosyl

The actinobacterium Kribbella flavida NBRC 14399(T) produces cyclobis-(1→6)-α-nigerosyl (CNN), a cyclic glucotetraose with alternate α-(1→6)- and α-(1→3)-glucosidic linkages, from starch in the culture medium. We identified gene clusters associated with the production and intracellular catabolism of CNN in the K. flavida genome. One cluster encodes 6-α-glucosyltransferase and 3-α-isomaltosyltransferase, which are known to coproduce CNN from starch. The other cluster contains four genes annotated as a transcriptional regulator, sugar transporter, glycoside hydrolase family (GH) 31 protein (Kfla1895), and GH15 protein (Kfla1896). Kfla1895 hydrolyzed the α-(1→3)-glucosidic linkages of CNN and produced isomaltose via a possible linear tetrasaccharide. The initial rate of hydrolysis of CNN (11.6 s(-1)) was much higher than that of panose (0.242 s(-1)), and hydrolysis of isomaltotriose and nigerose was extremely low. Because Kfla1895 has a strong preference for the α-(1→3)-isomaltosyl moiety and effectively hydrolyzes the α-(1→3)-glucosidic linkage, it should be termed 1,3-α-isomaltosidase. Kfla1896 effectively hydrolyzed isomaltose with liberation of β-glucose, but displayed low or no activity toward CNN and the general GH15 enzyme substrates such as maltose, soluble starch, or dextran. The kcat/Km for isomaltose (4.81 ± 0.18 s(-1) mm(-1)) was 6.9- and 19-fold higher than those for panose and isomaltotriose, respectively. These results indicate that Kfla1896 is a new GH15 enzyme with high substrate specificity for isomaltose, suggesting the enzyme should be designated an isomaltose glucohydrolase. This is the first report to identify a starch-utilization pathway that proceeds via CNN.

Draft Genome Sequence of Sporosarcina globispora W 25T (DSM 4), a Psychrophilic Bacterium Isolated from Soil and River Water

Sporosarcina globispora W 25^T (DSM 4) is a Gram-positive, round-spore-forming, and psychrophilic bacterium. Here, we report the 5.66-Mb genome sequence of S. globispora W 25^T, which will accelerate the application of this psychrophile and provide useful information for genomic taxonomy and phylogenomics of Bacillus-like bacteria.

Solvent- and phase-controlled photochirogenesis. Enantiodifferentiating photoisomerization of (Z)-cyclooctene sensitized by cyclic nigerosylnigerose-based nanosponges crosslinked by pyromellitate

The enantioselectivity of the (E)-cyclooctene produced critically depended on the solvent and also on the phase evolved, maximizing at the flowing/rigid gel border.

Improved yields of cyclic nigerosylnigerose from starch by pretreatment with a thermostable branching enzyme

Cyclic nigerosylnigerose (CNN) is produced enzymatically from starch by the combined action of 6-alpha-glucosyltransferase and 3-alpha-isomaltosyltransferase. In our previous study, alpha-1,6-branching chains found in the structure of amylopectin and glycogen were shown to be favorable for CNN formation by the two enzymes. Therefore, we examined whether the introduction of alpha-1,6-branch points into starch using the action of branching enzyme (BE) could improve the yield of CNN from starch. Thermostable BE from Geobacillus stearothermophilus TC-91 was prepared as a purified recombinant protein. Pretreatment of amylose with BE considerably increased the CNN yield from 5% to 38%. When BE acted on tapioca starch, the CNN yield was elevated from 47% to 60%. Conversely, BE treatment of waxy corn starch containing very little amylose resulted in a negligible increase in CNN yield. In addition, BE exerted a beneficial effect when starch with a lower degree of hydrolysis was used as a substrate. The present results indicate that the addition of alpha-1,6-glucosidic linkages to starch using BE is an effective strategy to improve the yield of CNN from starch.

An enzymatically produced novel cyclomaltopentaose cyclized from amylose by an α-(1→6)-linkage, 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→}

A bacterial strain AM7, isolated from soil and identified as Bacillus circulans, produced two kinds of novel cyclic oligosaccharides. The cyclic oligosaccharides were produced from amylose using a culture supernatant of the strain as the enzyme preparation. The major product was a cyclomaltopentaose cyclized by an alpha-(1-->6)-linkage, cyclo-{-->6)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->}. The other minor product was cyclomaltohexaose cyclized by an alpha-(1-->6)-linkage, cyclo-{-->6)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->}. We propose the names isocyclomaltopentaose (ICG5) and isocyclomaltohexaose (ICG6) for these novel cyclic maltooligosaccharides having one alpha-(1-->6)-linkage. ICG5 was digested by alpha-amylase derived from Aspergillus oryzae, cyclomaltodextrin glucanotransferase (CGTase) from Bacillus stearothermophilus, and maltogenic alpha-amylase. On the other hand, ICG6 was digested by CGTase from B. stearothermophilus and B. circulans, and maltogenic alpha-amylase. This is the first report of enzymatically produced cyclomaltopentaose and cyclomaltohexaose, which have an alpha-(1-->6)-linkage in their molecules.

Purification, characterization, and gene cloning of a novel maltosyltransferase from an Arthrobacter globiformis strain that produces an alternating alpha-1,4- and alpha-1,6-cyclic tetrasaccharide from starch

A glycosyltransferase, involved in the synthesis of cyclic maltosylmaltose [CMM; cyclo-{-->6)-alpha-D-Glcp(1-->4)-alpha-D-Glcp(1-->6)-alpha-D-Glcp(1-->4)-alpha-D-Glcp(1-->}] from starch, was purified to homogeneity from the culture supernatant of Arthrobacter globiformis M6. The CMM-forming enzyme had a molecular mass of 71.7 kDa and a pI of 3.6. The enzyme was most active at pH 6.0 and 50 degrees C and was stable from pH 5.0 to 9.0 and up to 30 degrees C. The addition of 1 mM Ca2+ enhanced the thermal stability of the enzyme up to 45 degrees C. The enzyme acted on maltooligosaccharides that have degrees of polymerization of > or =3, amylose, and soluble starch to produce CMM but failed to act on cyclomaltodextrins, pullulan, and dextran. The mechanism for the synthesis of CMM from maltotetraose was determined as follows: (i) maltotetraose + maltotetraose --> 6(4)-O-alpha-maltosyl-maltotetraose + maltose and (ii) 6(4)-O-alpha-maltosyl-maltotetraose --> CMM + maltose. Thus, the CMM-forming enzyme was found to be a novel maltosyltransferase (6MT) catalyzing both intermolecular and intramolecular alpha-1,6-maltosyl transfer reactions. The gene for 6MT, designated cmmA, was isolated from a genomic library of A. globiformis M6. The cmmA gene consisted of 1,872 bp encoding a signal peptide of 40 amino acids and a mature protein of 583 amino acids with a calculated molecular mass of 64,637. The deduced amino acid sequence showed similarities to alpha-amylase and cyclomaltodextrin glucanotransferase. The four conserved regions common in the alpha-amylase family enzymes were also found in 6MT, indicating that 6MT should be assigned to this family.

An enzymatically produced novel cyclic tetrasaccharide, cyclo-{-->6)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->} (cyclic maltosyl-(1-->6)-maltose), from starch

A bacterial strain M6, isolated from soil and identified as Arthrobacter globiformis, produced a novel nonreducing oligosaccharide. The nonreducing oligosaccharide was produced from starch using a culture supernatant of the strain as enzyme preparation. The oligosaccharide was purified as a crystal preparation after alkaline treatment and deionization of the reaction mixture. The structure of the oligosaccharide was determined by methylation analysis, mass spectrometry, and (1)H and (13)C NMR spectroscopy, and it was demonstrated that the oligosaccharide had a cyclic structure consisting of four glucose residues joined by alternate alpha-(1-->4)- and alpha-(1-->6)-linkages. The cyclic tetrasaccharide, cyclo-{-->6)-alpha-D-Glcp(1-->4)-alpha-D-Glcp(1-->6)-alpha-D-Glcp(1-->4)-alpha-D-Glcp(1-->}, was found to be a novel oligosaccharide, and was tentatively called cyclic maltosyl-maltose (CMM). CMM was not hydrolyzed by various amylases, such as alpha-amylase, beta-amylase, glucoamylase, isoamylase, pullulanase, maltogenic alpha-amylase, and alpha-glucosidase, but hydrolyzed by isomalto-dextranase to give rise to isomaltose. This is the first report of the cyclic tetrasaccharide, which has alternate alpha-(1-->4)- and alpha-(1-->6)-glucosidic linkages.

Enzymatic synthesis of a novel cyclic pentasaccharide consisting of α-d-glucopyranose with 6-α-glucosyltransferase and 3-α-isomaltosyltransferase

A novel cyclic pentasaccharide (CPS) and a branched cyclic pentasaccharide (6G-CPS) consisting of d-glucopyranose were synthesized with 6-alpha-glucosyltransferase (6GT) and 3-alpha-isomaltosyltransferase (IMT) from Bacillus globisporus N75. The structure of CPS was cyclo-[-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->]. The other, 6G-CPS, had the structure cyclo-[-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-[alpha-D-Glcp-(1-->6)]-alpha-D-Glcp-(1-->4)-alpha-D-Glcp-(1-->]. The formation of CPS was presumed to occur after the following four successive reactions: a 6-glucosyltransfer reaction with 6GT, a 4-glucosyltransfer reaction with 6GT, a 3-isomaltosyltransfer reaction with IMT, and a cyclization reaction with IMT.

Enzymatic synthesis of a 2-O-α-d-glucopyranosyl cyclic tetrasaccharide by kojibiose phosphorylase

The glucosyl transfer reaction of kojibiose phosphorylase (KPase) from Thermoanaerobacter brockii ATCC35047 was examined using cyclo-{-->6)-alpha-d-Glcp-(1-->3)-alpha-d-Glcp-(1-->6)-alpha-d-Glcp-(1-->3)-alpha-d-Glcp-(1-->} (CTS) as an acceptor. KPase produced four transfer products, saccharides 1-4. The structure of a major product, saccharide 4, was 2-O-alpha-d-glucopyranosyl-CTS, cyclo-{-->6)-alpha-d-Glcp-(1-->3)-alpha-d-Glcp-(1-->6)-[alpha-d-Glcp-(1-->2)]-alpha-d-Glcp-(1-->3)-alpha-d-Glcp-(1-->}. The other transfer products, saccharides 1-3, were 2-O-alpha-kojibiosyl-, 2-O-alpha-kojitriosyl-, and 2-O-alpha-kojitetraosyl-CTS, respectively. These results showed that KPase transferred a glucose residue to the C-2 position at the ring glucose residue of CTS. This enzyme also catalyzed the chain-extending reaction of the side chain of 2-O-alpha-d-glycopyranosyl-CTS.

Enzymatic synthesis of a β-d-galactopyranosyl cyclic tetrasaccharide by β-galactosidases

The galactosyl transfer reaction to cyclo-[-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->] (CTS) was examined using lactose as a donor and beta-galactosidases from Aspergillus oryzae and Bacillus circulans. The A. oryzae beta-galactosidase produced three galactosyl derivatives of CTS. The main galactosyl derivative produced by the A. oryzae enzyme was identified as 6-O-beta-D-galactopyranosyl-CTS, cyclo-[-->6)-alpha-D-Glcp-(1-->3)-[beta-D-Galp-(1-->6)]-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->]. The B. circulans beta-galactosidase also synthesized three galactosyl-transfer products to CTS. The structure of main transgalactosylation product was 3-O-beta-D-galactopyranosyl-CTS, cyclo-[-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-[beta-D-Galp-(1-->3)]-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->]. These results showed that beta-galactosidase transferred galactose directly to the ring glucose residue of CTS.

Enzymatic synthesis of glycosyl cyclic tetrasaccharide with 6-α-glucosyltransferase and 3-α-isomaltosyltransferase

Transglycosylation reactions to cyclic tetrasaccharide (CTS, cyclo[-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->]) and its derivatives were investigated. An enzyme, 6-alpha-glucosyltransferase, which is involved in CTS synthesis from starch, from Bacillus globisporus C11 produced 4-O-alpha-glucosyl-CTS (4G-CTS) from a mixture containing CTS and maltopentaose. Another enzyme, 3-alpha-isomaltosyltransferase, synthesized 3-O-alpha-isomaltosyl-CTS (3IM-CTS) from CTS and panose. Two novel branched CTSs, 3-O-alpha-isomaltosyl-4-O-alpha-glucosyl-CTS (3IM-4G-CTS) and 3-O-alpha-isomaltosyl-(4-O-alpha-glucosyl)-CTS [3IM-(4G)-CTS], were synthesized by the isomaltosyl transfer of IMT into 4G-CTS. IMT also produced a novel saccharide, 3-O-alpha-isomaltosyl-3-O-alpha-isomaltosyl-CTS (3IM-3IM-CTS) from 3IM-CTS. It was confirmed that the oligosaccharides, including 4G-CTS, 3IM-CTS, 3IM-4G-CTS, 3IM-(4G)-CTS and 3IM-3IM-CTS, remaining in the reaction mixture during the production of CTS from starch were the transfer products of 6GT and IMT into CTS.