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.

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.

A novel dextrin produced by the enzymatic reaction of 6-α-glucosyltransferase. â ¡. Practical advantages of the novel dextrin as a food modifier.

High-molecular-weight dextrin (WS-1000) was produced from waxy corn starch and enzymatically modified to link glucose by α-1,6 glycosidic bond at the terminal point of the glucose chain, forming MWS-1000. In this study, the physical properties of MWS-1000 were characterized, and the advantages of its use as a food modifier were described. From rheological and calorimetric studies, it was found that MWS-1000 does not undergo retrogradation, but it does not prevent the retrogradation of WS-1000, suggesting that they have no intermolecular interaction in solution. Investigation of the effect of MWS-1000 on the viscoelasticity of gelatinized wheat starch showed that in the linear viscoelastic region, storage modulus decreased and tan δ increased with increase in replaced MWS-1000 content. In addition, it was confirmed that gelatinized starch containing MWS-1000 showed viscoelastic behavior similar to that of commercially available custard cream.

Structural and mutational analysis of substrate recognition in kojibiose phosphorylase.

Glycoside hydrolase (GH) family 65 contains phosphorylases acting on maltose (Glc-α1,4-Glc), kojibiose (Glc-α1,2-Glc), trehalose (Glc-α1,α1,-Glc), and nigerose (Glc-α1,3-Glc). These phosphorylases can efficiently catalyze the reverse reactions with high specificities, and thus can be applied to the practical synthesis of α-glucosyl oligosaccharides. Here, we determined the crystal structures of kojibiose phosphorylase from Caldicellulosiruptor saccharolyticus in complex with glucose and phosphate and in complex with kojibiose and sulfate, providing the first structural insights into the substrate recognition of a glycoside hydrolase family 65 enzyme. The loop 3 region comprising the active site of kojibiose phosphorylase is significantly longer than the active sites of other enzymes, and three residues around this loop, Trp391, Glu392, and Thr417, recognize kojibiose. Various mutants mimicking the residue conservation patterns of other phosphorylases were constructed by mutation at these three residues. Activity measurements of the mutants against four substrates indicated that Trp391 and Glu392, especially the latter, are required for the kojibiose activity.

Protein N-myristoylation is required for cellular morphological changes induced by two formin family proteins, FMNL2 and FMNL3.

The subcellular localization of 13 recently identified N-myristoylated proteins and the effects of overexpression of these proteins on cellular morphology were examined with the aim of understanding the physiological roles of the protein N-myristoylation that occurs on these proteins. Immunofluorescence staining of HEK293T cells transfected with cDNAs coding for the proteins revealed that most of them were associated with the plasma membrane or the membranes of intracellular compartments, and did not affect cellular morphology. However, two proteins, formin-like2 (FMNL2) and formin-like3 (FMNL3), both of them are members of the formin family of proteins, were associated mainly with the plasma membrane and induced significant cellular morphological changes. Inhibition of protein N-myristoylation by replacement of Gly2 with Ala or by the use of N-myristoylation inhibitor significantly inhibited membrane localization and the induction of cellular morphological changes, indicating that protein N-myristoylation plays critical roles in the cellular morphological changes induced by FMNL2 and FMNL3.

Purification and characterization of highly branched α-glucan-producing enzymes from Paenibacillus sp. PP710.

Highly branched α-glucan molecules exhibit low digestibility for α-amylase and glucoamylase, and abundant in α-(1→3)-, α-(1→6)-glucosidic linkages and α-(1→6)-linked branch points where another glucosyl chain is initiated through an α-(1→3)-linkage. From a culture supernatant of Paenibacillus sp. PP710, we purified α-glucosidase (AGL) and α-amylase (AMY), which were involved in the production of highly branched α-glucan from maltodextrin. AGL catalyzed the transglucosylation reaction of a glucosyl residue to a nonreducing-end glucosyl residue by α-1,6-, α-1,4-, and α-1,3-linkages. AMY catalyzed the hydrolysis of the α-1,4-linkage and the intermolecular or intramolecular transfer of maltooligosaccharide like cyclodextrin glucanotransferase (CGTase). It also catalyzed the transfer of an α-1,4-glucosyl chain to a C3- or C4-hydroxyl group in the α-1,4- or α-1,6-linked nonreducing-end residue or the α-1,6-linked residue located in the other chains. Hence AMY was regarded as a novel enzyme. We think that the mechanism of formation of highly branched α-glucan from maltodextrin is as follows: α-1,6- and α-1,3-linked residues are generated by the transglucosylation of AGL at the nonreducing ends of glucosyl chains. Then AMY catalyzes the transfer of α-1,4-chains to C3- or C4-hydroxyl groups in the α-1,4- or α-1,6-linked residues generated by AGL. Thus the concerted reactions of both AGL and AMY are necessary to produce the highly branched α-glucan from maltodextrin.

Enzymatic properties of recombinant kojibiose phosphorylase from Caldicellulosiruptor saccharolyticus ATCC43494.

One kojibiose phoshorylase (KP) homolog gene was cloned from Caldicellulosiruptor saccharolyticus ATCC43494. Recombinant KP from C. saccharolyticus (Cs-KP) expressed in Escherichia coli showed highest activity at pH 6.0 at 85 °C, and was stable from pH 3.5 to 10.0 and up to 85 °C for phosphorolysis. Cs-KP showed higher productivity of kojioligosaccharides of DP ≧ 4 than KP from Thermoanaerobacter brockii ATCC35047.

Structure of a novel highly branched alpha-glucan enzymatically produced from maltodextrin.

The bacterial strain PP710, isolated from soil and identified as Paenibacillus species, produced a low-digestibility alpha-glucan containing a large amylase-resistant portion. This alpha-glucan was obtained in high yields from maltodextrin (dextrose equivalent 3) by using the condensed culture supernatant of the strain as the enzyme preparation. The water-soluble dietary fiber content of the low-digestibility alpha-glucan was 80.2%, and showed resistance to a rat intestinal enzyme preparation. The alpha-glucan was found to be a novel highly branched alpha-glucan by acid hydrolysis, NMR analysis, gel permeation chromatography, methylation analysis, and enzymatic digestion.

Construction and characterization of chimeric enzymes of kojibiose phosphorylase and trehalose phosphorylase from Thermoanaerobacter brockii.

Chimeric phosphorylases were constructed of the kojibiose phosphorylase (KP) gene and the trehalose phosphorylase (TP) gene from Thermoanaerobacter brockii. Four chimeric enzymes had KP activity, and another had TP activity. Chimera V-III showed not TP, but KP activity, although only 125 amino acid residues in 785 residues of chimera V-III were from that of KP. Chimera V-III had 1% of the specific activity of the wild-type KP. Furthermore, the temperature profile and kinetic parameters of chimera V-III were remarkably changed as compared to those of the wild-type KP. The results of the molecular mass of chimera V-III using GPC (76,000 Da) strongly suggested that the chimera V-III protein exists as a monomer in solution, whereas wild-type KP and TP are hexamer and dimer structures, respectively. The result of the substrate specificity for phosphorolysis was that the chimera acted on nigerose, sophorose and laminaribiose, in addition to kojibiose. Furthermore, chimera V-III was also able to act on sophorose and laminaribiose in the absence of inorganic phosphate, and produced two trisaccharides, beta-D-glucosyl-(1-->6)-laminaribiose and laminaritriose, from laminaribiose.

Acceptor recognition of kojibiose phosphorylase from Thermoanaerobacter brockii: syntheses of glycosyl glycerol and myo-inositol.

The glucosyl transfer reaction of kojibiose phosphorylase (KP; EC 2.4.1.230) was examined using glycerol or myo-inositol as an acceptor. In the case of glycerol, KP produced two main transfer products: saccharides A and B. The structure of saccharide A was O-alpha-D-glucopyranosyl-(1-->1)-glycerol and that of saccharide B was O-alpha-D-glucopyranosyl-(1-->2)-O-alpha-D-glucopyranosyl-(1-->1)-glycerol. These results show that KP transferred a glucose residue to the hydroxyl group at position 1 of glycerol. On the other hand, when myo-inositol was used as an acceptor, KP produced four transfer products: saccharides 1-4. The structures of saccharides 1 and 2 were O-alpha-D-glucopyranosyl-(1-->1)- and O-alpha-D-glucopyranosyl-(1-->5)-myo-inositol, respectively; those of saccharides 3 and 4 were O-alpha-D-glucopyranosyl-(1-->2)-O-alpha-D-glucopyranosyl-(1-->1)- and O-alpha-D-glucopyranosyl-(1-->2)-O-alpha-D-glucopyranosyl-(1-->5)-myo-inositol, respectively. KP transferred a glucose residue to the hydroxyl group at position 1 or 5 of myo-inositol. On the basis of the structures of their glucosyl transfer products, glycerol and myo-inositol were found to have a common structure with three hydroxyl groups corresponding to the hydroxyl group of the glucose molecule at positions 2, 3 and 4. The conformation of these three hydroxyl groups in the structure is equatorial. This structure is the substrate recognition site of KP. It has been suggested that KP strictly recognizes the structures of glycerol and myo-inositol, and catalyzes the transfer reaction of a glucose residue to the hydroxyl group at position 1 in glycerol, and at position 1 or 5 in myo-inositol, corresponding to position 2 in glucose.

Enhancement of thermostability of kojibiose phosphorylase from Thermoanaerobacter brockii ATCC35047 by random mutagenesis.

Random mutation by error-prone PCR was introduced into kojibiose phosphorylase from Thermoanaerobacter brockii ATCC35047. One thermostable mutant enzyme, D513N, was isolated. The D513N mutant enzyme showed an optimum temperature of 67.5-70 degrees C (the wild type, 65 degrees C), and thermostability up to 67.5 degrees C (the wild type, up to 60 degrees C). The half-lives of D513N were estimated to be 135 h at 60 degrees C, 110 min at 70 degrees C and 6 min at 75 degrees C, respectively. They were about 1.6-fold, 7-fold and 6-fold longer than those of the wild-type enzyme, respectively.

Hyper expression of kojibiose phosphorylase gene and trehalose phosphorylase gene from Thermoanaerobacter brockii ATCC35047 in Bacillus subtilis and selaginose synthesis utilizing two phosphorylases.

The kojibiose phosphorylase (KP) gene and trehalose phosphorylase (TP) gene from Thermoanaerobacter brockii ATCC35047 were intracellularly hyper-expressed under the control of the Bacillus amyloliquefaciens alpha-amylase promoter in Bacillus subtilis. The production yields were estimated to be 2.1 g of KP and 4.9 g of TP per liter of medium. Selaginose, non-reducing trisaccharide, was synthesized from trehalose utilizing the recombinant KP and TP from B. subtilis. Selaginose was not hydrolyzed by salivary amylase, artificial gastric juice, pancreatic amylase, or small intestinal enzymes.

Cloning and sequencing of kojibiose phosphorylase gene from Thermoanaerobacter brockii ATCC35047.

A gene encoding kojibiose phosphorylase was cloned from Thermoanaerobacter brockii ATCC35047. The kojP gene encodes a polypeptide of 775 amino acid residues. The deduced amino acid sequence was homologous to those of trehalose phosphorylase from T. brockii and maltose phosphorylases from Bacillus sp. and Lactobacillus brevis with 35%, 29% and 28% identities, respectively. Kojibiose phosphorylase was efficiently overexpressed in Escherichia coli JM109. The DNA sequence of 3956 bp analyzed in this study contains three open reading frames (ORFs) downstream of kojP. The four ORFs, kojP, kojE, kojF, and kojG, form a gene cluster. The amino acid sequences deduced from kojE and kojF are similar to those of the N-terminal and C-terminal regions of a sugar-binding periplasmic protein from Thermoanaerobacter tengcongensis MB4. Furthermore, the amino acid sequence deduced from kojG is similar to that of a permease of the ABC-type sugar transport systems from T. tengcongensis MB4. Each of three amino acid substitutions, D362N, K614Q and E642Q, caused a complete loss of kojibiose phosphorylase activity. These results suggest that D362, K614 and E642 play an important role in catalysis. Another mutation, D459N, increased K(m) values for kojibiose (7-fold that for the wild type), beta-G1P (11-fold) and glucose (7-fold), whereas K(m) for inorganic phosphate was minimally affected by this mutation, suggesting that D459 may be involved in the binding to saccharides.

Cloning and sequencing of the genes encoding cyclic tetrasaccharide-synthesizing enzymes from Bacillus globisporus C11.

The genes for isomaltosyltransferase (CtsY) and 6-glucosyltransferase (CtsZ), involved in synthesis of a cyclic tetrasaccharide from alpha-glucan, have been cloned from the genome of Bacillus globisporus C11. The amino-acid sequence deduced from the ctsY gene is composed of 1093 residues having a signal sequence of 29 residues in its N-terminus. The ctsZ gene encodes a protein consisting of 1284 residues with a signal sequence of 35 residues. Both of the gene products show similarities to alpha-glucosidases belonging to glycoside hydrolase family 31 and conserve two aspartic acids corresponding to the putative catalytic residues of these enzymes. The two genes are linked together, forming ctsYZ. The DNA sequence of 16,515 bp analyzed in this study contains four open reading frames (ORFs) upstream of ctsYZ and one ORF downstream. The first six ORFs, including ctsYZ, form a gene cluster, ctsUVWXYZ. The amino-acid sequences deduced from ctsUV are similar in to a sequence permease and a sugar-binding protein for the sugar transport system from Thermococcus sp. B1001. The third ctsW encodes a protein similar to CtsY, suggested to be another isomaltosyltransferase preferring panose to high-molecular-mass substrates.