Kazuhisa Mukai

Purification and characterization of glucosyltransferase and glucanotransferase involved in the production of cyclic tetrasaccharide in Bacillus globisporus C11.

Glucosyltransferase and glucanotransferase involved in the production of cyclic tetrasaccharide (CTS; cyclo {→6}-α-D-glucopyranosyl-(1→3)-α-D-glucopyranosyl-(1→6)-α-D-glucopyranosyl-(1→3)-α-D-glucopyranosyl- (1→)) from α-1,4-glucan were purified from Bacillus globisporus C11. The former was a 1,6-α-glucosyltransferase (6GT) catalyzing the α-1,6-transglucosylation of one glucosyl residue to the nonreducing end of maltooligosaccharides (MOS) to produce α-isomaltosyl-MOS from MOS. The latter was an isomaltosyl transferase (IMT) catalyzing α-1,3-, α-1,4-, and α,β-1,1-intermolecular transglycosylation of isomaltosyl residues. When IMT catalyzed α-1,3-transglycosylation, α-isomaltosyl-(1→3)-α-isomaltosyl-MOS was produced from α-isomaltosyl-MOS. In addition, IMT catalyzed cyclization, and produced CTS from α-isomaltosyl-(1→3)-α-isomaltosyl-MOS by intramolecular transglycosylation. Therefore, the mechanism of CTS synthesis from MOS by the two enzymes seemed to follow three steps: 1) MOS→α-isomaltosyl-MOS (by 6GT), 2) α-isomaltosyl-MOS→α-isomaltosyl-(1→3)-α- isomaltosyl-MOS (by IMT), and 3) α-isomaltosyl-(1→3)-α-isomaltosyl-MOS→CTS +MOS (by IMT). The molecular mass of 6GT was estimated to be 137 kDa by SDS-PAGE. The optimum pH and temperature for 6GT were pH 6.0 and 45°C, respectively. This enzyme was stable at from pH 5.5 to 10 and on being heated to 40°C for 60 min. 6GT was strongly activated and stabilized by various divalent cations. The molecular mass of IMT was estimated to be 102 kDa by SDS-PAGE. The optimum pH and temperature for IMT were pH 6.0 and 50°C, respectively. This enzyme was stable at from pH 4.5 to 9.0 and on being heated to 40°C for 60 min. Divalent cations had no effect on the stability or activity of this enzyme.

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.

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.

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

ABSTRACT A glycosyltransferase, involved in the synthesis of cyclic maltosylmaltose [CMM; cyclo-{→6)-α-d-Glcp(1→4)-α-d-Glcp(1→6)-α-d-Glcp(1→4)-α-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°C and was stable from pH 5.0 to 9.0 and up to 30°C. The addition of 1 mM Ca2+ enhanced the thermal stability of the enzyme up to 45°C. The enzyme acted on maltooligosaccharides that have degrees of polymerization of ≥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 → 64-O-α-maltosyl-maltotetraose + maltose and (ii) 64-O-α-maltosyl-maltotetraose → CMM + maltose. Thus, the CMM-forming enzyme was found to be a novel maltosyltransferase (6MT) catalyzing both intermolecular and intramolecular α-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 α-amylase and cyclomaltodextrin glucanotransferase. The four conserved regions common in the α-amylase family enzymes were also found in 6MT, indicating that 6MT should be assigned to this family.

Cyclic Tetrasaccharide-Synthesizing Enzymes from Arthrobacter globiformis A19

A bacterial strain Arthrobacter globiformis A19 producing cyclic tetrasaccharide (CTS) was isolated from soil. The enzymes, 6-α-glucosyltransferase (6GT) and 3-α-isomaltosyltransferase (IMT), involved in the synthesis of CTS were purified to homogeneity. The molecular and enzymatic properties of IMT from A. globiformis were similar to those of enzymes from Bacillus globisporus C11 and N75. Arthrobacter 6GT had a smaller molecular mass of 108 kDa and a higher optimum pH of 8.4 than the enzymes from strains of B. globisporus. The genes for IMT (ctsY) and 6GT (ctsZ) were cloned from the genome of A. globiformis A19. The two genes linked together in tandem and formed a gene cluster, ctsYZ. Both of the gene products showed similarities to α-glucosidases belonging to glycoside hydrolase family 31, and conserved two aspartic acids corresponding to the putative catalytic residues of the family enzymes. The enzymatic system for the production of CTS consisting of 6GT and IMT might be widespread among bacteria.

A Novel Glucanotransferase from a Bacillus circulans Strain That Produces a Cyclomaltopentaose Cyclized by an α-1,6-Linkage

A novel glucanotransferase, 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 purified to homogeneity from the culture supernatant of Bacillus circulans AM7. The pI was estimated to be 7.5. The molecular mass of the enzyme was estimated to be 184 kDa by gel filtration and 106 kDa by SDS–PAGE. These results suggest that the enzyme forms a dimer structure. It was most active at pH 4.5 to 8.0 at 50 °C, and stable from pH 4.5 to 9.0 at up to 35 °C. The addition of 1 mM Ca2+ enhanced the thermal stability of the enzyme up to 40 °C. It acted on maltooligosaccharides that have degrees of polymerization of 3 or more, amylose, and soluble starch, to produce ICG5 by an intramolecular α-1,6-glycosyl transfer reaction. It also catalyzed the transfer of part of a linear oligosaccharide to another oligosaccharide by an intermolecular α-1,4-glycosyl transfer reaction. Thus the ICG5-forming enzyme was found to be a novel glucanotransferase. We propose isocyclomaltooligosaccharide glucanotransferase (IGTase) as the trivial name of this enzyme.