• Journal of Microbiology and Biotechnology
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• v.31 no.1
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• pp.43-50
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• 2021

A newly cloned 4-α-glucanotransferase (αGT) from Deinococcus geothermalis and two typical bacterial αGTs from Thermus scotoductus and Escherichia coli (MalQ) were investigated. Among 4 types of catalysis, the cyclization activity of αGTs that produces cycloamylose (CA), a valuable carbohydrate making inclusion complexes, was intensively studied. The new αGT, DgαGT, showed close protein sequence to the αGT from T. scotoductus (TsαGT). MalQ was clearly separated from the other two αGTs in the phylogenetic and the conserved regions analyses. The reaction velocities of disproportionation, cyclization, coupling, and hydrolysis of three αGTs were determined. Intriguingly, MalQ exhibited more than 100-fold lower cyclization activity than the others. To lesser extent, the disproportionation activity of MalQ was relatively low. DgαGT and TsαGT showed similar kinetics results, but TsαGT had nearly 10-fold lower hydrolysis activity than DgαGT. Due to the very low cyclizing activity of MalQ, DgαGT and TsαGT were selected for further analyses. When amylose was treated with DgαGT or TsαGT, CA with a broad DP range was generated immediately. The DP distribution of CA had a bimodal shape (DP 7 and 27 as peaks) for the both enzymes, but larger DPs of CA quickly decreased in the DgαGT. Cyclomaltopentaose, a rare cyclic sugar, was produced at early reaction stage and accumulated as the reactions went on in the both enzymes, but the increase was more profound in the TsαGT. Taken together, we clearly demonstrated the catalytic differences between αGT groups from thermophilic and pathogenic bacteria that and showed that αGTs play different roles depending on their lifestyle.

• Journal of Microbiology and Biotechnology
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• v.29 no.12
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• pp.1938-1946
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• 2019

Isomaltooligosaccharides (IMOs) have good prebiotic effects, and long IMOs (LIMOs) with a degree of polymerization (DP) of 7 or above show improved effects. However, they are not yet commercially available, and require costly enzymes and processes for production. The N-terminal region of the thermostable Thermoanaerobacter thermocopriae cycloisomaltooligosaccharide glucanotransferase (TtCITase) shows cyclic isomaltooligosaccharide (CI)-producing activity owing to a catalytic domain of glycoside hydrolase (GH) family 66 and carbohydrate-binding module (CBM) 35. In the present study, we elucidated the activity of the C-terminal region of TtCITase (TtCITase-C; Met740-Phe1,559), including a CBM35-like region and the GH family 15 domain. The domain was successfully cloned, expressed, and purified as a single protein with a molecular mass of 115 kDa. TtCITase-C exhibited optimal activity at 40℃ and pH 5.5, and retained 100% activity at pH 5.5 after 18-h incubation. TtCITase-C synthesized α-1,6 glucosyl products with over seven degrees of polymerization (DP) by an α-1,6 glucosyl transfer reaction from maltopentaose, isomaltopentaose, or commercialized maltodextrins as substrates. These results indicate that TtCITase-C could be used for the production of α-1,6 glucosyl oligosaccharides with over DP7 (LIMOs) in a more cost-effective manner, without requiring cyclodextran.