earticle

영어

Endo-dextranases (EC 3.2.1.11), which hydrolyze α-1,6-glucosidic linkage of dextran at random, are classified into glycoside hydrolase (GH) family 49 and 66 based on the amino-acid sequence similarity. Cyclodextran glucanotransferase (CITase) is also classified into GH family 66. CITase is an interesting enzyme that catalyzes the conversion of dextran to cycloisomaltodextrins (CIs) by intramolecular transglycosylation. CI is of importance by preventing the dental caries since it strongly inhibits insoluble glucan formation by mutansucrase. Although endo-dextranase and CITase belong to GH family 66, their products from dextran are largely different in structure, such as cyclic- or linear-isomaltooligosaccharides, respectively. In this study, it was found that Paenibacillus sp. dextranase, a member of GH family 66, showed both of endo-dextranase activity and CITase activity, allowing us to classify the GH family 66 enzymes to three groups for the first time. These results may contribute to understand of the relationship between the structure and function of GH family 66 enzymes. Recently, several other Bacillus and Paenibacillus CI-producing bacterial strains were found and the larger CI molecules up to CI-17 were isolated from their culture supernatants. In order to produce CIs for commercial scale, a high dextran producing strain Leuconostoc sp. S-51 was obtained and the B. circulans T-3040 strain was mutated to produce CITase with about 110 times the activity of the wild type strain. All CIs well inhibit glucosyltransferase of mutans streptococci and especially CI-10 and larger molecules of CIs have strong inclusion-forming activity such as preservation of Victoria blue color or solubilization of isoflavones. There have been no problems arising from safety tests of CIs inratsand humans. The fact that CIs are present in brown sugar is indicative if their safety as natural oligosaccharides.