Substrate Specificity of Mutanase of Paenibacillus humicus from Fermented Food

概要

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Mutanase, α-1,3-glucanase, catalyzes the hydrolysis of α-1,3-glucans, and is expected for preventive medicine, since the enzyme has an ability for hydrolysis of insoluble glucans that are synthesized by cariogenic streptococci. We previously isolated the mutanase of Paenibacillus humicus from fermented soybeans. In the present study, Paenibacillus mutanase was characterized with respect to its hydrolysis efficiency of insoluble glucans, and mode of action on α-1,3-glucan oligosaccharides. Recombinant mutanase hydrolyzed insoluble glucans of cariogenic streptococci efficiently. Enzymatic reaction on hydrolysis of mutan, we assumed that the enzyme cleaved the substrate in an endo-catalytic manner. The hydrolysis of α-1,3-glucan oligosaccharides gave α-1,3-glucan tetrasaccharide as the primary final product but α-1,3-glucan pentasaccharide was the minimal size of substrate on which the enzyme catalyzed. Mutanase hydrolyzed borohydride-treated α-1,3-glucan hexasaccharide into the tetrasaccharide and the disaccharide-alditol. Thus, the enzyme cleaved the fourth α-1,3-glucosidic linkage from the non-reducing end of the oligosaccharides. Mutanase in fermented food should be capable of removing streptococcal insoluble glucans that can induce dental caries.