One of the enzymes belonging to GH13 is dextran glucosidase (DGase). DGase is characterized by its inclination to act on long-chain carbohydrates consisting of α-1,6-glucoside linkage, and in the nature, it is an important enzyme involved in the dextran metabolism (dextran is a polysaccharide consisting of α-1,6-glucoside linkage as the main chain). We discovered a structure factor connected with this characteristic feature of DGase. We further figured out its three-dimensinal structure and, based on the information, created a useful enzyme that synthesize oligosaccharides at a high yield rate. Apart from these studies, we have also been studying honeybee α-glucosidase isoenzymes involved in the production of honey.

Among GH15, we focus on dextran dextrinase (DDase). DDase is a unique enzyme that produces dextran by acting on dextrin (maltooligosaccharide) comprising of α-1,4-glucoside linkage. Dextran is highly in demand in the academic, medical, pharmaceutical, food, and other areas, and DDase enables the high-yield production of dextran. At our lab, we conducted foundation studies on the production of dextran and, for the first time in the world, succeeded in producing megalosaccharide (a form of carbohydrate composed of 10 – 200 glucoses), which is lower molecular mass than dextran. We discovered new function of megalosaccharide that increases systemic absorption of flavonoid, which is reported for its anti-diabetic and anti-atherogenic functions, and this carbohydrate has put it in the spotlight as an excellent functional food material. It has been further identified with a function to facilitate the enzyme degradation of an environmental pollutant, azo color, raising the expectations for its application to new methods for environmental cleanup.

In addition to DDase, we reported the discovery of a novel GH15 enzyme, isomaltose glucohydrolase, which specifically degrades isomaltose, and its unique catalytic mechanism.

We focus primarily on α-glucosidase, an enzyme that prefers generally short-chain maltooligosaccharides (hence the name maltase), but plant α-glucosidases can hydrolyze long-chain maltooligosaccharides and starch. We have been studying many plant α-glucosidases especially derived from rice and sugar beet. We have clarified the "unique structural factors that recognize long-chain carbohydrates" of plant enzymes by using X-ray crystal structure analysis and protein engineering techniques. Based on these results, we found that α-glucosidase is also a candidate for a key enzyme in the degradation of starch grains during plant seed germination, and proposed a new metabolic mechanism for starch grains.

In addition to plant enzymes, we are also actively engaged in applied research on α-glucosidases, such as the synthesis of functional oligosaccharides using fungal α-glucosidases.

GH97 is a quite unique family containing a retaining and an inverting enzymes. During the catalysis, the former retains the anomeric configuration, while the latter inverts it. In general, enzymes in a GH family conserve a catalytic mechanism, and GH97 is thus unique from other GH families. At our laboratory, we are working on the catalytic mechanisms of retaining and inverting enzymes while keeping the possibility of molecular evolution within the focus.