The Concept of the .ALPHA.-Amylase Family: A Rational Tool for Interconverting Glucanohydrolases/Glucanotransferases, and Their Specificities

We found a new enzyme, neopullulanase (EC 3.2.1.135), and showed that it catalyzes the hydrolysis of α-1,4- and α-1,6-glucosidic linkages, as well as transglycosylation to form α-1,4- and α-1,6-glucosidic linkages. Based on the series of experimental results using neopullulanase, we pointed out the same catalytic machinery and the common catalytic mechanism of the enzymes that catalyze these four reactions, and thus, proposed and defined the concept of the α-amylase family. Mutational analyses provided the evidence that one active center of neopullulanase participates in all four reactions; the hydrolysis of α-1,4- and α-1,6-glucosidic linkages and transglycosylation to form α-1,4- and α-1,6-glucosidic linkages. Structural analyses provided the conclusive proof that one active center of neopullulanase participates in all four reactions. We have been trying to interconvert glucanohydrolases/glucanotransferases, and their specificities and create tailor-made industrially useful enzymes based on the concept of the α-amylase family. Based on the concept, we engineered Thermus amylomaltase to essentially erase hydrolytic activity and created perfect 4-α-glucanotransferase for the industrial production of cycloamylose. The concept of the α-amylase family is demonstrated here again as a rational tool for interconverting glucanohydrolases/glucanotransferases, and their specificities.