Abstract
Disaccharide glycoside-specific glycosidases (diglycosidases) specifically hydrolyze the β-glycosidic bond between disaccharide and aglycons. Diglycosidases belong to glycosidase family 1, in which various monoglucosidases (β-glucosidases) are also classified. Disaccharide glycosides are found in diverse plants, suggesting the wide distribution of diglycosidases in the plant kingdom. Diglycosidases show over 50% amino acid identities with β-glucosidases, indicating that diglycosidases have evolved from β-glucosidases. To elucidate structural basis of alteration in their glycone specificities, we carried out X-ray crystallographic analysis of β-primeverosidase (PD, a diglycosidase from Camellia sinensis). The 3-D structure of PD complexed with a substrate analog inhibitor was determined at 1.8 Å resolution. The conformation of most catalytic residues was conserved between PD and β-glucosidases. Interestingly, Ser473 and Gln477 in PD were found to form the hydrogen bonds with the second xylose of primeverose. Thus, diglycosidases evolved from monooglucosidases as the consequence of slight structural change in the substrate binding pocket.
