Glycoside hydrolase family 15, N-terminal domainMembers of this family are N-terminal domains uniquely found in bacterial and archaeal glucoamylases and glucodextranases. Glucoamylase (glucan 1,4-alpha-glucosidase; 4-alpha-D-glucan glucohydrolase; amyloglucosidase; exo-1,4-alpha-glucosidase; gamma-amylase; lysosomal alpha-glucosidase; EC 184.108.40.206) hydrolyzes beta-1,4-glucosidic linkages of starch, glycogen and malto-oligosaccharides, releasing beta-D-glucose from the non-reducing end. Glucodextranase (glucan 1,6-alpha-glucosidase; exo-1,6-alpha-glucosidase; EC 220.127.116.11) uses an inverting reaction mechanism to hydrolyze alpha-1,6-glucosidic linkages of dextran and related oligosaccharides, releasing beta-D-glucose from the non-reducing end. These N-terminal domains adopt a structure consisting of antiparallel beta-strands, divided into two beta-sheets, with one sheet wrapped by an extended polypeptide, which appears to stabilize the domain. The function of these domains in the enzymes is as yet unknown. However, it is suggested that domain N of bacterial GA is involved in folding and/or the thermostability of the A domain that forms an (alpha/alpha)6-barrel structure.