Beta-amylase, C-terminal CBM20 (carbohydrate-binding module, family 20) domain. Beta-amylase has, in addition to its C-terminal CBM20 domain, an N-terminal catalytic domain belonging to glycosyl hydrolase family 14, which hydrolyzes the alpha-1,4-glucosidic bonds of starch, yielding beta-maltose from the nonreducing end of the substrate. Beta-amylase is found in both plants and microorganisms, however the plant members lack a C-terminal CBM20 domain and are not included in this group. The CBM20 domain is found in a large number of starch degrading enzymes including alpha-amylase, beta-amylase, glucoamylase, and CGTase (cyclodextrin glucanotransferase). CBM20 is also present in proteins that have a regulatory role in starch metabolism in plants (e.g. alpha-amylase) or glycogen metabolism in mammals (e.g. laforin). CBM20 folds as an antiparallel beta-barrel structure with two starch binding sites. These two sites are thought to differ functionally with site 1 acting as the initial starch recognition site and site 2 involved in the specific recognition of appropriate regions of starch.