Novamyl (also known as acarviose transferase, ATase, maltogenic alpha-amylase, glucan 1,4-alpha-maltohydrolase, and AcbD), C-terminal CBM20 (carbohydrate-binding module, family 20) domain. Novamyl has a five-domain structure similar to that of cyclodextrin glucanotransferase (CGTase). Novamyl has a substrate-binding surface with an open groove which can accommodate both cyclodextrins and linear substrates. 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.