Alpha-amylase, C-terminal CBM20 (carbohydrate-binding module, family 20) domain. This domain is found in several bacterial and fungal alpha-amylases including the maltopentaose-forming amylases (G5-amylases). Most alpha-amylases have, in addition to the C-terminal CBM20 domain, an N-terminal catalytic domain belonging to glycosyl hydrolase family 13, which hydrolyzes internal alpha-1,4-glucosidic bonds in starch and related saccharides, yielding maltotriose and maltose. Two types of soluble substrates are used by alpha-amylases including long substrates (e.g. amylose) and short substrates (e.g. maltodextrins or maltooligosaccharides). 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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",