In molecular biology, Glycoside hydrolasefamily 14 is a family of glycoside hydrolases. Glycoside hydrolases are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycoside hydrolases, based on sequence similarity, has led to the definition of >100 different families. This classification is available on the CAZyweb site, and also discussed at CAZypedia, an online encyclopedia of carbohydrate active enzymes. Glycoside hydrolase family 14 comprises enzymes with only one known activity; beta-amylase. A Glu residue has been proposed as a catalytic residue, but it is not known if it is the nucleophile or the proton donor. Beta-amylase is an enzyme that hydrolyzes 1,4-alpha-glucosidic linkages in starch-type polysaccharide substrates so as to remove successive maltose units from the non-reducing ends of the chains. Beta-amylase is present in certain bacteria as well as in plants. Three highly conserved sequence regions are found in all known beta-amylases. The first of these regions is located in the N-terminal section of the enzymes and contains an aspartate which is known to be involved in the catalytic mechanism. The second, located in a more central location, is centred on a glutamate which is also involved in the catalytic mechanism. The 3D structure of a complex of soybean beta-amylase with an inhibitor has been determined to 3.0A resolution by X-ray diffraction. The enzyme folds into large and small domains: the large domain has a 8 super-secondary structural core, while the smaller is formed from two long loops extending from the beta-3 and beta-4 strands of the 8 fold. The interface of the two domains, together with shorter loops from the 8 core, form a deep cleft, in which the inhibitor binds. Two maltose molecules also bind in the cleft, one sharing a binding site with alpha-cyclodextrin, and the other sitting more deeply in the cleft.
