InterPro domain: IPR001371

O-Glycosyl hydrolases ( 3.2.1. ) 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 glycosyl hydrolases, based on sequence similarity, has led to the definition of 85 different families [ 1 , 2 ]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) website.

Family 14 ( 3.2.1.2 , GH14 ) encompasses the beta-amylase enzymes.Beta-amylases, which are found in plants and bacteria, hydrolyse 1,4-alpha-glucosidic linkages in starch-type polysaccharide substrates, removingsuccessive maltose units from the non-reducing ends of the chains. In Solanum tuberosum (potato), the enzyme has been found to work optimally at 40 degrees C,becoming unstable above this temperature. On the basis of sequencecomparisons, plant and bacterial beta-amylases can be readily distinguishedfrom each other.

The 3D structure of a complex of soybean beta-amylase with an inhibitor(alpha-cyclodextrin) has been determined to 3.0A resolution by X-raydiffraction [ 3 ]. The enzyme folds into large and small domains: the largedomain has a (beta alpha)8 super-secondary structural core, while the smalleris formed from two long loops extending from the beta-3 and beta-4 strandsof the (beta alpha)8 fold [ 4 ]. The interface of the two domains, togetherwith shorter loops from the (beta alpha)8 core, form a deep cleft, in whichthe inhibitor binds [ 4 ]. Two maltose molecules also bind in the cleft,one sharing a binding site with alpha-cyclodextrin, and the other sittingmore deeply in the cleft [ 4 ].

1. Conserved catalytic machinery and the prediction of a common fold for several families of glycosyl hydrolases. Proc. Natl. Acad. Sci. U.S.A. 92, 7090-4
2. Structures and mechanisms of glycosyl hydrolases. Structure 3, 853-9
3. Three-dimensional structure of soybean beta-amylase determined at 3.0 A resolution: preliminary chain tracing of the complex with alpha-cyclodextrin. J. Biochem. 112, 541-6