Glycoside hydrolase, family 14B, plant <p>O-Glycosyl hydrolases <db_xref db="EC" dbkey="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 [<cite idref="PUB00004870"/>, <cite idref="PUB00005266"/>]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site.</p><p>Family 14 (<db_xref db="EC" dbkey="3.2.1.2"/>, <db_xref db="CAZY" dbkey="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 [<cite idref="PUB00004513"/>]. In <taxon tax_id="4113">Solanum tuberosum</taxon> (potato), the enzyme has been found to work optimally at 40 degrees C,becoming unstable above this temperature [<cite idref="PUB00004513"/>]. On the basis of sequencecomparisons, plant and bacterial beta-amylases can be readily distinguishedfrom each other.</p><p>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 [<cite idref="PUB00002354"/>]. 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 [<cite idref="PUB00002354"/>]. The interface of the two domains, togetherwith shorter loops from the (beta alpha)8 core, form a deep cleft, in whichthe inhibitor binds [<cite idref="PUB00002354"/>]. Two maltose molecules also bind in the cleft,one sharing a binding site with alpha-cyclodextrin, and the other sittingmore deeply in the cleft [<cite idref="PUB00002354"/>].</p>