Glycoside hydrolase, family 14, conserved site <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>Glycoside hydrolase family 14 <db_xref db="CAZY" dbkey="GH14"/> comprises enzymes with only one known activity; beta-amylase (<db_xref db="EC" dbkey="3.2.1.2"/>). A Glu residue has been proposed as a catalytic residue, but it is not known if it is the nucleophile or the proton donor. </p><p>Beta-amylase [<cite idref="PUB00005234"/>, <cite idref="PUB00005062"/>] is an enzyme that hydrolyses 1,4-alpha-glucosidic linkages in starch-type polysaccharide substrates so as to removesuccessive maltose units from the non-reducing ends of the chains. Beta-amylase is present in certain bacteria as well as in plants.</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><p>This entry represents two highly conserved sequence regions found in all known beta-amylases. The first of these regions (BETA_AMYLASE_1) is located in the N-terminal section of the enzymes and contains an aspartate which is known [<cite idref="PUB00002337"/>] to be involved in the catalytic mechanism. The second (BETA_AMYLASE_2), located in a more central location, is centred around a glutamate which is also involved [<cite idref="PUB00001450"/>] in the catalytic mechanism.</p>