<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 2 <db_xref db="CAZY" dbkey="GH2"/>comprises enzymes with several known activities; beta-galactosidase (<db_xref db="EC" dbkey="3.2.1.23"/>); beta-mannosidase (<db_xref db="EC" dbkey="3.2.1.25"/>); beta-glucuronidase (<db_xref db="EC" dbkey="3.2.1.31"/>).</p><p>These enzymes contain a conserved glutamic acid residue which has been shown [<cite idref="PUB00002709"/>], in <taxon tax_id="562">Escherichia coli</taxon> lacZ (<db_xref db="SWISSPROT" dbkey="P00722"/>), to be the general acid/base catalyst in the active site of the enzyme.</p>This pattern signature contains the active site glutamic acid residue.