<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 4 <db_xref db="CAZY" dbkey="GH4"/>comprises enzymes with several known activities; 6-phospho-beta-glucosidase (<db_xref db="EC" dbkey="3.2.1.86"/>); 6-phospho-alpha-glucosidase (<db_xref db="EC" dbkey="3.2.1.122"/>); alpha-galactosidase (<db_xref db="EC" dbkey="3.2.1.22"/>).</p><p>These enzymes require NAD and a divalent ion for their activity and are proteins of about 50 kDa; e.g. 6-phospho-alpha-glucosidase requires both NAD(H) and divalent metal (Mn2+, Fe2+, Co2+, or Ni2+) for activity [<cite idref="PUB00003025"/>]. The signature pattern is located to a conserved region located in the central section. This region does not contain residues directly shown to be important for the catalytic activity.</p>