<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 9 <db_xref db="CAZY" dbkey="GH9"/> comprises enzymes with several known activities; endoglucanase (<db_xref db="EC" dbkey="3.2.1.4"/>); cellobiohydrolase (<db_xref db="EC" dbkey="3.2.1.91"/>). These enzymes were formerly known as cellulase family E. </p><p>This entry contains two patterns that are centred on conserved residues which have been shown [<cite idref="PUB00002631"/>, <cite idref="PUB00000511"/>], in the endoglucanase D from Cellulomonas thermocellum, to be important for the catalytic activity. The first region contains an active site histidine and the second region contains two catalytically important residues: an aspartate and a glutamate.</p> Glycoside hydrolase, family 9, active site