<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 36 <db_xref db="CAZY" dbkey="GH36"/> comprises enzymes with only one known activity; alpha-galactosidase (<db_xref db="EC" dbkey="3.2.1.22"/>).</p><p>Alpha-galactosidase (melibiase) catalyses the hydrolysis of melibiose into galactose and glucose [<cite idref="PUB00005652"/>]. In man, deficiency in the enzyme results in Fabry's disease (X-linked sphingolipidosis). An <taxon tax_id="562">Escherichia coli</taxon> plasmid-encoded alpha-galactosidase (rafA) [<cite idref="PUB00002094"/>] contains a region of about 50 amino acids that is similar to a domain of the eukaryotic alpha-galactosidases.</p>