It has been shown [1,2,3,E1] that the following glycosyl hydrolases can be, on the basis of sequence similarities, classified into a single family:

• Lysosomal α-glucosidase (EC 3.2.1.20) (acid maltase) is a vertebrate glycosidase active at low pH, which hydrolyzes α(1->4) and α(1->6) linkages in glycogen, maltose, and isomaltose.
• α-glucosidase (EC 3.2.1.20) from the yeast Candida tsukunbaensis.
• α-glucosidase (EC 3.2.1.20) (gene malA) from the archebacteria Sulfolobus solfataricus.
• Intestinal sucrase-isomaltase (EC 3.2.1.48 / EC 3.2.1.10) is a vertebrate membrane-bound, multifunctional enzyme complex which hydrolyzes sucrose, maltose and isomaltose. The sucrase and isomaltase domains of the enzyme are homologous (41% of amino acid identity) and have most probably evolved by duplication.
• Glucoamylase 1 (EC 3.2.1.3) (glucan 1,4-α-glucosidase) from various fungal species.
• Yeast hypothetical protein YBR229c.
• Fission yeast hypothetical protein SpAC30D11.01c.

An aspartic acid has been implicated [4] in the catalytic activity of sucrase, isomaltase, and lysosomal α-glucosidase. The region around this active residue is highly conserved and can be used as a signature pattern. We have used a second region, which contains two conserved cysteines, as an additional signature pattern.

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