InterPro: IPR006046 Glycoside hydrolase family 13

O-Glycosyl hydrolases EC: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 [1, 2, 3]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site [4]. Because the fold of proteins is better conserved than their sequences, some of the families can be grouped in clans.

Glycoside hydrolase family 13 GH13 comprises enzymes with a variety of known activities; alpha-amylase (EC:3.2.1.1); pullulanase (EC:3.2.1.41); cyclomaltodextrin glucanotransferase (EC:2.4.1.19); cyclomaltodextrinase (EC:3.2.1.54); trehalose-6-phosphate hydrolase (EC:3.2.1.93); oligo-alpha-glucosidase (EC:3.2.1.10); maltogenic amylase (EC:3.2.1.133); neopullulanase (EC:3.2.1.135); alpha-glucosidase (EC:3.2.1.20); maltotetraose-forming alpha-amylase (EC:3.2.1.60); isoamylase (EC:3.2.1.68); glucodextranase (EC:3.2.1.70); maltohexaose-forming alpha-amylase (EC:3.2.1.98); branching enzyme (EC:2.4.1.18); trehalose synthase (EC:5.4.99.16); 4-alpha-glucanotransferase (EC:2.4.1.25); maltopentaose-forming alpha-amylase (EC:3.2.1); amylosucrase (EC:2.4.1.4); sucrose phosphorylase (EC:2.4.1.7).

Alpha-amylases are 1,4-alpha-D-glucan glucanohydrolases, which degrade both the branched and unbranched forms of starch by cleaving the internal alpha-1,4 bonds connecting the glucose monomers. The products of these reactions are maltose and maltotriose, which are further degraded to glucose by maltases. One atom of calcium is required to bind to each protein molecule to allow it to function, but excess calcium can inhibit activity by binding to amino acids that are required for the catalytic activity of the enzyme.