The enzymes of glycosyl hydrolase family 31 (GH31) occur in prokaryotes, eukaryotes, and archaea with a wide range of hydrolytic activities, including alpha-glucosidase (glucoamylase and sucrase-isomaltase), alpha-xylosidase, 6-alpha-glucosyltransferase, 3-alpha-isomaltosyltransferase and alpha-1,4-glucan lyase. All GH31 enzymes cleave a terminal carbohydrate moiety from a substrate that varies considerably in size, depending on the enzyme, and may be either a starch or a glycoprotein. In most cases, the pyranose moiety recognized in subsite -1 of the substrate binding site is an alpha-D-glucose, though some GH31 family members show a preference for alpha-D-xylose. Several GH31 enzymes can accommodate both glucose and xylose and different levels of discrimination between the two have been observed. Most characterized GH31 enzymes are alpha-glucosidases. In mammals, GH31 members with alpha-glucosidase activity are implicated in at least three distinct biological processes. The lysosomal acid alpha-glucosidase (GAA) is essential for glycogen degradation and a deficiency or malfunction of this enzyme causes glycogen storage disease II, also known as pompe disease. In the endoplasmic reticulum, alpha-glucosidase II catalyzes the second step in the N-linked oligosaccharide processing pathway that constitutes part of the quality control system for glycoprotein folding and maturation. The intestinal enzymes sucrase-isomaltase (SI) and maltase-glucoamylase (MGAM) play key roles in the final stage of carbohydrate digestion, making alpha-glucosidase inhibitors useful in the treatment of type 2 diabetes. GH31 alpha-glycosidases are retaining enzymes that cleave their substrates via an acid/base-catalyzed, double-displacement mechanism involving a covalent glycosyl-enzyme intermediate. Two aspartic acid residues have been identified as the catalytic nucleophile and the acid/base, respectively.

Alpha-glucosidase II (alpha-D-glucoside glucohydrolase) is a glycosyl hydrolase family 31 (GH31) enzyme, found in bacteria and plants, which has exo-alpha-1,4-glucosidase and oligo-1,6-glucosidase activities. Alpha-glucosidase II has been characterized in Bacillus thermoamyloliquefaciens where it forms a homohexamer. This family also includes the MalA alpha-glucosidase from Sulfolobus sulfataricus and the AglA alpha-glucosidase from Picrophilus torridus. MalA is part of the carbohydrate-metabolizing machinery that allows this organism to utilize carbohydrates, such as maltose, as the sole carbon and energy source.

This family includes the following closely related glycosyl hydrolase family 31 (GH31) enzymes: maltase-glucoamylase (MGAM), sucrase-isomaltase (SI), lysosomal acid alpha-glucosidase (GAA), neutral alpha-glucosidase C (GANC), the alpha subunit of neutral alpha-glucosidase AB (GANAB), and alpha-glucosidase II. MGAM is one of the two enzymes responsible for catalyzing the last glucose-releasing step in starch digestion. SI is implicated in the digestion of dietary starch and major disaccharides such as sucrose and isomaltose, while GAA degrades glycogen in the lysosome, cleaving both alpha-1,4 and alpha-1,6 glucosidic linkages. MGAM and SI are anchored to small-intestinal brush-border epithelial cells. The absence of SI from the brush border membrane or its malfunction is associated with malabsorption disorders such as congenital sucrase-isomaltase deficiency (CSID). The domain architectures of MGAM and SI include two tandem GH31 catalytic domains, an N-terminal domain found near the membrane-bound end and a C-terminal luminal domain. Both of the tandem GH31 domains of MGAM and SI are included in this family. The domain architecture of GAA includes an N-terminal TFF (trefoil factor family) domain in addition to the GH31 catalytic domain. Deficient GAA expression causes pompe disease, an autosomal recessive genetic disorder also known as glycogen storage disease type II (GSDII). GANC and GANAB are key enzymes in glycogen metabolism that hydrolyze terminal, non-reducing 1,4-linked alpha-D-glucose residues from glycogen in the endoplasmic reticulum. Alpha-glucosidase II is a GH31 enzyme, found in bacteria and plants, which has exo-alpha-1,4-glucosidase and oligo-1,6-glucosidase activities. Alpha-glucosidase II has been characterized in Bacillus thermoamyloliquefaciens where it forms a homohexamer. This family also includes the MalA alpha-glucosidase from Sulfolobus sulfataricus and the AglA alpha-glucosidase from Picrophilus torridus. MalA is part of the carbohydrate-metabolizing machinery that allows this organism to utilize carbohydrates, such as maltose, as the sole carbon and energy source. The MGAM-like family corresponds to subgroup 1 in the Ernst et al classification of GH31 enzymes.

Glycosyl hydrolases family 31. Glycosyl hydrolases are key enzymes of carbohydrate metabolism. Family 31 comprises of enzymes that are, or similar to, alpha- galactosidases.

This family includes the following three closely related glycosyl hydrolase family 31 (GH31) enzymes: maltase-glucoamylase (MGAM), sucrase-isomaltase (SI), and lysosomal acid alpha-glucosidase (GAA), also known as acid-maltase. MGAM is one of the two enzymes responsible for catalyzing the last glucose-releasing step in starch digestion. SI is implicated in the digestion of dietary starch and major disaccharides such as sucrose and isomaltose, while GAA degrades glycogen in the lysosome, cleaving both alpha-1,4 and alpha-1,6 glucosidic linkages. MGAM and SI are anchored to small-intestinal brush-border epithelial cells. The absence of SI from the brush border membrane or its malfunction is associated with malabsorption disorders such as congenital sucrase-isomaltase deficiency (CSID). The domain architectures of MGAM and SI include two tandem GH31 catalytic domains, an N-terminal domain found near the membrane-bound end, and a C-terminal luminal domain. Both of the tandem GH31 domains of MGAM and SI are included in this family. The domain architecture of GAA includes an N-terminal TFF (trefoil factor family) domain in addition to the GH31 catalytic domain. Deficient GAA expression causes pompe disease, an autosomal recessive genetic disorder also known as glycogen storage disease type II (GSDII).