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.

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

Alpha-glucosidases, family 31 of glycosyl hydrolases [Carbohydrate transport and metabolism]

YihQ is a bacterial alpha-glucosidase with a conserved glycosyl hydrolase family 31 (GH31) domain that catalyzes the release of an alpha-glucosyl residue from the non-reducing end of alpha-glucoside substrates such as alpha-glucosyl fluoride. Orthologs of YihQ that have not yet been functionally characterized are present in plants and fungi. YihQ has sequence similarity to other GH31 enzymes such as CtsZ, a 6-alpha-glucosyltransferase from Bacillus globisporus, and YicI, an alpha-xylosidase from Echerichia coli. In bacteria, YihQ (along with YihO) is important for bacterial O-antigen capsule assembly and translocation.

alpha-glucosidase; Provisional