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N-terminal domain of glycosyl hydrolase family 31 (GH31) This family is found N-terminal to the glycosyl-hydrolase domain of Glycoside hydrolase family 31 (GH31). GH31 includes the glycoside hydrolases alpha-glucosidase (EC 3.2.1.20), alpha-1,3-glucosidase (EC 3.2.1.84), alpha-xylosidase (EC 3.2.1.177), sucrase-isomaltase (EC 3.2.1.48 and EC 3.2.1.10), as well as alpha-glucan lyase (EC 4.2.2.13). 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 of the catalytic domain have been identified as the catalytic nucleophile and the acid/base, respectively. A loop of the N-terminal beta-sandwich domain is part of the active site pocket. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",