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Alpha amylase catalytic domain found in Alpha 1,3-glucan synthase (also called uridine diphosphoglucose-1,3-alpha-glucan glucosyltransferase and 1,3-alpha-D-glucan synthase) Alpha 1,3-glucan synthase (AGS, EC 2.4.1.183) is an enzyme that catalyzes the reversible chemical reaction of UDP-glucose and [alpha-D-glucosyl-(1-3)]n to form UDP and [alpha-D-glucosyl-(1-3)]n+1. AGS is a component of fungal cell walls. The cell wall of filamentous fungi is composed of 10-15% chitin and 10-35% alpha-1,3-glucan. AGS is triggered in fungi as a response to cell wall stress and elongates the glucan chains in cell wall synthesis. This group includes proteins from Ascomycetes and Basidomycetes. The Alpha-amylase family comprises the largest family of glycoside hydrolases (GH), with the majority of enzymes acting on starch, glycogen, and related oligo- and polysaccharides. These proteins catalyze the transformation of alpha-1,4 and alpha-1,6 glucosidic linkages with retention of the anomeric center. The protein is described as having 3 domains: A, B, C. A is a (beta/alpha) 8-barrel; B is a loop between the beta 3 strand and alpha 3 helix of A; C is the C-terminal extension characterized by a Greek key. The majority of the enzymes have an active site cleft found between domains A and B where a triad of catalytic residues (Asp, Glu and Asp) performs catalysis. Other members of this family have lost the catalytic activity as in the case of the human 4F2hc, or only have 2 residues that serve as the catalytic nucleophile and the acid/base, such as Thermus A4 beta-galactosidase with 2 Glu residues (GH42) and human alpha-galactosidase with 2 Asp residues (GH31). The family members are quite extensive and include: alpha amylase, maltosyltransferase, cyclodextrin glycotransferase, maltogenic amylase, neopullulanase, isoamylase, 1,4-alpha-D-glucan maltotetrahydrolase, 4-alpha-glucotransferase, oligo-1,6-glucosidase, amylosucrase, sucrose phosphorylase, and amylomaltase. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",