trehalose synthase, Pseudomonas stutzeri type. Trehalose synthase catalyzes a one-step conversion of maltose to trehalose. This is an alternative to the OtsAB and TreYZ pathways. This family includes a characterized example from Pseudomonas stutzeri plus very closely related sequences from other Pseudomonads. Cutoff scores are set to find a more distantly related sequence from Desulfovibrio vulgaris, likely to be functionally equivalent, between trusted and noise limits. [Energy metabolism, Biosynthesis and degradation of polysaccharides, Cellular processes, Adaptations to atypical conditions]
Alpha amylase catalytic domain found in oligo-1,6-glucosidase (also called isomaltase; sucrase-isomaltase; alpha-limit dextrinase), trehalose synthase (also called maltose alpha-D-glucosyltransferase), and related proteins. Oligo-1,6-glucosidase (EC 3.2.1.10) hydrolyzes the alpha-1,6-glucosidic linkage of isomaltooligosaccharides, pannose, and dextran. Unlike alpha-1,4-glucosidases (EC 3.2.1.20), it fails to hydrolyze the alpha-1,4-glucosidic bonds of maltosaccharides. Trehalose synthase (EC 5.4.99.16) catalyzes the isomerization of maltose to produce trehalulose. 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.
