N-terminal catalytic domain of thermoactive amylopullulanases; glycoside hydrolase family 57 (GH57). Pullulanases (EC 3.2.1.41) are capable of hydrolyzing the alpha-1,6 glucosidic bonds of pullulan, producing maltotriose. Amylopullulanases (APU, E.C 3.2.1.1/41) are type II pullulanases which can also degrade both the alpha-1,6 and alpha-1,4 glucosidic bonds of starch, producing oligosaccharides. This subfamily includes GH57 archaeal thermoactive APUs, which show both pullulanolytic and amylolytic activities. They have an acid pH optimum and the presence of Ca2+ might increase their activity, thermostability, and substrate affinity. Besides GH57 thermoactive APUs, all mesophilic and some thermoactive APUs belong to glycoside hydrolase family 13 with catalytic features distinct from GH57. This subfamily also includes many uncharacterized proteins found in bacteria and archaea.

Alpha-amylase/alpha-mannosidase, GH57 family [Carbohydrate transport and metabolism].

Glycosyl hydrolase family 57. This family includes alpha-amylase (EC:3.2.1.1), 4--glucanotransferase (EC:2.4.1.-) and amylopullulanase enzymes.

N-terminal catalytic domain of heat stable retaining glycoside hydrolase family 57. Glycoside hydrolase family 57(GH57) is a chiefly prokaryotic family with the majority of thermostable enzymes coming from extremophiles (many of these are archaeal hyperthermophiles), which exhibit the enzyme specificities of alpha-amylase (EC 3.2.1.1), 4-alpha-glucanotransferase (EC 2.4.1.25), amylopullulanase (EC 3.2.1.1/41), and alpha-galactosidase (EC 3.2.1.22). This family also includes many hypothetical proteins with uncharacterized activity and specificity. GH57s cleave alpha-glycosidic bonds by employing a retaining mechanism, which involves a glycosyl-enzyme intermediate, allowing transglycosylation.

N-terminal catalytic domain of alpha-galactosidase; glycoside hydrolase family 57 (GH57). Alpha-galactosidases (GalA, EC 3.2.1.22) catalyze the hydrolysis of alpha-1,6-linked galactose residues from oligosaccharides and polymeric galactomannans. Based on sequence similarity, the majority of eukaryotic and bacterial GalAs have been classified into glycoside hydrolase family GH27, GH36, and GH4, respectively. This subfamily is represented by a novel type of GalA from Pyrococcus furiosus (PfGalA), which belongs to the GH57 family. PfGalA is an extremely thermo-active and thermostable GalA that functions as a bacterial-like GalA, however, without the capacity to hydrolyze polysaccharides. It specifically catalyzes the hydrolysis of para-nitrophenyl-alpha-galactopyranoside, and to some extent that of melibiose and raffinose. PfGalA has a pH optimum between 5.0-5.5.