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.

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 4-alpha-glucanotransferase; glycoside hydrolase family 57 (GH57). 4-alpha-glucanotransferase (TLGT, EC 2.4.1.25) plays a key role in the maltose metabolism. It catalyzes the disproportionation of amylose and the formation of large cyclic alpha-1,4-glucan (cycloamylose) from linear amylose. TLGT functions as a homodimer. Each monomer is composed of two domains, an N-terminal catalytic domain with a (beta/alpha)7 barrel fold and a C-terminal domain with a twisted beta-sandwich fold. Some family members have been designated as alpha-amylases, such as the heat-stable eubacterial amylase from Dictyoglomus thermophilum (DtAmyA) and the extremely thermostable archaeal amylase from Pyrococcus furiosus(PfAmyA). However, both of these proteins are 4-alpha-glucanotransferases. DtAmyA was shown to have transglycosylating activity and PfAmyA exhibits 4-alpha-glucanotransferase activity.

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.

Crystalstructure of 4-alpha-glucanotransferase from thermococcus litoralis [Thermococcus litoralis]

Crystalstructure of 4-alpha-glucanotransferase from thermococcus litoralis [Thermococcus litoralis],1K1X_B Crystal structure of 4-alpha-glucanotransferase from thermococcus litoralis [Thermococcus litoralis],1K1Y_A Crystal structure of thermococcus litoralis 4-alpha-glucanotransferase complexed with acarbose [Thermococcus litoralis],1K1Y_B Crystal structure of thermococcus litoralis 4-alpha-glucanotransferase complexed with acarbose [Thermococcus litoralis]

Alpha-amylase OS=Pyrococcus horikoshii (strain ATCC 700860 / DSM 12428 / JCM 9974 / NBRC 100139 / OT-3) OX=70601 GN=amyA PE=3 SV=1

Alpha-amylase OS=Pyrococcus abyssi (strain GE5 / Orsay) OX=272844 GN=amyA PE=3 SV=1

4-alpha-glucanotransferase OS=Thermococcus kodakarensis (strain ATCC BAA-918 / JCM 12380 / KOD1) OX=69014 GN=TK1809 PE=3 SV=1

Alpha-amylase OS=Pyrococcus furiosus (strain ATCC 43587 / DSM 3638 / JCM 8422 / Vc1) OX=186497 GN=amyA PE=1 SV=2

4-alpha-glucanotransferase OS=Thermococcus litoralis (strain ATCC 51850 / DSM 5473 / JCM 8560 / NS-C) OX=523849 GN=jgt PE=1 SV=1