N-terminal catalytic domain of alpha-amylase ( AmyC ) and similar proteins. Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, EC 3.2.1.1) play essential roles in alpha-glucan metabolism by catalyzing the hydrolysis of polysaccharides such as amylose starch, and beta-limit dextrin. This subfamily is represented by a novel alpha-amylase (AmyC) encoded by hyperthermophilic organism Thermotoga maritime ORF tm1438, and its prokaryotic homologs. AmyC functions as a homotetramer and shows thermostable amylolytic activity. It is strongly inhibited by acarbose. AmyC is composed of a N-terminal catalytic domain, containing a distorted TIM-barrel structure with a characteristic (beta/alpha)7 fold motif, and two additional less conserved domains. There are other two canonical alpha-amylases encoded from T. maritime that lack the sequence similarity to AmyC, and belong to a different superfamily.

Predicted glycosyl hydrolase, contains GH57 and DUF1957 domains [Carbohydrate transport and metabolism].

N-terminal catalytic domain of Gh57 branching enzyme TK 1436 and similar proteins. The subfamily is represented by a novel branching-enzyme TK1436 of hyperthermophilic archaeon Thermococcus kodakaraensis KOD1. Branching enzymes (BEs, EC 2.4.1.18) play a key role in synthesis of alpha-glucans and they generally are classified into glycoside hydrolase family 13 (GH13). However, TK1436 belongs to the GH57 family. It functions as a monomer and possesses BE activity. TK1436 is composed of a distorted N-terminal (beta/alpha)7-barrel domain and a C-terminal five alpha-helical domain, both of which participate in the formation of the active-site cleft.

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.

Catalytic domain of glycoside hydrolase (GH) families 38 and 57, lactam utilization protein LamB/YcsF family proteins, YdjC-family proteins, and similar proteins. The superfamily possesses strong sequence similarities across a wide range of all three kingdoms of life. It mainly includes four families, glycoside hydrolases family 38 (GH38), heat stable retaining glycoside hydrolases family 57 (GH57), lactam utilization protein LamB/YcsF family, and YdjC-family. The GH38 family corresponds to class II alpha-mannosidases (alphaMII, EC 3.2.1.24), which contain intermediate Golgi alpha-mannosidases II, acidic lysosomal alpha-mannosidases, animal sperm and epididymal alpha -mannosidases, neutral ER/cytosolic alpha-mannosidases, and some putative prokaryotic alpha-mannosidases. AlphaMII possess a-1,3, a-1,6, and a-1,2 hydrolytic activity, and catalyzes the degradation of N-linked oligosaccharides by employing a two-step mechanism involving the formation of a covalent glycosyl enzyme complex. GH57 is a purely prokaryotic family with the majority of thermostable enzymes from extremophiles (many of them 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. GH57 cleaves alpha-glycosidic bond by employing a retaining mechanism, which involves a glycosyl-enzyme intermediate, allowing transglycosylation. Although the exact molecular function of LamB/YcsF family and YdjC-family remains unclear, they show high sequence and structure homology to the members of GH38 and GH57. Their catalytic domains adopt a similar parallel 7-stranded beta/alpha barrel, which is remotely related to catalytic NodB homology domain of the carbohydrate esterase 4 superfamily.

Crystalstructure of the novel alpha-amylase AmyC from Thermotoga maritima [Thermotoga maritima MSB8]

Crystalstructure of GH57-type branching enzyme from hyperthermophilic archaeon Pyrococcus horikoshii [Pyrococcus horikoshii OT3],5WU7_B Crystal structure of GH57-type branching enzyme from hyperthermophilic archaeon Pyrococcus horikoshii [Pyrococcus horikoshii OT3]

ChainA, alpha-amylase, GH57 family [Thermococcus kodakarensis],3N92_A Chain A, alpha-amylase, GH57 family [Thermococcus kodakarensis],3N98_A Chain A, alpha-amylase, GH57 family [Thermococcus kodakarensis]

Thermusthermophilus family GH57 branching enzyme: crystal structure, mechanism of action and products formed [Thermus thermophilus]

Crystalstructure of TT1467 from Thermus thermophilus HB8 [Thermus thermophilus]

1,4-alpha-glucan branching enzyme TK1436 OS=Thermococcus kodakarensis (strain ATCC BAA-918 / JCM 12380 / KOD1) OX=69014 GN=TK1436 PE=1 SV=1

1,4-alpha-glucan branching enzyme TTHA1902 OS=Thermus thermophilus (strain ATCC 27634 / DSM 579 / HB8) OX=300852 GN=TTHA1902 PE=1 SV=1

Probable 1,4-alpha-glucan branching enzyme MT3115 OS=Mycobacterium tuberculosis (strain CDC 1551 / Oshkosh) OX=83331 GN=MT3115 PE=3 SV=1

Probable 1,4-alpha-glucan branching enzyme Rv3031 OS=Mycobacterium tuberculosis (strain ATCC 25618 / H37Rv) OX=83332 GN=Rv3031 PE=1 SV=1