InterPro domain: IPR006048

Alpha-amylase is classified as family 13 of the glycosyl hydrolases and is present in archaea, bacteria, plants and animals. Alpha-amylase is an essential enzyme in alpha-glucan metabolism, acting to catalyse the hydrolysis of alpha-1,4-glucosidic bonds of glycogen, starch and related polysaccharides. Although all alpha-amylases possess the same catalytic function, they can vary with respect to sequence. In general, they are composed of three domains: a TIM barrel containing the active site residues and chloride ion-binding site (domain A), a long loop region inserted between the third beta strand and the alpha-helix of domain A that contains calcium-binding site(s) (domain B), and a C-terminal beta-sheet domain that appears to show some variability in sequence and length between amylases (domain C) [ 1 ]. Amylases have at least one conserved calcium-binding site, as calcium is essential for the stability of the enzyme. The chloride-binding functions to activate the enzyme, which acts by a two-step mechanism involving a catalytic nucleophile base (usually an Asp) and a catalytic proton donor (usually a Glu) that are responsible for the formation of the beta-linked glycosyl-enzyme intermediate.

This entry represents the all-beta C-terminal domain that is found in members of the glycosyl hydrolase 13 family, such as alpha-amylases and 1,4-alpha-glucan branching enzyme. This domain forms a Greek key beta-barrel fold in these enzymes [ 2 ].

Branching enzyme catalyses the formation of alpha-1,6 branch points in either glycogen or starch. It has an important role in the determination of the structure of starch in plants and of glycogen in animals and bacteria [ 3 ].

1. Evolution of alpha-amylases: architectural features and key residues in the stabilization of the (beta/alpha)(8) scaffold. Mol. Biol. Evol. 18, 38-54
2. Crystal structure of calcium-depleted Bacillus licheniformis alpha-amylase at 2.2 A resolution. J. Mol. Biol. 246, 545-59
3. The X-ray crystallographic structure of Escherichia coli branching enzyme. J. Biol. Chem. 277, 42164-70