InterPro domain: IPR044505

This E or "early" set domains are associated with the catalytic domain of glycogen branching enzymes at the N-terminal end. The N-terminal domain of the 1,4 alpha glucan branching enzyme may be related to the immunoglobulin and/or fibronectin type III superfamilies. These domains are associated with different types of catalytic domains at either the N-terminal or C-terminal end and may be involved in homodimeric/tetrameric/dodecameric interactions [ 1 ].

This entry represents the N-terminal Early set domain found in bacterial glycogen debranching enzymes and isoamylases from bacteria and plants. Glycogen debranching enzymes have 4-alpha-glucanotransferase activity, that transfers a segment of the 1,4-alpha-D-glucan to a new 4-position in an acceptor, which may be glucose or another 1,4-alpha-D-glucan, and amylo-1,6-glucosidase activity, which catalyses the endohydrolysis of 1,6-alpha-D-glucoside linkages at points of branching in chains of 1,4-linked alpha-D-glucose residues [ 2 ]. Isoamylase is one of the starch-debranching enzymes that catalyse the hydrolysis of alpha-1,6-glucosidic linkages specific in alpha-glucans such as amylopectin or glycogen [ 3 , 4 ].

1. The X-ray crystallographic structure of Escherichia coli branching enzyme. J. Biol. Chem. 277, 42164-70
2. Role of the Escherichia coli glgX gene in glycogen metabolism. J. Bacteriol. 187, 1465-73
3. Arabidopsis mutants Atisa1 and Atisa2 have identical phenotypes and lack the same multimeric isoamylase, which influences the branch point distribution of amylopectin during starch synthesis. Plant J. 41, 815-30
4. Crystal structure of the Chlamydomonas starch debranching enzyme isoamylase ISA1 reveals insights into the mechanism of branch trimming and complex assembly. J Biol Chem 289, 22991-3003