STARCH- AND GLYCOGEN-DEBRANCHING AND BRANCHING ENZYMES - PREDICTION OF STRUCTURAL FEATURES OF THE CATALYTIC (BETA ALPHA)(8)-BARREL DOMAIN AND EVOLUTIONARY RELATIONSHIP TO OTHER AMYLOLYTIC ENZYMES/

Sequence alignment and structure prediction are used to locate catalyt ic alpha-amylase-type (beta/alpha)(8)-barrel domains and the positions of their beta-strands and alpha-helices in isoamylase, pullulanase, n eopullulanase, alpha-amylase-pullulanase, dextran glucosidase, branchi ng enzyme, and glycogen branching enzymes-all enzymes involved in hydr olysis or synthesis of alpha-1,6-glucosidic linkages in starch and rel ated polysaccharides. This has allowed identification of the transfera se active site of the glycogen debranching enzyme and the locations of beta-->alpha loops making up the active sites of all enzymes studied. Activity and specificity of the enzymes are discussed in terms of con served amino acid residues and loop variations. An evolutionary distan ce tree of 47 amylolytic and related enzymes is built on 37 residues r epresenting the four best conserved beta-strands of the barrel. It exh ibits clusters of enzymes close in specificity, with the branching and glycogen debranching enzymes being the most distantly related.