Structural Similarity between a Starch-hydrolyzing Enzyme and an N-Glycan-Hydrolyzing Enzyme: Exohydrolases Cleaving α-1,X-Glucosidic Linkages to Produce β-Glucose

Abstract

Glucoamylase, glucodextranase, trehalase, and eukaryotic N-glycan processing α-glucosidase I have been identified as exo-acting enzymes that hydrolyze α-1,Xglucosidic linkages from the non-reducing end to produce β-glucose. While the physiological functions of these enzymes are different, they share a catalytic (α/α) 6 barrel domain and show many structural similarities. These enzymes, with few exceptions, belong to the glycoside hydrolase families (GHs) 15, 37, and 63 in the CAZy database, and all these enzymes have 2 conserved aspartic or glutamic acid residues in the catalytic domain. The observations led us to consider that the group of GH15, GH37, and GH63 may be designated as a "glucoamylase family." There are also many hydrolases and phosphorylases structurally related to GH15, GH37, and GH63.