Structure of the starch-debranching enzyme barley limit dextrinase reveals homology of the N-terminal domain to CBM21

Barley limit dextrinase (HvLD) is a debranching enzyme from glycoside hydrolase family 13 subfamily 13 (GH13_13) that hydrolyses alpha-1,6-glucosidic linkages in limit dextrins derived from amylopectin. The structure of HvLD was solved and refined to 1.9 angstrom resolution. The structure has a glycerol molecule in the active site and is virtually identical to the structures of HvLD in complex with the competitive inhibitors alpha-cyclodextrin and beta-cyclodextrin solved to 2.5 and 2.1 angstrom resolution, respectively. However, three loops in the N-terminal domain that are shown here to resemble carbohydrate-binding module family 21 were traceable and were included in the present HvLD structure but were too flexible to be traced and included in the structures of the two HvLDinhibitor complexes.