Figure 3: Structure and function of the GC domain.

(a) Structure of the GC domain. Structure of the Aspergillus awamori glucoamylase catalytic domain (right, PDB 1GAH) is shown for reference. Catalytic residues are highlighted. (b) Structure of the GC domain active-site pocket. Structure of the Aspergillus awamori glucoamylase is superimposed for reference (grey for the carbon atoms). Amino acid residue labels on the second lines are for glucoamylase. Catalytic residues are labelled in red. The +1 and −1 saccharide units of acarbose in the glucoamylase structure are shown. They mimic the +1 and −1 residues in its substrate, the glycosidic bond between which gets hydrolysed. (c) Specific debranching activities of CgGDE and its mutants. The specific activity is defined as the debranching reaction rate at the substrate concentration of 13 mg ml⁻¹ (the reaction rate of the wild-type CgGDE plateaus at this substrate concentration, see Supplementary Fig. 4a), divided by the concentration of CgGDE. The error bars indicate standard deviations of triplicate experiments. The numbers above each bar indicate ratios to the wild-type value. ND indicates not detected. (d) Specific debranching activities of combinations of a GT-defective mutant and a GC-defective mutant. In reactions catalysed by a combination of mutants, they were added in a 1:1 ratio, and the concentration of one is used in calculating the specific activity. The activity of the wild-type CgGDE is shown for reference.