Rational Design of Aspergillus awamori Glucoamylase for Activity Improvement

Glucoamylases are highly demanded by the industry for starch saccharification, which necessitates an increase in enzyme activity. To improve the activity of Aspergillus awamori VKPM F-1262 glucoamylase N181Q (AGAM), amino acid substitutions were made in the region of substrate binding. In the case of the variant D237G, there was a 1.3-1.4-fold increase in activity towards soluble starch for the individual enzyme and crude enzyme solution after cultivation in flasks. For the variants G57A and C319T, there was also a 1.1-1.4-fold increase in enzyme activity for the crude flask solution, while the increase in individual enzyme activity was minor. AGAM showed an increase in apparent molecular weight consistent with dimerization in the presence of soluble starch. A high T optimum of 70 °C was observed for AGAM and the variants in the hydrolysis of soluble starch. In further protein engineering, a high T optimum for hydrolysis, which may coincide with dimerization, may be considered as a hypothesis for the selection of thermostable glucoamylases, while an area of binding of oligo- and polysaccharides may be a site for mutagenesis.