Characterization of a Bifunctional Glucoamylase GA from with Dual Hydrolytic Activity on Starch and Chitosan.

Glucoamylase is essential for the hydrolysis of starch to glucose and has broad industrial applications. Although its catalytic domain shares similarities with GH8 family chitosanases, which are known for their bifunctional activity, no bifunctional glucoamylase has been reported to date. In this study, we identify and characterize GA, a glucoamylase from the pathogenic fungus 293, which exhibits a dual hydrolytic activity toward both starch and chitosan. GA demonstrated efficient starch hydrolysis at 70 °C with a specific activity of 503.28 ± 1.3 U/mg and chitosan hydrolysis at 90 °C with a specific activity of 3.67 ± 0.1 U/mg. Molecular docking and dynamics simulations revealed that the enhanced catalytic activity and substrate binding of GA for starch are attributed to increased interactions within the substrate-binding pocket. The Δ strain exhibited reduced growth, sporulation, and carbon utilization efficiency as well as hypersensitivity to cell wall-disrupting agents. These results highlight 's critical role in maintaining cell wall integrity and carbon metabolism in . Our findings provide new insights into the substrate promiscuity of glycoside hydrolases and underscore the potential of GA in both industrial biocatalysis and fungal biology.