ABSTRACT
Glucoamylase is a critical ingredient for saccharification in the starch decomposition, and widely used in food, pharmaceutical and fermentation industries. Glucoamylases are usually thermostable and have peak activities at high temperature, as required for the industrial process of glucose production. In this study, a glucoamylase gene belonging to the glycoside hydrolase (GH) family 15, Tlga15A, was cloned from Talaromyces leycettanus JCM12802, and successfully expressed in Pichia pastoris GS115. Recombinant glucoamylase TlGA showed optimal activities at pH 4.5 and 75 °C. The result of thermostability analysis showed that TlGA retained above 70% activity after incubating for 1 h at 65 °C, and 43% residual activity after 30 min at 70 °C. Moreover, TlGA had high resistance to most metal ions and chemical reagents tested. Various starch substrates could be hydrolyzed by TlGA, including soluble starch (255.6±15.3) U/mg, amylopectin (342.3±24.7) U/mg, glycogen (185.4±12.5) U/mg, dextrin (423.3±29.3) U/mg and pullulan (65.7±8.1) U/mg. The primary, secondary and tertiary structures of glucoamylase were further analyzed. The low ratio of Gly in the primary structure and low exposed nonpolarity solvent accessible surface in the tertiary structure may be the main reasons for TlGA's thermostability. These results show that TlGA is great promising for potential use in the commercial production of glucose syrups. Moreover, this research will provide knowledge and innovating ideas for the improvement of glucoamylase thermostability.