Identification, molecular and biochemical characterization of a novel thermoactive and thermostable glucoamylase from Thermoanaerobacter ethanolicus

Abstract

Purpose: We identified a new glucoamylase (TeGA) from Thermoanaerobacter ethanolicus, a thermophilic anaerobic bacterium. Structural studies suggest that TeGA belongs to the family 15 of glycosylhydrolases (GH15). Methods: The expression of this enzyme was optimized in E. coli (BL21) cells in order to have the highest amount of soluble protein (around 3 mg/l of culture medium). Results: TeGA showed a high optimum temperature of 75 °C. It also showed one of the highest specific activities reported for a bacterial glucoamylase (75.3 U/mg) and was also stable in a wide pH range (3.0–10.0). Although the enzyme was preferentially active with maltose, it was also able to hydrolyze different soluble starches such as those from potato, corn or rice. TeGA showed a high thermostability up to around 70 °C, which was increased in the presence of PEG8000, and also showed to be stable in the presence of moderate concentrations of ethanol. Conclusion: We propose that TeGA could be suitable for use in different industrial processes such as biofuel production and food processing.