Biochemical Characterization of a Novel Thermostable 1,4-α-Glucoamylase from Aspergillus brasiliensis Strain Isolated in the Brazilian Atlantic Forest

Glucoamylases are exo-enzymes that cleave the ends of the starch chain, releasing glucose units. In the current work, we described a novel 1,4-alpha-glucoamylase from an A. brasiliensis strain isolated from an environmental sample. The purified glucoamylase, GlaAb, has a molecular mass of 69 kDa and showed a starch binding domain. GlaAb showed a similar sequence to other fungal glucoamylases, and the molecular 3D model analysis of GlaAb suggests an overall structure as described in the literature, except by elongation in the loop connecting the 4th and 5th alpha-helices. The enzyme showed activity over a wide range of pH and temperature, with maximum activity at pH 4.5 and 60 degrees C. GlaAb was stable at 50 degrees C for 7 h, maintaining 67% residual activity, and it was not inhibited by glucose up to 0.1 M. The glucoamylase was 65% more active in the presence of Mn2+ and showed a Km of 2.21 mg mL(-1), Vmax of 155 U mg(-1), Kcat 179 s(-1), and Kcat/Km 81.06 mg mL(-1) s(-1) using potato starch as substrate. The results obtained are promising and provide the basis for the development of applications of GlaAb in the industrial process.