Biochemical Characterization of an Endoglucanase GH7 from Thermophile Thermothielavioides terrestris Expressed on Aspergillus nidulans

Endoglucanases (EC 3.2.1.4) are important enzymes involved in the hydrolysis of cellulose, acting randomly in the beta-1,4-glycosidic bonds present in the amorphous regions of the polysaccharide chain. These biocatalysts have been classified into 14 glycosyl hydrolase (GH) families. The GH7 family is of particular interest since it may act on a broad range of substrates, including cellulose, beta-glucan, and xylan, an attractive feature for biotechnological applications, especially in the renewable energy field. In the current work, a gene from the thermophilic fungus Thermothielavioides terrestris, encoding an endoglucanase GH7 (TtCel7B), was cloned in the secretion vector pEXPYR and transformed into the high-protein-producing strain Aspergillus nidulans A773. Purified TtCel7B has a molecular weight of approximately 66 kDa, evidenced by SDS-PAGE. Circular dichroism confirmed the high beta-strand content consistent with the canonical GH7 family beta-jellyroll fold, also observed in the 3D homology model of TtCel7B. Biochemical characterization assays showed that TtCel7B was active over a wide range of pH values (3.5-7.0) and temperatures (45-70 degrees C), with the highest activity at pH 4.0 and 65 degrees C. TtCel7B also was stable over a wide range of pH values (3.5-9.0), maintaining more than 80% of its activity after 24 h. The K-M and Vmax values in low-viscosity carboxymethylcellulose were 9.3 mg mL(-1) and 2.5 x 10(4) U mg(-1), respectively. The results obtained in this work provide a basis for the development of applications of recombinant TtCel7B in the renewable energy field.