Cloning, expression and characterization of an alkaline thermostable GH9 endoglucanase from Thermobifida halotolerans YIM 90462T

The endoglucanase gene, thcel9A, from Thermobifida halotolerans YIM 90462T was cloned and expressed in Escherichia coli BL 21(DE). The 2895-bp full-length gene encodes a 964-residue polypeptide (Thcel9A) containing a catalytic domain belonging to glycosyl hydrolases (GH) family 9. Phylogenetic analysis indicated that Thcel9A is closely related to Cel9A of Thermobifida fusca YX. Thcel9A was purified from the culture supernatant by Ni2+-affinity chromatography and the purified enzyme exhibited optimal activity at 55 °C and pH 8.0. Substrate specificity assays showed that it not only had CMCase activity, but also hydrolase activity on microcrystalline cellulose and filter paper. These properties suggested that Thcel9A is a classical GH9 group A endoglucanase.