Novel α-Glucosidase from Extreme Thermophile Thermus caldophilus GK24

摘要

α-Glucosidase of an extreme thermophile, Thermus caldophilus GK24 (TcaAG), was purified 80-fold from cells to a homogeneous state and characterized. The enzyme exhibited optimum activity at pH 6.5 and 90 ℃, and was stable from pH 6.0 to 8.5 and up to 90 ℃. The enzyme had half-life of 85 minutes at 90 ℃. An analysis of the substrate specificity showed that the enzyme hydrolyzed the non-reducing terminal unit of α-1,6-glucosidic linkages of isomaltosaccharides and panose, α-1,3-glycosidic bond of nigerose and turanose, and α-1,2-glycosidic bond of sucrose. The gene encoding the TcaAG was cloned, sequenced, and expressed in E. coli. The nucleotide sequence of the gene encoded a 530 amino acid polypeptide and had a G+C content of 68.4% with a strong bias for G or C in the third position of the codons (93.6%). A sequence analysis revealed that TcaAG belonged to the α-amylase family. We suggest that this monomeric, thermostable, and broad-acting α-glucosidase is a departure from previously exhibited specificities. It is, therefore, a novel α-glucosidase.