Purification, Biochemical Characterization, and Gene Cloning of a New Extracellular Thermotolerant and Glucose Tolerant Maltooligosaccharide-Forming [alpha]-Amylase from an Endophytic Ascomycete Fusicoccum sp. BCC4124

An endophytic fungus, Fusicoccum sp. BCC4124, showed strong amylolytic activity when cultivated on multi-enzyme induction enriched medium and agro-industry substrates. α-Amylase and α-glucosidase activities were highly induced in the presence of maltose and starch. The purified target α-amylase, Amy-FC1, showed strong hydrolytic activity on soluble starch (kcat/Km=6.47×103 min-1(ml/mg)) and selective activity on γ- and β-cyclodextrins, but not on α-cyclodextrin. The enzyme worked optimally at 70 °C in a neutral pH range with t1/2 of 240 min in the presence of Ca2+ and starch. Maltose, matotriose, and maltotetraose were the major products from starch hydrolysis but prolonged reaction led to the production of glucose, maltose, and maltotriose from starch, cyclodextrins, and maltooligosaccharides (G3-G7). The amylase showed remarkable glucose tolerance up to 1 M, but was more sensitive to inhibition by maltose. The deduced protein primary structure from the putative gene revealed that the enzyme shared moderate homology between α-amylases from Aspergilli and Lipomyces sp. This thermotolerant, glucose tolerant maltooligosaccharide-forming α-amylase is potent for biotechnological application.