Overexpression and characterization of an extremely thermostable maltogenic amylase, with an optimal temperature of 100 °C, from the hyperthermophilic archaeon Staphylothermus marinus

A gene encoding a hyperthermostable maltogenic amylase of Staphylothermus marinus (SMMA) was cloned and overexpressed in Escherichia coli. SMMA consisted of 696 amino acids with a predicted molecular mass of 82.5 kDa. The enzyme was active in acidic conditions (pH 3.5–5.0), with an optimal pH of 5.0, and was extremely thermostable, with a temperature optimum of 100 °C and a melting temperature of 109 °C, both of which extremely favored the starch conversion process. SMMA hydrolyzed linear malto-oligosaccharides, starch, cyclodextrins, and cycloamylose, primarily to maltose and glucose, and showed highest activity toward acarbose and pullulan, hydrolyzed to acarviosine-glucose and panose, respectively. Investigation of the cleavage mode using 14C-maltoheptaose revealed that SMMA preferentially hydrolyzed the first and second glycosidic bonds from the reducing end. To our knowledge, this enzyme is the most thermostable maltogenic amylase yet reported, and might be of potential value in the food and starch industries.