Cloning, expression and characterization of highly thermo- and pH-stable maltogenic amylase from a thermophilic bacterium Geobacillus caldoxylosilyticus TK4

Abstract

Maltogenic amylases (MAases), a subclass of cyclodextrin (CD)-hydrolyzing enzymes, belong to glycoside hydrolase family 13. A gene corresponding to MA in Geobacillus caldoxylosilyticus TK4 (GcaTK4MA) was cloned into pET28a(+) vector and expressed in Escherichia coli with 6xHis-tag at the N-terminus. Herein, we report on the biochemical properties of a new thermo- and pH-stable MA. GcaTK4MA has similar properties those of other MAases in terms of the primary structure, preference for CD over starch and having an extra domain at its N- and C-terminals. The recombinant protein was purified efficiently by using one-step nickel affinity chromatography. The purified enzyme exhibited optimal activity for β-CD hydrolysis at 50 °C and pH 7.0. When the enzyme was separately incubated at 4 °C and 50 °C in the buffer solutions (pH 3.0–9.0) up to 7 days, it was seen that the enzyme had the higher stability at 50 °C than 4 °C. The enzyme retained about 80% of its original activity when it was incubated at 50 °C for 7 days. The enzyme activity was significantly inhibited by SDS and EDTA at the final concentration of 1%. These results suggest that this is the first reported MA having an extremely pH- and thermal stabilities.