Fusion of Bacillus stearothermophilus leucine aminopeptidase II with the raw-starch-binding domain of Bacillus sp strain TS-23 α-amylase generates a chimeric enzyme with enhanced thermostability and catalytic activity

Bacillus stearothermophilus leucine aminopeptidase 11 (LAPII) was fused at its C-terminal end with the raw-starch-binding domain of Bacillus sp. strain TS-23 alpha-amylase. The chimeric enzyme (LAPsbd), with an apparent molecular mass of approximately 61 kDa, was overexpressed in IPTG-induced Escherichia coli cells and purified to homogeneity by nickel-chelate chromatography. The purified enzyme retained LAP activity and adsorbed raw starch. LAPsbd was stable at 70degreesC for 10 min, while the activity of wild-type enzyme was completely abolished under the same environmental condition. Compared with the wild-type enzyme, the twofold increase in the catalytic efficiency for LAPsbd was due to a 218% increase in the k(cat) value.