Impact of Arg210-Ser211 deletion on thermostability of a truncated Bacillus sp. strain TS-23 α-amylase

One deletion mutant was constructed from the structural gene of a truncated Bacillus sp. strain TS-23 α-amylase (BACΔNC) by site-directed mutagenesis. BACΔNC and BACΔNC/ΔR210-S211 were overexpressed in recombinant Escherichia coli M15 cells and purified to nearly homologous by nickel-chelate chromatography. BACΔNC and BACΔNC/ΔR210-S211 were very similar with respect to specific activity, kinetic parameters, pH–activity profile, and temperature–activity curve. An increased half-life at 70 °C was observed for BACΔNC/ΔR210-S211, suggesting that Arg210-Ser211 deletion leads to a conformational change of the enzyme. Tryptophan emission fluorescence and circular dichroism spectra were nearly identical for the wild-type enzyme and BACΔNC/ΔR210-S211, but they showed a different sensitivity towards temperature-induced denaturation. These results indicated that the rigidity of the enzyme has been altered by Arg210-Ser211 deletion.