Structural and biochemical features of acidic α-amylase of Bacillus acidicola

The investigation is aimed at understanding structure-function aspect of α-amylase of an acidophilic bacterium Bacillus acidicola (BAamy), which is Ca(2+)-independent and active at acidic pH of native starch, and thus, suits better in starch saccharification process. The CD spectroscopic data analysis revealed that the enzyme has 30% α-helices, 14.2% β-sheets, and 55.8% random coils at 60 °C and pH 4.0. Using Bacillus stearothermophilus α-amylase (BStA) as the template, 3-D structure of rBAamy has been proposed. A complete loss in α-amylase activity was recorded when the amino acid residues (D231, E261 and D328) were substituted that confirmed their role in catalysis. The CD studies indicated a decrease in the α-helices content below and beyond the optimum pH and temperature that suggests a critical role of α-helix in maintaining the structural conformation of the enzyme. Fluorescence-quenching by N-bromosuccinimide (NBS) suggested the role of tryptophan in maintaining structural integrity of α-amylase and that by acrylamide indicated interaction by simple collision process.