Spectroscopic Analysis of Chloride Ion-induced Structural Change of Bacillus Amyloliquefaciens α-Amylase

Abstract

The structural change of Bacillus amyloliquefaciens α -amylase (Ba α -amylase) induced by chloride ion was studied by fluorescence spectra, Fourier-transformation infrared (FT-IR) spectroscopy and circular dichroism (CD) spectroscopy. It was found that when chloride ion concentration was below 20.0 mM, the Ba α -amylase was activated by increasing chloride ion concentration; when chloride ion concentration was over 20.0 mM, the biological activity of Ba α -amylase was inhibited by increasing chloride ion concentration. The spectroscopic analyses illustrated that the change in Ba α -amylase biological activity was caused by the alteration in secondary structure of Ba α -amylase. When chloride ion showed activation effect to Ba α -amylase, part of the random coils in Ba α -amylase gradually transformed to α -helix and β -sheet with increasing chloride ion concentration and the Ba α -amylase transited from relatively disordered conformation to relatively ordered one. Whereas when chloride ion showed inhibition effect on the biological activity of Ba α -amylase, part of α -helix and β -sheet in Ba α -amylase gradually transformed to random coil with increasing chloride ion concentration and the Ba α -amylase went back from the relatively ordered conformation to the relatively disordered one. This work shows the dependency of change in biological activity to alteration in secondary structure of protein molecule, which may provide some useful information in the actual application and exploration on action mechanism of proteins. The biological activities of Ba α-amylases increased quickly with the increase of chloride ion concentrations under 20.0 mM that the change was caused by transforming random coil to α-helix and β-sheet; the relative activities of Ba α-amylases decreased slowly with the increase of chloride ion concentrations exceed 20.0 mM that the change was caused by transforming α-helix and β-sheet to random coil. When chloride ion concentration was 20.0 mM, the biological activity of Ba α-amylases was the maximum.