Biophysical characterization of a recombinant α-amylase from thermophilic Bacillus sp. strain TS-23.

Environmental variables can significantly influence the folding and stability of a protein molecule. In the present study, the biophysical properties of a truncated Bacillus sp. TS-23 α-amylase (BACΔNC) were characterized in detail by glutaraldehyde cross-linking, analytical ultracentrifugation, and various spectroscopic techniques. With cross-linking experiment and analytical ultracentrifuge, we demonstrated that the oligomeric state of BACΔNC in solution is monomeric. Far-UV circular dichroism analysis revealed that the secondary structures of BACΔNC were significantly altered in the presence of various metal ions and SDS, whereas acetone and ethanol had no detrimental effect on folding of the enzyme. BACΔNC was inactive and unstable at extreme pH conditions. Thermal unfolding of the enzyme was found to be highly irreversible. The native enzyme started to unfold beyond ~0.2 M guanidine hydrochloride (GdnHCl) and reached an unfolded intermediate, [GdnHCl](0.5, N-U), at 1.14 M. BACΔNC was active at the concentrations of urea below 6 M, but it experienced an irreversible unfolding by >8 M denaturant. Taken together, this work lays a foundation for the future structural studies with Bacillus sp. TS-23 α-amylase, a typical member of glycoside hydrolases family 13.