Bacillus licheniformis α-amylase: Structural feature in a biomimetic solution and structural changes in extrinsic conditions.

Bacillus licheniformis α-amylase (BLA) in a biomimetic buffer and extrinsic solutions (various pH values, temperatures, and metal ions) has been investigated for the first time in the view of three-dimensional (3D) structure by synchrotron X-ray and dynamic light scattering analyses. BLA in buffer is determined to have a structure resembling its crystallographic structure; but the 3D structure is slightly larger than the crystal structure. Such a structure is maintained with little variations in extrinsic solutions of pH 4.0-9.7, temperature 4-55 °C, and metal ions such as Ba, Mg, and Li. These results collectively inform that BLA tends to favorably form a stable monomeric structure, which could provide structural clues to its enzymatic activities in moderate levels. Interestingly, BLA is found to reveal highly expanded structures at 65-75 °C and in Co solution, which could correlate to the significantly pronounced enzymatic activities. However, BLA shows somewhat shrunken structures at pH 3.0 and in Hg solution, supporting for the suppressed activities under these conditions.