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

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 Ba²⁺, Mg²⁺, 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 Co²⁺ solution, which could correlate to the significantly pronounced enzymatic activities. However, BLA shows somewhat shrunken structures at pH 3.0 and in Hg²⁺ solution, supporting for the suppressed activities under these conditions.