Crystallization and preliminary X-ray diffraction studies of Tyr167His mutant α-cyclodextrin glucanotransferase from Bacillus macerans

Improving the specificity of α-cyclodextrin glucanotransferase is a significant issue in the field of α-cyclodextrin production. In this study, a constructed Y167H mutant α-cyclodextrin glucanotransferase with enhanced α-cyclodextrin specificity was successfully expressed and purified. Single crystals were grown using PEG 4000 as a precipitating agent by the hanging-drop vapour-diffusion method at 293 K. The crystals exhibited two kinds of morphology in different crystallization conditions. The crystals diffracted to at least 2.2 Å resolution (space group P2₁2₁2₁), with unit-cell parameters a = 65.69, b = 78.70, c = 137.00 Å. Assuming the asymmetric cell to be occupied by a monomer of 75 kDa, the unit cell contains 43.77% solvent with a crystal volume per protein mass, V_M, of 2.19 ų Da⁻¹.