LeBrun E, van Rapenbusch R
J Biol Chem. 1980 Dec 25;255(24):12034-6.
The tertiary structure of Bacillus subtilis levansucrase (EC 2.4.1.10) at 3.8 A resolution has been obtained from x-ray diffraction data by the method of multiple isomorphous replacements using three heavy atom derivatives. The crystals belong to space group P212121 with 1 molecule/crystallographic asymmetric unit. Unit cell dimensions are: a = 53.8 A, b = 67.7 A, and c = 125.6 A. Isomorphous heavy atom derivatives were prepared by soaking crystals in solutions containing K2Hg(CN)4, KAu(CN)2, and K2PtCl6. Precession photographs were taken of 29 reciprocal lattice planes of the native compound and three derivatives. The intensities were measured with an automatic integrating microdensitometer. The heavy atoms were located by means of two-dimensional difference Patterson and Fourier projections. The heavy atom parameters were refined by a least squares method. In the subsequent phases of calculatin, a final mean figure of merit equal to 0.74 was obtained for the independent reflectins. A 3.8 A electron density map based on phases from three heavy atom derivatives has been calculated. The electron density map of levansucrase suggests that the molecule is a very elongated ellipsoid with overall dimensions of 26 X 32 X 117 A. A model of levansucrae is also presented.
利用三种重原子衍生物，通过多同晶置换法从X射线衍射数据中获得了枯草芽孢杆菌果聚糖蔗糖酶（EC 2.4.1.10）在3.8埃分辨率下的三级结构。晶体属于空间群P212121，每个晶体学不对称单元中有1个分子。晶胞参数为：a = 53.8埃，b = 67.7埃，c = 125.6埃。通过将晶体浸泡在含有K2Hg(CN)4、KAu(CN)2和K2PtCl6的溶液中制备同晶重原子衍生物。对天然化合物和三种衍生物的29个倒易点阵平面拍摄了进动照片。用自动积分微密度计测量强度。通过二维差值帕特森图和傅里叶投影确定重原子的位置。用最小二乘法精修重原子参数。在后续的计算阶段，独立反射的最终平均品质因数为0.74。基于三种重原子衍生物的相位计算出了3.8埃的电子密度图。果聚糖蔗糖酶的电子密度图表明，该分子是一个非常细长的椭球体，总体尺寸为26×32×117埃。还给出了果聚糖蔗糖酶的模型。
