(E160A)和(E160D)天花粉蛋白两种突变体晶体结构研究

培养了（Ｅ１６０Ａ）ＴＣＳ和（Ｅ１６０Ｄ）ＴＣＳ的单晶。在ＭＡＲＲｅｓｅａｒｃｈ面探测器系统上分别收集了０．１９３ｎｍ和０．２０ｎｍ分辨率的Ｘ射线衍射数据。数据处理用ＭＡＲＳＣＡＬＥ程序系统完成。用同晶差值Ｆｏｕｒｉｅｒ法解析了突变体的晶体结构，结构修正利用Ｘ－ＰＬＯＲ程序。修正结果，晶体学Ｒ因子分别为０．１７５，０．１７９，键长和键角的ＲＭＳ偏差分别为０．００１１ｎｍ和２．４５７°，０．００１３ｎｍ和２．６７５°。在这两个突变体的结构中均未见到Ｇｌｕ１８９侧链方向的改变。通过对（Ｅ１６０Ａ）ＴＣＳ和（Ｅ１６０Ｄ）ＴＣＳ的结构比较，说明（Ｅ１６０Ｄ）ＴＣＳ活性低于（Ｅ１６０Ａ）ＴＣＳ的原因：这可能是由于在（Ｅ１６０Ｄ）ＴＣＳ中Ｔｙｒ１１１和Ｔｙｒ７０的侧链都具有较大的运动性，使它们与腺嘌呤碱基的芳香堆垛作用减弱，从而导致活性的降低

CRYSTAL STRUCTURE OF (E160A) AND (E160D) TRICHOSANTHIN

Crystals of (E160A)TCS and (E160D)TCS were grown by vapor diffusion method. X-ray diffraction data were collected to 0.193nm and 0.20nm resolution on a Mar Research area detector. The Mar Scale program was used for data processing and X-PLOR package. The structure analysis and their refinement were studied using Difference Fourier Method. The final crystallographic R factor is 0.175 and 0.179 respectively. The RMS deviations of bond length and angle of these mutants are 0.0011nm and 2.457, 0.0013nm and 2.675° respectively. The direction change of Glu189 side chain was not observed in these two crystal structures. The fact, that the activity of (E160D)TCS is less than (E160A)TCS, is elucidated by structure comparison .In (E160D)TCS structure the aromatic stack between Tyr111, Tyr70 and adenine is reduced because the movement of Tyr111 and Tyr70 side chain increase.