直接法应用于蛋白质二维晶体的电子晶体学图像处理

试把直接法应用于抗生蛋白链菌素(streptavidin)沿［001］方向投影的模拟像和相应的理论结构因子作图像处理.先用两张高分辨电子显微像作直接法解卷，以互补因衬度传递函数的作用而损失的结构信息，求得的欠焦值比用单张像解卷的结果更接近真实值.把从结构模型计算出的030nm以内的相位，以及025nm以内的振幅作为起始数据，进行直接法相位外 推，并借助团簇分析方法得到030nm至025nm之间的相位.所得分辨率为030nm的解卷像 和分辨率为025nm的晶体结构投影均与理论结构模型的相应投影电 关键词： 高分辨电子显微学 直接法 图像处理

APPLICATION OF DIRECT METHOD TO ELECTRON CRYSTALLOGRAPHIC IMAGE PROCESSING FOR T WO-DIMENSIONAL PROTEIN CRYSTALS

The direct method was applied to the image processing for 001] simulated high-r esolution electron microscope images of protein streptavidin.The image deconvolu tion was carried out for two images of different defocus values such that the st ructural information loss due to the zero crosses of contrast transfer function could be compensated.It is shown that the determined defocus values based on two images combined are closer to the true ones than those based on a single image. The phase extension was also carried out for this protein.The initial structure factors were calculated from the theoretical structure model,with the phases of 0.30nm resolution and amplitudes of 0.25nm resolution.Both the deconvoluted imag e of 0.30nm resolution and projected crystal structure of 0.25nm resolution obta ined are in agreement with the projected potential distribution maps of theoreti cal structure model.