Application of direct method to electron crystallographic image processingfor two-dimensional protein crystals

The direct method was applied to the image processing for [001] simulated h igh-resolution electron microscope images of protein streptavidin. The imag e deconvolution was carried out for two images of different defocus values such that the structural information loss due to the zero crosses of contra st transfer function could be compensated. It is shown that the determined defocus values based on two images combined are closer to the true ones tha n those based on a single image. The phase extension was also carried out f or this protein. The initial structure factors were calculated from the the oretical structure model, with the phases of 0.30 nm resolution and amplitu des of 0.25 nm resolution. Both the deconvoluted image of 0.30 nm resolutio n and projected crystal structure of 0.25 nm resolution obtained are in agr eement with the projected potential distribution maps of theoretical struct ure model.