Direct phase determination in protein electron crystallography: the pseudo-atom approximation.
The crystal structure of halorhodopsin is determined directly in its centrosymmetric projection using 6.0-A-resolution electron diffraction intensities, without including any previous phase information from the Fourier transform of electron micrographs. The potential distribution in the projection is assumed a priori to be an assembly of globular densities. By an appropriate dimensional re-scaling, these "globs" are then assumed to be pseudo-atoms for normalization of the observed structure factors. After this treatment, the structure is determined directly by conventional direct methods, followed by Fourier refinement, leading to a mean phase deviation of only 20 degrees (from the values originally found from the image transform) for the 45 most intense reflections.
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Electron Diffraction Department, Hauptman-Woodward Medical Research Institute, Inc., Buffalo, NY 14203-1196, USA.
D001436:Bacteriorhodopsins / Q000737:chemistry*; D003461:Crystallography; D005583:Fourier Analysis; D019617:Halobacterium salinarum / Q000737:chemistry*; D025602:Halorhodopsins; D008565:Membrane Proteins / Q000737:chemistry; D008854:Microscopy, Electron; D017433:Protein Structure, Secondary
D025602:Halorhodopsins; D008565:Membrane Proteins; D001436:Bacteriorhodopsins