Direct structure determination by electron crystallography: protein data sets.

Applications of the Sayre equation to the electron crystallographic analysis of protein structures are demonstrated. Starting with a lower-resolution basis phase set obtained from the Fourier-transform of an electron micrograph, it is possible, for example, to extend directly to the higher resolution of the electron diffraction pattern. Examples of such analyses include bacteriorhodopsin, halorhodopsin and the Omp F porin from the outer membrane of Escherichia coli. If a multisolution approach is taken, it may also be possible to carry out ab initio phase determinations, as demonstrated with low-resolution diffraction amplitudes from a negatively-stained membrane protein crystal.