Development of electron diffraction methods for protein crystallography

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Rotation camera and related methods for electron diffraction from thin protein crystals have been developed for facilitating the structure determination of membrane proteins of biological importance. This involved many modifications of the microscope and developments of computer control software and high tilt angle cryospecimen holder. Also developed was a set of programmes for indexing of reflections, integration and scaling of electron diffraction intensities. These developments were necessary because the diffraction patterns from multilayer crystals should be treated as those from 3-dimensional crystals, yet cannot be analysed by conventional X-ray crystallography.First version of the rotation camera used DC motor and integrated rotary encoder, and slow-scan CCD detector. This system was constructed without much investment and can be applied to most of modern electron microscopes. This system was applied to ultrathin crystals of Ca^<2+>-ATPase and yielded preliminary data to ±30゜ of tilt. By using"minimum dose electron diffraction procedures"developed in this study, up to 100 diffraction patters (rotation images) could be recorded from each area. The second version consisted of Heidenhein's high-precision rotary encoder and pulse motor. The hardware Was assembled but the control software was incomplete and yet to be developed. Nevertheless, the preliminary results obtained are very promising.