Towards the Measurement of Ideal Data for Macromolecular Crystallography using Synchrotron Sources

Abstract Synchrotron radiation has been used extensively to overcome a variety of technical challenges involved in data collection from macromolecular crystals. The next generation of such sources offer a higher bril- liance at much shorter wavelengths than hitherto available. Hence, the quality of X-ray diffraction data from crystals of biological macromolecules will be further improved in terms of reduced systematic and random errors, in conjunction with a very high degree of completeness of, and multiple measure- ments within, the data set. Real data sets should be able to approach closely the quality of ideal data sets. Tests at CHESS are described of the feasibility of recording protein crystal diffraction patterns at ultra-short wavelengths (,~ = 0.3 A) and very-short wavelengths (A = 0.5 A), in monochromatic rotating crystal geometry. 1. Introduction Short-wavelength monochromatized beams have been very effective in macromolecular crystal data collection at sources such as the Daresbury SRS, particularly from viruses. Crystal absorption errors have been reduced and crystal lifetimes improved. The use of 0.9 A wavelength maximized the absorp- tion of photographic film as detector, due to the Br K edge, in a wavelength region favourable to the sample. Also, it is where the Daresbury Wiggler emission peaked (,~c = 0.9 A).* The next generation