Reduction of radiation damage and other benefits of short wavelengths for macromolecular crystallography data collection

Circumventing radiation damage remains a major problem for X-ray macromolecular crystallography. Analysis of diffraction data collected from normal-sized cryocooled lysozyme crystals shows that the dose required to collect a data set of prescribed resolution and signal-to-noise ratio, assuming an ideally efficient detector, decreases with increasing photon energy in the investigated 6.533 keV range. For example, the data collection efficiency is increased by a factor of similar to 8 from 8 to 33 keV. Monte Carlo simulations on lysozyme crystals in the range 580 keV, taking into account electron escape from samples of different size, also show a positive effect of high energy (albeit less pronounced than in experiments), especially for micrometre-sized samples, and suggest that the optimum energy range is similar to 2441 keV, depending on crystal size. The importance of counting pixel detectors with a good efficiency at high energy is underlined. Macromolecular crystallography beamlines should be modified, or purposely designed, in order to benefit from higher-energy radiation through reduction of global radiation damage, better data accuracy and extension of phasing by anomalous dispersion.