Chapter 4: Radiation Damage in Macromolecular Crystallography

Macromolecular crystals used for X-ray diffraction experiments inevitably suffer radiation damage due to the unavoidable absorption of incident X-rays. Here, we summarise our current knowledge and understanding of the phenomena involved, which has been accumulated by protein crystallographers since the first observations of such damage in room temperature crystals in 1962 by Colin Blake and David Phillips. Although the cryo-cooling (to 100 K) techniques introduced in the 1990s significantly reduced the rate of radiation damage to protein crystals, damage observations at cryo-temperatures are now commonplace. These effects not only have the potential to confuse biological interpretations of macromolecular structures, affecting the reaction mechanisms extracted from them, but can also prevent structure solution in the first place. The 4th generation synchrotrons currently coming on-line are set to exacerbate these challenging issues. The recent introduction of X-ray free electron lasers supplying short (between 10 and 80 fs) and very intense (10¹² photons pulse⁻¹) X-ray beams now provides the possibility to determine damage-free macromolecular structures at room temperature, allowing questions about the dynamic behaviour of proteins to be addressed.