X-ray radiation damage to biological samples: recent progress.

With the continuing development of beamlines for macromolecular crystallography (MX) over the last few years providing ever higher X-ray flux densities, it has become even more important to be aware of the effects of radiation damage on the resulting structures. Nine papers in this issue cover a range of aspects related to the physics and chemistry of the manifestations of this damage, as observed in both MX and small-angle X-ray scattering (SAXS) on crystals, solutions and tissue samples. The reports include measurements of the heating caused by X-ray irradiation in ruby microcrystals, low-dose experiments examining damage rates as a function of incident X-ray energy up to 30 keV on a metallo-enzyme using a CdTe detector of high quantum efficiency as well as a theoretical analysis of the gains predicted in diffraction efficiency using these detectors, a SAXS examination of low-dose radiation exposure effects on the dissociation of a protein complex related to human health, theoretical calculations describing radiation chemistry pathways which aim to explain the specific structural damage widely observed in proteins, investigation of radiation-induced damage effects in a DNA crystal, a case study on a metallo-enzyme where structural movements thought to be mechanism related might actually be radiation-damage-induced changes, and finally a review describing what X-ray radiation-induced cysteine modifications can teach us about protein dynamics and catalysis. These papers, along with some other relevant literature published since the last Journal of Synchrotron Radiation Radiation Damage special issue in 2017, are briefly summarized below.