Observation of decreased radiation damage at higher dose rates in room temperature protein crystallography

Radiation damage can be a problem when utilizing ionizing X-radiation in macromolecular crystallography. The dose dependence of radiation damage to eight lysozyme crystals at room temperature (292 K) was investigated in order to provide an accurate comparison with cryotemperature (100 K) results and to allow researchers to calculate expected maximum room-temperature-crystal lifetimes prior to data collection. Results of intensity-loss analysis unexpectedly showed that the dose tolerated by a crystal is dependent on the dose rate according to a positive linear relationship (99% correlation coefficient); a 60% increase in dose rate gave a 4-fold increase in crystal lifetime over the range studied. Alternative metrics of damage were also assessed from room temperature data. In the dose-rate range tested (6 Gy s(-1) to 10 Gy s(-1)), data collection at 100 K appears to offer a 26-113 times increase in the lifetime of the crystal.