title: Dark progression reveals slow timescales for radiation damage between T = 180 and 240 K.
abstract: Can radiation damage to protein crystals be `outrun' by collecting a structural data set before damage is manifested? Recent experiments using ultra-intense pulses from a free-electron laser show that the answer is yes. Here, evidence is presented that significant reductions in global damage at temperatures above 200 K may be possible using conventional X-ray sources and current or soon-to-be available detectors. Specifically, `dark progression' (an increase in damage with time after the X-rays have been turned off) was observed at temperatures between 180 and 240 K and on timescales from 200 to 1200 s. This allowed estimation of the temperature-dependent timescale for damage. The rate of dark progression is consistent with an Arrhenius law with an activation energy of 14 kJ mol(-1). This is comparable to the activation energy for the solvent-coupled diffusive damage processes responsible for the rapid increase in radiation sensitivity as crystals are warmed above the glass transition near 200 K. Analysis suggests that at T = 300 K data-collection times of the order of 1 s (and longer at lower temperatures) may allow significant reductions in global radiation damage, facilitating structure solution on crystals with liquid solvent. No dark progression was observed below T = 180 K, indicating that no important damage process is slowed through this timescale window in this temperature range.
authors: Physics Department, Cornell University, Ithaca, NY 14853, USA.
authors: Matthew
authors: M
authors: Warkentin
authors: Ryan
authors: R
authors: Badeau
authors: Jesse
authors: J
authors: Hopkins
authors: Robert E
authors: RE
authors: Thorne
mesh_terms: D018360:Crystallography, X-Ray / Q000379:methods*; D011506:Proteins / Q000737:chemistry; D013696:Temperature
chemical_list: D011506:Proteins