Radiation Damage

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Macromolecular crystals suffer damage from ionizing radiation. This is especially problematic at the high intensity X-ray sources at 3rd generation synchrotrons. The problem of radiation damage in macromolecular crystallography has been studied quite extensively with focus on low temperature (100K and below). However, recently attention has moved to high temperatures. This interest has been spurred in part by the development of very fast detectors, which are opening the possibility of collecting X-ray data at synchrotrons at ~room temperature before radiation damage has had a chance to set in.

We looked at the temperature dependence of radiation damage to crystals of thermolysin (at 100K vs 160K), and tried to understand the results in terms of the relationship between protein atoms and their proximity to solvent channels. The take home message can be summarized in the following figures from our paper: Juers, D. H. & Weik, M. Similarities and differences in radiation damage at 100 K versus 160 K in a crystal of thermolysin. (2011) J. Synchrotron Rad. 18, 329-337.

Hotspots - the atoms most affected by radiation exposure (as measured by relative change in atom B-factor). Left - 100K and Right - 160 K. At the higher temperature the hotspots are more concentrated near the surface of the protein, while at 100 K the hotspots are distributed relatively uniformly throughout the molecule

Dependence of radiation susceptibility on residue depth (or distance to nearest solvent channel) as measured with map_channels.

The top graph shows that at 100 K, there is not a strong correlation between the susceptibility and the residue depth.

The bottom graph, at 160 K, shows a stronger correlation.

This implies "protection" from the effects of radiation for residues further from solvent channels at 160 K but not at 100 K.