Absorbed dose calculations for macromolecular crystals: improvements to RADDOSE

Radiation damage is an unwelcome and unavoidable aspect of macromolecular crystallography. In order to quantify the extent of X‐ray‐induced changes, knowledge of the dose (absorbed energy per unit mass) is necessary since it is the obvious metric against which to plot variables such as diffraction i...

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Bibliographic Details
Published in:Journal of synchrotron radiation 2009-03, Vol.16 (2), p.152-162
Main Authors: Paithankar, Karthik S., Owen, Robin Leslie, Garman, Elspeth F.
Format: Article
Language:English
Subjects:
absorbed dose
Algorithms
Biopolymers - chemistry
Biopolymers - radiation effects
Computer Simulation
Crystallization - methods
experimental dose limit
fluorescence escape
macromolecular crystallography
Macromolecular Substances - chemistry
Macromolecular Substances - radiation effects
Models, Chemical
photoelectric absorption
Radiation Dosage
Radiometry - methods
Software
X-Ray Diffraction - methods
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Summary:Radiation damage is an unwelcome and unavoidable aspect of macromolecular crystallography. In order to quantify the extent of X‐ray‐induced changes, knowledge of the dose (absorbed energy per unit mass) is necessary since it is the obvious metric against which to plot variables such as diffraction intensity loss and B factors. Significant improvements to the program RADDOSE for accurately calculating the dose absorbed by macromolecular crystals are presented here. Specifically, the probability of energy loss through the escape of fluorescent photons from de‐excitation of an atom following photoelectric absorption is now included. For lighter elements, both the probability of fluorescence and of its subsequent escape from the crystal are negligible, but for heavier atoms the chance of fluorescence becomes significant (e.g. 30% as opposed to Auger electron decay from a K‐shell excited iron atom), and this has the effect of reducing the absorbed dose. The effects of this phenomenon on dose calculations are presented for examples of crystals of an iron‐containing protein, 2‐selenomethionine proteins, a uranium derivatised protein, and for a nucleic acid sample. For instance, the inclusion of fluorescent escape results in up to a 27% decrease in the calculated absorbed dose for a typical selenomethionine protein crystal irradiated at the selenium K‐edge.
ISSN:1600-5775
0909-0495
1600-5775
DOI:10.1107/S0909049508040430