Open AccessAbsorbed dose calculations for macromolecular crystals: improvements to RADDOSE
Author(s) -
Paithankar Karthik S.,
Owen Robin Leslie,
Garman Elspeth F.
Publication year - 2009
Publication title -
journal of synchrotron radiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.172
H-Index - 99
ISSN - 1600-5775
DOI - 10.1107/s0909049508040430
Subject(s) - macromolecule , absorbed dose , protein crystallization , crystal (programming language) , fluorescence , chemistry , absorption (acoustics) , absorption edge , atom (system on chip) , excited state , crystallography , radiochemistry , radiation , atomic physics , materials science , physics , crystallization , optics , biochemistry , optoelectronics , organic chemistry , band gap , computer science , embedded system , programming language , composite material
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.