Absorbed dose calculations for macromolecular crystals: improvements to RADDOSE
Absorbed dose calculations for macromolecular crystals: improvements to RADDOSE
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DOI：
10.1107/s0909049508040430
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发表时间：
2009-03-01
影响因子：
2.5
通讯作者：
Garman, Elspeth F.
中科院分区：
文献类型：
--
作者：
Paithankar, Karthik S.;Owen, Robin Leslie;Garman, Elspeth F.
辐射损伤是大分子结晶学中一个不受欢迎和不可避免的方面。为了量化X射线引起的变化的程度，了解剂量(单位质量的吸收能量)是必要的，因为它是绘制诸如衍射强度损失和B因子等变量的明显度量。本文对RADDOSE程序进行了重大改进，以精确计算大分子晶体吸收剂量。具体地说，现在包括了由于光电吸收后原子的去激发而逃逸的荧光光子造成的能量损失的概率。对于较轻的元素，荧光及其随后从晶体中逃逸的可能性都是可以忽略的，但对于较重的原子，荧光的可能性变得很大(例如，与K壳层激发的铁原子的俄歇电子衰减相反，30%)，这具有减少吸收剂量的效果。以含铁蛋白质、2-硒蛋氨酸蛋白质晶体、铀衍生物蛋白质晶体和核酸样品为例，给出了这种现象对剂量计算的影响。例如，包含荧光逃逸导致在硒K边缘照射的典型硒蛋氨酸蛋白质晶体的计算吸收剂量减少高达27%。
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.