Neutze R, Wouts R, van der Spoel D, Weckert E, Hajdu J
Department of Biochemistry, Biomedical Centre, Uppsala University, Sweden.
Nature. 2000 Aug 17;406(6797):752-7. doi: 10.1038/35021099.
Sample damage by X-rays and other radiation limits the resolution of structural studies on non-repetitive and non-reproducible structures such as individual biomolecules or cells. Cooling can slow sample deterioration, but cannot eliminate damage-induced sample movement during the time needed for conventional measurements. Analyses of the dynamics of damage formation suggest that the conventional damage barrier (about 200 X-ray photons per A2 with X-rays of 12 keV energy or 1 A wavelength) may be extended at very high dose rates and very short exposure times. Here we have used computer simulations to investigate the structural information that can be recovered from the scattering of intense femtosecond X-ray pulses by single protein molecules and small assemblies. Estimations of radiation damage as a function of photon energy, pulse length, integrated pulse intensity and sample size show that experiments using very high X-ray dose rates and ultrashort exposures may provide useful structural information before radiation damage destroys the sample. We predict that such ultrashort, high-intensity X-ray pulses from free-electron lasers that are currently under development, in combination with container-free sample handling methods based on spraying techniques, will provide a new approach to structural determinations with X-rays.
X射线及其他辐射造成的样品损伤限制了对非重复性和不可复制结构（如单个生物分子或细胞）的结构研究分辨率。冷却可以减缓样品降解，但无法消除传统测量所需时间内损伤引起的样品移动。对损伤形成动力学的分析表明，传统的损伤阈值（对于能量为12keV或波长为1Å的X射线，每Ų约200个X射线光子）在非常高的剂量率和非常短的曝光时间下可能会提高。在此，我们利用计算机模拟来研究从单个蛋白质分子和小聚集体对强飞秒X射线脉冲的散射中可以恢复的结构信息。对辐射损伤作为光子能量、脉冲长度、积分脉冲强度和样品尺寸的函数的估计表明，使用非常高的X射线剂量率和超短曝光的实验可能在辐射损伤破坏样品之前提供有用的结构信息。我们预测，目前正在研发的自由电子激光产生的这种超短、高强度X射线脉冲，与基于喷雾技术的无容器样品处理方法相结合，将为利用X射线进行结构测定提供一种新方法。
