Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy
Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy
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DOI：
10.1016/j.ultramic.2015.05.017
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发表时间：
2015-11-01
期刊：
影响因子：
2.2
通讯作者：
Henderson, R.
中科院分区：
文献类型：
--
作者：
McMullan, G.;Vinothkumar, K. R.;Henderson, R.
我们在Falcon II直接电子探测器上用300keV电子记录了纯闪冻无定形冰和预辐照无定形碳薄膜的剂量分级电子冷冻显微镜图像。我们在求和框架的功率谱和单个框架的功率谱中都观察到Thon环[1]。来自非晶态碳图像的Thon环总是在总和图像的功率谱中更明显，而无定形冰的那些在单个图像的功率谱总和中更明显。这一差异表明，尽管预先辐照的碳在暴露期间表现得像固体一样，但无定形冰的行为像流体，单个水分子经历了束流诱导的运动。根据测量的功率谱幅度随每幅图像中的电子数的变化，我们推导出，对于每300keV(-)/埃(2)的入射，水分子被随机移动了约1.1埃(2)的平均平方距离。诱导运动导致了300keV电子的最佳曝光，每幅图像的电子数为4.0e/埃(2)，用来观测围绕着无定形冰的3.7埃散射峰的Thon环。束诱导的水分子运动产生嵌入的大分子的伪布朗运动。由此产生的单粒子图像模糊，在辐射损伤的基础上，为确定大分子结构所能达到的最小B因子增加了一项额外的项。(C)2015年提交人。爱思唯尔出版公司(Elsevier B.V.)
We have recorded dose-fractionated electron cryo-microscope images of thin films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on a Falcon II direct electron detector using 300 keV electrons. We observe Thon rings [1] in both the power spectrum of the summed frames and the sum of power spectra from the individual frames. The Thon rings from amorphous carbon images are always more visible in the power spectrum of the summed frames whereas those of amorphous ice are more visible in the sum of power spectra from the individual frames. This difference indicates that while pre-irradiated carbon behaves like a solid during the exposure, amorphous ice behaves like a fluid with the individual water molecules undergoing beam-induced motion. Using the measured variation in the power spectra amplitude with number of electrons per image we deduce that water molecules are randomly displaced by a mean squared distance of similar to 1.1 angstrom(2) for every incident 300 keV e(-)/angstrom(2). The induced motion leads to an optimal exposure with 300 keV electrons of 4.0 e /angstrom(2) per image with which to observe Thon rings centred around the strong 3.7 angstrom scattering peak from amorphous ice. The beam-induced movement of the water molecules generates pseudo-Brownian motion of embedded macromolecules. The resulting blurring of single particle images contributes an additional term, on top of that from radiation damage, to the minimum achievable B-factor for macromolecular structure determination. (C) 2015 The Authors. Published by Elsevier B.V.