Chemical bonding effects in the determination of protein structures by electron crystallography.
Chemical bonding effects in the determination of protein structures by electron crystallography.
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电子晶体学测定蛋白质结构中的化学键效应。
DOI：
10.1107/s0108767398009726
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Downing,KH
中科院分区：
文献类型：
--
作者：
Chang,S;Head-Gordon,T;Glaeser,RM;Downing,KH
电子的散射受到价电子分布的影响，价电子参与化学键，从而改变原子核的静电屏蔽。这一效果对于低角度散射尤为显著。因此，虽然化学键效应很难用小单位细胞材料来测量，但它们可以在用电子结晶学研究蛋白质方面发挥重要作用。这项工作研究了在电子结晶学通常用于确定蛋白质结构的分辨率范围内，具有代表性的蛋白质片段和核苷酸结合蛋白质的模型配体的化学键效应的大小。用从头算方法计算了这两个实验分子及其自由原子的静电势。在低于5 ä的分辨率范围内，散射幅度的差异可以远远超过10%，尤其是在电离侧链和配体的情况下。我们的结论是，使用基于分子的散射因子可以更准确地表示在电子结晶学研究中获得的低分辨率数据。在分辨率低于5 ä的情况下比较中性和离子结构因子还可以灵敏地确定电荷状态，这对生物功能很重要，而X射线晶体测量无法获得这一结果。
Scattering of electrons is affected by the distribution of valence electrons that participate in chemical bonding and thus change the electrostatic shielding of the nucleus. This effect is particularly significant for low-angle scattering. Thus, while chemical bonding effects are difficult to measure with small-unit cell materials, they can be substantial in the study of proteins by electron crystallography. This work investigates the magnitude of chemical bonding effects for a representative collection of protein fragments and a model ligand for nucleotide-binding proteins within the resolution range generally used in determining protein structures by electron crystallography. Electrostatic potentials were calculated by ab initio methods for both the test molecules and for superpositions of their free atoms. Differences in scattering amplitudes can be well over 10% in the resolution range below 5 Å and are especially large in the case of ionized side chains and ligands. We conclude that the use of molecule-based scattering factors can provide a much more accurate representation of the low-resolution data obtained in electron crystallographic studies. The comparison of neutral and ionic structure factors at resolutions below 5 Å can also provide a sensitive determination of charge states, important for biological function, that is not accessible from X-ray crystallographic measurements.