Department of Chemistry and Chemical Biology, BioMaPS Institute, Rutgers University, Piscataway, NJ 08854, USA.
J Biomol NMR. 2011 Nov;51(3):303-12. doi: 10.1007/s10858-011-9556-7. Epub 2011 Aug 26.
Individual peptide groups in proteins must exhibit some variation in the chemical shift anisotropy (CSA) of their constituent atoms, but not much is known about the extent or origins of this dispersion. Direct spectroscopic measurement of CSA remains technically challenging, and theoretical methods can help to overcome these limitations by estimating shielding tensors for arbitrary structures. Here we use an automated fragmentation quantum mechanics/molecular mechanics (AF-QM/MM) approach to compute (15)N, (13)C' and (1)H chemical shift tensors for human ubiquitin and the GB1 and GB3 fragments of staphylococcal protein G. The average and range of variation of the anisotropies is in good agreement with experimental estimates from solid-state NMR, and the variation among residues is somewhat smaller than that estimated from solution-state measurements. Hydrogen-bond effects account for much of the variation, both between helix and sheet regions, and within elements of secondary structure, but other effects (including variations in torsion angles) may play a role as well.
蛋白质中的各个肽段，其组成原子的化学位移各向异性（CSA）必然存在一定程度的变化，但人们对此变化的程度和起源知之甚少。CSA 的直接光谱测量在技术上具有挑战性，而理论方法可以通过估计任意结构的屏蔽张量来帮助克服这些限制。在这里，我们使用自动化碎片量子力学/分子力学（AF-QM/MM）方法来计算人泛素以及葡萄球菌蛋白 G 的 GB1 和 GB3 片段的 (15)N、(13)C' 和 (1)H 化学位移张量。各向异性的平均值和变化范围与固态 NMR 的实验估计值吻合良好，残基之间的变化也比溶液状态测量估计的要小一些。氢键效应解释了大部分变化，包括螺旋区和片层区之间的变化，以及二级结构元素内的变化，但其他效应（包括扭转角的变化）也可能起作用。
