Cai Ling, Fushman David, Kosov Daniel S
Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 20742-2021, USA.
J Biomol NMR. 2009 Nov;45(3):245-53. doi: 10.1007/s10858-009-9358-3. Epub 2009 Jul 31.
We performed density functional calculations of backbone (15)N chemical shielding tensors in selected helical residues of protein G. Here we describe a computationally efficient methodology to include most of the important effects in the calculation of chemical shieldings of backbone (15)N. We analyzed the role of long-range intra-protein electrostatic interactions by comparing models with different complexity in vacuum and in charge field. Our results show that the dipole moment of the alpha-helix can cause significant deshielding of (15)N; therefore, it needs to be considered when calculating (15)N chemical shielding. We found that it is important to include interactions with the side chains that are close in space when the charged form for ionizable side chains is adopted in the calculation. We also illustrate how the ionization state of these side chains can affect the chemical shielding tensor elements. Chemical shielding calculations using a 8-residue fragment model in vacuum and adopting the charged form of ionizable side chains yield a generally good agreement with experimental data.
我们对蛋白质G选定螺旋残基中的主链（15）N化学屏蔽张量进行了密度泛函计算。在此，我们描述了一种计算效率高的方法，以在主链（15）N化学屏蔽计算中纳入大多数重要效应。我们通过比较在真空和电荷场中具有不同复杂度的模型，分析了蛋白质内远程静电相互作用的作用。我们的结果表明，α-螺旋的偶极矩可导致（15）N显著去屏蔽；因此，在计算（15）N化学屏蔽时需要予以考虑。我们发现，在计算中采用可电离侧链的带电形式时，纳入与空间上接近的侧链的相互作用很重要。我们还说明了这些侧链的电离状态如何影响化学屏蔽张量元素。在真空下使用8残基片段模型并采用可电离侧链的带电形式进行的化学屏蔽计算，与实验数据总体上吻合良好。
