Paramagnetic relaxation enhancement (PRE) can be used to determine long-range distance restraints in biomolecules. The PREs are typically determined by analysis of intensity differences in HSQC experiments of paramagnetic and diamagnetic spin labels. However, this approach requires both isotope- and spin-labelling. Herein, we report a novel method to evaluate NOESY intensities in the presence of a paramagnetic moiety to determine PRE restraints. The advantage of our approach over HSQC-based approaches is the increased number of available signals without the need for isotope labelling. NOESY intensities affected by a paramagnetic center were evaluated during a structure calculation within the paramagnetic iterative relaxation matrix approach (P-IRMA). We applied P-IRMA to a 14-mer RNA with a known NMR solution structure, which allowed us to assess the quality of the PRE restraints. To this end, three different spin labels have been attached at different positions of the 14-mer to test the influence of flexibility on the structure calculation. Structural disturbances introduced by the spin label have been evaluated by chemical shift analysis. Furthermore, the impact of P-IRMA on the quality of the structure bundles were tested by intentionally leaving out available diamagnetic restraints. Our analyses show that P-IRMA is a powerful tool to refine RNA structures for systems that are insufficiently described by using only diamagnetic restraints.

中文翻译：

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顺磁迭代弛豫矩阵方法：从NOESY光谱中提取PRE约束，以阐明生物分子的3D结构。

顺磁弛豫增强（PRE）可用于确定生物分子中的远程距离约束。通常通过分析顺磁性和反磁性自旋标记的HSQC实验中的强度差异来确定PRE。但是，这种方法需要同位素标记和自旋标记。在这里，我们报告了一种新颖的方法来评估在顺磁性部分的存在下NOESY强度，以确定PRE约束。与基于HSQC的方法相比，我们的方法的优势在于无需同位素标记即可增加可用信号的数量。在顺磁迭代弛豫矩阵方法（P-IRMA）中的结构计算过程中，评估了受顺磁中心影响的NOESY强度。我们将P-IRMA应用于具有已知NMR溶液结构的14-mer RNA，这使我们能够评估PRE约束的质量。为此，在14-mer的不同位置附加了三个不同的自旋标记，以测试柔性对结构计算的影响。自旋标记引入的结构扰动已通过化学位移分析进行了评估。此外，通过有意排除可用的抗磁性约束，测试了P-IRMA对结构束质量的影响。我们的分析表明，P-IRMA是一种功能强大的工具，可以通过仅使用抗磁性约束物来完善描述不足的系统的RNA结构。自旋标记引入的结构扰动已通过化学位移分析进行了评估。此外，通过有意排除可用的抗磁性约束，测试了P-IRMA对结构束质量的影响。我们的分析表明，P-IRMA是一种功能强大的工具，可以通过仅使用抗磁约束来完善描述不足的系统的RNA结构。自旋标记引入的结构扰动已通过化学位移分析进行了评估。此外，通过有意排除可用的抗磁性约束，测试了P-IRMA对结构束质量的影响。我们的分析表明，P-IRMA是一种功能强大的工具，可以通过仅使用抗磁性约束物来完善描述不足的系统的RNA结构。