Howard Hughes Medical Institute and Department of Chemistry and Biochemistry, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA.
J Biomol NMR. 2010 Jul;47(3):205-19. doi: 10.1007/s10858-010-9424-x. Epub 2010 Jun 15.
Ribonucleic acid structure determination by NMR spectroscopy relies primarily on local structural restraints provided by (1)H- (1)H NOEs and J-couplings. When employed loosely, these restraints are broadly compatible with A- and B-like helical geometries and give rise to calculated structures that are highly sensitive to the force fields employed during refinement. A survey of recently reported NMR structures reveals significant variations in helical parameters, particularly the major groove width. Although helical parameters observed in high-resolution X-ray crystal structures of isolated A-form RNA helices are sensitive to crystal packing effects, variations among the published X-ray structures are significantly smaller than those observed in NMR structures. Here we show that restraints derived from aromatic (1)H- (13)C residual dipolar couplings (RDCs) and residual chemical shift anisotropies (RCSAs) can overcome NMR restraint and force field deficiencies and afford structures with helical properties similar to those observed in high-resolution X-ray structures.
通过核磁共振波谱法确定核糖核酸结构主要依赖于（1）H-（1）H NOE 和 J 耦合提供的局部结构约束。当这些约束条件宽松时，它们与 A 型和 B 型螺旋几何形状大致兼容，并产生对精修过程中使用的力场高度敏感的计算结构。最近报道的 NMR 结构调查显示，螺旋参数存在显著差异，特别是大沟宽度。尽管在分离的 A 型 RNA 螺旋的高分辨率 X 射线晶体结构中观察到的螺旋参数对晶体堆积效应敏感，但发表的 X 射线结构之间的变化明显小于 NMR 结构中观察到的变化。在这里，我们表明，源自芳香族（1）H-（13）C 残剩偶极耦合（RDC）和残差化学位移各向异性（RCSA）的约束条件可以克服 NMR 约束和力场缺陷，并提供具有与高分辨率 X 射线结构中观察到的相似螺旋特性的结构。
