Department of Chemistry, Queen's University, 90 Bader Lane, Kingston, Ontario, Canada K7L 3N6.
J Am Chem Soc. 2011 Feb 2;133(4):920-32. doi: 10.1021/ja1079207. Epub 2010 Dec 22.
We demonstrate a general nuclear magnetic resonance (NMR) spectroscopic approach in obtaining high-resolution (17)O (spin-5/2) NMR spectra for biological macromolecules in aqueous solution. This approach, termed quadrupole central transition (QCT) NMR, is based on the multiexponential relaxation properties of half-integer quadrupolar nuclei in molecules undergoing slow isotropic tumbling motion. Under such a circumstance, Redfield's relaxation theory predicts that the central transition, m(I) = +1/2 ↔ -1/2, can exhibit relatively long transverse relaxation time constants, thus giving rise to relatively narrow spectral lines. Using three robust protein-ligand complexes of size ranging from 65 to 240 kDa, we have obtained (17)O QCT NMR spectra with unprecedented resolution, allowing the chemical environment around the targeted oxygen atoms to be directly probed for the first time. The new QCT approach increases the size limit of molecular systems previously attainable by solution (17)O NMR by nearly 3 orders of magnitude (1000-fold). We have also shown that, when both quadrupole and shielding anisotropy interactions are operative, (17)O QCT NMR spectra display an analogous transverse relaxation optimized spectroscopy type behavior in that the condition for optimal resolution depends on the applied magnetic field. We conclude that, with the currently available moderate and ultrahigh magnetic fields (14 T and higher), this (17)O QCT NMR approach is applicable to a wide variety of biological macromolecules. The new (17)O NMR parameters so obtained for biological molecules are complementary to those obtained from (1)H, (13)C, and (15)N NMR studies.
我们展示了一种通用的核磁共振（NMR）光谱方法，用于在水溶液中获得生物大分子的高分辨率（17）O（自旋-5/2）NMR 谱。这种方法称为四极中心转变（QCT）NMR，基于经历慢各向同性旋转运动的分子中半整数四极核的多指数弛豫特性。在这种情况下，Redfield 弛豫理论预测，中央转变，m（I）=+1/2↔-1/2，可以表现出相对较长的横向弛豫时间常数，从而导致相对较窄的谱线。使用三个尺寸范围从 65 到 240 kDa 的稳健的蛋白质-配体复合物，我们获得了前所未有的分辨率的（17）O QCT NMR 谱，首次能够直接探测到目标氧原子周围的化学环境。新的 QCT 方法将通过溶液（17）O NMR 以前可达到的分子系统的大小限制提高了近 3 个数量级（1000 倍）。我们还表明，当四极和屏蔽各向异性相互作用都起作用时，（17）O QCT NMR 谱显示出类似的横向弛豫优化光谱类型行为，即最佳分辨率的条件取决于所施加的磁场。我们得出结论，在当前可用的中等和超高磁场（14 T 及更高）下，这种（17）O QCT NMR 方法适用于各种生物大分子。从生物分子获得的新（17）O NMR 参数与从（1）H、（13）C 和（15）N NMR 研究获得的参数互补。
