O'Neil-Cabello Erin, Bryce David L, Nikonowicz Edward P, Bax Ad
Laboratory of Chemical Physics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0520, USA.
J Am Chem Soc. 2004 Jan 14;126(1):66-7. doi: 10.1021/ja038314k.
A new three-dimensional NMR experiment is described that yields five scalar or dipolar couplings from a single cross-peak between three spins. The method is based on the E.COSY principle and is demonstrated for the H1'-C1'-C2' fragment of ribose sugars in a uniformly 13C-enriched 24-nucleotide RNA stem-loop structure, for which a complete set of couplings was obtained for all nonmodified nucleotides. The values of the isotropic J couplings and the 13C1' and 13C2' chemical shifts define the sugar pucker. Once the sugar pucker is known, the five dipolar couplings between C1'-H1', C2'-H2', H1'-H2', C1'-H2', and C2'-H1', together with C1'-C2', C3'-H3', and C4'-H4' available from standard experiments, can be used to derive the five unknowns that define the local alignment tensor, thereby simultaneously providing information on relative orientation and dynamics of the ribose units. Data indicate rather uniform alignment for all stem nucleotides in the 24-nt stem-loop structure, with only a modest reduction in order for the terminal basepair, but significantly increased mobility in part of the loop region. The method is applicable to proteins, nucleic acids, and carbohydrates, provided 13C enrichment is available.
本文描述了一种新的三维核磁共振实验，该实验可从三个自旋之间的单个交叉峰中得到五个标量或偶极耦合。该方法基于E.COSY原理，并在一个均匀富集13C的24核苷酸RNA茎环结构中的核糖糖的H1'-C1'-C2'片段上得到了验证，对于所有未修饰的核苷酸都获得了完整的耦合集。各向同性J耦合值以及13C1'和13C2'化学位移定义了糖的折叠构象。一旦知道了糖的折叠构象，C1'-H1'、C2'-H2'、H1'-H2'、C1'-H2'和C2'-H1'之间的五个偶极耦合，连同从标准实验中获得的C1'-C2'、C3'-H3'和C4'-H4'，可用于推导定义局部排列张量的五个未知数，从而同时提供有关核糖单元相对取向和动力学的信息。数据表明，在24核苷酸茎环结构中，所有茎核苷酸的排列相当均匀，只有末端碱基对的有序性略有降低，但环区域的一部分流动性显著增加。如果有13C富集，该方法适用于蛋白质、核酸和碳水化合物。
