3D TEDOR NMR experiments for the simultaneous measurement of multiple carbon-nitrogen distances in uniformly 13C, 15N-labeled solids
3D TEDOR NMR experiments for the simultaneous measurement of multiple carbon-nitrogen distances in uniformly 13C, 15N-labeled solids
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DOI：
10.1021/ja026385y
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发表时间：
2002-09-11
影响因子：
15
通讯作者：
Griffin, RG
中科院分区：
文献类型：
--
作者：
Jaroniec, CP;Filip, C;Griffin, RG
我们描述了三维魔角旋转核磁共振实验，用于同时测量均匀 C-13、N-15 标记固体中的多个碳-氮距离。这些方法采用转移回波双共振 (TEDOR) 进行 C-13-N-15 相干转移，并采用 N-15 和 C-13 频率标记进行特定位点分辨率，并建立在之前的几种 3D TEDOR 技术的基础上。这里介绍的 3D TEDOR 脉冲序列的新颖特征是，它们专门设计用于规避同核 C-13-C-13 J 耦合对弱 C-13-N-15 偶极耦合测量的不利影响。特别是，同核 J 耦合会导致两种不良效应：(I) 它们产生反相和多量子 (MQ) 自旋相干性，从而导致 2D N-15-C-13 相关光谱中出现虚假交叉峰和相位扭曲线，从而降低光谱分辨率并阻止提取可靠的交叉峰强度，(ii) 它们显着降低强 J 耦合的交叉峰强度C-13 位点（例如 CO 和 C-α）。第一个实验采用 z 滤波器周期来抑制反相和 MQ 相干性，并针对所有 TEDOR 混合时间生成具有纯吸收峰的 2D 光谱。第二种方法使用带选择性 C-13 脉冲来重新聚焦选择性脉冲带宽内的 C-13 自旋和带宽外的 C-13 自旋之间的 J 耦合。核间距离是通过使用简单的分析模型提取的，该模型明确地解释了导致交叉峰形成的多个自旋-自旋耦合。该实验在两种 U-C-13,N-15 标记的肽 N-乙酰基-L-Val-L-Leu (N-ac-VL) 和 N-甲酰基-L-Met-L-Leu-L-Phe (N-f-MLF) 中得到证实，其中分别测量了 20 和 26 C-13-N-15 距离，高达相似的 5-6 埃。在测量的距离中，N-ac-VL 中的 10 个距离和 N-f-MLF 中的 13 个距离大于 3 埃，并提供了有价值的结构约束。
We describe three-dimensional magic-angle-spinning NMR experiments for the simultaneous measurement of multiple carbon-nitrogen distances in uniformly C-13,N-15-labeled solids. The approaches employ transferred echo double resonance (TEDOR) for C-13-N-15 coherence transfer and N-15 and C-13 frequency labeling for site-specific resolution, and build on several previous 3D TEDOR techniques. The novel feature of the 3D TEDOR pulse sequences presented here is that they are specifically designed to circumvent the detrimental effects of homonuclear C-13-C-13 J-couplings on the measurement of weak C-13-N-15 dipolar couplings. In particular, homonuclear J-couplings lead to two undesirable effects: (I) they generate anti-phase and multiple-quantum (MQ) spin coherences, which lead to spurious cross-peaks and phase-twisted lines in the 2D N-15-C-13 correlation spectra, and thus degrade the spectral resolution and prohibit the extraction of reliable cross-peak intensities, and (ii) they significantly reduce cross-peak intensities for strongly J-coupled C-13 sites (e.g., CO and C-alpha). The first experiment employs z-filter periods to suppress the anti-phase and MQ coherences and generates 2D spectra with purely absorptive peaks for all TEDOR mixing times. The second approach uses band-selective C-13 pulses to refocus J-couplings between C-13 spins within the selective pulse bandwidth and C-13 spins outside the bandwidth. The internuclear distances are extracted by using a simple analytical model, which accounts explicitly for multiple spin-spin couplings contributing to cross-peak buildup. The experiments are demonstrated in two U-C-13,N-15-labeled peptides, N-acetyl-L-Val-L-Leu (N-ac-VL) and N-formyl-L-Met-L-Leu-L-Phe (N-f-MLF), where 20 and 26 C-13-N-15 distances up to similar to5-6 Angstrom were measured, respectively. Of the measured distances, 10 in N-ac-VL and 13 in N-f-MLF are greater than 3 Angstrom and provide valuable structural constraints.