Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA.
J Chem Phys. 2012 Oct 7;137(13):134201. doi: 10.1063/1.4754149.
(13)C and (15)N chemical shift (CS) interaction is a sensitive probe of structure and dynamics in a wide variety of biological and inorganic systems, and in the recent years several magic angle spinning NMR approaches have emerged for residue-specific measurements of chemical shift anisotropy (CSA) tensors in uniformly and sparsely enriched proteins. All of the currently existing methods are applicable to slow and moderate magic angle spinning (MAS) regime, i.e., MAS frequencies below 20 kHz. With the advent of fast and ultrafast MAS probes capable of spinning frequencies of 40-100 kHz, and with the superior resolution and sensitivity attained at such high frequencies, development of CSA recoupling techniques working under such conditions is necessary. In this work, we present a family of R-symmetry based pulse sequences for recoupling of (13)C∕(15)N CSA interactions that work well in both natural abundance and isotopically enriched systems. We demonstrate that efficient recoupling of either first-rank (σ(1)) or second-rank (σ(2)) spatial components of CSA interaction is attained with appropriately chosen γ-encoded RN(n)(v) symmetry sequences. The advantage of these γ-encoded RN(n)(v)-symmetry based CSA (RNCSA) recoupling schemes is that they are suitable for CSA recoupling under a wide range of MAS frequencies, including fast MAS regime. Comprehensive analysis of the recoupling properties of these RN(n)(v) symmetry sequences reveals that the σ(1)-CSA recoupling symmetry sequences exhibit large scaling factors; however, the partial homonuclear dipolar Hamiltonian components are symmetry allowed, which makes this family of sequences suitable for CSA measurements in systems with weak homonuclear dipolar interactions. On the other hand, the γ-encoded symmetry sequences for σ(2)-CSA recoupling have smaller scaling factors but they efficiently suppress the homonuclear dipole-dipole interactions. Therefore, the latter family of sequences is applicable for measurements of CSA parameters in systems with strong homonuclear dipolar couplings, such as uniformly-(13)C labeled biological solids. We demonstrate RNCSA NMR experiments and numerical simulations establishing the utility of this approach to the measurements of (13)C and (15)N CSA parameters in model compounds, [(15)N]-N-acetyl-valine (NAV), [U-(13)C, (15)N]-alanine, [U-(13)C,(15)N]-histidine, and present the application of this approach to [U-(13)C∕(15)N]-Tyr labeled C-terminal domain of HIV-1 CA protein.
(13)C 和 (15)N 化学位移 (CS) 相互作用是广泛的生物和无机体系结构和动力学的灵敏探针，近年来，几种魔角旋转 NMR 方法已经出现，用于在均匀和稀疏富集的蛋白质中进行残基特异性的化学位移各向异性 (CSA) 张量测量。目前所有的方法都适用于缓慢和适度的魔角旋转 (MAS) 范围，即 MAS 频率低于 20 kHz。随着能够旋转 40-100 kHz 频率的快速和超快 MAS 探头的出现，以及在如此高的频率下获得的优越分辨率和灵敏度，有必要开发在这种条件下工作的 CSA 重聚技术。在这项工作中，我们提出了一组基于 R 对称的脉冲序列，用于在天然丰度和同位素富集系统中重聚 (13)C∕(15)N CSA 相互作用。我们证明，通过选择适当的γ编码 RN(n)(v) 对称序列，可以获得 CSA 相互作用的一阶（σ(1)）或二阶（σ(2)）空间分量的有效重聚。这些基于γ编码 RN(n)(v)-对称的 CSA（RNCSA）重聚方案的优点在于，它们适用于包括快速 MAS 范围在内的各种 MAS 频率下的 CSA 重聚。对这些 RN(n)(v) 对称序列的重聚性质进行综合分析表明，σ(1)-CSA 重聚对称序列具有较大的比例因子；然而，部分同核偶极子哈密顿分量是对称允许的，这使得该序列家族适用于同核偶极子相互作用较弱的系统中的 CSA 测量。另一方面，用于σ(2)-CSA 重聚的γ编码对称序列具有较小的比例因子，但它们有效地抑制了同核偶极子-偶极子相互作用。因此，后一种序列适用于具有强同核偶极子偶合的系统中的 CSA 参数测量，例如均匀-(13)C 标记的生物固体。我们演示了 RNCSA NMR 实验和数值模拟，证明了这种方法在模型化合物[(15)N]-N-乙酰-缬氨酸（NAV）、[U-(13)C，(15)N]-丙氨酸、[U-(13)C，(15)N]-组氨酸中测量(13)C 和 (15)N CSA 参数的适用性，并展示了这种方法在 HIV-1 CA 蛋白 C 末端结构域[U-(13)C∕(15)N]-Tyr 标记物中的应用。
