Optimized NMR experiments are developed for isolating magnetization belonging to the I=1/2 manifolds of ¹³CH₃ methyl groups in proteins, enabling the manipulation of the magnetization of a ¹³CH₃ moiety as if it were an AX (¹H‐¹³C) spin‐system. These experiments result in the same ‘simplification’ of a ¹³CH₃ spin‐system that would be obtained from the production of {¹³CHD₂}‐methyl‐labeled protein samples. The sensitivity of I=1/2 manifold‐selection experiments is a factor of approximately 2 less than that of the corresponding experiments acquired on {¹³CHD₂}‐labeled methyl groups. The methodology described here is primarily intended for small‐to‐medium sized proteins, where the losses in sensitivity associated with the isolation of I=1/2 manifold transitions can be tolerated. Several NMR applications that benefit from simplification of the ¹³CH₃ (AX₃) spin‐systems are described, with an emphasis on the measurements of methyl ¹H‐¹³C residual dipolar couplings in a {¹³CH₃}‐methyl‐labeled deletion mutant of the human chaperone DNAJB6b, where modulation of NMR signal intensities due to evolution of methyl ¹H‐¹³C scalar and dipolar couplings follows a simple cosine function characteristic of an AX (¹H‐¹³C) spin‐system, significantly simplifying data analysis.

中文翻译：

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用于分离蛋白质甲基中的 I=1/2 歧管跃迁的优化 NMR 实验。

开发了优化的 NMR 实验，用于分离属于蛋白质中¹³ CH ₃甲基的I =1/2 流形的磁化，从而能够像 AX ( ¹ H- ¹³ C一样) 操纵¹³ CH ₃部分的磁化) 自旋系统。这些实验导致了¹³ CH ₃自旋系统的相同“简化”，该系统可以从生产{ ¹³ CHD ₂ }-甲基标记的蛋白质样品中获得。我的敏感度= 1/2 歧管选择实验比在 { ¹³ CHD ₂ } 标记的甲基上获得的相应实验小约 2 倍。此处描述的方法主要用于中小型蛋白质，其中与I = 1/2 歧管跃迁的隔离相关的灵敏度损失是可以容忍的。描述了一些受益于简化¹³ CH ₃ (AX ₃ ) 自旋系统的 NMR 应用，重点是测量{ ¹³ CH _{3中的甲基}¹ H- ¹³ C 残余偶极耦合}-甲基标记的人类伴侣 DNAJB6b 缺失突变体，其中由于甲基¹ H- ¹³ C 标量和偶极耦合的演变而对 NMR 信号强度的调制遵循 AX ( ¹ H- ¹³ C) 自旋的简单余弦函数特征‐系统，显着简化数据分析。