Direct measurement of dipole-dipole/CSA cross-correlated relaxation by a constant-time experiment
Direct measurement of dipole-dipole/CSA cross-correlated relaxation by a constant-time experiment
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DOI：
10.1016/j.jmr.2008.03.013
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发表时间：
2008-07-01
影响因子：
2.2
通讯作者：
Prestegard, James H.
中科院分区：
文献类型：
--
作者：
Liu, Yizhou;Prestegard, James H.
NMR 中的弛豫率通常通过强度调制作为弛豫延迟的函数来测量，在此期间感兴趣的弛豫机制是有效的。其他机制通常在弛豫延迟期间被脉冲序列抑制，从而消除它们的影响，或者当添加具有适当的弛豫率影响组合的两个数据集时消除它们的影响。涉及偶极-偶极和 CSA 相互作用的互相关弛豫 (CCR) 与自相关弛豫 (ACR) 不同，因为可以通过反转偶极-偶极相互作用中涉及的一个自旋的状态来改变贡献的符号。先前已利用 CPMG 序列在 ACR 演化时重新聚焦 CCR 来利用此特性。在这里，我们报告了一种新的脉冲方案，该方案消除了 ACR 的强度调制，从而允许直接测量 CCR。该序列使用恒定时间松弛周期，在此期间 ACR 的贡献不会改变。在序列中的各个点应用反转脉冲以实现仅取决于 CCR 的衰减。还描述了二维实验，其中间接维度的化学位移演化可以共享相同的恒定周期。这通过避免增加单独的间接维度采集时间来提高灵敏度。我们举例说明了非肉豆蔻酰化酵母 ARF1 蛋白上残基特异性 CCR 率的测量，并将结果与按照测量慢速和快速松弛 N-15 双联体衰减率的传统方法获得的结果进行比较。还通过仿真对两种方法的性能进行了定量评估。分析表明，共享恒定时间CCR（SCT-CCR）方法显着提高了灵敏度。 (c) 2008 Elsevier Inc. 保留所有权利。
Relaxation rates in NMR are usually measured by intensity modulation as a function of a relaxation delay during which the relaxation mechanism of interest is effective. Other mechanisms are often suppressed during the relaxation delay by pulse sequences which eliminate their effects, or cancel their effects when two data sets with appropriate combinations of relaxation rate effects are added. Cross-correlated relaxation (CCR) involving dipole-dipole and CSA interactions differ from auto-correlated relaxation (ACR) in that the signs of contributions can be changed by inverting the state of one spin involved in the dipole-dipole interaction. This property has been exploited previously using CPMG sequences to refocus CCR while ACR evolves. Here we report a new pulse scheme that instead eliminates intensity modulation by ACR and thus allows direct measurement of CCR. The sequence uses a constant time relaxation period for which the contribution of ACR does not change. An inversion pulse is applied at various points in the sequence to effect a decay that depends on CCR only. A 2-D experiment is also described in which chemical shift evolution in the indirect dimension can share the same constant period. This improves sensitivity by avoiding the addition of a separate indirect dimension acquisition time. We illustrate the measurement of residue specific CCR rates on the non-myristoylated yeast ARF1 protein and Compare the results to those obtained following the conventional method of measuring the decay rates of the slow and fast-relaxing N-15 doublets. The performances of the two methods are also quantitatively evaluated by simulation. The analysis shows that the shared constant-time CCR (SCT-CCR) method significantly improves sensitivity. (c) 2008 Elsevier Inc. All rights reserved.