Dept. of NMR-based Structural Biology, Max-Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany.
J Magn Reson. 2012 Aug;221:1-4. doi: 10.1016/j.jmr.2012.05.005. Epub 2012 May 14.
Internal motions in the microsecond timescale have been proposed to play an active part in a protein's biological function. Nuclear magnetic resonance (NMR) relaxation dispersion is a robust method sensitive to this timescale with atomic resolution. However, due to technical limitations, the observation of motions faster than ∼40 μs for ¹⁵N nuclei was not possible. We show that with a cryogenically cooled NMR probehead, a high spin-lock field strength can be generated that is able to detect motions as fast as 25 μs. We apply this high spin-lock field strength in an NMR experiment used for characterizing dynamical processes. An on-resonance rotating-frame transverse relaxation experiment was implemented that allows for the detection of a 25 μs process from a dispersion curve, and transverse relaxation rates were compared at low and high spin-lock field strengths showing that at high field strengths contributions from chemical exchange with lifetimes up to 25 μs can be removed. Due to the increase in sensitivity towards fast motion, relaxation dispersion for a residue that undergoes smaller chemical shift variations due to dynamics was identified. This technique reduces the previously inaccessible window between the correlation time and the relaxation dispersion window that covers four orders of magnitude by a factor of 2.
在微秒时间尺度内的内部运动被认为在蛋白质的生物功能中起着积极的作用。核磁共振（NMR）弛豫分散是一种对该时间尺度具有原子分辨率的稳健方法。然而，由于技术限制，对于 ¹⁵N 核，观察速度快于 ∼40 μs 的运动是不可能的。我们表明，通过使用低温 NMR 探头，可以产生高自旋锁定场强，能够检测快至 25 μs 的运动。我们将这种高自旋锁定场强应用于用于表征动力学过程的 NMR 实验中。实现了一个在共振旋转框架中的横向弛豫实验，允许从弥散曲线中检测到 25 μs 的过程，并且在低自旋锁定场强和高自旋锁定场强下比较了横向弛豫率，表明在高场强下，可以去除化学交换的贡献，其寿命长达 25 μs。由于对快速运动的灵敏度提高，鉴定了由于动力学而经历较小化学位移变化的残基的弛豫弥散。该技术将以前无法访问的覆盖四个数量级的相关时间和弛豫弥散窗口之间的窗口减小了 2 倍。
