Li Y C, Montelione G T
Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854-5638.
J Magn Reson B. 1994 Sep;105(1):45-51. doi: 10.1006/jmrb.1994.1098.
Artifacts due to solvent saturation-transfer effects result in incorrect measurements of 1H-15N heteronuclear NOE (HNOE). These artifacts are commonly observed in aqueous protein solutions at neutral pH. We describe the application of pulsed field gradients (PFGs) together with long recycle delays in overcoming errors in HNOE measurements which arise from H2O solvent preirradiation and solvent saturation transfer. Even in the absence of explicit solvent irradiation, the HNOE pulse sequence itself results in a nonequilibrium spin-state distribution of solvent nuclei which can then be transferred by chemical exchange into amide-proton sites. This effect can be avoided by using PFGs for suppression of solvent H2O together with a recycle delay sufficiently long for the magnetization of water to relax back to equilibrium values during the preparation period. These effects were studied in 15N-enriched human type alpha transforming growth factor at pH 7.1. Comparisons of PFG-HNOE experiments with and without selective H2O irradiation and with different recycle times provide estimates of the effects of solvent irradiation on HNOE measurements, which are different for different amide nitrogen-15 nuclei. The amplitudes of these artificial HNOE enhancements are roughly correlated with solvent accessibilities of amide sites in the three-dimensional structure of hTGF alpha.
由于溶剂饱和转移效应产生的伪影会导致对1H-15N异核NOE（HNOE）的测量不准确。这些伪影在中性pH值的蛋白质水溶液中很常见。我们描述了脉冲场梯度（PFG）与长循环延迟一起应用于克服HNOE测量中由H2O溶剂预辐照和溶剂饱和转移引起的误差。即使在没有明确的溶剂辐照的情况下，HNOE脉冲序列本身也会导致溶剂核的非平衡自旋态分布，然后可以通过化学交换转移到酰胺质子位点。通过使用PFG抑制溶剂H2O以及足够长的循环延迟，以使水的磁化在制备期间弛豫回到平衡值，可以避免这种效应。在pH 7.1的15N富集的人α型转化生长因子中研究了这些效应。对有无选择性H2O辐照以及不同循环时间的PFG-HNOE实验进行比较，提供了溶剂辐照对HNOE测量影响的估计，不同的酰胺氮-15核的影响不同。这些人为的HNOE增强幅度与hTGFα三维结构中酰胺位点的溶剂可及性大致相关。
