Wang Tianzhi, Cai Sheng, Zuiderweg Erik R P
Biophysics Research Division, Department of Biological Chemistry, The University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109-1055, USA.
J Am Chem Soc. 2003 Jul 16;125(28):8639-43. doi: 10.1021/ja034077+.
The measurement of (15)N NMR spin relaxation, which reports the (15)N-(1)H vector reorientational dynamics, is a widely used experimental method to assess the motion of the protein backbone. Here, we investigate whether the (15)N-(1)H vector motions are representative of the overall backbone motions, by analyzing the temperature dependence of the (15)N-(1)H and (13)CO-(13)C(alpha) reorientational dynamics for the small proteins binase and ubiquitin. The latter dynamics were measured using NMR cross-correlated relaxation experiments. The data show that, on average, the (15)N-(1)H order parameters decrease only by 2.5% between 5 and 30 degrees C. In contrast, the (13)CO-(13)C(alpha) order parameters decrease by 10% over the same temperature trajectory. This strongly indicates that there are polypeptide-backbone motions activated at room temperature that are not sensed by the (15)N-(1)H vector. Our findings are at variance with the common crank-shaft model for protein backbone dynamics, which predicts the opposite behavior. This study suggests that investigation of the (15)N relaxation alone would lead to underestimation of the dynamics of the protein backbone and the entropy contained therein.
(15)N NMR自旋弛豫测量可反映(15)N-(1)H矢量的重定向动力学，是评估蛋白质主链运动的一种广泛应用的实验方法。在此，我们通过分析小蛋白binase和泛素的(15)N-(1)H以及(13)CO-(13)Cα重定向动力学的温度依赖性，来研究(15)N-(1)H矢量运动是否代表整体主链运动。后者的动力学通过NMR交叉相关弛豫实验进行测量。数据表明，平均而言，(15)N-(1)H序参量在5至30摄氏度之间仅下降2.5%。相比之下，(13)CO-(13)Cα序参量在相同温度范围内下降了10%。这有力地表明，在室温下存在一些多肽主链运动，而(15)N-(1)H矢量无法感知到这些运动。我们的发现与蛋白质主链动力学的常见曲轴模型不一致，该模型预测的情况相反。这项研究表明，仅对(15)N弛豫进行研究将导致对蛋白质主链动力学及其所含熵的低估。
