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Temperature Dependence of Anisotropic Protein Backbone Dynamics

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journal contribution
posted on 21.06.2003, 00:00 by Tianzhi Wang, Sheng Cai, Erik R. P. Zuiderweg
The measurement of 15N NMR spin relaxation, which reports the 15N−1H vector reorientational dynamics, is a widely used experimental method to assess the motion of the protein backbone. Here, we investigate whether the 15N−1H vector motions are representative of the overall backbone motions, by analyzing the temperature dependence of the 15N−1H and 13CO−13Cα 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 15N−1H order parameters decrease only by 2.5% between 5 and 30 °C. In contrast, the 13CO−13Cα 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 15N−1H 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 15N relaxation alone would lead to underestimation of the dynamics of the protein backbone and the entropy contained therein.